The effects of spatially correlated heterogeneities on acidising wormhole development

Abstract

A commonly used rock stimulation technique in subsurface geoenergy technologies is matrix acidisation. During this process, an acidic solution is injected into the hydrocarbon or geothermal reservoirs to dissolve certain minerals and enhance the injectivity and productivity of the hydrocarbon or heat recovery operation. This study aims to investigate the influence of three-dimensional (3D) lithological heterogeneity of the rock on reactive transport of acid in the porous domain. Through a development and application of a reactive transport model with restricting assumptions (linear calcite dissolution kinetics with hydrochloric acid (HCl)) and simplifications (mineralogical homogeneity) on the geochemistry embedded into the model, we present the results of a series of 3D simulation of carbonate acidisation in presence of varying spatial correlation lengths of petrophysical properties of the domain. The results are compared with the case where petrophysical properties are distributed randomly throughout the domain. The study provides new insights into the impact of increasing correlation lengths that lack in the existing literature. Under the conditions of case studies, the pore volume of the acid injected reduces 10·5 and 12·2% for Damköhler number of 100, when correlation lengths of only 0·0667 and 0·1667 cm are considered in core of length 5 cm.