科研之友
微信
新浪微博
Facebook
分享链接
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 petro-physical properties. We apply an inversion algorithm to simultaneously estimate the intrinsic permeability (k(i)), effective porosity at ambient condition (phi(0)), pore-volume compressibility (C-p), and Klinkenberg-slip factor (b) of an ultra-tight pyrophyllite sample from a single laboratory-based pressure-step-decay measurement. The inversion algorithm is valid for nitrogen injection pressure in the range of 50-500 psi. The algorithm assumes ideal-gas behavior of the injected nitrogen, 1D 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, square of pressure gradient is significantly smaller than pressure times second derivative of pressure along the entire length of the core plug, and time-invariant confining pressure. Parameter-estimation results based on the proposed inversion scheme are shown to be independent of the values of the initial guess for ki in the range of 1 nd to 10 mu d, phi(0) in the range of 0.01-0.20, C-p in the range of 10(-2) to 10(-6) psi(-1), and b in the range of 0-200 psi. Estimated apparent permeability and effective porosity" of the pyrophyllite samples exhibit strong pore-pressure dependence; consequently, both the properties vary substantially along the sample length during the pressure-step-decay measurement. The "pyrophyllite samples studied in this work are assumed to be homogeneous. The numerical model of the pressure step decay measurement accounts for the variation in porosity and permeability along the length of core due to the time-dependent pore pressure variation during the experiment. On an average, the effective porosity of the pyrophyllite samples increased by 100% and the apparent permeability decreased by 75% when the pore pressure increased from 50 psi to 500 psi during the measurement. The average values k(i), phi(0), C-p, and b of the nine pyrophyllite samples were estimated to be 40 nd, 0.03, 2 x 10(-3) psi(-1), and 100 psi, respectively.
- 出版日期2017-7
