Advances in Earth Science ›› 2022, Vol. 37 ›› Issue (7): 742-755. doi: 10.11867/j.issn.1001-8166.2022.036
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Feng CAO 1( ), Jianhua HE 1 , 2( ), Yuanyuan WANG 3, Hucheng DENG 1 , 2, Qinglong XU 4
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Feng CAO, Jianhua HE, Yuanyuan WANG, Hucheng DENG, Qinglong XU. Methods to Evaluate Present-Day In⁃situ Stress Direction for Low Anisotropic Reservoirs in the Second Member of the Xujiahe Formation in Hechuan Area[J]. Advances in Earth Science, 2022, 37(7): 742-755.
The Hechuan area is rich in dense sandstone gas resources in the second member of the Xujiahe formation, and the complex geological conditions in this area have a great impact on the current exploration and development of oil and gas resources. One of the issues resulting from this complexity is an unclear understanding of how present-day in-situ stress direction restricts the later horizontal well deployment and the promotion of fracture transformation. Based on an analysis of wave velocity anisotropy, differential strain, and paleomagnetism, combined with special logging and microseismic monitoring data, the applicability of various types of in situ stress direction testing frameworks in dense sandstone reservoirs was evaluated, and the distribution of present-day in situ stress directions in the Hechuan area were determined. The results show that the maximum principal stress orientation of the second member of the Xujiahe Formation in the Hechuan area is mainly distributed between N103.1°E-N134.3°E, and the azimuth angle of the average maximum principal stress is N117.4°E; that is, the present-day maximum principal stress orientation of the sandstone in this area is NWW-SEE. The change in the direction of the in situ stress in the plane is not significant, and its weaker in situ stress deflection is mainly influenced by the sedimentary structure. In the Hechuan area, the dense sandstone in the second member of the Xujiahe Formation is relatively homogeneous, and the anisotropy is weak; therefore, the wave velocity anisotropy test cannot be applied in this area. The experimental test results of differential strain combined with paleomagnetism are highly congruent with the results above. Therefore, the test more applicable to sandstone formations in this area, specifically the ones with a homogeneous and weak anisotropy, is microseismic monitoring and well wall image logging to evaluate the in-situ stress direction. Combined with the direction of the in situ stress and fracture development, the recommended orientation for horizontal well deployment is N40°E-N55°E.