325. 提高采收率和二氧化碳封存的双重效益：CO2注入方式对采收率的影响

Dual Benefits of Enhanced Oil Recovery and CO₂ Sequestration: The Impact of CO₂ Injection Approach on Oil Recovery

由于其多重优势，如促进油的流动和二氧化碳的封存，CO2注入提高油藏采收率技术被广泛应用。注入CO2可以降低油的粘度，提高整体流体流动性来提高采收率。然而，CO2注入也存在一些问题，例如粘性指进、重力超覆及CO2窜流等，导致气体提前突破、驱替效率低和最终采收率低。通过使用CMG软件，模拟了不同现场尺度CO2注入期间的原油采收率。

本研究分别研究了三个情况：CO2注入到油藏中、CO2注入到含水层中以及先注入CO2再注水。同时，我们采用了三种不同的井型：所有注入井和生产井均为垂直井、所有井均为水平井，以及垂直注入井和水平生产井。在20年的时间范围内，对九种方案进行了原油采收情况进行研究。在所有模拟模型中，从残余油饱和度（Sor）条件开始进行CO2注入，以代表枯竭的油藏情况。

Injection of CO₂ to enhance oil recovery is widely used due to its multiple advantages such as mobilizing the oil and sequestration of carbon dioxide. Injection of CO₂ can enhance oil recovery by reducing oil viscosity and improving overall fluid mobility. However, several problems are associated with CO₂ injection such as viscous fingering, gravity override, and CO₂ channeling that results in early gas breakthrough, low sweep efficiency, and low ultimate oil recovery. In this study, dual benefits of CO₂ injection are presented: enhancing oil recovery and sequestering carbon dioxide. In this work, different scenarios of field scale simulation were conducted to evaluate oil recovery during CO₂ injection, and the CMG (Computer Modeling Group) software package was used. Three main scenarios were examined which are CO₂ injection into the reservoir, CO₂ injection into the aquifer, and CO₂ injection into the aquifer followed by waterflooding. Also, three well configurations were utilized—all injectors and producers are drilled vertically, all wells are drilled horizontally, and vertical injectors and horizontal producers are used. Therefore, the oil recovery profiles were examined for nine scenarios over a 20-year period. In all simulated models, CO₂ injection was started at the residual oil saturation (S_or) conditions, to represent the cases of depleted oil reservoirs. The results indicated that the highest oil recovery of 73% of the original oil-in-place (OOIP) can be achieved by injecting CO₂ into the reservoir, utilizing vertical injectors and producers. While injecting CO₂ into aquifers can significantly enhance oil recovery by around 68–70% of the OOIP, using horizontal wells can provide more oil recovery (67.7%) than that using vertical wells (54.8%), in the same conditions. Moreover, around 7,928 tons of carbon dioxide can be sequestered in underground formations, on average. Finally, CO₂ injection outperformed the conventional waterflooding, where 68 and 12% of the OOIP were obtained, respectively. Overall, injection of CO₂ into the depleted reservoir can provide dual benefits of CO₂ sequestration and improved oil recovery. CO₂ can be injected into the water zone resulting in a slow release of CO₂ which will reduce the fluid viscosity, enhance oil recovery, and reduce the greenhouse effect.