The Effect of Core Dimensions on the Optimum Acid Flux in Carbonate Acidizing
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AbstractThe results of matrix stimulation in carbonate formation strongly depend on the acid injection condition. Large amounts of lab tests indicate that an optimum acid interstitial velocity, vi-opt, exists, which results in the minimum volume of acid required for wormhole propagation (optimal breakthrough pore volume) and the most efficient stimulation. During the last decade, much progress has been made to identify the factors that affect the optimum conditions of linear coreflood experiments, including temperature, acid type, acid concentration and lithology. However, there lacks a discussion on the effect of core dimensions on the optimal conditions. Experimental results published before show strong evidence that the optimal condition changes as the dimension of core samples changes. Since the optimal condition from experimental studies is the critical information used in treatment design, it is necessary to investigate the relationship between the optimal condition and the core geometry.In this work, a series of coreflood experiments were conducted with Indiana limestone cores at room temperature. The cores selected are relatively homogeneous to eliminate the effect of heterogeneity. The acid used is 15% plain hydrochloric acid. The core lengths range from 1-in. to 10-in. and the core diameters are 1-in., 1.5-in. and 4-in. From the experimental results, the effects of core length and core diameter are examined. The results showed that the vi-opt becomes independent of the core length when the core length reaches a value of 6 inches. These observations can help with the recommendations of the proper core length and core diameter to be used in future laboratory experiments.The core-size dependence is important while scaling up the laboratory results to field applications. The results of this work can give a better understanding of how upscaling works. Also, with these results, the existing wormhole growth models can take into account the core-size dependence, resulting in more accurate upscaling of experimental results.
