CO₂ flooding has become one of most effective methods to improve oil recovery in low-permeability reservoirs. Thus, influencing factors have been specifically analyzed for their impact on oil displacement. Factors that are difficult to observe, such as capillary pressure and CO₂ dissolution, have often been neglected in specific analysis. To do so, this paper combined laboratory experimentation with numerical simulation analysis to understand the specific functions of capillary pressure and CO₂ dissolution in the CO₂-flooding process in low-permeability reservoirs. Based on laboratory experiments with long cores applying different CO₂-flooding methods, the authors established a one-dimensional numerical simulation model for CO₂ flooding. After that, the model was simulated to analyze the effects of capillary pressure and CO₂ dissolution for different CO₂-flooding processes. The results show that the function of capillary pressure in different CO₂-flooding modes is not consistent in low-permeability reservoirs; furthermore, capillary pressure is a driving force in the process of flooding and is a resistance force in the CO₂-flooding process after pressure recovery. When considering CO₂ dissolution in different flooding modes, its function was shown to be inconsistent in low-permeability reservoirs compared with CO₂ flooding without considering CO₂ dissolution; oil recovery is reduced in the CO₂-flooding process, but oil recovery increases in the CO₂-flooding process after pressure recovery. Therefore, in order to promote the rational and effective development of low-permeability reservoirs, it is necessary to understand the functions of capillary pressure and CO₂ dissolution clearly in the process of CO₂ flooding.

中文翻译：

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低渗透油藏CO 2注水过程中毛细管压力和溶解的作用

CO ₂驱油已经成为提高低渗透油藏采油率的最有效方法之一。因此，已经专门分析了影响因素对油驱替的影响。难以观察到的因素，例如毛细压力和CO ₂溶解度，在特定分析中通常被忽略。为此，本文将实验室实验与数值模拟分析相结合，以了解毛细压力和CO ₂溶解在低渗透油藏CO ₂驱替过程中的具体功能。基于长芯应用不同CO _2的实验室实验驱方法，作者建立了CO ₂驱的一维数值模拟模型。之后，对该模型进行仿真，以分析毛细管压力和CO ₂溶解对不同CO ₂驱替过程的影响。结果表明，在低渗透油藏中，毛细管压力在不同CO ₂驱替方式下的作用不一致。此外，毛细管压力是驱油过程中的驱动力，并且是压力恢复后的CO ₂驱油过程中的阻力。考虑CO _2时在不考虑CO ₂溶解的情况下，与低CO ₂驱相比，在低渗透油藏中，其功能不一致。在CO ₂驱油过程中，油的采收率降低，但是在压力恢复后，在CO ₂驱油过程中，油的采收率增加。因此，为了促进低渗油藏的合理有效开发，有必要在CO ₂驱替过程中清楚地了解毛细压力和CO ₂溶解的作用。