Composite Strike-Slip Deformation Belts and Their Control on Oil and Gas Reservoirs: A Case Study of the Northern Part of the Shunbei 5 Strike-Slip Deformation Belt in Tarim Basin, Northwestern China

Abstract

Strike-slip deformation belts are interesting structures in the crust and are of significance in petroleum exploration. The Shunbei 5 fault belt (SB5), a long strike-slip deformation belt in the Tarim Basin, played an important role in the formation of a recently discovered major oilfield known as the Shunbei oilfield. In this study, models of plan view and vertical profile were established to interpret SB5 with multi-cycled tectonic activities. To this end, its structural framework, tectonic evolution, and associated plate tectonics were investigated using 2D and 3D seismic data. SB5 was formed as a dextral simple shear belt at the end of the Middle Ordovician. In the plan view, R-shears and P-shears with local transpressional and transtensional structures were observed. Along the vertical profiles, various structural styles occurred at various depths and strata in response to various stratigraphy mechanisms. Although these structures show clear boundaries between them, they correspond to the same formation time, indicating that they underwent deformation simultaneously. The second activity of SB5 occurred at the end of the late Ordovician, during which it was a dextral transtensional strike-slip deformation belt consisting of left-stepping en echelon R-shears. The R-shears were transtensional during the progressive deformation. Subsequently, SB5 underwent several strike slips of weak strength. Notably, SB5 cut through a deep Middle Cambrian gypsum salt layer and connected the deep Lower Cambrian source rock with deep Lower and Middle Ordovician carbonates to form the oil and gas reservoirs. The established models are of reference value in the interpretation of other subsurface strike-slip deformation belts.

Methods and Case Studies of Ultra‐deep Fault Seal Evaluation

“…Based on the types and sizes of the flower-type structures, the wrench time can be determined (Deng et al, 2018;Wang et al, 2021;Yuan et al, 2021). The first wrench occurred at the end of the Middle Ordovician, matching the first epoch of the middle Caledonian movement.…”

“…The Shunbei 5 fault (F sb5 ) has typical characteristics of strike-slip faulting (Ghosh and Chattopadhyay, 2008;Yuan et al, 2021) and important petroleum discoveries have been made there. In the top surface of the Upper Ordovician (T70), the branch faults of the main F sb5 were composed of right-stepping en-echelon belts (Fig.…”

“…11) in seismic profiles. Due to mechanical stratigraphy in the vertical sections, various propertied flowers may superpose to form a multiple flower (Yuan et al, 2021).…”

“…Therefore, in essence, methods of fault sealing factors and evaluation in the general sense are suitable for the sealing evaluation of ultra-deep faults. However, in recent years, oil exploration has proved that strike-slip faults are of great significance in both the preservation and destruction of ultra-deep oil and gas, because strike-slip faults often have a large cutting depth resulting in great changes in stress with large effects in different sections along the strike direction (Neng et al, 2018;Yang et al, 2020;Yuan et al, 2021).…”