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This paper describes a series of experiments designed to investigate the influence of lithology 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 similar to 10(-10) m s(-1) to 10(-12) m s(-1) while that of the finer-grained sample ranges from similar to 4 x 10(-12) m s(-1) to 5 x 10(-14) m s(-1) 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 lithology (clay fraction) influence the permeability of mudstones should allow the development of more realistic porosity-permeability relationships which take into account lithological variations exhibited by mudstones.
Author(s): Dewhurst DN, Aplin AC, Sarda JP, Yang YL
Publication type: Article
Publication status: Published
Journal: Journal of Geophysical Research: Solid Earth
Year: 1998
Volume: 103
Issue: B1
Pages: 651-661
Print publication date: 01/01/1998
ISSN (print): 1934-8843
ISSN (electronic): 1934-2098
URL: http://dx.doi.org/10.1029/97JB02540
DOI: 10.1029/97JB02540
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