STRIKE-SLIP FAULTS IN HALAHATANG AREA, NORTH TARIM BASIN, NW CHINA: INSIGHTS FROM 3D SEISMIC IMAGERY

Tarim Basin is one of the largest oil and gas bearing basins in China. Halahatang oilfield located in the north of Tarim Basin is a large carbonate oil field discovered in recent years. The main reservoir types are fracturing and karsting carbonate reservoirs controlled by strike-slip faults.

The seismic data used in this paper are acquired by Tarim Oilfield Company in 2010. The Eigen-structure coherency and SO semblance are used to identify the distribution of the strike-slip fault.

There were several groups of strike-slip faults trending Northeast and Northwest in this area. Nine kinds of typical structural styles of strike-slip fault were founded such as Tulip/Palm tree structure and En-echelon structure. On the plane, the master strike-slip faults were conjugate shear faults like chessboard, and secondary faults extending shortly intersected with the master faults at a small angle. Single strike-slip fault had segmentation, so different parts had different structural styles in one strike-slip fault.

Judging form the age of rocks subjected to strike-slip dislocation and the structutal styles in different strata, the strike-slip faults had three epochs of activity in Halahatang area. In Late Ordovician period, the strike-slip faults were formed as conjugate strike-slip faults by pure shear. That was caused by a pulse of horizontal pressure along the north-south direction due to the closure of the West Kunlun ocean. In Late Permian period, some NW trending Ordovician strike-slip faults were reactivated and generated normal faults in Late Paleozoic strata. The normal faults converged downward to the Ordovician strike-slip faults vertically. In Late Cretaceous period, some NE trending Ordovician strike-slip faults were reactivated and en-echelon faults were formed in Mesozoic strata. The En-echelon fault systems forming spatial “Tulip” structures are the most distinctive feature and principal diagnostic indicator for the strike-slip faults. They have more gentle dip angles ranging from 40°to 60°in the upper part of the section and steeper angles ranging from 70°to 90°in the lower part. Individual faults extend vertically down to the Ordovician strike-slip faults.

The strike-slip fault systems controlled the distribution of hydrocarbon in Halahatang oilfield.