Literature Review of Hybrid CO2 Low Salinity Water-Alternating-Gas Injection and Investigation on Hysteresis Effect

Abstract

Low salinity water injection (LSWI) is considered to be more cost-effective and has less environmental impacts over conventional chemical Enhanced Oil Recovery (EOR) methods. CO2 Water-Alternating-Gas (WAG) injection is also a leading EOR flooding process. The hybrid EOR method, CO2 low salinity (LS) WAG injection, which incorporates low salinity water into CO2 WAG injection, is potentially beneficial in terms of optimizing oil recovery and decreasing operational costs. Experimental and simulation studies reveal that CO2 LSWAG injection is influenced by CO2 solubility in brine, brine salinity and composition, rock composition, WAG parameters, and wettability. However, the mechanism for increased recovery using this hybrid method is still debatable and the conditions under which CO2 LSWAG injection is effective are still uncertain. Hence, a comprehensive review of the existing literature investigating LSWI and CO2 WAG injection, and laboratory and simulation studies of CO2 LSWAG injection is essential to understand current research progress, highlight knowledge gaps and identify future research directions. With the identified research gap, a core-scale simulation study on hysteresis effect in CO2 LSWAG injection is carried out. The results indicate different changing trend in oil recovery due to the impact of salinity on hysteresis and excluding of hysteresis effect in CO2 LSWAG injection simulation and optimization might lead to significant errors.

Experimental Study of the Dynamic Water–Gas Ratio of Water and Gas Flooding in Low-Permeability Reservoirs

“…For 9 long-core samples in the low-permeability reservoir, 9 cases of displacement experiments were designed to simulate the flooding effects of 3 different flooding methods, namely, continuous gas flooding, WAG flooding with a fixed water-gas ratio, and WAG flooding with a dynamic water-gas ratio, after elastic development, water flooding, and gas flooding. Based on the results of previous research [21][22][23][24][25], the water-gas ratio values of WAG flooding and the dynamic water-gas ratio order were designed. The specific design cases of the displacement experiment are shown in Table 3.…”

Critical Contribution of Water in Hybrid CO2/Water Enhanced Shale Oil Recovery: Insights from Molecular Dynamics

“…Consequently, during the subsequent injection of CO 2 , the interplay between the subsurface water and CO 2 gives rise to a CO 2 /water composite fluid. Besides, recent studies − have reported positive results using the CO 2 /water composite system for enhanced recovery, and water alternating gas (WAG) is recognized as one efficient injection scheme in some reported field operations. Thus, a comprehensive understanding of the CO 2 /water composite system holds paramount importance in elucidating the mechanisms that underpin the enhanced recovery efficiency.…”

Hybrid EOR Performance Optimization through Flue Gas–Water Alternating Gas (WAG) Injection: Investigating the Synergistic Effects of Water Salinity and Flue Gas Incorporation

“…Carbonate reservoirs pose unique challenges for EOR due to their intricate pore structures and variable wettability. To address these challenges and mitigate environmental impacts, the application of flue gas and CO 2 injection in WAG and low salinity WAG (LSWAG) techniques has gained attention. , Low salinity water injection (LSWI) is considered a cost-effective and environmentally friendly option compared to conventional chemical EOR methods . WAG injection, which involves the simultaneous CO 2 injection and low salinity water in a hybrid approach known as the CO 2 -LSWAG injection, shows promise in enhancing oil recovery and reducing operational costs.…”