特低渗透高含水油藏CO2驱油参数优化

Optimization of CO2 Flooding Parameters in Ultra-Low Permeability Oil Reservoirs with High Water Cut

  • 摘要: 为明确生产参数对特低渗透油藏高含水期CO2驱油提高采收率的影响,进行了CO2驱油数值模拟研究。通过CO2连续注气驱参数优化发现:CO2注入速度的提高会提高产油速度,但同时也会导致气窜的加剧和换油率的降低,并存在压裂地层的风险。生产井底流压的提高短期内会限制产油速度,但有利于提升地层压力水平,促进CO2同地层油传质混相进而提高阶段采出程度和换油率。开发时在能够保证注采平衡的条件下,应尽可能提高井底流压。区块含水率的提高会使CO2驱油效果变差,导致CO2驱油阶段采出程度和换油率降低。CO2驱油开发时换油率会随着生产气油比的提高而降低,因此,注CO2开采过程应适时关井停注保证合理的CO2注入量。优化得出CO2注入速度15 000 m3/d、生产井底流压25 MPa、CO2注入时机为区块含水率60%时、关井时机为生产气油比达到1 000 m3/m3时、合理的CO2注入量为9.2万吨。应用优化所得参数进行模拟预测结果表明:注CO2开发9年后,区块原油产量相比水驱阶段增加了21.3万吨,采出程度提高了27.4%,阶段累计换油率0.58,累计埋存率0.67。

     

    Abstract: A numerical simulation of CO2 flooding was conducted to determine the impact of production parameters on enhanced oil recovery. Optimizing the CO2 flooding parameters revealed that increasing the CO2 injection rate enhances the oil production rate but also intensifies gas channelling, reduces the oil exchange rate, and poses a risk of fracturing the formation. While an increase in bottomhole pressure may temporarily limit the oil production rate, it is beneficial in the long term as it helps to elevate formation pressure, facilitating CO2 miscibility with reservoir oil to improve stage recovery and oil exchange rate. Bottomhole pressure should be increased as much as possible, ensuring an injection-production balance. An increase in water cut in the block diminishes CO2 flooding effectiveness, leading to lower recovery and oil exchange rate. During CO2 flooding development, oil exchange rate will decline with rising production gas-oil ratio. Therefore, injection wells should be shut in timely to ensure reasonable CO2 injection amounts. Based on these findings, optimal parameters were determined: a CO2 injection rate of 15, 000 m3/d, a production bottomhole pressure of 25 MPa, CO2 injection timing at a block water cut of 60%, and shut-in timing when the production gas-oil ratio reaches 1 000 m3/m3, with a reasonable CO2 injection amount of 92 000 tons. Simulation results using these optimized parameters indicated that after 9 years of CO2 injection, crude oil production from the block increased by 213 000 tons, with a corresponding oil recovery improvement of 27.4%. The cumulative oil exchange rate reached 0.58, while the cumulative storage rate reached 0.67.

     

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