Effect of Matrix Acidizing on Different Core Samples at Different Temperatures: An Experimental Study

Abstract

The economic production of hydrocarbons from reservoirs is reliant on the natural capability of the reservoir to produce fluids (HCs) economically. However, a decrease in porosity, permeability, or both, can lead to damage near the wellbore face or deep into the rock, resulting in positive skin and resistance to fluid flow. This resistance causes a loss in production, which can be overcome by removing the impairments near the wellbore using stimulation methods. Matrix acidizing is a type of stimulation method that involves injecting an acid/solvent into the formation to dissolve/disperse materials that impair well production in sandstone reservoirs or to create new, unimpaired flow channels in carbonate reservoirs. The main aim of this study is to investigate and compare the effect of matrix acidizing on different rock formations at different temperatures, as well as to measure rock physical porosities (porosity, permeability) before and after acidizing. For this purpose, laboratory experiments were conducted on limestone (Tiyon formation) and sandstone (Gaj formation) of Thano Bulla Khan, Sindh, Pakistan. The experiments were conducted in two phases: pre-investigation of core samples and post-investigation of core samples. In the pre-investigation phase, experiments were performed before acidizing. These experiments included porosity, permeability, XRD, SEM, and EDS testing. In the post-investigation phase, experiments were performed after acidizing, except for XRD and EDS testing, which was only used for acid selection. The purpose of the post-investigation phase was to compare the results with the pre-investigation phase. Three samples of each formation were used to compare the results after injecting an acid combination (30-50ml) with a ratio of 15%HCL: 9% HCOOH, 13% CH3COOH at 60°C, 90°C, and 120°C. The results of the study showed that the effect of matrix acidizing was greater on limestone rock samples than on sandstone rock samples. Limestone rock is composed of calcium carbonate, which reacts vigorously with acid, while sandstone forms fewer bubbles. The petrophysical properties of the rock were successfully restored and recovered by doing the matrix acidizing job. In limestone rock samples, porosity values were recovered to 20.27% -23.18%%, and permeability values were recovered to 19.26 md to 24.16, 25.02, and 27.98 millidarcies at temperatures of 60°C, 90°C, and 120°C, respectively. In sandstone rock samples, porosity values were recovered to 7.5.