Effects of non-Darcy flow on pressure buildup analysis of hydraulically fractured gas reservoirs

Abstract

Conventional well-testing techniques are commonly used to evaluate pressure transient tests of hydraulically fractured wells to estimate values such as formation permeability, fracture length, and fracture conductivity. When non-Darcy flow occurs along the fracture, analysis of the pressure transient test using conventional analysis methods will produce incorrect values of fracture conductivity and fracture half-length. The objective of this project is to emphasize the importance of non-Darcy flow in the hydraulic fracture and its effects on pressure buildup analysis of hydraulically fractured gas reservoirs. A reservoir simulator was used to generate pressure drawdown and buildup data both with and without the effects of non-Darcy flow. These synthetic buildup tests were then analyzed using conventional well-testing techniques. It was found that when non-Darcy flow occurs along the fracture, the estimated fracture conductivity and fracture half-length represent only a small fraction of the actual values. Also, the degree to which the non-Darcy flow affects the well-test results depends upon the values of fracture permeability, water saturation inside the fracture, and the production rate during the drawdown period. If the incorrect fracture properties obtained from conventional analysis are used in reservoir simulation forecasting, critical values such as production rate and total recovery will be miscalculated. Since conventional well-test analysis cannot be used to determine fracture parameters reliably, simulation history matching is the appropriate method to correctly analyze buildup pressure response from hydraulically fractured reservoirs with significant non-Darcy flow effects.