Analysis of the Efficacy of CO2 Sequestranration into Depleted Shale Gas Reservoirs
Kulga, Ihsan B.; Ertekin, Turgay
Due to the characteristics of shale gas reservoirs, including their naturally and hydraulically fractured geology with an existing infrastructure, they are considered as possible industrial carbon dioxide (CO2) storage formations once they are depleted. Injection of CO2 is also considered to enhance production of the remaining gas from shale gas reservoirs. In this study, the possibility of industrial CO2 storage is investigated numerically by using one of the most advanced computational simulators in oil and gas industry, PSU-SHALECOMP, which is a compositional dual porosity, dual permeability, multi-phase reservoir simulator. The simulator treats the shale gas reservoir as a dual porosity, dual permeability system consisting of coal matrix and fracture network. It is also capable of investigating the effects of water presence in the micropore structure and those of matrix shrinkage and swelling in relation to CO2 injection and production operations. Marcellus shale reservoir, rock and fluid properties will be entered to examine potential injection rates of CO2 and final CO2 capacities from a single or multiple well system.
The results that are produced using the numerical models with the discrete fracture plane approach in shale gas models are not considered accurate enough because of the complex fracture nature of shale gas reservoirs. In this study, "stimulated reservoir volume" (SRV) is introduced to the PSU-SHALECOMP models to define the hydraulic fractures. It is shown that the simulator has yielded perfect matches with the normalized field data with the implementation of SRV approach. The SRV approach also helps us to obtain more simulations in shorter time periods in our study. The simulations are more stable with the SRV approach because less converge problems are experienced.
Preliminary results show that adsorption and storage of CO2 in gridblocks around the wellbore is possible without injected CO2 being encountered in neighboring production wells over a long period of injection. Matrix permeabilities within the nano-scale strictly prevent the injection of CO2, which means the displacement efficiency of CO2 injection to enhance CH4 production is rather low in shale gas reservoirs.
It is also shown that the fracture connectivity in between a producer and an injector leads to produce large amount of CO2 production. Therefore, CO2 injection should not be used to displace methane if there is possible fracture connectivity in between wells.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013