Abstract
CO2 flooding is regarded as an important method for enhanced oil recovery (EOR) and greenhouse gas control. However, the heterogeneity prevalently distributed in reservoirs inhibits the performance of this technology. The sweep efficiency can be significantly reduced especially in the presence of “thief zones”. Hence, gas channeling blocking and mobility control are important technical issues for the success of CO2 injection. Normally, crosslinked gels have the potential to block gas channels, but the gelation time control poses challenges to this method. In this study, a new method for selectively blocking CO2 channeling is proposed, which is based on a type of CO2-sensitive gel system (modified polyacrylamide-methenamine-resorcinol gel system) to form gel in situ. A CO2-sensitive gel system is when gelation or solidification will be triggered by CO2 in the reservoir to block gas channels. The CO2-sensitivity of the gel system was demonstrated in parallel bottle tests of gel in N2 and CO2 atmospheres. Sand pack flow experiments were conducted to investigate the shutoff capacity of the gel system under different conditions. The injectivity of the gel system was studied via viscosity measurements. The results indicate that this gel system was sensitive to CO2 and had good performance of channeling blocking in porous media. Advantageous viscosity-temperature characteristics were achieved in this work. The effectiveness for EOR in heterogeneous formations based on this gel system was demonstrated using displacement tests conducted in double sand packs. The experimental results can provide guidelines for the deployment of the CO2-sensitive gel system for field applications.
Highlights
In recent years, sequestration and utilization of CO2 is becoming an important research topic (Ren et al 2010; Zhang et al 2010)
The results indicate that this gel system was sensitive to CO2 and had good performance of channeling blocking in porous media
It has been demonstrated that CO2 flooding can be one of the most effective enhanced oil recovery (EOR) technologies proven in field tests and indoor experiments
Summary
Sequestration and utilization of CO2 is becoming an important research topic (Ren et al 2010; Zhang et al 2010). A large-scale CO2 EOR project has been under way in China since 2006 in the Jinlin Oilfield (Northeast China) (Li and Fang 2007), in which CO2 produced and separated from natural gas reservoirs nearby is utilized, and about 0.3–0.5 million tons of CO2 per year have been injected into oil reservoirs since . Gel polymer systems have been applied successfully in oil and gas wells to control unwanted water production in recent years. The CO2 sensitive gel system is gelation that will be triggered by CO2 in the reservoir, and the chemical can be dissolved in water and injected separately via a simple and economic slug injection technique This method based on CO2 sensitivity makes the gelation process more reliable because the gelation needs the gelation time and the presence of CO2. The performance of EOR in simulated heterogeneous formations assisted by this gel system was exhibited through displacement tests conducted in double sand packs
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