Study On CO₂ Foam Breakthrough Prevention System In A Reservoir Of Changqing

With the development of CO₂ flooding in the tight reservoirs,problems such as early gas breakthrough and short effective time due to the gas channeling and fingering caused by high mobility of CO₂,which limit the application of CO₂ flooding.The CO₂ foam system is applied to control the gas breakthrough,adjust the reservoir profile,increase the reservoir sweep volume and recovery factor,thereby prolong the effective time of CO₂ flooding and enhance oil recovery.Aiming at the reservoir with strong heterogeneity,high temperature,high salinity of formation water and high content of divalent ions,a CO₂ foam system for gas breakthrough prevention that adapted to the formation conditions was optimized.We also investigated the effects of temperature,pressure,pH,oil content,salinity,shearing and aging time on the performance of the optimized foam system.The performance of optimized foam system in preventing gas channeling and EOR was evaluated using core flooding with sandcore and heterogeneous core.The microscope model was used to study the mechanism of preventing foaming and enhancing oil recovery of regenerated cellulose-stabilized foam systems.The mechanism of regenerated cellulose-stabilized CO₂ foams was further explored.The results showed that 1.0%SS163+1.0%regenerated cellulose?RC?CO₂ foam system has the best compatibility with simulated formation water,foaming performance and stability.The stability of the foam system rises with pressure,and reduces with temperature,salinity,oil content,and shearing time.Regenerated cellulose significantly improves the performance of CO₂ foam at high temperature with shearing or oil.The long-term stability of the foam system was good within 21 days,the foam stability was high with low oil content,poor with relative higher oil content.Overall,it can meet application requirements.At 85°C,the resistance coefficient of 1%SS163+1%RC CO₂ foam system was 37.8 and 138.6 by sandcore and heterogeneous core respectively.It shows that the presence of RC effectively increases the resistance coefficient and plugging effect of the foam system,and reoinforces its temperature resistance.Research on EOR in heterogeneous cores has found that foam flooding recovery increased EOR from 35.5%by water flooding to 59.4%by 20.9%.Foam flooding can block high-permeability layer through Jiamin effect,improving the apparent viscosity of flooding fluid to increase the sweep efficency,and improving the oil displacement efficiency through emulsification,foam deformation,and etc.,thereby improves the overall EOR.RC has both the viscosity-thickening properties of the polymer and the stability mechanism of the particles,which effectively improves the stability of foam system,and is more stable than SiO₂ and Al₂O₃ particles.Stabilization mechanism of RC-stabilized CO₂ foam mainly includes:viscosity thickening liquid to slow liquid drainage;RC particles stabilizing foam interfacial and liquid film;sustained releasing of water stabilizing foam liquid film.The RC-stabilized CO₂ foam exhibits good stability,anti-liability performance,preventing gas breakthrough and EOR effects.As a bio-sourced environmentally friendly material,RC effectively improves the stability and resistance of the system,therefore,have great potential application prospects and practical significance.