An Efficient Laboratory Method to Measure Stress-Dependent Tight Rock Permeability With the Steady-State Flow Method

Abstract

The matrix permeability of tight formations is important for many geological and engineering applications, such as CO2 geological sequestration, disposal of nuclear waste, and production of unconventional hydrocarbon and coalbed methane. In the case of hydrocarbon production, the reservoir permeability decreases with decreasing pore pressure or increasing effective stress. Laboratory characterization of the relationship between matrix permeability and effective stress (and pore pressure) is generally time consuming since the current methods are based on the so-called point-by-point approach that measures one permeability data point only with one test run, and the relationship is generally represented with multiple data points. In this paper, we present a method to determine matrix permeability, its relationship with effective stress, and the Biot coefficient of a tight rock sample with three steady-state flow test runs using large pressure gradients. Unlike the traditional steady-state flow method based on linear flow theories, analytical results based on a nonlinear flow theory are used for determining the related relationship and parameters. The gas properties and permeability along the core sample vary with gas pressure and effective stress, while the traditional method treats them as constants for a given test run. To get the same set of parameters, our method only requires three test runs, and each test run of our method takes a much shorter time than the traditional method because our method is based on nonlinear flow theory and thus allows for the use of large pressure gradients. Comparisons of the permeability measurements with those obtained using traditional methods and numerical simulations demonstrate that our new method can get satisfactory results.