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.