Evaluation of After-Closure Analysis Techniques for Tight and Shale Gas Formations

Abstract

Optimized hydraulic fracture design requires formation permeability as an input, but it is difficult to quantify in tight gas and shale gas reservoirs. After closure analysis (ACA) following a minifrac or fracture calibration test may offer a means to determine the formation permeability in cases for which both a formation test and a conventional pressure buildup test are impractical and/or unable to provide the permeability. However, ACA techniques use a variety of specialized plots, and there is a risk that apparent straight lines may lead to erroneous results. This paper proposes a technique that provides a simple way to calculate formation permeability, initial reservoir pressure, fracture length, and closure pressure from a single specialized plot. The proposed technique is compared with the G-function method for the estimation of the closure pressure. In addition, it is compared with 3 ACA techniques (Benelkadi, Gu, and G-Function) used in the literature to calculate formation permeability for tight gas and shale gas wells. Three field examples of pressure fall-off tests (in tight sand gas wells and shale gas well) are analyzed. The results show that the proposed technique provides a clear and rigorous analysis procedure for determination of permeability and other parameters required for the hydraulic fracture design. This proposed technique uses only a single plot comparing to the multiple plots required by the other techniques.