Quantitatively determine CO2 geosequestration capacity in depleted shale reservoir: A model considering viscous flow, diffusion, and adsorption

Abstract Depleted hydrocarbon reservoirs have been gradually recognized as the potential candidates for geological storage of carbon dioxide due to their wide geographical spread and large storage capacity. Reliably assess CO2 geosequestration capacity (CGC) of depleted hydrocarbon reservoirs lays the foundation of CO2 long-term geosequestration security. In this study, a model, considering CO2 viscous flow, diffusion, and adsorption in shale reservoirs, is established to determine bottom-hole pressure during CO2 injection through a hydraulic fractured multiwell-pad. The computational efficient semi-analytical solution is obtained by superposition principle and Laplace numerical inverse technique. Applying the developed model, a workflow is accordingly proposed to evaluate CGC of depleted shale reservoirs. As a case verification, the calculation on the CGC of a depleted shale reservoir from Barnett Shale in Texas is conducted, which illustrates that its CGC reaches up to 3.8 × 1012m3 when the constrained injection pressure (CIP) is high. Moreover, sensitivity analyses suggest that most reservoir parameters exhibit ignorable impacts on CGC when CIP is low whereas their effects on CGC are significant at high CIP. For instance, for the low-CIP, CGC just increases by approximately 6.7% when adsorption index increases from 2.5 to 250. As for the high-CIP scenario, CGC significantly increases 164 times for the same adsorption index range. In contrast to reservoir parameters, engineering parameters generally show great impacts on CGC at low CIP whereas their effects on CGC are negligible when CIP is high. To be more specific, CGC increases by 2.42 times when injection rate ratio of two wells ranges from 8 to 0.5 under low-CIP condition whereas CGC increases just by 0.47 times when CIP is high. The findings obtained in this study pave the way for the long-term CO2 geosequestration in depleted hydrocarbon reservoirs with much less efforts.