Experimental Study on the Influence of Heavy Mud Pollution on Tight Sandstone for Deep Wells

Abstract

Heavy mud pollution tends to occur during the workover of deep tight sandstone gas wells in Tarim, resulting in a significant reduction in gas well production. In order to study the impact of heavy mud pollution in deep sandstone gas reservoirs in the Tarim Basin, the physical properties and mechanical parameters of cores before and after heavy mud pollution were tested by non-destructive testing methods such as porosity, permeability, and acoustic waves. The results show that after the matrix core is polluted by heavy mud, the overall damage of permeability is ≥60%. Low-density mud causes more damage than high-density mud. The effect of increasing displacement time on permeability damage is higher than that of increasing displacement pressure. Heavy mud has an obvious influence on matrix porosity, but with the change in displacement pressure and displacement time, the change in core porosity has no obvious regularity. After the matrix core is polluted by heavy mud, the Poisson’s ratio increases by about 70% on average, but the change in elastic modulus is small, only -1.15%−4.25%. The experimental results provide significant guidance for reservoir damage assessment of mud-contaminated wells in Tarim.