An Experimental Study of Acid Matrix Treatment Performance On Shale Core Samples

Abstract

Experimental and numerical studies have demonstrated that there is great potential of enhancing the oil recovery from tight formations. This study investigated the effect of acid matrix treatment by applying gas flooding on the core samples before and after the treatment. The aim of the acid stimulation treatment was to improve the low-permeability of the cores. Four core samples (0.5 in, 1.0 in, 1.5 in, and 2.0 in) from an outcrop of the Eagle Ford formation were used in this study. Permeability was measured before and after the acid treatment. The cores were CT-scanned to identify natural fractures. Different gas injection pressures were used to study the oil recovery and the time needed to penetrate through core samples. Furthermore, a solubility test was applied to identify the optimal acid concentration. The cores were re-scanned after the acid flooding treatments to detect any change. Gas flooding was applied to acidized core samples to detect changes in penetration time and recovery factor. A solubility test demonstrated that 15% of HCL was the optimal acid concentration for the Eagle Ford formation. The study showed the porosity, permeability, recovery factor, and penetration time before and after the acidizing treatment. Permeability was enhanced from 1.04 nanodarcies to 2.10 microdarcies. Furthermore, the study showed the effect of core length on penetration rate (in/min) of gas flooding and the recovery factor at each injecting pressure. The penetration time in this study varied from 207 to 112 minutes/inch when the injecting pressure increased from 1500 to 2500 psi. After acidizing, however, the penetration rate decreased to 8.4 minutes/inch using flooding of 300 psi. The CT scan showed improvement of the micro fracture width.

Impact of HCl Acidizing Treatment on Mechanical Integrity of Carbonaceous Shale

“… 16 Highly permeable conductive channels are formed in the formation as a result of matrix acidizing to enhance the flow of fluids toward the wellbore. 17 …”

“…Significant increase in the permeability (from nanoDarcies to microDarcies) was observed as a result of matrix acidizing on Eagle Ford shale using 15% HCl. 17 An experimental study was conducted by Morsy et al 18 to investigate the effect of HCl acid on pore volume, crack distribution, and imbibition in different shale formations including Marcellus shale, Mancos shale, Barnett shale, and Eagle Ford shale. Experiments were conducted using different concentrations of acid, that is, 4%, 15%, and 20%.…”

“…Acidizing treatment caused the width of fractures to increase in addition to the permeability enhancement. 17 Wu and Sharma 21 conducted an experimental program to evaluate the effects of matrix acidizing on Bakken shale. HCl (3 wt %) treatment caused the dissolution of Bakken shale by almost 35% by weight.…”

Comparison of Chemical-Induced Fracturing by Na2S2O8, NaClO, and H2O2 in Marcellus Shale

“…In the oil and gas industry, acid stimulation is a commonly used treatment in sandstone and carbonate formations. The acid reacts with soluble substances like calcite to improve the permeability. − Different chemical reactions lead to different mechanisms of improving oil and gas recovery. The final goal of our study was to understand what chemicals should be used under specific conditions.…”

An experimental study of acidizing operation performances on the wellbore productivity index enhancement

“…Tight reservoirs like fractured carbonated reservoir are the most susceptible formations to the matrix acidizing due to their low permeability, and dealing with the complexity of these formations is still a major concern of the petroleum industries (Al-Muhareb et al 2003;Khalil et al 2017;Msharrafieh et al 2006). However, conductivity property of the fractures plays the substantial role in the acid fracturing, regarding the random reactions between rock and acid, and this phenomenon might be difficult to estimate.…”