Shale Gas Resource Potential and Accumulation Model of the Middle Jurassic Yangye Formation in the Piedmont Zone of the Southwestern Margin of the Tarim Basin, Northwest China

Abstract To elucidate the shale gas resource potential and accumulation model in the complex structural zone on the piedmont of the southwestern margin of the Tarim Basin, this study conducted geological surveys, core descriptions, organic shale geochemistry, X-ray diffraction (XRD) on shale reservoirs, and scanning electron microscopy (SEM) to investigate the characteristics of the source rocks and reservoirs in the Middle Jurassic Yangye Formation in the southwestern Tarim Basin. This study establishes a shale gas accumulation model of the study area and identifies a favourable area for shale gas exploration. The results showed that the total organic carbon (TOC) content of the Yangye Formation source rocks ranges from 0.51%-2.68%, with an average value of 1.41%, the hydrocarbon generation potential (S1 + S2) ranges from 0.0411–4.5625 mg/g, with an average value of 1.7706 mg/g, and the chloroform bitumen “A” content ranges from 0.002%-0.177%, with an average value of 0.090%. Organic matter mainly consists of type II1 kerogen. Overrall, the Yangye Formation exhibits moderate to good mature source rocks, with estimated resources reaching 1029.51×108 m3. The porosity of the reservoirs is between 1.18% and 1.47%, the permeability is between 0.000480 and 0.001778 mD, and the brittle mineral content is 55.18%. The types of microscopic reservoir spaces are mainly primary intergranular pores and intragranular pores. The “monocline-retention” type and “syncline core type” shale gas accumulation models are developed for the study area. Therefore, it is recommended to conduct shale gas exploration in the northern monocline of the study area and the deep part of the Jurassic intermountain basin, which are areas where the oil and gas preservation conditions are good.