Influence of porosity and permeability heterogeneity on liquid invasion in tight gas reservoirs

Liquid invasion in tight gas reservoirs may damage near-wellbore permeability during the well drilling, completion, and stimulation processes. This study focused on a tight gas reservoir in the Sichuan basin. The physical properties of the basin and correlations among them were analyzed. The analysis indicated an obvious porosity and permeability heterogeneity for the Xujiahe Formation in the Dayi area and showed a relatively high correlation between porosity and permeability. Statistical analysis confirmed that both porosity and permeability generally followed the Weibull distribution and that the permeability heterogeneity was greater than the porosity heterogeneity. The Weibull distribution function and convection-dispersion model were both used to estimate the effect of heterogeneity on liquid invasion in tight gas reservoirs. The results showed that a smaller coefficient of permeability heterogeneity corresponded to a larger irreducible water saturation value. The dimensionless concentration profile propagated deeper into heterogeneous reservoirs than homogeneous reservoirs. The influence of heterogeneity on liquid invasion depended primarily on the permeability heterogeneity of the tight gas reservoir. As the coefficient of permeability heterogeneity decreased, the liquid invasion depth and invasion rate increased. Comparatively, the porosity heterogeneity had little effect on the liquid invasion rate but caused the invading liquid to travel deeper into tight gas reservoirs.