Investigation of Geomechanical Response of Fault in Carbonate Reservoir and Its Application to Well Placement Optimization in YM2 Oilfield in Tarim Basin

摘要

YM2 Oilfield is an ultra-deep carbonate oilfield located in the northern uplift of Tarim Basin in western China. We have identified 108 seismically resolvable faults formed over three periods. These faults control the distribution of oil and gas accumulation units. Permeability differs significantly amongst various faults, and various sections of the fault planes. There has been no effective quantitative evaluation measure on the relative opening or sealing of faults for a long time, the sealing capacity of the faults have not been evaluated so far. This has a negative impact on the evaluation of accurate reservoir compartmentalization and partitioning, and evaluation of various oil and gas flow units which are critical for constraining the development program and production performance of oil field. There are many geological factors that influence the permeability of faults, such as burial depth, fault throw, dip angle, strike, lithology variation, pore pressure and the in-situ stress field. After evaluating these factors in the YM2 oilfield, we determined that the critical factor that controls fault permeability is the geomechanical response of faults under the current stress field. In order to determine if the faults are permeable relatively in the current stress state, we established the geomechanical model of YM2 reservoir which describes the present-day stress regime, along with the vertical and horizontal distribution of the geomechanical parameters of this reservoir. Based on the interpretation of 3D seismic data, we characterized the spatial combination relations of faults in the reservoir and extracted the occurrence information of each fault according to certain step size. Then, we calculated the normal and shear stress acting on the various fault planes in order to evaluate whether those faults are permeable relatively in the current stress state.