Permeability and petrophysical properties of 30 natural mudstones

Abstract

We present permeability and other petrophysical data (including pore size distribution, porosity, particle size distribution, grain density, specific surface area, total carbon content, organic carbon content, and sulphur content) for 30 deeply buried mudstones. Permeabilities were measured at different effective consolidation stresses ranging from 2.5 to 60 MPa with a 30,000 mg L−1 NaCl solution. Samples represent a wide spectrum of mudstone types with clay size particle contents ranging from 13 to 66%. Porosities range from 6 to 27%; pore size data show that porosity loss is driven primarily by collapse of the largest pores. Our results confirm and considerably extend previously reported results indicating the influence of clay content on pore size distributions and the way they evolve as a result of compaction. Vertical permeabilities, measured using the transient pulse decay technique, range from 2.4 × 10−22 m2 to 1.6 × 10−19 m2. Horizontal permeabilities range from 3.9 × 10−21 m2 to 9.5 × 10−19 m2, overlapping with but generally higher than vertical permeabilities. In general, permeability decreases logarithmically with porosity. The relationship between permeability and porosity is strongly influenced by clay content, especially at higher porosities. Ratios of horizontal to vertical permeability measured on four samples range from 1.7 to 11.8, implying the influence of both particle alignment and sedimentological heterogeneity. We have used the data to calibrate two permeability models. For the Kozeny‐Carman model, values of 200 and 1000 for the product of shape and tortuosity factors provide the best fit for the vertical and horizontal permeabilities, respectively. The calibrated Yang‐Aplin model predicts the permeability of almost all the samples to within a factor of ±3 over a 4 orders of magnitude range of permeability.