STUDY ON THE FORMATION MECHANISM AND HYDROCARBON ACCUMULATION EFFECT OF SIGMOIDAL TENSION GASHES DEVELOPED IN THE STRIKE-SLIP DISPLACEMENT ZONE IN THE SHUNNAN AREA OF THE TARIM BASIN

The strike-slip faults and their associated tectonics are important tectonic units controlling hydrocarbon accumulation in the Shunnan area of the Tarim Basin. Affected by the multi-stage of tectonic movements, the strike slip faults highly controlled the distribution of hydrocarbon resources due to the special fault characteristics and fault-related structures. On the other hand, the unclear formation mechanism of these strike slip associated structures limits the discussion of hydrocarbon accumulation. In this paper, we first found the sigmoidal tension gashes associated with strike slip faults in deep strata in Shunnan area, which differs significantly from the findings of other scholars in terms of scale. In order to further investigate the role of sigmoidal tension gashes in controlling hydrocarbon accumulation in this area, we investigate the geometrical characteristics, formation mechanism and reservoir formation mode of this formation using 3D seismic body, ant-tracking of petrel for fracture identification and stress analysis. We first finely characterize the development of the sigmoidal tension gashes in plan and section, and model the fractures of the sigmoidal tension gashes using petrel. Secondly, based on the structural modeling, we measured the strain at each point of the tectonic body according to the degree of sigmoidal tension gashes geometry deformation to obtain strain data. Afterwards, the measured data were used to recover the tectonic evolution process and formation mechanism. It is found that (1) the sigmoidal tension gashes developed in Shunnan area are distributed in a wide range and a tensile fault arranged in en échelon pattern, showing as S-shaped bending. The formation of these tension gashes endured multiple stages, and differential rotation will occur along the direction of strike-slip stress in the process of formation; (2) Near the PDZ (principle displacement zone) of strike-slip faults, the stress value of sigmoidal tension gashes is higher, and gradually decreases to both ends. The shallow layer deformation is greater than the deep layer deformation; (3) Sigmoidal tension gashes are critical for connecting source rocks, migrating hydrocarbon, sealing horizontally, and developing efficient reservoirs.