CO2-化学助剂复合体系吞吐提高页岩油采收率机理研究

CO2 huff-n-puff is a promising technology to improve the shale oil recovery. However, the miscibility condition of CO2 and crude oil in shale reservoirs is harsh, which restricts the field application of CO2 huff-n-puff. This project screens, evaluates and optimizes chemical additives based on several criteria, which include the effects to reduce CO2-oil interfacial tension, to improve CO2-oil extraction, and the efficiency in shale oil reservoir environment. And then the CO2-chemical additive composite system which can effectively reduce CO2-oil miscible requirements is constructed. After that, adsorption experiments, microfluidic experiments and microscopic flow experiments are designed to investigate the huff-n-puff process of CO2-chemical additive composite system. The adsorption, replacement, diffusion, and displacement processes are conducted through these experiments. The dominate mechanism to produce free oil in inorganic and trapped oil in kerogen under complicated reservoir conditions are explored. The synergy EOR mechanisms of CO2-chemical additive composite system during huff-n-puff process are elucidated, as well as the enhanced oil recovery of the composite system. And then, the laboratory core-scale experiments are implemented to evaluate the huff-n-puff EOR performance of the CO2-chemical additive composite system. Based upon these results, the optimization and control methods of huff-n-puff procedures under complex reservoir conditions are established. The outcomes of this research will provide theoretical basis and technical support for the industrial application of CO2 huff-n-puff EOR in shale oil reservoirs.

CO2吞吐是一项极具潜力的提高页岩油采收率技术，但在页岩储层环境下，CO2与页岩油混相条件苛刻，制约CO2吞吐技术的现场应用。本项目以化学助剂降低油气界面张力及提高CO2萃取原油能力为标准，结合在油藏条件下的作用效果对化学助剂进行筛选、评价及优化，最终构建能够有效降低油气混相条件的CO2-化学助剂复合体系；通过自主设计的竞争吸附实验、微流控实验以及微观可视化实验模拟复合体系在页岩油储层中的吸附-置换-扩散-驱替作用过程，探究复合体系对吸附互溶态和游离态页岩油的动用机制，阐明复合体系的协同作用机理，明确在复杂条件下开采页岩油的主导机制，从本质上揭示复合体系提高采收率机理；开展室内岩心物理模拟实验，评价复合体系提高采收率效果，建立复杂储层条件下CO2-化学助剂复合体系吞吐提高页岩油采收率的优化调控方法，为页岩油CO2吞吐高效开发提供理论依据和技术支撑。

本课题筛选优化了化学助剂，构建了能够降低CO2与页岩油混相条件的CO2-化学助剂复合体系，可成功降低混相压裂24.47%；利用自主设计的竞争吸附实验、微流控芯片实验、微观可视化实验，系统研究了CO2复合体系与有机质及吸附互溶态页岩油的吸附、置换作用，复合体系对吸附互溶态原油的动用量在15%-25%；通过自主设计的高温高压微观可视化实验发现CO2呈“漏斗状”萃取抽提原油中的轻质或中间组分的烃类物质，明确了CO2复合体系在游离态页岩油中的扩散能力以及驱替能力；阐明了复合体系在吞吐过程中的协同作用机理及复杂储层条件下页岩油的动用机制；采用室内岩心物理模拟技术，评价了复合体系提高采收率效果，复合体系对小孔、中孔内原油的动用效果分别加强26.4%和16.8%，对微孔内原油的动用基本无影响；对复合体系吞吐注采参数进行了敏感性分析，研究表明，加入表面活性剂辅助CO2吞吐能提高采收率3.5%-9%。焖井时间越长，注入压力增大，注入携带表活剂的水相量越少，页岩油采收率明显提高。最终建立了适合复杂储层条件下的CO2-化学助剂复合体系吞吐提高页岩油采收率的注采参数优化方法。本项目的成功实施可进一步完善CO2吞吐技术，对CO2吞吐开采页岩油的工业化应用具有重要的现实意义。