Experimental Investigation of the Damage Mechanisms of Drilling Mud in Fractured Tight gas Reservoir

Mud pollution seriously restricts the development of tight gas reservoirs. For the Dabei tight gas field in Tarim Basin, lots of wells show a higher skin factor on the pressure buildup test curves after drilling. Little researches on mud damage have been conducted for the fracture gas reservoir. Based on the previous researches, a dynamic filtration experimental method utilizing full diameter cores is established for fracture-porous cores under reservoir temperature. Twelve sets of dynamic filtration tests with full diameter cores (D = 10 cm) on the established device and some cuttings microscopic analysis on environmental-scanning-electron microscope/energy dispersive X-ray detector (ESEM/EDX) have been conducted. The effects of core type, fracture width, pressure difference, and mud type on mud damage are all investigated. The results show that the fractured cores suffer a more serious damage degree and exhibit lower return permeability ratio, compared with the porous cores. And the damage degree of fractured cores is proportional to the fracture width and pressure difference. The solids invasion is the key factor damaging the fractured cores, while the porous is mainly impaired by the filtrate invasion. This paper provides a scientific, in-depth understanding of the behaviors, laws, and characteristics of mud damage in fractured and porous cores.