The Effect of Carbonate Cement Type on Sandstone Matrix Acidizing

This study aims to numerically determine the roles of the geochemical reactions during the injection of a strong acid into a sandstone sample. As a case study, we used laboratory results of hydrochloric acid (HCl) injection into a sandstone core plug sample from the literature. As the exact cement composition of the implemented sandstone was not available, two probable cement compositions were considered (i.e., calcite and dolomite cement). A fully-implicit model, coded in Python, was used to simulate the underlying geochemical reactions during the HCl injection (i.e., equilibrium and kinetical reactions). In addition, the reactive surface area and porosity-permeability changes of the rock sample were included in the model. The modelling results show that dolomite cement matched better than calcite cement with the experimental acidizing data. A perfect effluent pH prediction was therefore achieved when the reactive surface area was considered as a function of mineral volume fraction. Moreover, a detailed analysis of the dissolution/precipitation rate of different minerals involved in simulations was provided. The presented model improves our understanding of sandstone acidizing by determining dominant reactions.