Assessment of Saturation-Dependent Relative Permeability in Irregular-Shaped Tight Sandstone Samples Through Integration of Experimental Measurements and Numerical Modeling

Abstract Conventional laboratory-based rock measurement techniques, including saturation-dependent relative permeability measurements, require perfectly-cut cylindrical core plugs. Saturating tight rock samples for saturation-dependent measurements can also be time-consuming in tight rocks, making these measurements expensive and unreliable. Moreover, achieving a perfectly-cut cylindrical core sample is difficult in the case of brittle rock types or naturally fractured rocks. In this paper, we introduce a new method for the assessment of permeability and saturation-dependent relative permeability measurements using any regular- and irregular-shaped rock samples. The permeability of the rock samples are estimated using a pressure decay experimental setup, which records the decay of pressure with respect to time using Helium as the penetrating gas. We solve the pressure diffusion equation numerically using the finite volume method (cylindrical- and irregular-shaped sample) and the finite difference method (cylindrical-shaped sample). We get the geometric profile of the samples from Computed Tomography (CT)-scan imaging. The next step involves partially saturating the sample to a desired water saturation level using the recently developed enhanced saturation setup and workflow, which expedites saturation of tight rocks. We then estimate the permeability of the partially-saturated sample through integration of the numerical solver and the experimental measurements, and repeat the process to obtain the saturation-dependent relative permeability values of the samples. In this paper, we tested the introduced workflow on regular-shaped cylindrical and irregular-shaped samples belonging to Scioto Sandstone (Sample 1: irregular-shaped and Sample 2: cylindrical) and Nugget Sandstone (Sample 4: irregular-shaped and Sample 5: cylindrical). We also performed pulse-decay measurement on Scioto Sandstone (Sample 3: cylindrical) and Nugget Sandstone (Sample 6: cylindrical) for verification of the saturation-dependent relative permeability results. The estimated gas permeability values ranged from 33–83 µD at dry conditions, and these values reduced to 0.3–0.7 µD at maximum water saturation levels for the respective samples. The total time duration of the experiment for each sample was reduced from a minimum of 25 days for conventional techniques, such as steady-state, to 7 days using the introduced method. We achieved similar permeability results for the cylindrical-shaped samples using the finite difference and the finite volume methods. The permeability results for irregular-shaped samples were similar to those of the cylindrical-shaped samples from the same formation, verifying the reliability of the introduced method for assessment of saturation-dependent relative permeability in irregular-shaped samples. The introduced workflow enables (a) for the first time relative permeability and absolute permeability measurements in irregular-shaped samples such as cuttings, broken core samples, and outcrop samples, (b) integration of numerical modeling and experimental methods to estimate permeability values in tight formations, (c) reducing the time duration of the experiments for tight rocks by shortening the time for the saturation process, and (d) maintaining control on the water saturation level for performing saturation-dependent petrophysical measurements.