Modeling of CO2 Injection Considering Multi-Component Transport and Geomechanical Effect in Shale Gas Reservoirs

Abstract

Although several researches have been conducted for CO 2 injection in shale gas reservoirs, there is definite lack of study that concentrates on the multi-component transport and geomechanical effect. This paper presents shale gas model for CO 2 injection considering dissolution, molecular diffusion and stress-dependent permeability as well as multi-component adsorption. Based on information of Barnett shale reservoir, a simulation model is constructed for CO 2 flooding. Extended Langmuir isotherm is used to simulate the competitive sorption among the molecules involved. Gas solubility is represented by Henry's law. Co-and counter-diffusive transportsare depicted by Sigmund correlation. Stress-dependent permeability in shale reservoir is considered by exponential correlation with the linear-elastic constitutive model. In the proposed model, the mechanisms and parameters which could influence on CO 2 injection are studied. A series of reservoir simulations based on these effects are performed to study effective injection of CO 2 .Mechanisms of CO 2 injection in shale gas reservoir contribute to both enhanced CH 4 recovery and storage of CO 2 . Desorption of CH 4 in the model with the multi-component adsorption is activated by competitive sorption with the CO 2 which is preferentially adsorbed over CH 4 with a ratio up to 5:1. Molecular diffusion enables CO 2 to displace CH 4 in ultra-low matrix permeability condition. The model with molecular diffusion presents wide spread CO 2 in the reservoir compared with the model not considering molecular diffusion. Because of ultra-low permeability of shale reservoir, effect of diffusion is higher than conventional reservoirs so that it should be considered in the CO 2 injection model of shale reservoir. CO 2 injection supports the reservoir pressure so that effect of stress-dependent permeability is mitigated compared with primary recovery model. In this model, CO 2 injection improves shale gas recovery about 12%. The CO 2 injected in the reservoir exists as a super-critical phase, adsorption trapping, and dissolution trapping of 45.8, 46.5, and 3.6%, respectively. According to reservoir and fracture parameters, amount of each state would be changed. The sensitivity analysis for either enhanced CH 4 recovery or CO 2 storage is conducted to investigate the critical parameters that control these CO 2 -EGR process and CO 2 storage, respectively.This work presents study for mechanisms of CO 2 injection in shale gas reservoir taking account of multi-component adsorption, dissolution, molecular diffusion, and geomechanical effect and sensitivity analysis for uncertain parameters of the shale reservoir. The investigation is important for better understanding and design of CO 2 injection in order to enhance CH 4 recovery and CO 2 storage.

A Literature Review of CO2, Natural Gas, and Water-Based Fluids for Enhanced Oil Recovery in Unconventional Reservoirs

“…CO 2 can be adsorbed by the kerogen , or clays within the shale. , The strong preferential adsorption of CO 2 over methane is the primary mechanism behind CO 2 enhanced natural gas recovery from unconventional gas reservoirs. ,,− Experimental ,,, and computational ,− techniques have been used to study CO 2 adsorption in shale. CO 2 adsorbs to shale approximately 3.7–7 times more strongly than methane. , One study reported that up to 17 mg of CO 2 /g can be adsorbed to Lower Bakken shale at a pressure of 40 MPa .…”

“…A few other studies have attempted to accurately quantify CO 2 storage potential in shale during EOR. ,,,− Sorensen et al applied the U.S. Department of Energy Methodology for Estimating CO 2 Storage Capacity demonstrated in the Carbon Sequestration Atlas of the United States and Canada, 2007, and concluded that, depending on the scenario employed in the analysis, the CO 2 storage potential could range from 0.12 to 3.16 GT of CO 2 …”

A Review of Gas Injection in Shale Reservoirs: Enhanced Oil/Gas Recovery Approaches and Greenhouse Gas Control

“…Some simulation results indicated that gas flooding [19,20,[88][89][90] and huff-n-puff [13] approaches for EGR were promising for enhanced gas recovery.…”

“…They observed that the CO 2 flooding increased the CH 4 recovery by more than 2% and the conclusion was that re-pressurization was the primary mechanism for the CO 2 -EGR process. Kim et al [90] performed CO 2 flooding in a shale reservoir based on the history-matched data from Barnett shale, with the mechanisms of multi-component adsorption, molecular diffusion, and dissolution incorporated in the simulation model. The results indicated that after 40 years of production, only 4% of injected CO 2 was produced, leaving a huge amount of CO 2 stored in the reservoir.…”

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

“…Consequently, porosity and permeability of them will be decreased [12]. Also, by implementing fluid injection into these reservoirs and decreasing net stress on these bedrocks and increasing pore pressure, porosity and permeability may have an increase [13].…”