A molecular informed poroelastic model for organic-rich, naturally occurring porous geocomposites

Abstract

Molecular simulation results on organic maturity (mature and immature kerogen as the two asymptotic cases) are introduced into a continuum micromechanics based model for organic-rich shales. Through a fundamental functional relationship that constrains microporous kerogen density and elasticity variable spaces and within the framework of effective media theory; the model bridges the gap between asymptotic cases of organic maturity with texture as the overriding theme, specifically a matrix/inclusion (Mori–Tanaka) texture for immature systems and a granular (self-consistent) texture for mature ones. The utility of the molecular results merged into a continuum framework is demonstrated by estimating kerogen's microporosity (<2nm) from nanoindentation measurements. The effect of burial and diagenetic processes on the effective poroelasticity of these porous, naturally occurring geocomposites are captured by introduction of imperfect interfaces. Finally, the performance of the model is fully characterized by ranking the normalized contribution of uncertainty of input to the overall behavior and parameters of interest to geophysicists and geomechanicians such as degree of anisotropy and in situ stresses.