Characteristics and genetic mechanisms of fault-controlled ultra-deep carbonate reservoirs: A case study of Ordovician reservoirs in the Tabei paleo-uplift, Tarim Basin, western China

Abstract

To reveal the effect of faults in the deep and ultra-deep oil and gas reservoirs, based on the comprehensive analysis of drilling logs and the core and seismic data, the development and fault-controlled regularity of the reservoirs in the high and low inner part of the Ordovician carbonate of the Tabei paleo-uplift have been discussed. The results show that large fracture-cave reservoirs are developed in the Tabei paleo-uplift, and as main reservoir, the cave-type reservoirs usually appeared as lumps or patches in the north of the pinch-out line of O₃s, and gradually transitioned to isolated dots to the south. Due to the difference in control effect of faults, the degree of reservoir development differs greatly from north to south. The effective reservoir thicknesses are relatively stable and the porosity are relatively high in north, which are mainly controlled by karst and fractures, and the effect of faults on reservoir is not obvious. To the south, the reservoirs are gradually banded along the fault, and the control effect of large strike-slip faults are enhanced. This indicates that the strike-slip faults are more important to the development of reservoir in the low inner part. This difference is caused by the differences in fault controlling factors during different evolution periods of the paleo-uplift.