Compaction‐driven evolution of porosity and permeability in natural mudstones: An experimental study

Abstract

Abstract. This paper describes a series of experiments designed to investigate the influence of litho!ogy on the compactional loss of porosity and permeability in mudstones. Two intact samples of London Clay with clay fractions of 40% and 67% were compacted to 33 MPa effective stress. Clay fraction, permeability, porosity, pore size distribution, and specific surface area were measured and their evolution was monitored throughout the compaction process. Electron microscopy was combined with mercury porosimetry to trace the collapse of the pore structure with increasing effective stress. In both cases, porosity loss occurred primarily by the collapse of large pores. This process is more obvious in the coarser-grained sample because throughout the compaction process it has a much broader range of pore radii and a much greater mean pore radius. Consistent with the pore size distributions, the permeability of the coarser sample ranges from ,• 1040 rn s 4 to 1042 rn s 4 while that of the finer-grained sample ranges from ~ 4 x 1042 rn s 4 tO 5 x 104'* rn s 4 during progressive compaction from 2 to 33 MPa. The compressibility of the finer-grained sample is greater than that of the coarser-grained sample (0.15 as opposed to 0.07). However, in both cases the compressibility is much lower than that inferred for lithologically similar samples compacted over geological timescales. The demonstration that both porosity and litho!ogy (clay fraction) influence the permeability of mudstones should allow the development of more realistic porositypermeability relationships which take into account lithological variations exhibited by mudstones.

Fracture transmissivity as a function of normal and shear stress: First results in Opalinus Clay

“…Many researchers have shown that the permeability of shale decreases with externally applied stress (Dewhurst et al, 1999a;Dewhurst et al, 1999b;Katsube, 2000;Katsube et al, 1996a;Katsube et al, 1998;Kwon et al, 2001;Neuzil et al, 1984) and decreased porosity (Dewhurst et al, 1998;Schloemer and Kloss, 1997). A range of non-linear relationships have been proposed between permeability, porosity, and pressure in shale and mudstones, including exponential and power laws (Dewhurst et al, 1999a;Katsube et al, 1991).…”

Firmness Profiles Associated with Tidal-Creek Deposits: The Temporal Significance of Glossifungites Assemblages

“…Admittedly, establishing acceptable criteria from which the compactional parameters of a firmground might be derived is an all but impossible task. In addition to the aforementioned parameters, organic content, grain sorting, grain shape, and initial pore pressure undoubtedly have a notable effect on the kinetics of the compaction process (Krumbein 1959;Hoyt and Henry 1964;Tokunaga et al 1994;Dewherst and Aplin 1998).…”

“…In fact, the depth required varies with sediment texture (Fig. 7A,B), initial pore-water content, sedimentation rate, and length of time that the substrate was buried (Dewherst and Aplin 1998).…”

Estimation of hydraulic anisotropy of unconsolidated granular packs using finite element methods

“…Most of the observed variation in permeability of shale formations can be attributed to porosity variations [15,[21][22][23][24][25][26][27], grain size and pore size distributions [15,23,[25][26][27][28]. Furthermore, high anisotropy ratios observed in apparently homogeneous aquifers are caused to a lesser degree by orientation but caused mainly by micro-stratification [29].…”