CO2 Capture and Storage Performance Simulation in Depleted Shale Gas Reservoirs as Sustainable Carbon Resources

Underground carbon capture and sequestration (CCS) is a useful technique for separating this kind of greenhouse gas from atmosphere and store it under the surface of the earth. As a matter of fact, CO2 can be transferred to underground petroleum reservoirs which are initially contained oil and gas, or aquifers which are initially saturated with water. This kind of CCS takes place using an injection well which is drilled from surface to the target underground bedrocks. A shale gas reservoir (SGR) is a type of petroleum gas reservoir in which natural gas is stored in ultra-tight pores of the shale rock. In this study, a flow modeling analysis in SGR with a multi-stage fractured horizontal well (MSFHW) is conducted using numerical simulation. In this shale layer, a horizontal well is drilled and several transverse hydraulic fractures, for increasing the flow efficiency between the well and porous medium, are created. The studied SGR – a depleted reservoir acting as a macroscopic sustainable material for the CCS – is initially saturated with methane gas, and carbon dioxide is required to be injected for the storage. The most outstanding results of this study is about sensitivity analyses for SGR permeability with different conditions of gas adsorption and stress-dependent permeability which are from important features of SGRs. The results show a minor reduction in cumulative gas injection due to the effect of stress-dependent permeability in all measures for reservoir permeabilities. Furthermore, gas sorption shows a considerable positive correlation with CO2 storage response in high-permeability SGR and a minor increasing effect on SGRs with lower permeability values.