Statistical Analysis of Controlling Factors on Enhanced Gas Recovery by CO₂ Injection in Shale Gas Reservoirs

Abstract

Development of shale gas reservoirs is the fastest growing area on a large scale globally due to their potential reserves. CO2 has a great affinity to be adsorbed on shale organic surface over CH4. Therefore, CO2 injection into shale reservoirs initiates a potential for enhanced gas recovery and CO2 geological sequestration. The efficiency of CO2 enhanced gas recovery (CO2-EGR) is mainly dominated by several shale properties and engineering design parameters. However, due to the heterogeneity of shale reservoirs and the complexity of modeling the CO2–CH4 displacement process, there are still uncertainties in determining the main factors that control CO2 sequestration and enhanced CH4 recovery in shale reservoirs. Therefore, in view of the previous sensitivity analysis studies, no quantitative framework, accurate CO2-EGR modeling, or design process has been identified. Thus, this work aimed to provide a practical screening tool to manage and predict the efficiency of enhanced gas recovery and CO2 sequestration in shale reservoirs. To meet our objectives, we performed correlation analysis to identify the strength of the relationship between the examined shale properties and engineering design parameters and the efficiency of CO2-EGR. Data for this study was gathered across publications on a wide subset of numerical modeling studies and experimental investigations. The sensitivity of data was further improved by a hybrid approach adopted for handling the missing values to avoid bias in our data set. Our results indicate that CO2 flooding might be the best applicable option for CO2 injection in shale reservoirs, whereas the huff-and-puff scenario does not seem to be a viable option. The efficiency of CO2-EGR increases as the pressure difference between injection pressure and reservoir pressure increases. The results show that shallow shale reservoirs with high fracture permeability, total organic content, and CO2–CH4 preferential adsorption capacity are favorable targets for CO2-EGR. Moreover, our results indicate that a successful hydraulic-fracture network with effective values of fracture permeability and conductivity is essential for a higher CO2-EGR efficiency. Well spacing and fracture half-length are crucial engineering features in CO2-EGR process design that must be carefully optimized due to their negative effect on CH4 production and positive effect on CO2 storage. Our statistical analysis lays a foundation for efficient CO2-EGR design and implementation and presents an important contribution to the field of reaching the target of net-zero CO2 emissions for energy transitions.

Advancements, Challenges, and Perspectives of Flue Gas Injection in Subsurface Formations: A Comprehensive Review

“…In fact, the oil recovery from fractured core samples exhibited an increase of approximately 14% compared to core samples without fractures. 48 Mansi et al 49 investigated the influence of permeability on the performance of flue gas injection. Their experimental findings highlight that flue gas injection is particularly advantageous for enhancing gas recovery (EGR) in shallow shale reservoirs characterized by high fracture permeability.…”

“…50 Table 4 provides a concise summary of the effects of matrix and fracture permeability on flue gas projects. (46) experimental in reservoirs with high matrix permeabilities, crude oil migrated from macro pores to medium and fine pores, resulting in higher oil production compared to reservoirs with low matrix permeabilities (47) simulation using CMG-STARS if the matrix permeability falls below a certain threshold, the oil production rate remains unchanged even in the presence of cyclic steam-assisted flue gas injection scenarios (48) experimental fractures played a major role in facilitating crude oil migration; in fact, the oil recovery from fractured core samples exhibited an increase of approximately 14% compared to core samples without fractures (49) experimental applying hydraulic fracturing method for increasing the permeability of the rock and improving the conductivity in pore scale can increase the efficiency of flue gas injection (50) experimental under immiscible conditions, the oil recovery factor was lower in the highly permeable core compared to that in the low-permeable core Since flue gas primarily consists of nitrogen gas, which plays a crucial role in maintaining pressure during flue gas injection, it is imperative to investigate how variations in flue gas composition affect pressure drop and oil recovery. Shokoya et al 51 conducted experimental investigations on the impact of three distinct flue gas compositions within a slim tube.…”

“…Their experimental results clearly demonstrated a significant improvement in the efficiency of CO 2 injection as the pressure difference between the injected gas and the reservoir increased. 49 Furthermore, elevating the injection rate of flue gas can increase the miscibility of gas within the crude oil at the pore scale. However, there exists an optimal range for both the flue gas injection rate and the injected pressure.…”

“…Mansi et al investigated the influence of permeability on the performance of flue gas injection. Their experimental findings highlight that flue gas injection is particularly advantageous for enhancing gas recovery (EGR) in shallow shale reservoirs characterized by high fracture permeability.…”

Virtual Special Issue of Recent Advances in Shale Gas Exploration and Exploitation

“…In comparison to a constant TPG, the changes with water saturation in the TPG have a more significant effect on productivity. Mansi et al 8 provided a practical screening tool to manage and predict the efficiency of enhanced gas recovery (EGR) and CO 2 sequestration in shale reservoirs based on the gathered data from across publications of numerical modeling studies and experimental investigations. They found that shallow shale reservoirs with high fracture permeability, total organic content, and CO 2 −CH 4 preferential adsorption capacity are favorable targets for CO 2 -EGR.…”