A critical examination of diffuse double layer alterations in clay-electrolyte systems at elevated temperatures

The objective of this work was to explore the impact of temperature on shale swelling and explain it in terms of diffuse double layer mechanics; Debye Hückel length alterations. This was made possible through the use of our newly developed thermo linear swelling test. Moreover, combined impact of temperature, dielectric constant of water and ionic strength (ionic concentration) of salt solutions on Debye Hückel length and resultant shale swelling and shrinkage was investigated. For dilute solutions, results showed that the product of temperature and dielectric constant of water ( T*e r ) remained near constant for a wide range of temperature (25C – 90C). When shale interacted with 12% and 20% w/w NaCl and CaCl 2 solutions, the % change in shale shrinkage as temperature incrementally increased from 25C to 90C is quite large and cannot be neglected. Results suggests that dielectric constant of water may have been reduced by both temperature and ionic strength of solution, all of which caused a greater reduction in Debye Hückel length and subsequent shale shrinkage. As for saturated NaCl and CaCl 2 solutions, shale exhibited swelling behavior at moderate temperatures (up to 50C for NaCl and up to 70C for CaCl 2 ) followed by shale shrinkage thereafter. This could be attributed to the development of repulsive forces between alike ions with diffuse double layer which may have overcome their electrostatic screening effect on charged clay surfaces. At higher temperatures, the contribution of dielectric constant of water on lowering Debye Hückel length may have soften the repulsion action produced by ions.