Laboratorial and analytical study for prediction of porosity changes in carbonaceous shale coupling reactive flow and dissolution

Abstract

Molecular diffusion of acid into a porous carbonate medium is usually referred to as acid imbibition. Accurate prediction of acid penetration into a formation and reaction with rock is not possible without a comprehensive understanding of the acid diffusion process and associated parameters.This work aimed to derive an analytical solution for mineral-dissolution reactive diffusion when acid imbibes into a rock surface and where there is no flow condition under laboratory conditions. For the experimental part of the study, different disk samples of Eagle Ford shale were selected, and the effect of acid diffusion on the rock surface was fully investigated. Digital microscopic images confirm that with differing concentrations of consumed acid and saturation front movement, varying degrees of reactivity are conceivable, including surface reaction, surface dissolution, matrix acidizing, and induced fracturing.For the mathematical modeling section, a continuity equation without an advection term and only a diffusion term was considered. An analytical solution was found for the dissolution of minerals as a result of reactive imbibition in a porous medium with porosity variations. The final form of the equation and the analytical solution is proposed here for the first time. Additional experiments were performed on Indiana limestone samples as control tests, with all experimental results matching perfectly with the developed analytical solution. Data from the literature relating to different temperatures also matched appropriately with the mathematical solution, effectively affirming the validity of the suggested solution. The proposed approach can be used as a predictive tool to verify the reactive models leading to porosity creation in the field scale.