A method for determining transverse permeability of tight reservoir cores by radial pressure pulse decay measurement

摘要

A transverse pressure pulse decay (TPPD) method is presented to measure transverse permeability of tight reservoir cores in a cell with finite volume. Given appropriate assumptions, a mathematical model based on the specially designed experiment is formulated, and its general solution is proposed. Early-time and late-time techniques are further presented for convenient postprocessing applications of experimental data. Meanwhile, sensitivity analysis of TPPD method is given. It is found that a good TPPD experimental principle can be obtained by adjusting test gas, experimental pressure, dimension of core sample, and volume ratio (lambda). The volume ratio error (lambda(error)) analysis reveals the following: (1) a larger lambda(error) results in increased transverse permeability error (k(error)); (2) the volume ratio (lambda) is better not very close to 0.754; (3) when lambda is equal to or greater than 1, the k(error) resulting from lambda(error) is monotonic decreasing as the volume ratio increases. In practice, lambda is usually equal to or greater than 1 due to the very small pore volume of a tight core. But this does not mean that the volume ratio should be as large as possible. The reason for this is that a pressure transducer with higher resolution is needed to record pressure change. That means experimental apparatus is much more costly. And such a TPPD experiment requires a much longer time to attain the late-time straight line behavior. The best choice is to find an optimal balance point among experimental cost, time, and accuracy.