Acid Fracturing Feasibility Study for Heterogeneous Carbonate Formation



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Acid fracturing is a stimulation technique that is commonly used by the industry to increase productivity or injectivity of wells in carbonate reservoirs. To determine a feasibility of acid fracturing treatment for a heterogeneous formation, the effect of rock properties on the created fracture conductivity needs to be investigated experimentally. In this study, the influence of rock lithology, porosity, and permeability on the resultant fracture conductivity was investigated for the Middle Canyon formation.

Six carbonate cores collected from different depths of Middle Canyon interval were selected for this study. The cores had the permeability ranging from 0.07 to 28 md and the porosity ranging from 1.7 to 15.4%. The acid etching experimental conditions, such as injection rate, reaction temperature, and acid type, were selected to simulate field treatment conditions. The fracture surface of each sample was scanned before and after the acid treatment to characterize the change in surface profile and to calculate the etched volume of rock.

The results of the study indicated that the final conductivity values under the maximum closure stress of 4000 psi were similar to each other (6.4 - 13.5 md-ft) for all the cores, regardless the variation in cores? porosity and permeability. It was also observed that the cores with a lower porosity had a lower decline rate of acid fracture conductivity with increasing closure stress. Based on the results of this study, it was concluded that acid fracturing stimulation of the Middle Canyon formation may not be effective to achieve the goals defined by the operator.