A techno-economic analysis and life cycle assessment of woody biochar as an additive for orphan well plugging

A techno-economic analysis and life cycle assessment of woody biochar as an additive for orphan well plugging | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article A techno-economic analysis and life cycle assessment of woody biochar as an additive for orphan well plugging Brooke Ballenger, Kerry Miller, Thomas Borch, Jason C. Quinn This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6823444/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Well plugging mitigates methane emissions and protects groundwater, yet conventional cement-based methods carry a high carbon footprint. To explore more sustainable alternatives, this study developed a techno-economic analysis (TEA) and cradle-to-gate life cycle assessment (LCA) for an orphan well in Colorado, comparing a baseline cement-plugging scenario to one that integrates woody biochar in both the cement slurry (3% by weight) and spacer plugging fluid (15% by volume). Various thermochemical conversion pathways were evaluated to understand how different biochar properties influence net greenhouse gas emissions. Results indicate that adding 4.2 tonnes of biochar per well increases plugging costs by 2% but can reduce total emissions from 11.4 tonnes CO₂e to as low as 0.64 tonnes CO₂e per well. Further analysis showed that carbon credit revenues (121 USD per tonne)—if appropriately established for biochar’s use in well plugging—could offset this additional cost, making biochar-additive plugging economically competitive under certain market conditions. These findings demonstrate a promising approach for lowering the environmental impact of well decommissioning and transitioning the industry toward more climate-resilient practices. Woody biochar Life cycle assessment Techno-economic analysis Plugging & Abandonment Figures Figure 1 Figure 2 Figure 3 1 Introduction Well plugging refers to the permanent sealing of oil and gas wells that have reached the end of their operational lifetime. Plug and abandonment operations generally involve placing cement plugs in the wellbore to isolate the reservoir and other fluid-bearing formations (Vrålstad et al., 2019 ). Since the mid-1800s, millions of wells have been drilled across the United States; as of 2018, approximately 2.1 million remain unplugged (EPA, 2024 ). In Colorado—the fifth-largest crude oil producer in the nation—around 33,000 wells are either abandoned or unplugged as of 2023 (U.S. Energy Information Administration, 2023; COGA, 2024; COGCC, 2023). Some of these wells are “orphaned,” meaning the original operators abandoned them with no financially responsible party left to cover plugging costs (Raimi et al., 2021 ). State governments often rely on taxpayer funds to manage these wells. Properly plugging them is crucial for preventing methane emissions and groundwater or surface water contamination (Raimi et al., 2021 ; Kang et al., 2016 ). Portland cement is one of the main materials used in well plugging due to its effectiveness in sealing the wellbore (Vrålstad et al., 2019 ). However, cement production is a significant source of anthropogenic greenhouse gas (GHG) emissions which leads to a high carbon footprint of plugging and abandonment operations (Miller et al., 2021 ). As the shift toward renewable energy accelerates, more oil and gas wells will reach the end of their productive lifetimes and require decommissioning (Bogdanov et al., 2021 ). Using alternatives to conventional cement-based methods can help in reducing GHG emissions associated with the process and assist in meeting Colorado’s GHG reduction goals, 50% by 2030 and net-zero by 2050 (GHG Pollution Reduction Roadmap 2.0, 2023 ). Recent studies show that using biochar, a stable carbon-rich material produced by pyrolysis, in cement slurries can improve mechanical strength of cement and increase the lifetime of plugging operations (Lin et al., 2023 ). Biochar may also be able to offset GHG emissions associated with the plugging process by indefinitely sequestering large amounts of carbon (Hansson et al., 2020 ; Tisserant and Cherubini, 2019 ). Although biochar has been extensively studied in soil amendment applications, its use in well plugging is still in the early conceptual stages (Nogués et al., 2023 ; Roth et al., 2024 ). Preliminary studies suggest that biochar may integrate well with cement, yet there is a lack of robust techno-economic analysis (TEA) and life cycle assessment (LCA) data to evaluate the trade-offs between environmental benefits and additional costs (Roth et al., 2024 ). Without detailed insights into the economic and environmental implications, it remains difficult to determine whether plugging materials using biochar as an additive can meaningfully reduce GHG emissions and whether any extra expense is warranted. In this work, a TEA is carried out to estimate the incremental cost of incorporating woody biomass–based biochar as an additive to orphan well plugging operations. Simultaneously, a cradle-to-gate LCA quantifies changes in GHG emissions compared to standard conventional well plugging scenarios. Various thermochemical conversion pathways are evaluated to explore how different biochar properties may influence overall emissions. Through concurrent TEA and LCA, this analysis provides a more comprehensive understanding of potential biochar adoption in plugging and abandonment practices, supporting both Colorado and nationwide strategies for GHG mitigation as an increasing number of wells become inactive and require decommissioning. 2 Methods 2.1 Techno-economic analysis A TEA was conducted to compare two orphan well plugging scenarios (Fig. 1 ): a baseline scenario using conventional Portland class G cement and a novel scenario that integrated woody biochar into both the cement plugs and the spacer plugging fluid—used to fill the volume of the well not occupied by the cement (Salimi et al., 2024 ). Plugging costs vary widely depending on factors such as well depth, geological conditions, and the length of time the well has been idle (Interstate Oil and Gas Compact Commission, 2021). To establish a representative baseline, a single conventional vertical well at an approximate depth of 2074 m was chosen, reflecting the average depth profile among 94,793 wells in Colorado (COGCC, 2023). Cost components included labor, material inputs, equipment rental, various plugging procedures (e.g., wireline and cement squeezing operations, pressure testing, and cut-and-cap operation), all converted to 2024 USD (Hawthorn et al., 2022 ; Pamon and Abbom, 1982 ). Rental costs and diesel use for vehicles such as bulk cement trucks, triplex trucks, and workover rigs were included based on standard industry practice (National Petroleum Council, 2011). The conventional cement slurry consisted of Portland class G cement mixed with 19 L of water per cement sack, while the spacer plug fluid was modeled as a water with 5% vol. bentonite mixture, a configuration widely used in routine operations (Khalifeh & Saasen, 2020 ; Scherer, 2021 ). Data for the baseline scenario came from detailed logs that well plugging operators must submit to the Colorado Energy & Carbon Management Commission (ECMC) when performing plugging and abandonment activities (COGCC, 2023). These logs specify the number of cement plugs, the volumes of cement and spacer plugging fluids, and other key parameters used in plugging operations. Additional operational assumptions were informed by literature and local plugging operators. Typical labor rates, mixing charges, rig rental fees, and associated operating costs (vehicle usage, fuel, equipment rentals) were aggregated to capture a representative profile of conventional well plugging in Colorado. More detailed inputs regarding TEA parameters can be found in Table S1 of the online resources. The second scenario involved using biochar as an additive in the spacer plugging fluid and cement plugs. Due to the mountain pine beetle endemic in Colorado—which has resulted in large volumes of beetle-killed timber with minimal commercial value—this study focused exclusively on woody biochar (USFS, 2020; Price et al., 2010 ). The biochar scenario mirrored the baseline operational procedures, equipment, and rental fees but replaced part of the cement slurry and spacer plugging fluid with biochar at a purchase price of 209 USD per tonne derived from reported values by U.S. biochar manufacturers (COGIS, 2024; Puro.earth, 2024 ; Rogue Biochar Pricing, 2024.; Go Biochar, 2024 ; Blue Sky Biochar, 2024 ; AirTerra, 2024 ). The cement slurry was modeled as a blend of Portland class G cement, 19 L of water per cement sack, and 3% wt. biochar, while the spacer plugging fluid was composed of water, 5% vol. bentonite, and 15% vol. biochar, as advised by communication with local plugging operators (Greenfield Environmental Solutions, 2024). The 3% wt. biochar was determined through mechanical testing of cured cement with or without biochar added in. Briefly, Portland cement was combined with 44% water, then 0–10% biochar by mass added to the mixture. The cement was cured at standard temperature and pressure, then evaluated for its compressive strength after 1, 4, 7, and 28 days, as well as their viscosities as slurry. Mixtures higher than 3% wt. biochar were not able to match the compressive strength of cement with no added biochar and were eliminated from further testing. More detailed protocols regarding physical testing of the cement-biochar composites can be found in Methods S1, S2, and S3 of the online resources. Additional costs included transportation to the well site and on-site mixing. Considering that biochar market prices vary substantially by manufacturer, further analysis varied biochar costs between 58 and 347 USD, the minimum and maximum reported by U.S. biochar manufacturers. The baseline scenario excluded any carbon credit revenue, providing an initial benchmark of the direct cost changes. However, because carbon credits could improve overall project economics, additional scenarios examined credit values ranging from 50 USD to 200 USD per tonne CO 2 e (Trove Research, 2024 ; Puro.earth, 2024 ). As of February 2024, the average market price was approximately 150 USD per tonne CO 2 e (Puro.earth, 2024 ). This analysis did not assume any well plugging complications, abnormal well conditions, or well surface environmental remediation, and instead focused on the most common operational conditions for routine well plugging of a conventional vertical well. 2.2 Life cycle assessment Using a cradle-to-grave LCA methodology according to the International Organization for Standardization (ISO, 2006), an environmental analysis was carried out similarly to the TEA to compare the GHG emissions from conventional orphan well plugging against scenarios incorporating biochar into both the cement slurry and the spacer plugging fluid. The functional unit was defined as “one plugged well” with a conventional vertical depth of 2074 m. The primary objective was to determine whether potential net emission reductions resulting from biochar use are substantial enough to justify further adoption. The system boundary for the baseline scenario extended from raw material production to the final plugging of the orphan well. The biochar-additive scenario followed the same boundary conditions as the baseline scenario and included any biochar-related emissions and reductions from biomass procurement, thermochemical conversion into biochar, transportation of the final biochar product to the well site and well-site operations. Feedstock-related upstream timber management activities were excluded to focus on direct emissions associated with biochar production and well plugging (She et al., 2019 ). Emissions factors were taken from Ecoinvent 3.9.1 and the United States Life Cycle Inventory Database (Wernet et al., 2016 ) and were characterized via global warming potential (GWP) using the EPA’s Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI) version 2.1 (Bare, 2011 ). Material quantities on conventional well plugging followed the same conditions as the TEA. The European Biochar Certificate (EBC) standard provided the basis for calculating a carbon sequestration value (Eq. 1), assuming a 100% permanence factor for carbon sequestered within the wellbore (EBC, 2020 ). Where \(\:{Q}_{biochar}\) is the quantity of biochar generated, \(\:{C}_{org}\) is the organic carbon content of biochar, \(\:{F}_{p}^{TH}\) is the permanence factor over a time horizon TH , and \(\:\frac{44}{12}\) is the molecular weight ratio of CO 2 to carbon. Equation 1 \(\:{E}_{stored}={Q}_{biochar}\:x\:{C}_{org}\:x\:{F}_{p}^{TH}\:x\:\frac{44}{12}\) Multiple pyrolysis configurations frequently used in North American biochar production were evaluated, including stationary auger reactors, stationary rotary kilns, stationary batch reactors, portable retorts, and mobile carbonizers (USBI, 2024). In all stationary systems, after collection, biomass was transported as whole logs over an estimated 161-km round trip to the pyrolysis facility for any necessary processing (Amoneme et al., 2023 ). The biomass feedstock—forest harvest residue with an initial moisture content of 30%—was dried in an industrial rotary dryer to approximately 10% moisture and subsequently reduced in size using a hammer mill (Zajec, 2009 ; Cheng et al., 2020 ). The auger and rotary kiln reactors operated continuously at 500°C under an inert nitrogen atmosphere and relied on electricity and natural gas for heating and operation (Moser et al., 2023 ; Brassard et al., 2017 ). The batch reactor processed biomass under the same temperature and atmosphere conditions but utilized a start-stop approach rather than a continuous feed. While the auger reactor employed a rotating screw to transport the biomass, the rotary kiln reactor featured a rotating cylindrical tube without a screw. For each of these stationary systems, any co-generated syngas was recycled at a 75% efficiency rate to supply part of the process heat, and a mass allocation approach was employed for distributing emissions among biochar and its co-products (Brassard et al., 2024 ). Portable retorts and mobile carbonizers enable on-site production, reducing transport needs. Both systems used diesel or propane for startup, allowing them to process biomass up to 20–25% moisture without extensive drying (Wrobel-Tobiszewska et al., 2015 ; Biochar Now, 2023 ; Puemmann et al., 2020 ). The portable retort operated at 550–600°C and required a diesel-powered chipper for size reduction, where the mobile carbonizer—modeled after air curtain burner systems—handled unchipped biomass at 680–750°C and used an excavator for loading (Puemmann et al., 2020 ). Once pyrolysis was complete, the resulting biochar was assumed to be transported in bulk over a 185-km round trip to the plugging site (COGIS, 2024). Detailed information on operational data for the various manufacturing methods can be found in Table S2 of the online resources. 3 Results & Discussion 3.1 Technoeconomic analysis A scenario analysis was conducted to estimate the cost of plugging a single orphan well with and without the addition of biochar to the cement slurry and spacer plugs (Fig. 2 ). In the baseline scenario, where no biochar is used, the total well plugging cost is estimated at 46,216 USD. This aligns with an average plugging cost of 51,141 USD reported by the ECMC (COGCC, 2022). The principal cost components are equipment use (notably the workover rig), bulk material mixing charges, and labor. In the biochar scenario, a 3% wt. biochar addition to the cement slurry and a 15% vol. biochar addition to the spacer plugging fluid translates into a total of 4.2 tonnes of biochar used per well. At a biochar purchase price of 209 USD per tonne, biochar integration increases total plugging costs by 983 USD, bringing the new total to 47,199 USD. This accounts for the biochar purchase itself, transportation to the well site, and marginally higher mixing costs. Among these additional expenses, the biochar purchase price is the primary contributor, while transport and extra bulk mixing fees have smaller impacts. Biochar prices are further evaluated to understand its impact on overall well plugging cost. While 209 USD per tonne reflects an average derived from multiple U.S. biochar manufacturers, local Colorado producers offer prices around 188 USD per tonne. Substituting this local rate lowers total well plugging costs to 47,108 USD. Conversely, considering a broader range of 58–347 USD per tonne that represent the minimum and maximum prices in the U.S., this results in final plugging costs varying from approximately 46,556 − 47,787 USD. These estimates exclude any revenue from carbon credits or other incentives. Because only a small volume of biochar was used, the overall cost impact has little fluctuations even under the highest and lowest price assumptions. Carbon credit valuations are also explored as a potential offset mechanism. The 4.2 tonnes of biochar used per well represent 7.5 tonnes of CO 2 e sequestered. At a carbon credit price of 150 USD per tonne CO 2 e, the potential credit per well would more than cover the additional biochar expense. The break-even price for carbon credits is approximately 121 USD per tonne CO 2 e if those credits are allocated to the well plugging operator. Consequently, in regions where robust carbon markets exist, biochar-inclusive well plugging may become cost-neutral or even cost-advantageous compared to conventional cement-only methods. 3.2 Life cycle assessment The carbon sequestration values and net GHG emissions for conventional well plugging (no biochar) and for plugging scenarios that incorporate biochar from five different production methods are shown in Fig. 3 , highlighting variations in the biochar’s carbon content and the energy requirements of each system. Results of the LCA show that for a conventional vertical well without biochar, emissions total 11.4 tonnes of CO₂e. Portland cement is the highest emission source in standard well plugging operations, accounting for 96% of the total—an outcome consistent with existing research on cement’s role as a major contributor to anthropogenic GHG emissions. Diesel follows as the second-largest contributor, responsible for around 2% of emissions, mainly due to transportation and on-site equipment use. Incorporating biochar decreases emissions in all scenarios, resulting in values ranging from 0.64 to 6.11 tonnes of CO₂e per well depending on the biomass’s thermochemical conversion method. The portable retort exhibits the highest carbon content and lowest moisture content, yielding high sequestration potential but also incurring the highest emissions due to substantial diesel and propane use during startup. By contrast, the mobile carbonizer balances high carbon content with lower startup requirements, achieving the greatest net negative emissions of the non-stationary methods analyzed. Both the portable retort and mobile carbonizer carry higher uncertainties, as they are newer technologies with less peer-reviewed data. Among the three stationary systems—injection auger, rotary kiln, and batch reactor—GHG emissions and reductions are comparable due to sharing preprocessing strategies, energy needs, and similar biochar carbon content. The injection auger requires additional electricity to power the auger mechanism, raising its emissions slightly above those of the rotary kiln, while the batch reactor’s start-stop operation also leads to marginally higher overall emissions. The rotary kiln runs continuously and does not rely on an auger, making it the lowest-emission option among these three systems. This analysis does not account for potential long-term impacts of removing forest residues on below- and above-ground carbon stocks. Such residue harvesting may alter wildfire risk, soil nutrient cycling, and overall forest productivity, potentially diminishing the net climate benefits of biochar use (Achat et al., 2015 ). Ultimately, the effectiveness of biochar production as a GHG emissions reductions strategy depends on maximizing the biochar used in well plugging, the fraction of biomass carbon retained in the char and minimizing operational emissions during pyrolysis. 3.3 Discussion Cement slurry used in well plugging must adhere to strict guidelines relating to its composition, compressive strength, and rheology as defined by the American Petroleum Institute (API) and Colorado law. Although Colorado code 404-1-434 specifies that all compressive strength testing of cement used for well plugging operations must be evaluated at 95 o F (COGCC, 2025), this study evaluated compressive strength at standard temperature and pressure due to equipment constraints. Additionally, due to the variation of equipment and plugging protocols in place, an exact viscosity to aim for was difficult to ascertain, and the viscosity of a biochar-free cement was chosen as the ideal viscosity to attain for the biochar-cements. To keep viscosity constant, a polycarboxylate superplasticizer was added to samples containing biochar (Tkaczewska, 2014 ). In samples containing > 3% biochar, even the addition of excess superplasticizer could not lower viscosity sufficiently. These samples also suffered from incomplete curing after a full 28 days. To further lower viscosity, a 3% sample with additional water was evaluated. This mix was very different than the mix ratios advised by the API (API, 2013 ) and performed poorly when compressed. Due to these findings, a 3% mix was identified as the mix containing the maximum amount of biochar without compromising strength or viscosity—both critical for maintaining wellbore integrity and ensuring efficient pumpability downhole. Full descriptions of the methods (Methods S1, S2, and S3) and data (Table S3 and S4; Figure S1 , S2, and S3) related to these cement-biochar composites can be found in the online resources. Cement incorporating 7% biochar by weight has been demonstrated to enhance compressive and flexural strength properties (Barbhuiya et al., 2024 ). However, the limited testing in this study indicates that such a mix would not comply with current regulations or recommendations and optimizing this formulation falls outside the study’s scope. A 7% biochar addition in the cement slurry would increase total biochar usage to 4.7 tonnes and lower well-plugging emissions to an average of 1.53 tonnes CO₂e across the five biochar production scenarios. The variability in biochar usage and emissions underscores the need for further investigation into the maximum feasible biochar content in well plugging. While only 8% of the 4.2 tonnes of biochar used in this study was incorporated into the cement slurry, incorporating biochar directly into cement may reduce cement permeability and mitigate gas migration (Barbhuiya et al., 2024 ). This would improve sealing by restricting the pathways through which gases or fluids might otherwise escape, a critical consideration in highly pressurized wellbores that risk leaks once plugged. When scaled to a state or national level, the widespread adoption of using biochar as an additive in well plugging could yield substantial GHG reductions. Plugging the 1,000 orphan wells in Colorado with biochar at an average emission rate of 2.4 tonnes of CO₂e would reduce emissions by approximately 8,994 tonnes CO₂e, corresponding to a 0.04% decrease in the state’s 2005 oil and gas emissions that serve as baseline levels for Colorado’s GHG climate goals (EPA, 2024 ). Extending this practice to the 33,000 abandoned wells in Colorado could produce an overall reduction of up to 1.5%. At the national scale, with an estimated 2.1 million unplugged wells, a cumulative reduction of approximately 18.9 million tonnes of CO₂e could be realized, underscoring biochar’s potential role in achieving broader climate objectives. Currently, there is a lack of carbon credit structures or universally accepted standards for using biochar in well plugging. Although carbon credit systems are emerging for other biochar applications, methodologies specific to well plugging have yet to be fully developed, verified, or codified. Establishing a dedicated protocol for biochar-based plugging would involve defining baseline conditions, measurement and verification processes, and long-term monitoring practices. Without these frameworks, operators lack clear avenues to monetize the climate benefits of biochar in well plugging, and broader adoption may be limited until robust regulatory and crediting mechanisms are established. Future work should include both laboratory studies and pilot-scale evaluations to determine the optimal characteristics of biochar feedstocks for well integrity and carbon sequestration while also providing operational data to validate biochar’s long-term stability, build regulatory confidence, and support broader industry adoption (Ballenger et al., 2024 ). Such demonstrations would provide empirical data on the efficacy of biochar in both spacer plugging fluid and cement slurries, while also revealing any unforeseen technical or economic challenges. Additionally, investigations around integrating biochar into surface site remediation could further reduce GHG emissions and potentially generate further credits once corresponding standards are developed. By validating biochar in well plugging through in-field implementations, researchers and industry stakeholders can advance the real-world applicability of biochar-based well plugging and develop a more sustainable approach to plugging and abandonment. 4 Conclusion This study integrated TEA and LCA to assess the economic and environmental implications of incorporating biochar as an additive into cement plugs and spacer plugging fluid in orphan well plugging and abandonment. Results indicate that while biochar can increase plugging costs by roughly 2%, the use of carbon credits could offset these additional plugging costs. The use of biochar can also decrease net GHG emissions from 11.4 t to 0.64–6.11 t CO 2 e per well, depending on the chosen biochar manufacturing method. Aggregating these emissions reductions across unplugged wells in the country demonstrate measurable emissions savings, resulting in biochar’s potential role in well plugging aligning with broader climate objectives. Declarations Acknowledgements We acknowledge the contributions of industry contacts, Colorado House Bill 23-1069 committee, and academic colleagues who provided insights and data whose expertise helped inform and validate the accuracy and depth of this study’s approach. The authors have no relevant financial or non-financial interests to disclose. CRediT Brooke Ballenger: Methodology, Writing – original draft, Writing – review & editing, Visualization Kerry Miller: Investigation, Writing – original draft Thomas Borch: Writing – review & editing, Supervision Jason Quinn: Writing – review & editing, Supervision Funding sources This work was supported by Colorado House Bill 23-1069. References Achat, D.L., Deleuze, C., Landmann, G., Augusto, L., 2015. Quantifying consequences of removing harvesting residues on forest soils and tree growth – A meta-analysis. Forest Ecology and Management, 348, 124–141. https://doi.org/10.1016/j.foreco.2015.03.042. AirTerra, 2024. About AirTerra. https://www.airterra.ca/about-airterra/ (accessed 21 May 2024). Amoneme, J.E., Yorgey, G.G., Schiller, S., 2023. Technical assessment of potential climate impact and economic viability of biochar technologies for small-scale agriculture in the Pacific Northwest. Pacific Northwest National Laboratory, Richland, WA. API, 2013. Recommended Practice 10B-2. American Petroleum Institute, second edition. Ballenger, B., Miller, K., Prentice, A., West Fordham, A., Malin, S., Collett, J., Riddick, S., Rosenbaum, E., Quinn, J., Borch, T., 2024. Pilot program recommendation outline—Colorado House Bill 23-1069. Barbhuiya, S., Das, B.B., Kanavaris, F., 2024. Biochar-concrete: A comprehensive review of properties, production and sustainability. Case Studies in Construction Materials, 20, e02859. https://doi.org/10.1016/j.cscm.2024.e02859. Bare, J., 2011. TRACI 2.0: The tool for the reduction and assessment of chemical and other environmental impacts 2.0. Clean Technologies and Environmental Policy, 13(5), 687–696. Blue Sky Biochar, 2024. Product Collections. https://blueskybiochar.com/collections/all (accessed 21 May 2024). Bogdanov, D., Gulagi, A., Fasihi, M., Breyer, C., 2021. Full energy sector transition towards 100% renewable energy supply: Integrating power, heat, transport, and industry sectors including desalination. Applied Energy, 283, 116273. https://doi.org/10.1016/j.apenergy.2020.116273. Brassard, P., Godbout, S., Hamelin, L., 2024. Framework for consequential life cycle assessment of pyrolysis biorefineries: A case study for the conversion of primary forestry residues. Brassard, P., Godbout, S., Raghavan, V., 2017. Pyrolysis in auger reactors for biochar and bio-oil production: A review. Biosystems Engineering, 161, 80–92. Cheng, F., Luo, H., Colosi, L.M., 2020. Slow pyrolysis as a platform for negative emissions technology: An integration of machine learning models, life cycle assessment, and economic analysis. Energy Conversion and Management, 223. Colorado Oil and Gas Association (COGA), 2024. Additional Resources. https://www.coga.org/additionalresources.html (accessed 5 Feb 2024). Colorado Oil and Gas Conservation Commission (COGCC), 2022. Orphaned Well Program FAQ. https://ecmc.state.co.us/documents/OWE/2022%20OWP%20FAQ.pdf (accessed 15 May 2024) Colorado Oil and Gas Conservation Commission (COGCC), 2023. Colorado Oil and Gas Information System (COGIS). https://cogcc.state.co.us/data.html (accessed 21 May 2024) Colorado Oil and Gas Conservation Commission (COGCC). (2025). Abandonment (2 Colo. Code Regs. § 404-1-434). Vol. 48, No. 1. https://www.law.cornell.edu/regulations/colorado/2-CCR-404-1-434 (accessed 15 May 2024) Colorado Oil and Gas Information System (COGIS), 2024. COGIS Data. https://ecmc.state.co.us/data.html#/cogis (accessed 21 May 2024). Colorado State Energy Profile, 2023. U.S. Energy Information Administration. EBC, 2020. Certification of the carbon sink potential of biochar. Ithaka Institute, Arbaz, Switzerland. EPA, 2024. Inventory of U.S. greenhouse gas emissions and sinks: 1990–2022. U.S. Environmental Protection Agency. https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks. Biochar Now, 2023. Personal communication. GHG Pollution Reduction Roadmap 2.0, 2023. https://energyoffice.colorado.gov/climate-energy/ghg-pollution-reduction-roadmap-20 (accessed 22 Apr 2024) Go Biochar, 2024. Products. https://gobiochar.com/shop/ (accessed 21 May 2024). Greenfield Environmental Solutions, 2025. Personal communication. Hansson, A., et al., 2020. Biochar as a multi-purpose sustainable technology: Experiences from projects in Tanzania. Environment, Development and Sustainability, 23(4), 5182–5214. Hawthorn, A., Steinsiek, R., Rahman, S., 2022. Casing and cement evaluation on drillpipe: New tool acquires well integrity data in parallel with existing drillpipe deployed operations from drilling to plug and abandonment. Offshore Technology Conference Asia. International Standards Organization, 2006. ISO 14040, Environmental management: Life cycle assessment—Requirements and regulations. International Standards Organization, 2006. ISO 14044, Environmental management: Life cycle assessment—Principles and framework. Interstate Oil and Gas Compact Commission (IOGCC), 2021. Idle and orphan wells: A national assessment. https://oklahoma.gov/content/dam/ok/en/iogcc/documents/news/iogcc_idle_and_orphan_wells_2021_final_web_0.pdf (accessed 17 Jan 2024). Kang, M., et al., 2016. Identification and characterization of high methane-emitting abandoned oil and gas wells. Proceedings of the National Academy of Sciences, 113(48), 13636–13641. Khalifeh, M., Saasen, A., 2020. Introduction to Permanent Plug and Abandonment of Wells. Ocean Engineering & Oceanography, Volume 12. Lin, X., et al., 2023. Biochar-cement concrete toward decarbonization and sustainability for construction: Characteristic, performance, and perspective. Journal of Cleaner Production. Miller, S.A., Habert, G., Myers, R.J., Harvey, J.T., 2021. Achieving net zero greenhouse gas emissions in the cement industry via value chain mitigation strategies. One Earth, 4(10), 1398–1411. https://doi.org/10.1016/j.oneear.2021.09.011. Moser, K., et al., 2023. Screw reactors and rotary kilns in biochar production: A comparative review. Journal of Analytical and Applied Pyrolysis, 174. National Petroleum Council (NPC), 2011. Plugging and abandoning oil and gas wells. Working Document of the NPC North American Resource Development Study, Paper #2–25, 1–21. Nogués, I., Mazzurco Miritana, V., Passatore, L., Zacchini, M., Peruzzi, E., Carloni, S., Pietrini, F., Marabottini, R., Chiti, T., Massaccesi, L., Marinari, S., 2023. Biochar soil amendment as carbon farming practice in a Mediterranean environment. Geoderma Regional, 33, e00634. https://doi.org/10.1016/j.geodrs.2023.e00634. Pamon, L.D., Abbom, W.A., 1982. Well completions and workovers: The systems approach. Energy Publications. Price, J.I., McCollum, D.W., Berrens, R.P., 2010. Insect infestation and residential property values: A hedonic analysis of the mountain pine beetle epidemic. Forest Policy and Economics, 12(6), 415–422. https://doi.org/10.1016/j.forpol.2010.05.004. Puemmann, M., et al., 2020. Life cycle assessment of biochar produced from forest residues using portable systems. Journal of Cleaner Production, 250. Puro.earth, 2024. CORC CO₂ Removal Certificate Supplier Listings. https://carbon.puro.earth/CORC-co2-removal-certificate/supplier-listings (accessed 21 May 2024). Puro.earth, 2024. CORC carbon removal indexes. https://puro.earth/corc-carbon-removal-indexes (accessed 22 May 2024) Raimi, D., et al., 2021. Decommissioning orphaned and abandoned oil and gas wells: New estimates and cost drivers. Environmental Science & Technology, 55(15), 10224–10230. Rogue Biochar, 2024. Pricing. Oregon Biochar Solutions. https://www.chardirect.com/rogue-biochar-pricing (accessed 21 May 2024). Roth, H., Silagy, B., Miller, K., Woolman, A., West Fordham, A., Martin, A.M., Quinn, J., Borch, T., 2024. Study biochar in plugging of oil and gas wells—Colorado House Bill 23-1069. Salimi, A., Beni, A.H., Bazvand, M., 2024. Evaluation of a water-based spacer fluid with additives for mud removal in well cementing operations. Heliyon, 10(4), e25638. Scherer, T., 2021. A guide to plugging abandoned wells. She, Chung, Han, 2019. Economic and environmental optimization of the forest supply chain for timber and bioenergy production from beetle-killed forests in northern Colorado. Forests, 10(8). Tisserant, A., Cherubini, F., 2019. Potentials, limitations, co-benefits, and trade-offs of biochar applications to soils for climate change mitigation. Land, 8(12). Tkaczewska, E., 2014. Effect of the superplasticizer type on the properties of the fly ash blended cement. Construction and Building Materials, 70(15), 388-393. https://doi.org/10.1016/j.conbuildmat.2014.07.096 Trove Research, 2024. Outlook for the global biochar market. https://trove-research.com/report/outlook-for-the-global-biochar-market (accessed 22 May 2024) US Biochar Initiative (USBI), 2024. 2023 Global Biochar Market Report. U.S. Forest Service (USFS), 2020. Forest Insect and Disease Conditions in the United States: 2020. Vrålstad, T., Saasen, A., Fjær, E., Øia, T., Ytrehus, J.D., Khalifeh, M., 2019. Plug & abandonment of offshore wells: Ensuring long-term well integrity and cost-efficiency. Journal of Petroleum Science and Engineering, 173, 478–491. https://doi.org/10.1016/j.petrol.2018.10.049. Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., Weidema, B., 2016. The ecoinvent database version 3 (part I): overview and methodology. The International Journal of Life Cycle Assessment, 21 (9), 1218–1230. https://doi.org/10.1007/s11367-016-1087-8. Wrobel-Tobiszewska, A., et al., 2015. An economic analysis of biochar production using residues from Eucalypt plantations. Biomass and Bioenergy, 81, 177–182. Zajec, L., 2009. Slow pyrolysis in a rotary kiln reactor: Optimization and experiments. RES, University of Iceland and the University of Akureyri, Akureyri, Iceland. Additional Declarations No competing interests reported. Supplementary Files SupplementaryMaterial.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 14 Apr, 2026 Reviews received at journal 28 Mar, 2026 Reviews received at journal 27 Mar, 2026 Reviewers agreed at journal 22 Feb, 2026 Reviewers agreed at journal 22 Feb, 2026 Reviews received at journal 09 Sep, 2025 Reviewers agreed at journal 29 Jul, 2025 Reviewers invited by journal 27 Jul, 2025 Editor assigned by journal 15 Jun, 2025 Submission checks completed at journal 05 Jun, 2025 First submitted to journal 04 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6823444","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":492854574,"identity":"8bf61fb9-c554-44e9-acd8-5b18f0aecb04","order_by":0,"name":"Brooke Ballenger","email":"","orcid":"","institution":"Colorado State University","correspondingAuthor":false,"prefix":"","firstName":"Brooke","middleName":"","lastName":"Ballenger","suffix":""},{"id":492854575,"identity":"ca6cafe7-967b-4fa1-a515-3063424d76dd","order_by":1,"name":"Kerry Miller","email":"","orcid":"","institution":"Colorado State University","correspondingAuthor":false,"prefix":"","firstName":"Kerry","middleName":"","lastName":"Miller","suffix":""},{"id":492854577,"identity":"48a20713-cc1b-4595-af08-7d1654c7b54d","order_by":2,"name":"Thomas Borch","email":"","orcid":"","institution":"Colorado State University","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"","lastName":"Borch","suffix":""},{"id":492854578,"identity":"1699ddab-65ef-421d-8c50-93cfc91c0f14","order_by":3,"name":"Jason C. Quinn","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYBACxgYogw3IfsDAYIEpg08LswEDgwSIBRbEqQUZsEkQpYW5/fjDxwUM1ol90r3HKn5USMjJz29+/uADg43shgM4HNaTY2w8gyE9sU3mXNrNnjMSxgbH2AwbZzCkGePU0pDDJs3DcDixTSLH7DZjm0TiBjYGw2aQCE4t/c+fwbUUg7TMb2P/2PyH4T9uLTMSzOBamEFaGo7xGDYzMBzAo+WNsTGPQboxUIuxJMQvOYUzewySjWfi0GLYn/7wMU+Ftez8GTmGH35U2MjJNx/fAGTYyfbh0tIAIg2Y0cUNsCsHAXkIhaFlFIyCUTAKRgECAACRnliSRB5t1AAAAABJRU5ErkJggg==","orcid":"","institution":"Colorado State University","correspondingAuthor":true,"prefix":"","firstName":"Jason","middleName":"C.","lastName":"Quinn","suffix":""}],"badges":[],"createdAt":"2025-06-04 20:38:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6823444/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6823444/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88000686,"identity":"ea8ef5a6-5936-4037-a928-e72451fdb444","added_by":"auto","created_at":"2025-07-31 10:20:57","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":570717,"visible":true,"origin":"","legend":"\u003cp\u003eConventional (a) and biochar-additive (b) well plugging configurations. The conventional scenario (left) uses Portland Class G cement, while the biochar-additive scenario (right) incorporates biochar in both the cement slurry and spacer plugging fluid. Arrows indicate cement plugs and spacer placement. The wellbore is 2074 m deep, with a diameter of 0.232 m down to 442 m, then reducing to 0.127 m. The surface plug has a plug length of 8 m, while all other plugs have lengths of 61 m\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6823444/v1/2bb00944e51d891dde3fae30.png"},{"id":88000689,"identity":"d3eb9a14-c04e-4408-ab63-d69f8e0691a1","added_by":"auto","created_at":"2025-07-31 10:20:57","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":82048,"visible":true,"origin":"","legend":"\u003cp\u003eCost comparison of conventional and biochar-enhanced well plugging. The conventional scenario (bottom) uses only Portland class G cement, while the biochar-additive scenario (top) incorporates 3% biochar in the cement slurry and 15% biochar in the spacer plugging fluid. Other procedures include the wireline and cement squeezing operations, pressure testing, and cut-and-cap operation. Total costs increase by 983 USD, or 2%, primarily due to biochar purchase, but remain within the typical range for well plugging. Labor, use of workover rig, and cement remain the largest contributors in both cases, with biochar expenses offsetting minor reductions in cement use\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6823444/v1/b9cdc68364c4d3383c65d8dd.png"},{"id":88002816,"identity":"2fb27629-ae9d-4a60-bad3-50db736f733c","added_by":"auto","created_at":"2025-07-31 10:28:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":148913,"visible":true,"origin":"","legend":"\u003cp\u003eNet greenhouse gas (GHG) emissions per well plugged across conventional and biochar-enhanced scenarios. The conventional approach (far left) emits 11.4 tonnes CO₂e per well, primarily from Portland cement. Biochar integration reduces emissions across all thermochemical conversion methods, ranging from 0.64 to 6.11 tonnes CO₂e per well\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6823444/v1/b7650233dfd8f4b0e59515a7.png"},{"id":88004440,"identity":"eaa5a0a8-9069-4e02-9722-960e0a6a1bcf","added_by":"auto","created_at":"2025-07-31 10:36:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1171780,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6823444/v1/471aad7b-2123-4df7-8a5d-992a22fe0a61.pdf"},{"id":88000699,"identity":"946cf019-763a-4ff0-868c-8ca8909a0791","added_by":"auto","created_at":"2025-07-31 10:20:58","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":16037483,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-6823444/v1/9cf269a54ab031189c422952.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"A techno-economic analysis and life cycle assessment of woody biochar as an additive for orphan well plugging","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eWell plugging refers to the permanent sealing of oil and gas wells that have reached the end of their operational lifetime. Plug and abandonment operations generally involve placing cement plugs in the wellbore to isolate the reservoir and other fluid-bearing formations (Vr\u0026aring;lstad et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Since the mid-1800s, millions of wells have been drilled across the United States; as of 2018, approximately 2.1\u0026nbsp;million remain unplugged (EPA, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In Colorado\u0026mdash;the fifth-largest crude oil producer in the nation\u0026mdash;around 33,000 wells are either abandoned or unplugged as of 2023 (U.S. Energy Information Administration, 2023; COGA, 2024; COGCC, 2023). Some of these wells are \u0026ldquo;orphaned,\u0026rdquo; meaning the original operators abandoned them with no financially responsible party left to cover plugging costs (Raimi et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). State governments often rely on taxpayer funds to manage these wells. Properly plugging them is crucial for preventing methane emissions and groundwater or surface water contamination (Raimi et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kang et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003cp\u003ePortland cement is one of the main materials used in well plugging due to its effectiveness in sealing the wellbore (Vr\u0026aring;lstad et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, cement production is a significant source of anthropogenic greenhouse gas (GHG) emissions which leads to a high carbon footprint of plugging and abandonment operations (Miller et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As the shift toward renewable energy accelerates, more oil and gas wells will reach the end of their productive lifetimes and require decommissioning (Bogdanov et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Using alternatives to conventional cement-based methods can help in reducing GHG emissions associated with the process and assist in meeting Colorado\u0026rsquo;s GHG reduction goals, 50% by 2030 and net-zero by 2050 (GHG Pollution Reduction Roadmap 2.0, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Recent studies show that using biochar, a stable carbon-rich material produced by pyrolysis, in cement slurries can improve mechanical strength of cement and increase the lifetime of plugging operations (Lin et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Biochar may also be able to offset GHG emissions associated with the plugging process by indefinitely sequestering large amounts of carbon (Hansson et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Tisserant and Cherubini, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAlthough biochar has been extensively studied in soil amendment applications, its use in well plugging is still in the early conceptual stages (Nogu\u0026eacute;s et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Roth et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Preliminary studies suggest that biochar may integrate well with cement, yet there is a lack of robust techno-economic analysis (TEA) and life cycle assessment (LCA) data to evaluate the trade-offs between environmental benefits and additional costs (Roth et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Without detailed insights into the economic and environmental implications, it remains difficult to determine whether plugging materials using biochar as an additive can meaningfully reduce GHG emissions and whether any extra expense is warranted.\u003c/p\u003e\u003cp\u003eIn this work, a TEA is carried out to estimate the incremental cost of incorporating woody biomass\u0026ndash;based biochar as an additive to orphan well plugging operations. Simultaneously, a cradle-to-gate LCA quantifies changes in GHG emissions compared to standard conventional well plugging scenarios. Various thermochemical conversion pathways are evaluated to explore how different biochar properties may influence overall emissions. Through concurrent TEA and LCA, this analysis provides a more comprehensive understanding of potential biochar adoption in plugging and abandonment practices, supporting both Colorado and nationwide strategies for GHG mitigation as an increasing number of wells become inactive and require decommissioning.\u003c/p\u003e"},{"header":"2 Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Techno-economic analysis\u003c/h2\u003e\u003cp\u003eA TEA was conducted to compare two orphan well plugging scenarios (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e): a baseline scenario using conventional Portland class G cement and a novel scenario that integrated woody biochar into both the cement plugs and the spacer plugging fluid\u0026mdash;used to fill the volume of the well not occupied by the cement (Salimi et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Plugging costs vary widely depending on factors such as well depth, geological conditions, and the length of time the well has been idle (Interstate Oil and Gas Compact Commission, 2021). To establish a representative baseline, a single conventional vertical well at an approximate depth of 2074 m was chosen, reflecting the average depth profile among 94,793 wells in Colorado (COGCC, 2023). Cost components included labor, material inputs, equipment rental, various plugging procedures (e.g., wireline and cement squeezing operations, pressure testing, and cut-and-cap operation), all converted to 2024 USD (Hawthorn et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Pamon and Abbom, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1982\u003c/span\u003e). Rental costs and diesel use for vehicles such as bulk cement trucks, triplex trucks, and workover rigs were included based on standard industry practice (National Petroleum Council, 2011). The conventional cement slurry consisted of Portland class G cement mixed with 19 L of water per cement sack, while the spacer plug fluid was modeled as a water with 5% vol. bentonite mixture, a configuration widely used in routine operations (Khalifeh \u0026amp; Saasen, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Scherer, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eData for the baseline scenario came from detailed logs that well plugging operators must submit to the Colorado Energy \u0026amp; Carbon Management Commission (ECMC) when performing plugging and abandonment activities (COGCC, 2023). These logs specify the number of cement plugs, the volumes of cement and spacer plugging fluids, and other key parameters used in plugging operations. Additional operational assumptions were informed by literature and local plugging operators. Typical labor rates, mixing charges, rig rental fees, and associated operating costs (vehicle usage, fuel, equipment rentals) were aggregated to capture a representative profile of conventional well plugging in Colorado. More detailed inputs regarding TEA parameters can be found in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e of the online resources.\u003c/p\u003e\u003cp\u003eThe second scenario involved using biochar as an additive in the spacer plugging fluid and cement plugs. Due to the mountain pine beetle endemic in Colorado\u0026mdash;which has resulted in large volumes of beetle-killed timber with minimal commercial value\u0026mdash;this study focused exclusively on woody biochar (USFS, 2020; Price et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). The biochar scenario mirrored the baseline operational procedures, equipment, and rental fees but replaced part of the cement slurry and spacer plugging fluid with biochar at a purchase price of 209 USD per tonne derived from reported values by U.S. biochar manufacturers (COGIS, 2024; Puro.earth, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Rogue Biochar Pricing, 2024.; Go Biochar, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Blue Sky Biochar, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; AirTerra, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe cement slurry was modeled as a blend of Portland class G cement, 19 L of water per cement sack, and 3% wt. biochar, while the spacer plugging fluid was composed of water, 5% vol. bentonite, and 15% vol. biochar, as advised by communication with local plugging operators (Greenfield Environmental Solutions, 2024). The 3% wt. biochar was determined through mechanical testing of cured cement with or without biochar added in. Briefly, Portland cement was combined with 44% water, then 0\u0026ndash;10% biochar by mass added to the mixture. The cement was cured at standard temperature and pressure, then evaluated for its compressive strength after 1, 4, 7, and 28 days, as well as their viscosities as slurry. Mixtures higher than 3% wt. biochar were not able to match the compressive strength of cement with no added biochar and were eliminated from further testing. More detailed protocols regarding physical testing of the cement-biochar composites can be found in Methods S1, S2, and S3 of the online resources.\u003c/p\u003e\u003cp\u003eAdditional costs included transportation to the well site and on-site mixing. Considering that biochar market prices vary substantially by manufacturer, further analysis varied biochar costs between 58 and 347 USD, the minimum and maximum reported by U.S. biochar manufacturers. The baseline scenario excluded any carbon credit revenue, providing an initial benchmark of the direct cost changes. However, because carbon credits could improve overall project economics, additional scenarios examined credit values ranging from 50 USD to 200 USD per tonne CO\u003csub\u003e2\u003c/sub\u003ee (Trove Research, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Puro.earth, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). As of February 2024, the average market price was approximately 150 USD per tonne CO\u003csub\u003e2\u003c/sub\u003ee (Puro.earth, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This analysis did not assume any well plugging complications, abnormal well conditions, or well surface environmental remediation, and instead focused on the most common operational conditions for routine well plugging of a conventional vertical well.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Life cycle assessment\u003c/h2\u003e\u003cp\u003eUsing a cradle-to-grave LCA methodology according to the International Organization for Standardization (ISO, 2006), an environmental analysis was carried out similarly to the TEA to compare the GHG emissions from conventional orphan well plugging against scenarios incorporating biochar into both the cement slurry and the spacer plugging fluid. The functional unit was defined as \u0026ldquo;one plugged well\u0026rdquo; with a conventional vertical depth of 2074 m. The primary objective was to determine whether potential net emission reductions resulting from biochar use are substantial enough to justify further adoption.\u003c/p\u003e\u003cp\u003eThe system boundary for the baseline scenario extended from raw material production to the final plugging of the orphan well. The biochar-additive scenario followed the same boundary conditions as the baseline scenario and included any biochar-related emissions and reductions from biomass procurement, thermochemical conversion into biochar, transportation of the final biochar product to the well site and well-site operations. Feedstock-related upstream timber management activities were excluded to focus on direct emissions associated with biochar production and well plugging (She et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Emissions factors were taken from Ecoinvent 3.9.1 and the United States Life Cycle Inventory Database (Wernet et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) and were characterized via global warming potential (GWP) using the EPA\u0026rsquo;s Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI) version 2.1 (Bare, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Material quantities on conventional well plugging followed the same conditions as the TEA.\u003c/p\u003e\u003cp\u003eThe European Biochar Certificate (EBC) standard provided the basis for calculating a carbon sequestration value (Eq.\u0026nbsp;1), assuming a 100% permanence factor for carbon sequestered within the wellbore (EBC, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{Q}_{biochar}\\)\u003c/span\u003e\u003c/span\u003e is the quantity of biochar generated, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{org}\\)\u003c/span\u003e\u003c/span\u003e is the organic carbon content of biochar, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{F}_{p}^{TH}\\)\u003c/span\u003e\u003c/span\u003e is the permanence factor over a time horizon \u003cem\u003eTH\u003c/em\u003e, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{44}{12}\\)\u003c/span\u003e\u003c/span\u003e is the molecular weight ratio of CO\u003csub\u003e2\u003c/sub\u003e to carbon.\u003c/p\u003e\u003cp\u003e\u003cem\u003eEquation 1\u003c/em\u003e \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{E}_{stored}={Q}_{biochar}\\:x\\:{C}_{org}\\:x\\:{F}_{p}^{TH}\\:x\\:\\frac{44}{12}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eMultiple pyrolysis configurations frequently used in North American biochar production were evaluated, including stationary auger reactors, stationary rotary kilns, stationary batch reactors, portable retorts, and mobile carbonizers (USBI, 2024). In all stationary systems, after collection, biomass was transported as whole logs over an estimated 161-km round trip to the pyrolysis facility for any necessary processing (Amoneme et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The biomass feedstock\u0026mdash;forest harvest residue with an initial moisture content of 30%\u0026mdash;was dried in an industrial rotary dryer to approximately 10% moisture and subsequently reduced in size using a hammer mill (Zajec, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cheng et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The auger and rotary kiln reactors operated continuously at 500\u0026deg;C under an inert nitrogen atmosphere and relied on electricity and natural gas for heating and operation (Moser et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Brassard et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The batch reactor processed biomass under the same temperature and atmosphere conditions but utilized a start-stop approach rather than a continuous feed. While the auger reactor employed a rotating screw to transport the biomass, the rotary kiln reactor featured a rotating cylindrical tube without a screw. For each of these stationary systems, any co-generated syngas was recycled at a 75% efficiency rate to supply part of the process heat, and a mass allocation approach was employed for distributing emissions among biochar and its co-products (Brassard et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003ePortable retorts and mobile carbonizers enable on-site production, reducing transport needs. Both systems used diesel or propane for startup, allowing them to process biomass up to 20\u0026ndash;25% moisture without extensive drying (Wrobel-Tobiszewska et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Biochar Now, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Puemmann et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The portable retort operated at 550\u0026ndash;600\u0026deg;C and required a diesel-powered chipper for size reduction, where the mobile carbonizer\u0026mdash;modeled after air curtain burner systems\u0026mdash;handled unchipped biomass at 680\u0026ndash;750\u0026deg;C and used an excavator for loading (Puemmann et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Once pyrolysis was complete, the resulting biochar was assumed to be transported in bulk over a 185-km round trip to the plugging site (COGIS, 2024). Detailed information on operational data for the various manufacturing methods can be found in Table S2 of the online resources.\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results \u0026 Discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Technoeconomic analysis\u003c/h2\u003e\u003cp\u003eA scenario analysis was conducted to estimate the cost of plugging a single orphan well with and without the addition of biochar to the cement slurry and spacer plugs (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In the baseline scenario, where no biochar is used, the total well plugging cost is estimated at 46,216 USD. This aligns with an average plugging cost of 51,141 USD reported by the ECMC (COGCC, 2022). The principal cost components are equipment use (notably the workover rig), bulk material mixing charges, and labor.\u003c/p\u003e\u003cp\u003eIn the biochar scenario, a 3% wt. biochar addition to the cement slurry and a 15% vol. biochar addition to the spacer plugging fluid translates into a total of 4.2 tonnes of biochar used per well. At a biochar purchase price of 209 USD per tonne, biochar integration increases total plugging costs by 983 USD, bringing the new total to 47,199 USD. This accounts for the biochar purchase itself, transportation to the well site, and marginally higher mixing costs. Among these additional expenses, the biochar purchase price is the primary contributor, while transport and extra bulk mixing fees have smaller impacts.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eBiochar prices are further evaluated to understand its impact on overall well plugging cost. While 209 USD per tonne reflects an average derived from multiple U.S. biochar manufacturers, local Colorado producers offer prices around 188 USD per tonne. Substituting this local rate lowers total well plugging costs to 47,108 USD. Conversely, considering a broader range of 58\u0026ndash;347 USD per tonne that represent the minimum and maximum prices in the U.S., this results in final plugging costs varying from approximately 46,556\u0026thinsp;\u0026minus;\u0026thinsp;47,787 USD. These estimates exclude any revenue from carbon credits or other incentives. Because only a small volume of biochar was used, the overall cost impact has little fluctuations even under the highest and lowest price assumptions.\u003c/p\u003e\u003cp\u003eCarbon credit valuations are also explored as a potential offset mechanism. The 4.2 tonnes of biochar used per well represent 7.5 tonnes of CO\u003csub\u003e2\u003c/sub\u003ee sequestered. At a carbon credit price of 150 USD per tonne CO\u003csub\u003e2\u003c/sub\u003ee, the potential credit per well would more than cover the additional biochar expense. The break-even price for carbon credits is approximately 121 USD per tonne CO\u003csub\u003e2\u003c/sub\u003ee if those credits are allocated to the well plugging operator. Consequently, in regions where robust carbon markets exist, biochar-inclusive well plugging may become cost-neutral or even cost-advantageous compared to conventional cement-only methods.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Life cycle assessment\u003c/h2\u003e\u003cp\u003eThe carbon sequestration values and net GHG emissions for conventional well plugging (no biochar) and for plugging scenarios that incorporate biochar from five different production methods are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, highlighting variations in the biochar\u0026rsquo;s carbon content and the energy requirements of each system. Results of the LCA show that for a conventional vertical well without biochar, emissions total 11.4 tonnes of CO₂e. Portland cement is the highest emission source in standard well plugging operations, accounting for 96% of the total\u0026mdash;an outcome consistent with existing research on cement\u0026rsquo;s role as a major contributor to anthropogenic GHG emissions. Diesel follows as the second-largest contributor, responsible for around 2% of emissions, mainly due to transportation and on-site equipment use.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIncorporating biochar decreases emissions in all scenarios, resulting in values ranging from 0.64 to 6.11 tonnes of CO₂e per well depending on the biomass\u0026rsquo;s thermochemical conversion method. The portable retort exhibits the highest carbon content and lowest moisture content, yielding high sequestration potential but also incurring the highest emissions due to substantial diesel and propane use during startup. By contrast, the mobile carbonizer balances high carbon content with lower startup requirements, achieving the greatest net negative emissions of the non-stationary methods analyzed. Both the portable retort and mobile carbonizer carry higher uncertainties, as they are newer technologies with less peer-reviewed data.\u003c/p\u003e\u003cp\u003eAmong the three stationary systems\u0026mdash;injection auger, rotary kiln, and batch reactor\u0026mdash;GHG emissions and reductions are comparable due to sharing preprocessing strategies, energy needs, and similar biochar carbon content. The injection auger requires additional electricity to power the auger mechanism, raising its emissions slightly above those of the rotary kiln, while the batch reactor\u0026rsquo;s start-stop operation also leads to marginally higher overall emissions. The rotary kiln runs continuously and does not rely on an auger, making it the lowest-emission option among these three systems.\u003c/p\u003e\u003cp\u003eThis analysis does not account for potential long-term impacts of removing forest residues on below- and above-ground carbon stocks. Such residue harvesting may alter wildfire risk, soil nutrient cycling, and overall forest productivity, potentially diminishing the net climate benefits of biochar use (Achat et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Ultimately, the effectiveness of biochar production as a GHG emissions reductions strategy depends on maximizing the biochar used in well plugging, the fraction of biomass carbon retained in the char and minimizing operational emissions during pyrolysis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Discussion\u003c/h2\u003e\u003cp\u003eCement slurry used in well plugging must adhere to strict guidelines relating to its composition, compressive strength, and rheology as defined by the American Petroleum Institute (API) and Colorado law. Although Colorado code 404-1-434 specifies that all compressive strength testing of cement used for well plugging operations must be evaluated at 95\u003csup\u003eo\u003c/sup\u003eF (COGCC, 2025), this study evaluated compressive strength at standard temperature and pressure due to equipment constraints. Additionally, due to the variation of equipment and plugging protocols in place, an exact viscosity to aim for was difficult to ascertain, and the viscosity of a biochar-free cement was chosen as the ideal viscosity to attain for the biochar-cements. To keep viscosity constant, a polycarboxylate superplasticizer was added to samples containing biochar (Tkaczewska, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In samples containing\u0026thinsp;\u0026gt;\u0026thinsp;3% biochar, even the addition of excess superplasticizer could not lower viscosity sufficiently. These samples also suffered from incomplete curing after a full 28 days. To further lower viscosity, a 3% sample with additional water was evaluated. This mix was very different than the mix ratios advised by the API (API, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and performed poorly when compressed. Due to these findings, a 3% mix was identified as the mix containing the maximum amount of biochar without compromising strength or viscosity\u0026mdash;both critical for maintaining wellbore integrity and ensuring efficient pumpability downhole. Full descriptions of the methods (Methods S1, S2, and S3) and data (Table S3 and S4; Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e, S2, and S3) related to these cement-biochar composites can be found in the online resources.\u003c/p\u003e\u003cp\u003eCement incorporating 7% biochar by weight has been demonstrated to enhance compressive and flexural strength properties (Barbhuiya et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, the limited testing in this study indicates that such a mix would not comply with current regulations or recommendations and optimizing this formulation falls outside the study\u0026rsquo;s scope. A 7% biochar addition in the cement slurry would increase total biochar usage to 4.7 tonnes and lower well-plugging emissions to an average of 1.53 tonnes CO₂e across the five biochar production scenarios. The variability in biochar usage and emissions underscores the need for further investigation into the maximum feasible biochar content in well plugging. While only 8% of the 4.2 tonnes of biochar used in this study was incorporated into the cement slurry, incorporating biochar directly into cement may reduce cement permeability and mitigate gas migration (Barbhuiya et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This would improve sealing by restricting the pathways through which gases or fluids might otherwise escape, a critical consideration in highly pressurized wellbores that risk leaks once plugged.\u003c/p\u003e\u003cp\u003eWhen scaled to a state or national level, the widespread adoption of using biochar as an additive in well plugging could yield substantial GHG reductions. Plugging the 1,000 orphan wells in Colorado with biochar at an average emission rate of 2.4 tonnes of CO₂e would reduce emissions by approximately 8,994 tonnes CO₂e, corresponding to a 0.04% decrease in the state\u0026rsquo;s 2005 oil and gas emissions that serve as baseline levels for Colorado\u0026rsquo;s GHG climate goals (EPA, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Extending this practice to the 33,000 abandoned wells in Colorado could produce an overall reduction of up to 1.5%. At the national scale, with an estimated 2.1\u0026nbsp;million unplugged wells, a cumulative reduction of approximately 18.9\u0026nbsp;million tonnes of CO₂e could be realized, underscoring biochar\u0026rsquo;s potential role in achieving broader climate objectives.\u003c/p\u003e\u003cp\u003eCurrently, there is a lack of carbon credit structures or universally accepted standards for using biochar in well plugging. Although carbon credit systems are emerging for other biochar applications, methodologies specific to well plugging have yet to be fully developed, verified, or codified. Establishing a dedicated protocol for biochar-based plugging would involve defining baseline conditions, measurement and verification processes, and long-term monitoring practices. Without these frameworks, operators lack clear avenues to monetize the climate benefits of biochar in well plugging, and broader adoption may be limited until robust regulatory and crediting mechanisms are established.\u003c/p\u003e\u003cp\u003eFuture work should include both laboratory studies and pilot-scale evaluations to determine the optimal characteristics of biochar feedstocks for well integrity and carbon sequestration while also providing operational data to validate biochar\u0026rsquo;s long-term stability, build regulatory confidence, and support broader industry adoption (Ballenger et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Such demonstrations would provide empirical data on the efficacy of biochar in both spacer plugging fluid and cement slurries, while also revealing any unforeseen technical or economic challenges. Additionally, investigations around integrating biochar into surface site remediation could further reduce GHG emissions and potentially generate further credits once corresponding standards are developed. By validating biochar in well plugging through in-field implementations, researchers and industry stakeholders can advance the real-world applicability of biochar-based well plugging and develop a more sustainable approach to plugging and abandonment.\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThis study integrated TEA and LCA to assess the economic and environmental implications of incorporating biochar as an additive into cement plugs and spacer plugging fluid in orphan well plugging and abandonment. Results indicate that while biochar can increase plugging costs by roughly 2%, the use of carbon credits could offset these additional plugging costs. The use of biochar can also decrease net GHG emissions from 11.4 t to 0.64\u0026ndash;6.11 t CO\u003csub\u003e2\u003c/sub\u003ee per well, depending on the chosen biochar manufacturing method. Aggregating these emissions reductions across unplugged wells in the country demonstrate measurable emissions savings, resulting in biochar\u0026rsquo;s potential role in well plugging aligning with broader climate objectives.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eWe acknowledge the contributions of industry contacts, Colorado House Bill 23-1069 committee, and academic colleagues who provided insights and data whose expertise helped inform and validate the accuracy and depth of this study\u0026rsquo;s approach.\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\u003ch2\u003eCRediT\u003c/h2\u003e\n\u003cp\u003eBrooke Ballenger: Methodology, Writing \u0026ndash; original draft, Writing \u0026ndash; review \u0026amp; editing, Visualization\u003c/p\u003e\n\u003cp\u003eKerry Miller: Investigation, Writing \u0026ndash; original draft\u003c/p\u003e\n\u003cp\u003eThomas Borch: Writing \u0026ndash; review \u0026amp; editing, Supervision\u003c/p\u003e\n\u003cp\u003eJason Quinn: Writing \u0026ndash; review \u0026amp; editing, Supervision\u003c/p\u003e\n\u003ch2\u003eFunding sources\u003c/h2\u003e\n\u003cp\u003e\u003cem\u003eThis work was supported by Colorado House Bill 23-1069.\u0026nbsp;\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAchat, D.L., Deleuze, C., Landmann, G., Augusto, L., 2015. Quantifying consequences of removing harvesting residues on forest soils and tree growth \u0026ndash; A meta-analysis. Forest Ecology and Management, 348, 124\u0026ndash;141. https://doi.org/10.1016/j.foreco.2015.03.042.\u003c/li\u003e\n\u003cli\u003eAirTerra, 2024. About AirTerra. https://www.airterra.ca/about-airterra/ (accessed 21 May 2024).\u003c/li\u003e\n\u003cli\u003eAmoneme, J.E., Yorgey, G.G., Schiller, S., 2023. Technical assessment of potential climate impact and economic viability of biochar technologies for small-scale agriculture in the Pacific Northwest. Pacific Northwest National Laboratory, Richland, WA.\u003c/li\u003e\n\u003cli\u003eAPI, 2013. Recommended Practice 10B-2. American Petroleum Institute, second edition. \u003c/li\u003e\n\u003cli\u003eBallenger, B., Miller, K., Prentice, A., West Fordham, A., Malin, S., Collett, J., Riddick, S., Rosenbaum, E., Quinn, J., Borch, T., 2024. Pilot program recommendation outline\u0026mdash;Colorado House Bill 23-1069.\u003c/li\u003e\n\u003cli\u003eBarbhuiya, S., Das, B.B., Kanavaris, F., 2024. Biochar-concrete: A comprehensive review of properties, production and sustainability. Case Studies in Construction Materials, 20, e02859. https://doi.org/10.1016/j.cscm.2024.e02859.\u003c/li\u003e\n\u003cli\u003eBare, J., 2011. TRACI 2.0: The tool for the reduction and assessment of chemical and other environmental impacts 2.0. Clean Technologies and Environmental Policy, 13(5), 687\u0026ndash;696.\u003c/li\u003e\n\u003cli\u003eBlue Sky Biochar, 2024. Product Collections. https://blueskybiochar.com/collections/all (accessed 21 May 2024).\u003c/li\u003e\n\u003cli\u003eBogdanov, D., Gulagi, A., Fasihi, M., Breyer, C., 2021. Full energy sector transition towards 100% renewable energy supply: Integrating power, heat, transport, and industry sectors including desalination. Applied Energy, 283, 116273. https://doi.org/10.1016/j.apenergy.2020.116273.\u003c/li\u003e\n\u003cli\u003eBrassard, P., Godbout, S., Hamelin, L., 2024. Framework for consequential life cycle assessment of pyrolysis biorefineries: A case study for the conversion of primary forestry residues.\u003c/li\u003e\n\u003cli\u003eBrassard, P., Godbout, S., Raghavan, V., 2017. Pyrolysis in auger reactors for biochar and bio-oil production: A review. Biosystems Engineering, 161, 80\u0026ndash;92.\u003c/li\u003e\n\u003cli\u003eCheng, F., Luo, H., Colosi, L.M., 2020. Slow pyrolysis as a platform for negative emissions technology: An integration of machine learning models, life cycle assessment, and economic analysis. Energy Conversion and Management, 223.\u003c/li\u003e\n\u003cli\u003eColorado Oil and Gas Association (COGA), 2024. Additional Resources. https://www.coga.org/additionalresources.html (accessed 5 Feb 2024).\u003c/li\u003e\n\u003cli\u003eColorado Oil and Gas Conservation Commission (COGCC), 2022. Orphaned Well Program FAQ. https://ecmc.state.co.us/documents/OWE/2022%20OWP%20FAQ.pdf (accessed 15 May 2024)\u003c/li\u003e\n\u003cli\u003eColorado Oil and Gas Conservation Commission (COGCC), 2023. Colorado Oil and Gas Information System (COGIS). https://cogcc.state.co.us/data.html (accessed 21 May 2024)\u003c/li\u003e\n\u003cli\u003eColorado Oil and Gas Conservation Commission (COGCC). (2025). Abandonment (2 Colo. Code Regs. \u0026sect; 404-1-434). Vol. 48, No. 1. https://www.law.cornell.edu/regulations/colorado/2-CCR-404-1-434 (accessed 15 May 2024)\u003c/li\u003e\n\u003cli\u003eColorado Oil and Gas Information System (COGIS), 2024. COGIS Data. https://ecmc.state.co.us/data.html#/cogis (accessed 21 May 2024).\u003c/li\u003e\n\u003cli\u003eColorado State Energy Profile, 2023. U.S. Energy Information Administration.\u003c/li\u003e\n\u003cli\u003eEBC, 2020. Certification of the carbon sink potential of biochar. Ithaka Institute, Arbaz, Switzerland.\u003c/li\u003e\n\u003cli\u003eEPA, 2024. Inventory of U.S. greenhouse gas emissions and sinks: 1990\u0026ndash;2022. U.S. Environmental Protection Agency. https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks.\u003c/li\u003e\n\u003cli\u003eBiochar Now, 2023. Personal communication.\u003c/li\u003e\n\u003cli\u003eGHG Pollution Reduction Roadmap 2.0, 2023. https://energyoffice.colorado.gov/climate-energy/ghg-pollution-reduction-roadmap-20 (accessed 22 Apr 2024)\u003c/li\u003e\n\u003cli\u003eGo Biochar, 2024. Products. https://gobiochar.com/shop/ (accessed 21 May 2024).\u003c/li\u003e\n\u003cli\u003eGreenfield Environmental Solutions, 2025. Personal communication.\u003c/li\u003e\n\u003cli\u003eHansson, A., et al., 2020. Biochar as a multi-purpose sustainable technology: Experiences from projects in Tanzania. Environment, Development and Sustainability, 23(4), 5182\u0026ndash;5214.\u003c/li\u003e\n\u003cli\u003eHawthorn, A., Steinsiek, R., Rahman, S., 2022. Casing and cement evaluation on drillpipe: New tool acquires well integrity data in parallel with existing drillpipe deployed operations from drilling to plug and abandonment. Offshore Technology Conference Asia.\u003c/li\u003e\n\u003cli\u003eInternational Standards Organization, 2006. ISO 14040, Environmental management: Life cycle assessment\u0026mdash;Requirements and regulations.\u003c/li\u003e\n\u003cli\u003eInternational Standards Organization, 2006. ISO 14044, Environmental management: Life cycle assessment\u0026mdash;Principles and framework.\u003c/li\u003e\n\u003cli\u003eInterstate Oil and Gas Compact Commission (IOGCC), 2021. Idle and orphan wells: A national assessment. https://oklahoma.gov/content/dam/ok/en/iogcc/documents/news/iogcc_idle_and_orphan_wells_2021_final_web_0.pdf (accessed 17 Jan 2024).\u003c/li\u003e\n\u003cli\u003eKang, M., et al., 2016. Identification and characterization of high methane-emitting abandoned oil and gas wells. Proceedings of the National Academy of Sciences, 113(48), 13636\u0026ndash;13641.\u003c/li\u003e\n\u003cli\u003eKhalifeh, M., Saasen, A., 2020. Introduction to Permanent Plug and Abandonment of Wells. Ocean Engineering \u0026amp; Oceanography, Volume 12.\u003c/li\u003e\n\u003cli\u003eLin, X., et al., 2023. Biochar-cement concrete toward decarbonization and sustainability for construction: Characteristic, performance, and perspective. Journal of Cleaner Production.\u003c/li\u003e\n\u003cli\u003eMiller, S.A., Habert, G., Myers, R.J., Harvey, J.T., 2021. Achieving net zero greenhouse gas emissions in the cement industry via value chain mitigation strategies. One Earth, 4(10), 1398\u0026ndash;1411. https://doi.org/10.1016/j.oneear.2021.09.011.\u003c/li\u003e\n\u003cli\u003eMoser, K., et al., 2023. Screw reactors and rotary kilns in biochar production: A comparative review. Journal of Analytical and Applied Pyrolysis, 174.\u003c/li\u003e\n\u003cli\u003eNational Petroleum Council (NPC), 2011. Plugging and abandoning oil and gas wells. Working Document of the NPC North American Resource Development Study, Paper #2\u0026ndash;25, 1\u0026ndash;21.\u003c/li\u003e\n\u003cli\u003eNogu\u0026eacute;s, I., Mazzurco Miritana, V., Passatore, L., Zacchini, M., Peruzzi, E., Carloni, S., Pietrini, F., Marabottini, R., Chiti, T., Massaccesi, L., Marinari, S., 2023. Biochar soil amendment as carbon farming practice in a Mediterranean environment. Geoderma Regional, 33, e00634. https://doi.org/10.1016/j.geodrs.2023.e00634.\u003c/li\u003e\n\u003cli\u003ePamon, L.D., Abbom, W.A., 1982. Well completions and workovers: The systems approach. Energy Publications.\u003c/li\u003e\n\u003cli\u003ePrice, J.I., McCollum, D.W., Berrens, R.P., 2010. Insect infestation and residential property values: A hedonic analysis of the mountain pine beetle epidemic. Forest Policy and Economics, 12(6), 415\u0026ndash;422. https://doi.org/10.1016/j.forpol.2010.05.004.\u003c/li\u003e\n\u003cli\u003ePuemmann, M., et al., 2020. Life cycle assessment of biochar produced from forest residues using portable systems. Journal of Cleaner Production, 250.\u003c/li\u003e\n\u003cli\u003ePuro.earth, 2024. CORC CO₂ Removal Certificate Supplier Listings. https://carbon.puro.earth/CORC-co2-removal-certificate/supplier-listings (accessed 21 May 2024).\u003c/li\u003e\n\u003cli\u003ePuro.earth, 2024. CORC carbon removal indexes. https://puro.earth/corc-carbon-removal-indexes (accessed 22 May 2024)\u003c/li\u003e\n\u003cli\u003eRaimi, D., et al., 2021. Decommissioning orphaned and abandoned oil and gas wells: New estimates and cost drivers. Environmental Science \u0026amp; Technology, 55(15), 10224\u0026ndash;10230.\u003c/li\u003e\n\u003cli\u003eRogue Biochar, 2024. Pricing. Oregon Biochar Solutions. https://www.chardirect.com/rogue-biochar-pricing (accessed 21 May 2024).\u003c/li\u003e\n\u003cli\u003eRoth, H., Silagy, B., Miller, K., Woolman, A., West Fordham, A., Martin, A.M., Quinn, J., Borch, T., 2024. Study biochar in plugging of oil and gas wells\u0026mdash;Colorado House Bill 23-1069.\u003c/li\u003e\n\u003cli\u003eSalimi, A., Beni, A.H., Bazvand, M., 2024. Evaluation of a water-based spacer fluid with additives for mud removal in well cementing operations. Heliyon, 10(4), e25638.\u003c/li\u003e\n\u003cli\u003eScherer, T., 2021. A guide to plugging abandoned wells.\u003c/li\u003e\n\u003cli\u003eShe, Chung, Han, 2019. Economic and environmental optimization of the forest supply chain for timber and bioenergy production from beetle-killed forests in northern Colorado. Forests, 10(8).\u003c/li\u003e\n\u003cli\u003eTisserant, A., Cherubini, F., 2019. Potentials, limitations, co-benefits, and trade-offs of biochar applications to soils for climate change mitigation. Land, 8(12).\u003c/li\u003e\n\u003cli\u003eTkaczewska, E., 2014. Effect of the superplasticizer type on the properties of the fly ash blended cement. Construction and Building Materials, 70(15), 388-393. https://doi.org/10.1016/j.conbuildmat.2014.07.096 \u003c/li\u003e\n\u003cli\u003eTrove Research, 2024. Outlook for the global biochar market. https://trove-research.com/report/outlook-for-the-global-biochar-market (accessed 22 May 2024)\u003c/li\u003e\n\u003cli\u003eUS Biochar Initiative (USBI), 2024. 2023 Global Biochar Market Report.\u003c/li\u003e\n\u003cli\u003eU.S. Forest Service (USFS), 2020. Forest Insect and Disease Conditions in the United States: 2020.\u003c/li\u003e\n\u003cli\u003eVr\u0026aring;lstad, T., Saasen, A., Fj\u0026aelig;r, E., \u0026Oslash;ia, T., Ytrehus, J.D., Khalifeh, M., 2019. Plug \u0026amp; abandonment of offshore wells: Ensuring long-term well integrity and cost-efficiency. Journal of Petroleum Science and Engineering, 173, 478\u0026ndash;491. https://doi.org/10.1016/j.petrol.2018.10.049.\u003c/li\u003e\n\u003cli\u003eWernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., Weidema, B., 2016. The ecoinvent database version 3 (part I): overview and methodology. \u003cem\u003eThe International Journal of Life Cycle Assessment, 21\u003c/em\u003e(9), 1218\u0026ndash;1230. https://doi.org/10.1007/s11367-016-1087-8.\u003c/li\u003e\n\u003cli\u003eWrobel-Tobiszewska, A., et al., 2015. An economic analysis of biochar production using residues from Eucalypt plantations. Biomass and Bioenergy, 81, 177\u0026ndash;182.\u003c/li\u003e\n\u003cli\u003eZajec, L., 2009. Slow pyrolysis in a rotary kiln reactor: Optimization and experiments. RES, University of Iceland and the University of Akureyri, Akureyri, Iceland.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"clean-technologies-and-environmental-policy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ctep","sideBox":"Learn more about [Clean Technologies and Environmental Policy](https://www.springer.com/journal/10098)","snPcode":"10098","submissionUrl":"https://submission.nature.com/new-submission/10098/3","title":"Clean Technologies and Environmental Policy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Woody biochar, Life cycle assessment, Techno-economic analysis, Plugging \u0026 Abandonment","lastPublishedDoi":"10.21203/rs.3.rs-6823444/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6823444/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWell plugging mitigates methane emissions and protects groundwater, yet conventional cement-based methods carry a high carbon footprint. To explore more sustainable alternatives, this study developed a techno-economic analysis (TEA) and cradle-to-gate life cycle assessment (LCA) for an orphan well in Colorado, comparing a baseline cement-plugging scenario to one that integrates woody biochar in both the cement slurry (3% by weight) and spacer plugging fluid (15% by volume). Various thermochemical conversion pathways were evaluated to understand how different biochar properties influence net greenhouse gas emissions. Results indicate that adding 4.2 tonnes of biochar per well increases plugging costs by 2% but can reduce total emissions from 11.4 tonnes CO₂e to as low as 0.64 tonnes CO₂e per well. Further analysis showed that carbon credit revenues (121 USD per tonne)\u0026mdash;if appropriately established for biochar\u0026rsquo;s use in well plugging\u0026mdash;could offset this additional cost, making biochar-additive plugging economically competitive under certain market conditions. These findings demonstrate a promising approach for lowering the environmental impact of well decommissioning and transitioning the industry toward more climate-resilient practices.\u003c/p\u003e","manuscriptTitle":"A techno-economic analysis and life cycle assessment of woody biochar as an additive for orphan well plugging","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-31 10:20:53","doi":"10.21203/rs.3.rs-6823444/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-14T20:24:04+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-29T02:16:52+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-27T15:45:09+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"246695720699816468364287376781573143814","date":"2026-02-23T01:36:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"106505027097345629824860726407928721863","date":"2026-02-23T00:27:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-09T05:48:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"134423440328901694157749215823156622768","date":"2025-07-29T20:03:21+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-27T20:01:16+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-15T18:36:21+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-05T10:24:11+00:00","index":"","fulltext":""},{"type":"submitted","content":"Clean Technologies and Environmental Policy","date":"2025-06-04T20:35:28+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"clean-technologies-and-environmental-policy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ctep","sideBox":"Learn more about [Clean Technologies and Environmental Policy](https://www.springer.com/journal/10098)","snPcode":"10098","submissionUrl":"https://submission.nature.com/new-submission/10098/3","title":"Clean Technologies and Environmental Policy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1860859b-a097-4f9d-a85e-29ff0782ca51","owner":[],"postedDate":"July 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-18T12:23:48+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-31 10:20:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6823444","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6823444","identity":"rs-6823444","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}