Experimental Investigation on the Effect of Permeability on the Optimum Acid Flux in Carbonate Matrix Acidizing
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Determination of optimal acidizing conditions through laboratory experimental study is crucial for designing matrix acid stimulation jobs in the field. Optimum interstitial velocity, vi-opt (the velocity of injected fluid that yields the minimum volume of acid needed to propagate wormholes) can be determined though curve fitting of experimental data. This optimum interstitial velocity coincides with the minimum volume of acid required for wormhole breakthrough, and therefore, the most efficient stimulation design. Optimum interstitial velocity determines the injection rate for a treatment, and the optimum pore volume to breakthrough, PVbt-opt, suggests the total volume of acid needed. Studies of carbonate matrix acidizing have focused on the role of many parameters, such as acid concentration, acid type, temperature, and core dimensions. However, under the same experimental conditions, different limestone rocks exhibit different optimal conditions. It is important to explore how changes in rock properties, such as permeability and pore structure, can also impact the efficacy of matrix acidizing techniques. In this work, a series of linear coreflood experiments on relatively homogenous Indiana limestone and Desert Pink limestone cores were performed at ambient temperature. Cores of 1.5-in. diameter by 8-in. long were acidized using 15% hydrochloric acid. The average permeabilities of the cores tested were 6, 11, 33 and 239 mD with varied porosity. The effects of permeability and porosity were isolated using thin section analysis to study pore structure. Based on experimental results, a detailed explanation of the pore structure and permeability effects on optimum interstitial velocity is presented. The coreflood acidizing results show that at low permeabilities, optimum interstitial velocity increases with permeability. When permeability of the rock reaches a certain value, the effect of permeability on the optimum injection condition diminishes. In addition, the optimum pore volume to breakthrough increases across the entire range of permeabilities tested. This work also briefly quantifies the differences in pore structure of the samples, leading to recommendations for future work. The implications and applications of this work are far-reaching; better understanding of optimal acidizing conditions based on the studied rock properties has significant potential economic and operational impact.
Etten, Jordan Ruby (2015). Experimental Investigation on the Effect of Permeability on the Optimum Acid Flux in Carbonate Matrix Acidizing. Master's thesis, Texas A & M University. Available electronically from