Permeability and physical properties of semi-compacted fine-grained sediments – A laboratory study to constrain mudstone compaction trends

Helge Hellevang,Nazmul Haque Mondol,Mohammad Nooraiepour

doi:10.1016/j.marpetgeo.2019.01.019

Helge Hellevang, Nazmul Haque Mondol + Show 1 more

Open Access

https://doi.org/10.1016/j.marpetgeo.2019.01.019

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Abstract

Permeability and physical properties of fine-grained clastic sediments show a wide range of variations. Despite rather intensive research, the impact of grain size distribution and mineralogical composition of individual rock constituents is not thoroughly investigated. We performed mechanical compaction of brine-statured reconstituted borehole cuttings and synthetic quartz-clay mixtures to study the evolution of properties in fine-grained clastic sediments during burial. The primary objective was to examine whether the hydraulic and physical properties of fine-grained sediments could be described and constrained by binary quartz-clay mixtures. The synthetic binary mixtures were prepared by mixing quartz with non-swelling (kaolinite) and strongly-swelling (smectite) clays, which can represent the endmember properties within the clay minerals. In addition to vertical permeability, physical and seismic properties, stress-dependence of permeability, and two-phase relative permeability of brine-oil system were investigated. Experimental results show that grain size distribution and mineralogical composition control the vertical permeability. A well-constrained porosity-permeability bound is defined, where the compaction trends of pure quartz and quartz-smectite 15:85 (wt %) mixtures describe the maximum and minimum boundaries, respectively. The quartz-clay mixtures, however, fail to provide bounds to constrain the broad range of variations in physical and seismic properties of reconstituted aggregates, and consequently natural mudstones. It is crucial to incorporate microstructure into the permeability prediction models because the experiments indicated that the microscale characteristics control the macroscale fluid flow properties.

Highlights

Fine-grained clastic sediments are the most abundant deposits of sedimentary basins, and yet among the least investigated sedimentary rocks
Because of the markedly distinct petrophysical characteristics of mudstones and shales compared to the coarser clastic rocks such as sandstones, they are of fundamental importance as caprocks for anthropogenic-related storage sites such as geological CO2 sequestration and waste repositories (Mallants et al, 2001; Song and Zhang, 2013; Nooraiepour et al, 2018b)
We have found no correlation between the vertical permeability of reconstituted aggregates and the content of kaolinite, illite, and chlorite clay minerals in the bulk mineralogy

Summary

Introduction

Fine-grained clastic sediments are the most abundant deposits of sedimentary basins, and yet among the least investigated sedimentary rocks. The compaction trends for different mudstone properties are, difficult to study in natural settings, because various factors such as mineralogy, grain size, depositional environment, excess pore pressure, biogenic content, maximum burial, and exhumation collectively impact the mudstone properties (Revil and Cathles, 1999; Schneider et al, 2011; Bjørlykke, 2015; Daigle and Screaton, 2015; Nooraiepour et al, 2017a,b; Nooraiepour, 2018). Regardless of these complexities, it is necessary to define boundaries, in which physical and hydraulic properties may vary

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