Geometry and formation mechanism of tension gashes and their implication on the hydrocarbon accumulation in the deep-seated strata of sedimentary basin: A case from Shunnan area of Tarim Basin

Abstract

With the theoretical and technological developments related to cratonic strike-slip faults, the Shuntuoguole Low Uplift in the Tarim Basin has attracted considerable attention recently. Affected by multi-stage tectonic movements, the strike-slip faults have controlled the distribution of hydrocarbon resources owing to the special fault characteristics and fault-related structures. In contrast, the kinematics and formation mechanism of strike-slip faults in buried sedimentary basins are difficult to investigate, limiting the discussion of these faults and hydrocarbon accumulation. In this study, we identified the characteristics of massive sigmoidal tension gashes (STGs) that formed in the Shunnan area of the Tarim Basin. High-resolution three-dimensional seismic data and attribute analyses were used to investigate their geometric and kinematic characteristics. Then, the stress state of each point of the STGs was calculated using seismic curvature attributes. Finally, the formation mechanism of the STGs and their roles in controlling hydrocarbon migration and accumulation were discussed. The results suggest that: (1) the STGs developed in the Shunnan area have a wide distribution, with a tensile fault arranged in an en échelon pattern, showing an S-shaped bending. These STGs formed in multiple stages, and differential rotation occurred along the direction of strike-slip stress during formation. (2) Near the principal displacement zone of the strike-slip faults, the stress value of the STGs was higher, gradually decreasing at both ends. The shallow layer deformation was greater than the deep layer deformation. (3) STGs are critical for connecting source rocks, migrating oil and gas, sealing horizontally, and developing efficient reservoirs. This study not only provides seismic evidence for the formation and evolution of super large STGs, but also provides certain guidance for oil and gas exploration in this area.