A laboratory approach to predict the water-based drill-in fluid damage on a shale formation

Abstract

Shale gas production after drill-in, completion, and hydraulic fracturing is strongly affected by formation damage. In order to determine the damage mechanisms for nonmarine shale reservoir, a series of assessments of sensitivity damage, water block damage, water-based drill-in fluids damage, and water damage to gas diffusion on 20 shale samples obtained from Chang 7 Formation were conducted and analyzed. Results indicate that, in the Chang 7 Formation shale, there is extremely strong stress sensitivity and moderately weak water sensitivity damage. Although the liquid phase invasion depth is shallow and the water block damage is limited, the liquid phase and solid particles would enter the microfractures in the reservoir.The P-1 water-based drill-in fluid is compatible with the Chang 7 Formation shale reservoir which can meet the requirement of Chang 7 Formation shale damage controlling, the effect of water-based drill-in fluid on wellbore stability should be paid more attention. The diffusion coefficient of the shale decreases with the presence of water.A systematic damage evaluation method of working fluid considering the multi-mechanism and multi-scale mass transfer process of shale gas is needed to establish.