Experimental assessment of pore fluid distribution and geomechanical changes in saline sandstone reservoirs during and after CO₂ injection

Abstract

Responsible CO₂ geosequestration requires a comprehensive assessment of the geomechanical integrity of saline reservoir formations during and after CO₂ injection. We assessed the geomechanical effects of CO₂ injection and post-injection aquifer recharge on weakly cemented, synthetic-sandstone (38% porosity) sample in the laboratory under dry and brine-saturated conditions, before and after subjecting the sample to variable pore pressure brine-CO₂ flow-through tests (∼170 h). We measured ultrasonic P- and S-wave velocities (V_p V_s) and attenuations, electrical resistivity and volumetric strain (ε_v). V_s was found to be an excellent indicator of mechanical deformation during CO₂ injection; V_p gives mechanical and pore fluid distribution information, allowing quantification of the individual contribution of both phenomena when combined with resistivity. Abrupt strain recovery during imbibition suggests that aquifer recharge after ceasing CO₂ injection might affect the geomechanical stability of the reservoir. Static and dynamic parameters indicate the sample experienced minor geomechanical changes during CO₂ exposure, with an increase of Δε_{v <}3% and a drop in ΔV_s ∼1%. In contrast, due to brine-induced hydro-mechanical alteration, Δε_v increased by ∼10% and ΔV_s by ∼6%. This study provides a multiparameter, thermo-hydro-mechanical-chemical database needed to validate monitoring tools and simulators, for prediction of the geomechanical behaviour of CO₂ storage reservoirs.

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