Effects of Homogeneous and Heterogeneous Mineralogy in Carbonate Acidizing

A series of carbonate acidizing coreflood experiments using HCl was conducted on core samples from the Kujung Formation, offshore Northwest Java. Using XRD, SEM, and thin-section petrography, these samples were characterized as exhibiting varying degrees of heterogeneity. X-ray diffraction analysis showed that core plug Sample 7 consists of about 93% calcite, 3% dolomite, and 1–2% gypsum and pyrite, whereas core plug Sample 2 contains nearly 99% calcite. Mineralogical heterogeneity can affect the success of acidizing stimulation by determining the geometry (shape and size) of the wormholes that form. In addition to mineralogical heterogeneity, the presence of impurities in the rock may also influence the acidizing process and its outcomes. Conversely, in more homogeneous carbonate samples, a more uniform acid attack is observed. In homogeneous samples, carbonate dissolution was found to extensively “clean” clays and fine particles from the pore space. This study is expected to demonstrate different processes for enhancing permeability and porosity when using core samples of heterogeneous versus homogeneous mineralogy in carbonate acidizing applications.