Geological storage of CO2 in deep saline sandstone aquifers: A geomechanical perspective

Abstract

One of the pathways to attain NET ZERO is CO 2 injection into deep saline aquifers (DSAs), which alters the saturation and pore pressure of the reservoir rocks, hence the effective stress, σ ʹ. This, in turn, would change their geomechanical (i.e. peak deviatoric stress, elastic modulus, Poisson's ratio) and petrophysical (porosity and permeability) properties. Such a situation might trigger geo-hazards, like induced seismicity , ground deformation, caprock failure. Hence, reducing the risk of such hazards necessitates quantifying the spatial and temporal changes in σ ʹ, under specific CO 2 and/or brine saturation, designated as S CO2 and S b , respectively, and resultant pore pressure. With this in view, a conceptual model depicting the reservoir, demarcated by five zones based on variations in saturation, pore-pressure, temperature, etc., and the corresponding effective stress equations have been proposed based on the available literature. Furthermore, a critical review of literature has been carried out to decipher the limitations and contradictions associated with the findings from (i) laboratory studies to estimate S CO2 employing p-wave velocity and electrical resistivity, (ii) analytical and numerical approaches for estimating the variation of pore-pressure in the reservoir rocks, and (iii) laboratory studies on variation in geomechanical and petrophysical properties under the conditions representative of the above-mentioned zones of the conceptual model. The authors consider that extensive experiments should be conducted on the rocks from different sources and tested under various conditions of the CO 2 injection to validate the proposed model for the execution of risk-free CO 2 storage in DSAs.

Topics & Concepts