A modified acid system to enhance carbonate matrix acid stimulation: An experimental study

Abstract

In carbonate matrix acidizing, the critical design parameters are interstitial velocity and pore volume to breakthrough for wormhole propagation (vi, opt and PVBT,opt). Hydrochloric acid (HCl), the most commonly used acid in carbonate acidizing, sometimes shows low efficiency because the injection rate needed for optimal wormhole propagation is not attainable, especially for when long completion intervals, low permeability carbonates, or coiled tubing operations are involved. It also raises safety, corrosion, and environmental concerns. When conventional retarded acid systems are used to overcome these challenges, the efficiency of acid stimulation often suffers from low reaction rate. This study presents testing results of a modified acid system that has controlled reaction rate with favourable wormhole propagation characteristics, especially at low interstitial velocities. Due to the increased activation energy barriers utilized in these modified‐acid systems, it is possible to control the reaction rate of the hydrogen proton and optimize the wormholing effect based on the completion method and formation specifications. Laboratory linear core flooding experiments and acid jetting experiments were conducted to study the wormhole efficiency with the new acid systems. The experimental results showed clear advantages of the modified acid systems. The modified acids have similar or better wormhole efficiency parameters compared with HCl having comparable dissolving power. When combined with acid jetting, further improvement in wormhole growth in low permeability limestone is achieved. In addition to minimizing the hazardous exposure levels and corrosion rates compared with HCl, the new acid system provides the positive aspects of solubilizing ability, thus improving optimal wormhole conditions.

Impact of Acid–Base Stimulation Sequence on Mineral Stability for Tight/Impermeable Unconventional Carbonate-Rich Rocks: A Delaware Basin Case Study

“…Efficient wormhole creation into low permeability carbonate systems is a well-recognized challenge due to the fast rection rate between HCl and calcium carbonate. ,− The rapid neutralization of the acid spearhead in these high carbonate samples suggests that the acid spearhead may be useful for initiating fractures in extremely calcite-rich rocks but does little to enhance rock porosity. If 100% of the acid spearhead is assumed to be neutralized by calcite, 90–99% of the total calcite remains unreacted (see Table S7 for calculations).…”

“…Dissolution of carbonates ( e.g. , calcite and dolomite) in shales due to the injection of acid, most commonly HCl, has been shown to increase porosity and open pore throats in the shale matrix. ,,− This is particularly crucial for carbonate-rich systems. − Lu et al observed a limited increase in the permeability of Eagle Ford shale (52 wt % calcite) pre- and post-exposure to NaCl brine; however, Marcellus shale (6 wt % calcite, 3 wt % dolomite) exposed to the same brine showed a 5 times increase in permeability, which was assumed to be due to differences in mineral dissolution that either limited or enhanced further penetration of the fluid for the Eagle Ford and Marcellus shales, respectively. Li et al compared the chemically altered zone of a carbonate-poor Marcellus shale (1 wt % calcite, 6 wt % dolomite) and a carbonate-rich Eagle Ford shale (52 wt % calcite) exposed to HFF and quantified that carbonate dissolution extended deeper into the carbonate-poor matrix compared to the carbonate-rich matrix (100–200 vs 30–40 μm, respectively).…”

Comparative analysis of matrix-retarded acidizing methods for tight carbonate reservoirs: Gelled acid, micro-emulsified acid, and foamed acid

“…Due to the shorter residence time of the acid in the formation, especially at high temperatures, the wormholes created are less efficient hydrocarbon channels (Chacon and Pournik, 2022). Therefore, gelled acid, foamed acid, micro-emulsified acids, and other chemical agents have been formulated in an effort to circumvent the drawbacks of the fast acid-rock reaction by lowering H + ion dissociation, reducing H+ ion mass transfer, and changing the wettability of the rock surface (Zhu et al, 2022).…”

Preface for the Special Issue Honouring Professor Hisham Nasr‐El‐Din

“…The Canadian Journal of Chemical Engineering is acknowledged for dedicating this special issue to the living memory of Dr. Nasr‐El‐Din. This acknowledgment is also extended to the authors who contributed to this special issue [ 1–28 ] as well as the guest editors:…”