Investigation of Effect of Fracturing Fluid on After-Closure Analysis in Gas Reservoirs

Abstract

Summary Published techniques for analysis of after-closure fracture data usually assume single-phase flow. These procedures generally rely on the techniques developed for the analysis of buildup tests. Applying the buildup techniques implies that the injected fluid and reservoir fluid have approximately the same properties. This assumption is generally incorrect in case of minifrac tests where the injected fluid may be very different from the reservoir fluids. This situation is at an extreme when the minifrac test is conducted on a gas reservoir and the injected fluid may be a relatively high-viscosity gelled fluid. In this paper, we review the basic theory behind after-closure analysis. Using a numerical simulator, minifrac tests are simulated and analyzed for both oil- and gas-reservoir cases where an aqueous phase is injected as a fracturing fluid. Analyses of the numerically simulated falloff data are presented. Guidelines for the analysis of such data have been developed and presented. Field data are also presented. In one case, breakdown, step-rate, and fluid-efficiency tests (FETs) were performed on a tight gas formation and the data were analyzed. The results of using these various techniques are presented. The consistency of results validates conclusions achieved using the numerically simulated data.