Application of Two Methods to Evaluate Matrix Acidizing Using Real-Time Skin Effect in Saudi Arabia

Abstract

Abstract The effectiveness of acid treatment is commonly evaluated by a reduction in skin factor determined through pre-and/or post- well test analysis. However, mathematical models have been developed to monitor the change in skin while injecting acid and therefore obtaining real time skin values. This work demonstrates the application of monitoring real change in skin effect during the acid treatment with several field examples in carbonate formation. Two real-time monitoring methods1,2 were used to capture the effect of treating fluids on the formation. The field applications using the two methods were conducted on two water injectors in Saudi Arabia to evaluate stimulation performance with in-situ Gelled Acid systems. From the calculated bottomhole pressure and injection rate, skin effect was determined as a function of time. In this manner, the effectiveness of acid injection into the formation was estimated. The Paccaloni's method, which is a direct result of the steady state assumption, was conducted to monitor the skin factor during the acid job. The second method, by Prouvost and Economides was also used to illustrate the effect of the treating fluid on formation damage, but is based on transient flow equations. Both methods can readily be included in acid treatment monitoring; however, the latter method is preferred due to the better agreement in the field cases. This study provides a field application comparing the two methods and demonstrates the ability to capture the effect of diversion when the gelled acid increased viscosity in the formation by a subsequent increase in skin, and also the cleanup (decrease skin) that occurred when the regular acid reacts with the formation. This study also helps field engineers to ensure that no damage remains and no excessive acid is injected. The benefits of applying these two methods result not only in an operation cost reduction but also in a higher return on the stimulation investments.