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Characteristics of the Strike-slip Faults and the Fault-karst Reservoirs in the Halahatang Oil Field, Tarim Basin

Abstract

Controlled by the well-developed strike-slip faults in the Ordovician carbonate strata, the unique “fault-karst” traps were formed in the Halahatang area, northern Tarim Basin. Previous studies have indicated these traps were highly related to the geometries of the strike-slip faults and carbonate karstifications. In this research, coherence, amplitude attribute of high-resolution 3D seismic data, well drilling and production dynamic data were integrated to investigate the relationships between the strike-slip faults and the characteristics of the “fault-karst” reservoirs. Results show that the strike-slip faults geometries in the Halahatang area vary vastly between different segments. The northern principle fault zones are composed of braided and horsetail structures, while the southern zones are mostly linear and en echelon faults. Four types of fault-karst traps were developed accordingly, i.e., the plate, en echelon, braided and leaf types respectively. The hydrocarbons migrate vertically through the principle faults, and accumulate along the branch faults to form a tree-shaped fault-karst pool. Moreover, the well drillings proved the hydrocarbons accumulated at the relatively high positions within a trap, other than the regional tectonic high. The industrial production is highly determined by the connectivity and positions of karst caves within a single trap. The research of this kind of carbonate reservoir is of great significance for the explorations in the Tarim Basin and other basins with similar backgrounds.