Abstract:

The minimum miscible pressure （MMP） of CO₂ flooding is a crucial parameter to judge whether miscible flooding is attainable. In order to reduce the application threshold of miscible flooding, the MMP between CO₂ and crude oil needs to be reduced urgently. Adding miscible flooding assistants to oil reservoir is an effective means for minimum miscible pressure reduction. At present, according to the elements contained, the miscible flooding assistants can be divided into three categories including fluorocarbon, siloxane, and hydrocarbon （oxygenated）. In order to reduce the cost and improve the MMP reduction performance, the hydrocarbon structure should be added to the fluorocarbon assistants to make the assistants develop in the direction of mixing type. The hydrocarbon assistants have sound MMP reduction performances and room for improvement. The key is to find a suitable CO₂-phlic structure. Computer simulation is also a vital means to study micro mechanism and assist structure designing. Compared with fluorocarbon and siloxane, the cost of hydrocarbon （oxygenated） is lower, and it has the most application potential from the prospective of cost. At present, the main factor affecting the large-scale application of miscible assistants is the limitation of cost. The promotion and application in the future needs the close cooperation of petroleum and chemical practitioners. In this paper, the mechanisms of CO₂ miscible flooding assistants reducing MMP are introduced. The structures of existing miscible flooding assistants, MMP reduction effectiveness are summarized, and the influencing factors on MMP reduction efficiency are analyzed. The developing directions CO₂ miscible flooding assistants designing are prospected.

Key words: CO₂ miscible flooding, assistants for miscible flooding, reduce MMP, surfactant, microscopic mechanism