The shale reservoir of Shanxi Formation in Ordos Basin has high clay mineral content, fast lithofacies change, high thermal evolution degree and poor reservoir performance. The unclear understanding of reservoir characteristics and the unclear enrichment law restrict the optimization of favorable intervals of shale reservoir in Shanxi Formation. Based on the logging data analysis, scanning electron microscopy, porosity and permeability analysis, gas content test, nitrogen adsorption test, methane adsorption test and rock mechanics test of 7 wells in Yan’an Area, the characteristics and exploration potential of shale reservoirs in Shanxi Formation in Yan’an area were evaluated. The results show that the mineral composition of shale rocks in Shanxi Formation is complex, with an average quartz content of 30.3% and an average clay mineral content of 65.8%. The type of organic matter is mainly type III, the average organic Ro(vitrinite reflectivity) is 2.64%, which is in the over-mature stage, and the average TOC (total organic carbon)is 2.12%. The average porosity is 2.94%, and the average permeability is 0.017 3×10-3 μm2. Scanning electron microscopy results show that shale samples develop four types of microscopic pores, including organic matter pores, intergranular pores, intragranular pores, and microfractures. The microscopic pore structure is dominated by micropores and mesopores and the pore type is mainly semi-closed pores. CT(computed tomography) scanning shows that the dual structure of main connected pore group-isolated micropore’ is developed in the rock, and there is a dominant pore development area. The isothermal adsorption capacity of shale methane in the Shanxi Formation is 0.50~2.38 m3/t,the on-site analytical gas content is 0.04~16.86 m3/t, and the average recovery coefficient is 81.4%. The shale of Shanxi Formation has the characteristics of high Yang’s modulus, low Poisson’s ratio and moderate compressive strength, and has the potential to form complex fracture network. Combined with the mature thermal evolution degree, good hydrocarbon generation conditions, adsorption performance and compressibility basis of Shanxi Formation shale, it constitutes the core element of shale gas accumulation. In addition, the gas source supplement of coal seam in Shanxi Formation has good exploration potential. The organic-rich strata and high gas-bearing dominant lithofacies of Shan 2 member are the potential strata for further exploration.
LI Fu-kang, LIU Shuai, SUN Jian-bo, WEN Jing, ZHAO Wei-wei, ZHAO Qian-ping, SHI Peng, CAO Wen-qi, QI Pan-wen, LÜ Yuan.
Shale Reservoir Characteristics and Exploration Potential of Shanxi Formation in Yan’an Area, Ordos Basin[J].
Science Technology and Engineering, 2026, 26(18): 7641-7654 DOI:10.12404/j.issn.1671-1815.2505639
针对研究区山西组页岩,还进行了40样次低压液氮吸附试验。绝大部分样品吸附脱附曲线形态与Y108-3样品曲线[图8(a)]形态相似,根据国际理论化学与应用化学协会(International Union of Pure and Applied Chemistry,IUPAC)的分类方案,研究区山西组页岩氮气吸附等温线属于Ⅱ型,吸附质分压(P)与吸附质饱和蒸气压(Po)的比值:相对压力(P/Po)从0上升到0.9,吸附曲线上升缓慢,相对压力从0.9上升至1时,吸附曲线迅速爬升,呈现了氮气由单分子层向多分子层吸附过渡,并最终发生毛细凝聚现象。吸附曲线与解吸曲线近乎重叠,没有明显吸附回线与拐点,显示微观孔隙系统主要发育半封闭孔,并存在连续的孔隙系统。所有样品中,仅有Y336-6样品出现明显拐点[图8(b)],显示内部存在细颈瓶状孔。
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