Segmentation characteristics of deep strike slip faults in the Tarim Basin and its control on hydrocarbon enrichment: taking the Ordovician strike slip fault in the Halahatang Oilfield in the Tabei area as an example

The Ordovician strike slip fault in the Tarim Basin is a type of small strike slip fault developed in the internal stable area of a craton. It plays an important role in controlling the formation and enrichment of deep oil and gas reservoirs. In this work, we collected 3-D seismic data covering 4140 km2 of the Halahatang-Yueman area, from which we extracted high resolution coherence slice and performed fine seismic interpretation to characterize the segmentation of the Ordovician strike slip fault. We also discussed segmentation control on reservoir development and oil and gas enrichment. Our findings are as following: (1) The Halahatang-Yueman Ordovician fault is a conjugate strike slip fault with regional boundaries: the north is of NE- and NW-trending while the south developed only NE-trending faults. The two fault branches have Riedel type structures and mainly developed around the main fault. (2) Segmentation development model of small strike slip fault can be established according to structural style and stress state in different parts of the strike slip fault: the stress divergence area at the termination of the strike slip fault has mostly extensional and contractional horsetail structures, while the interior of the strike slip fault is made of translational, overlapping, branch fault and braided structural sections. The translational section is a linear extension of the fault plane with isolated high and steep vertical fault profile. The overlapping section may contain extensional or contractional structural segments depending on its rotational direction relative to the step. The branch fault structure is mostly oblique-compression style with lesser development of feather fault. Finally, the braided section contains interlocking extensional and transtensional structural segments. (3) Reservoir development differs according to segment types: reservoirs of horsetail and braided sections are most developed, followed by that of branch fault section. Reservoirs of translational section are relatively undeveloped. (4) Six hydrocarbon accumulation patterns associated with strike slip faults are delineated. Among them, the "clamping site" intercepting R shear fault and main fault, the transtensional segment, and the horsetail section represent three enrichment model areas for Ordovician fracture-cavity reservoirs in the northern buried hill-bedding karst area. The transpressional segment and the transtensial segment are more oil and gas enriched locations in the southern fault-controlled karst area. The results of this paper have important theoretical significance for improving the segmentation rule of small strike slip fault in the stable area of cratonic basin, and may provide guidance for developing and prospecting strike slip fault controlled karst fractured vuggy reservoirs. © 2019, Editorial Office of Earth Science Frontiers. All right reserved.