Compaction trends of full stiffness tensor and fluid permeability in artificial shales

Abstract

Summary We present a methodology and describe a set-up that allows simultaneous acquisition of all five elastic coefficients of a transversely isotropic (TI) medium and its permeability in the direction parallel to the symmetry axis during mechanical compaction experiments. We apply the approach to synthetic shale samples and investigate the role of composition and applied stress on their elastic and transport properties. Compaction trends for the five elastic coefficients that fully characterize TI anisotropy of artificial shales are obtained for a porosity range from 40 per cent to 15 per cent. A linear increase of elastic coefficients with decreasing porosity is observed. The permeability acquired with the pressure-oscillation technique exhibits exponential decrease with decreasing porosity. Strong correlations are observed between an axial fluid permeability and seismic attributes, namely, VP/VS ratio and acoustic impedance, measured in the same direction. These correlations might be used to derive permeability of shales from seismic data given that their mineralogical composition is known.

Assessing mineral composition and permeability of a shale seal

“…The amplitude of these fluctuations can reach 0.1. This observation is in good agreement with previously published results (Beloborodov et al 2018) where it has been shown that even a small variation of smectite content in shales results in significant change of the # / % ratio and # .…”

“…Background shale permeability is an important parameter for the assessment of shale sealing capacity. In recent experimental work, Beloborodov et al (2018) showed that the logarithm of vertical, or normal-to-the-bedding, permeability of shale is linearly proportional to porosity in a wide porosity range from 0.40 to 0.15. Depending on the amount of clay and its composition the trend is shifted in the permeabilityporosity space.…”

Experimental mechanical compaction of reconstituted shale and mudstone aggregates: Investigation of petrophysical and acoustic properties of SW Barents Sea cap rock sequences

“…A series of laboratory experiments have measured petrophysical properties of synthetic mixtures of clay minerals (e.g., Mesri and Olson, 1971;Al-Tabbaa and Wood, 1987;Vasseur et al 1995;Mondol et al, 2007). Other researchers looked into the compaction behavior of quartz-clay mixtures (e.g., Knoll and Knight, 1994;Mondol, 2009;Beloborodov et al, 2018). A number of studies have carried out resedimentation experiments (e.g., Seah, 1990;Sheahan, 1991;Santagata and Kang, 2007;Adam et al, 2013).…”

Modeling of Compaction Trends of Anisotropic Elastic Properties of Shales

“…In this study, we use the data obtained as the result of compaction experiments on two artificial shale samples, hereafter, samples A0100 and A2080 (Beloborodov et al., 2018). The solid phases of these samples comprise 100% kaolinite (A0100), and 20/80% quartz/kaolinite (A2080), respectively.…”

“…In order to better understand the parameters that affect the elastic properties of shales, we use recent experimental results of Beloborodov et al. (2018), who obtained all five elastic constants of shale samples with controlled porosity and mineralogy. The experimentally measured elastic coefficients obtained at the maximum compaction state, where the ODF of clay platelets are known from neutron diffraction experiments (Beloborodov et al., 2016), are first inverted for elastic properties of an individual kaolinite wet clay pack.…”