The constraint of deep rock stresses in H underground gas storage based on a modified stress polygon and focal mechanism solution

Abstract

H underground gas storage (H-UGS), located in the junction of the southern margin of the Junggar Basin and the eastern part of the northern Tianshan Mountains, is one of the large natural gas storage in China. It is of significance to study the deep rock stresses in H-UGS for fault slip tendency, safe storage of energy and other research. Most of the regional stress information in H-UGS data from in-suit measurements lacks deep in-suit stress data in this region. This research proposes a hybrid constrain stress magnitudes present in deep rock masses. First, the fault friction strength, an essential parameter of lateral pressure coefficient polygon, is established by the stress accumulation index method and apparent friction strength evaluation method. Second, we inverse the stress factor R from the focal mechanism solutions in this area, and the lateral pressure coefficient polygon is qualified quadratic to narrow down the range of results by this parameter. Finally, the complete stress profile of H-UGS is obtained by using the simple transition relationship between lateral pressure coefficient and in-situ stress. The result shows that the principal compressive stress of the H-UGS region is determined by the N22°E, the maximum lateral pressure coefficient K max (or S H) at three depths (3.0km, 6.5km, and 12.0km ) are 1.2 (80.22 MPa), 1.22 (202.72 MPa), 1.28 (421.34 MPa) respectively, and the minimum lateral pressure coefficient K min (or S h) are 0.87 (58.21 MPa), 0.86 (142.12 MPa), 0.86 (282.61 MPa) respectively. The result is primarily consistent with in-situ measurement from the depth of 3.0km to 3.7km. The maximum horizontal principal stress and the minimum coincidence ratio are 54% and 69%. The result of estimating deep rock stresses established in this research provides sufficient regional stress field data in H-UGS.