高温高压CO2-近临界挥发油-地层水三相相平衡规律表征基础研究

Practice proved that oil reservoir is one of the best place for CO2 geological sequestration. Since oil and water coexist in oil reservoirs, CO2-oil-formation water three-phase equilibrium forms after dissolution of injected CO2 into oil and formation water, which influences CO2 sequestration capacity directly. However, CO2-oil-formation water three-phase equilibrium research has not been performed. This study mainly focuses on the CO2-near critical volatile oil-formation water three-phase equilibrium, systematic researches in this study will be conducted by comprehensive methods such as data investigation, experiment and theory analysis. Firstly, the special phase behaviors of near critical volatile oil will be quantitatively studied using the full-visualization mercury-free PVT instrument and laser instrument; the law of CO2-near critical volatile oil-formation water three-phase equilibrium will be performed at different temperature, pressure, salinity, and water saturation; finally, based on experiment results, three-phase equilibrium solubility theoretical model will be established to suitable for CO2-near critical volatile oil-formation water by using the cubic disturbance hard chain equations and combined with molecular simulation, which reveals the law of CO2 dissolution sequestration and CO2 sequestration capacity in the near critical volatile oil reservoir. This study will provide basic data and scientific basis for studying mechanism of oil displacement by CO2 and CO2 sequestration in the near critical volatile oil reservoir, and will also promote large-scale development of safe and effective CO2 sequestration in the near critical volatile oil reservoir.

实践证明油藏是CO2地质封存的最佳场所之一。油藏中总是油水同存，注入的CO2不断溶解到原油和地层水中形成CO2-原油-地层水三相相平衡，将直接影响CO2的溶解封存潜力。然而，调研未发现CO2-原油-地层水三相相平衡研究。本项目重点研究CO2-近临界挥发油-地层水三相相平衡规律，拟采用资料调研、物理模拟、理论分析等手段开展系统研究。首先利用全可视化的无汞PVT仪和激光仪定量研究近临界挥发油特殊的相态特征；其次，分别开展不同温度压力、不同矿化度及不同油水饱和度下的CO2-近临界挥发油-地层水三相相平衡规律实验；最后，基于实验结果，利用立方型扰动硬链方程并结合分子模拟建立CO2-近临界挥发油-地层水三相相平衡理论模型，揭示CO2在近临界挥发油藏中溶解封存的规律及埋存潜力，为近临界挥发油藏中CO2驱油与封存研究提供基础数据和科学依据，同时可推动CO2在近临界挥发油藏中安全有效埋存的规模化发展。

油藏中总是油水同存，注入的CO2不断溶解到原油和地层水中形成CO2-原油-地层水三相相平衡，将直接影响CO2驱油的效果和CO2溶解封存潜力。因此，高温高压CO2-近临界挥发油-地层水三相相平衡规律研究是近临界挥发油藏中CO2驱油与封存技术成功应用的关键问题，近临界挥发油藏中CO2驱油效果很大程度上取决于高温高压CO2-近临界挥发油-地层水三相相态特征的认识程度。然而，调研未发现CO2-原油-地层水三相相平衡的系统研究。本项目通过三年的研究，以物理模拟和理论分析相结合的手段，本着由简单到复杂的研究思路，开展了近临界挥发油单相流体相态特征实验研究、CO2-近临界挥发油和CO2-地层水两相相平衡规律实验研究、不同油水饱和度下的CO2-近临界挥发油-地层水三相相平衡规律实验研究。通过上述实验揭示了近临界挥发油独特的相态特征、CO2-近临界挥发油和CO2-地层水两相相平衡特征以及CO2-近临界挥发油-地层水三相相平衡特征。基于实验数据，建立了表征CO2-近临界挥发油-地层水三相相平衡的立方扰动硬球型理论模型，并对模型进行了可靠性验证。本项目的研究成果有助于突破现有挥发油藏或者近临界挥发油藏注CO2提高采收率效果差的瓶颈，加速注CO2大幅度提高挥发油藏或者近临界挥发油藏原油采收率的开发步伐，同时，可推动CO2在挥发油藏或者近临界挥发油藏中安全有效埋存的规模化发展。