Geological problems in the effective development of deep shale gas: a case study of Upper Ordovician Wufeng-Lower Silurian Longmaxi formations in Sichuan Basin and its periphery
He Zhiliang1,2,3, Nie Haikuan1,2,4, Hu Dongfeng5, Jiang Tingxue1,6, Wang Ruyue1,2,4, Zhang Yuying7, Zhang Guangrong8, Lu Zhiyuan8
1. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100083, China;
2. Sinopec Key Laboratory of Shale Oil/Gas Exploration & Production, Beijing 100083, China;
3. Department of Science and Technology, China Petroleum & Chemical Corporation, Beijing 100728, China;
4. Sinopec Petroleum Exploration and Production Research Institute, Beijing 100083, China;
5. Sinopec Exploration Company, Sichuan Chengdu 610041, China;
6. Sinopec Research Institute of Petroleum Engineering, Beijing 100101, China;
7. School of Earth Resources, China University of Geosciences, Hubei Wuhan 430074, China;
8. School of Energy Resources, China University of Geosciences, Beijing 100083, China
Deep shale gas is the main alternative field for shale gas exploration and development in China. The deep shale gas in Wufeng Formation and Longmaxi Formation in Sichuan Basin and its periphery has a geological environment of high temperature, high pressure and high crustal stress. With the increase of deep overburden pressure, the reservoir porosity is reduced by 15%-20%, the permeability by 90%-95%, and the contribution of fractures in shale to permeability is decreased significantly. The deep gas content varies in different regions in Wufeng Formation and Longmaxi Formation, but generally varies little in the middle-shallow shale that has been exploited. The gas content is mainly controlled by the original sedimentary conditions and later preservation conditions. Deep shale underwent less structural uplift and erosion, and had good oil and gas preservation conditions. Deep shale formations are characterized by high temperature, large crustal stress, and high stress difference, which can easily lead to the enhanced shale plasticity, difficulties in fracture initiation and propagation, and high closure pressure in shale. For this reason, the proppant was cracked, thus influencing the propping degree of fracturing fractures; fracture conductivity decreases rapidly, and it is difficult to maintain the long-term conductivity. The biogenic siliceous shale in the WF2-LM4 graptolite zone is characterized by high quartz content and strong resistance to compaction, which are conducive to the formation and preservation of effective reservoirs. However, due to the large brittleness and rapid development of natural fractures, the lower limit of "sweet window" of the shale may exceed 5 km, which is the optimal interval for deep shale gas development. The enrichment degree of deep shale gas is mainly related to the superior congenital sedimentary and diagenetic conditions, burial and hydrocarbon generation and expulsion history, amplitude of later uplift, and differences in structural deformation. Shale gas can be fully exploited to successfully achieve the large-scale effective development of deep shale gas by optimizing the distribution areas of deep shale with high brittleness, high porosity and permeability, high pressure coefficient and high gas conten, establishing a suitable method of volume fracturing treatment in deep shale, and a reasonable production system through continuous optimization.
何治亮, 聂海宽, 胡东风, 蒋廷学, 王濡岳, 张钰莹, 张光荣, 卢志远. 深层页岩气有效开发中的地质问题——以四川盆地及其周缘五峰组—龙马溪组为例[J]. 石油学报, 2020, 41(4): 379-391.
He Zhiliang, Nie Haikuan, Hu Dongfeng, Jiang Tingxue, Wang Ruyue, Zhang Yuying, Zhang Guangrong, Lu Zhiyuan. Geological problems in the effective development of deep shale gas: a case study of Upper Ordovician Wufeng-Lower Silurian Longmaxi formations in Sichuan Basin and its periphery[J]. Acta Petrolei Sinica, 2020, 41(4): 379-391.
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2020, Vol. 41 
