53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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ABSTRACT: Compactive deformation in brittle-ductile transition involves particle crushing, cement bond breakage and pore collapse in porous reservoir rocks while subjected to high confining stresses. Despite knowing the overall hydro-mechanical response of porous reservoir rocks, quantitative prediction of permeability evolution based on the mechanical response alone is not trivial and requires microstructural insight. In the present study, the hydro-mechanical response of bonded granular assembly (as a proxy to natural reservoir rock) during compactive deformation is examined using discrete element modelling (DEM). We simulate drained triaxial compression in DEM while accounting the microstructural evolutions like bond breakage and particle crushing. In order to simulate fluid flow, pore network is extracted from the deformed granular assembly. Results indicate an order of magnitude reduction in permeability due to the combined effect of particle crushing and porosity reduction. It has been observed that, crushing of particle influences the flow in two different ways, reduction in the hydraulic radius and tortuosity reduction via creating new flow paths.
Permeability evolution in porous granular rocks primarily depends on, the deformation mechanism under various confining conditions, e.g., permeability increases due to brittle fracture in low confinement and permeability reduces in high confining compression due to pore collapse (Zhu and Wong 1997). In the high confining compression regime, development of localized zone of deformation is a significant issue in the petroleum industry, since the localized zones compartmentalize the pore fluid and hence reduces the hydrocarbon extraction efficiency. The rate of permeability evolution also varies with microstructural alteration, and on this basis, Vajdova et al. (2004) identified three different zones of permeability evolution. Initially, due to elastic compression of rock, a gradual reduction in permeability is noticed. In the second phase, a rapid drop in the permeability is observed due to the formation of localized deformation zones. Finally, again a gradual decay is noticed when the entire sample is compacted. Laboratory scale experiment analysis by Vajdova et al. (2004), demonstrates around two orders of magnitude reduction in permeability during localized deformation.
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