Simultaneous Estimation of intrinsic Permeability, Effective Porosity, PoreVoiume Compressibility, and Klinkenberg-Slip Factor of Ultra-Tight Rock Samples Based on Laboratory Pressure-Step-Decay Method

摘要

Conventional laboratory characterization of ultra-tight reservoir rock samples involves separate laboratory measurements on different core plugs or on crushed rock samples. Heterogeneity and anisotropy of ultra-tight reservoir samples adversely influence the laboratory correlation among various measured and estimated petrophysical properties. We apply an inversion algorithm to simultaneously estimate the intrinsic permeability, effective porosity at ambient condition, pore-volume compressibility, and Klinkenberg-slip factor of an ultra-tight pyrophyllite sample from a single laboratory-based pressure-step-decay measurement. In doing so, we circumvent the effects of heterogeneity and account for the pore-pressure dependency of apparent permeability and effective porosity. Moreover, the time and resource requirements are drastically reduced in comparison to those required when performing multiple experiments that separately estimate the aforementioned petrophysical properties. The inversion algorithm is valid for nitrogen injection pressure in the range of 50 to 500 psi. The algorithm assumes ideal-gas behavior of the injected nitrogen, ID isothermal laminar gas flow, homogeneity of the core, pressure-independent gas viscosity, inverse-pressure dependence of the apparent permeability, pressure-independent Klinkenberg-slip factor, non-negligible pore-volume compressibility, pressure-dependent effective porosity, negligible inertial effects, negligibly small pressure gradients, and time-invariant confining pressure.