Carbon dioxide (CO2) injection into shale enables enhanced gas recovery (EGR) associated with geological CO2 sequestration. Although primary research has been conducted on the CO2-based EGR technique in shale, the factors that influence the EGR efficiency remain unclear and need to be examined. This study presents a novel nuclear magnetic resonance (NMR)-based methodology to measure the EGR efficiency caused by CO2 injection into shale samples with various properties. Accordingly, the effects of shale properties on the CO2-based EGR efficiency were revealed, and a calculation model for estimating the EGR efficiency was established. The results indicated that CO2 injection enables significant production enhancement of shale gas, with the EGR efficiency averaging 23.54% and ranging from 16.22 to 34.34%, thus indicating that the EGR efficiency varies with the shale properties. The results also indicated that a higher CO2-based EGR efficiency, while adhering to a higher CO2-sequestration capacity, usually occurs in shales with a higher content of total organic carbon, higher methane-adsorption capacity, lower permeability, and lower clay mineral content. Moreover, an estimation model is developed to forecast the CO2-based EGR efficiency according to the shale properties. In general, these far-reaching results are of significance for predicting the benefit of CO2 utilization in different shale reservoirs.
- carbon capture and utilization (CCU)
- CO geological sequestration
- enhanced gas recovery (EGR)
- gas shale
- reservoir characteristics