页岩油流动机理与开发优化的基础理论研究

The primary storage space of shale lies in its micro/nano- pore-microfracture system, and it also has the characteristics of multiscale and multi-minerals, causing that the conventional theory for oil & gas transport in porous media and the phase behavior prediction method cannot apply to shale oil. Moreover, limited by the simulation technique, current optimization methods developed for hydraulic fracturing in shale always separate fractures propagation simulation from the production performance forecast, which cannot effectively guide the shale oil development. This has been the bottleneck in the industrialization exploration of oil in shale. The study intends to solve some key scientific issues in the shale oil development. Using the comprehensive methods of physical experiments, numerical simulations, as well as theoretical analyses, the phase change principles of hydrocarbon mixtures in the micro/nano- pore-microfracture system of shale will be elucidated, the multiphase multiscale transport mechanisms of shale oil will be also disclosed, then the multiphysics numerical simulation method for shale oil under the conditions of multi-fields coupling will be developed based on the propagation laws of hydraulic fractures. Eventually, the integration optimization technology of hydraulic fracturing and well schedule for shale oil will be put forward. From this research, the fundamental theoretical system of shale oil reservoir engineering will be built, which will promote the scientific and efficient development of shale oil, and provide an outstanding significance for the large-scale development of shale oil and national energy security guarantee.

页岩的储集空间主体为微纳米级孔喉–裂隙系统，而且具有多尺度多矿物相的特征，这使得传统的油气渗流理论与相态预测方法不能有效描述页岩油的流动。受模拟方法的限制，目前的页岩油体积压裂参数优化方法往往将裂缝扩展模拟与油藏的生产动态预测相隔离，无法有效指导页岩油的工业化开发，这已经成为制约我国页岩油工业化探索的瓶颈。本课题将针对页岩油开发的若干关键科学问题，通过物模实验、数值模拟和理论分析等相结合的方法，阐明页岩微纳米孔隙–裂隙系统内多组分烷烃的相变规律，揭示页岩油的多相多尺度流动机理，并在明确页岩体积压裂缝网扩展规律的基础上研发多场耦合作用下页岩油的多机理数值模拟方法，建立页岩油体积压裂和工作制度的整体优化设计技术，形成页岩油开发的油藏工程基础理论体系，促进页岩油资源的科学有效开发。这对于我国页岩油事业的工业化规模化发展和保障国家能源安全具有重要意义。

与常规油藏相比，页岩油储层中大量发育的纳米级孔隙、复杂矿物组成和较高比例的轻质组分等造成页岩微纳米孔网系统内流体的相变规律和多相多尺度流动机理异常复杂，传统理论难以描述；而且，由于缺少能够耦合压裂缝扩展和页岩油复杂相态行为与流动机理的油藏数值模拟器，目前基于开发效果优化的压裂参数在工艺上无法实现，而基于工艺设计优化的压裂参数其开发效果不一定最佳，这已经成为制约页岩油工业化探索的瓶颈。在页岩油相变行为、流动机理和裂缝扩展规律研究的基础上，建立页岩油开发的多机理数值模拟方法，形成压裂施工参数和工作制度的整体优化设计技术，有望为页岩油的高效开发提供指导。本研究首先采用分子模拟和热分析实验技术，明确了孔隙尺寸和矿物组成等因素对页岩纳米孔内烷烃临界参数的影响，揭示了储层条件下多组分烷烃的竞争吸附机制，构建了页岩油相平衡计算的理论模型，阐明了页岩微纳米孔隙内多组分烷烃的相变规律。进而研究了压差驱动下不同化学组成的页岩纳米孔内油水两相运动规律，阐明了固液界面和液液界面控制下的多相微观流动机制，建立了油水两相流动的数学模型，并基于多尺度数字岩心，建立了页岩微纳米孔网系统内油水两相流动的孔隙网络模拟方法，阐明了页岩油非线性流动机理，实现了页岩油水两相相渗曲线的预测。随后，在厘清页岩储层内水力压裂裂缝起裂和扩展规律的基础上，构建了页岩油储层裂缝扩展-弹性开采的一体化多机理数值模拟方法，实现了页岩油压裂和生产两个过程的耦合模拟，解决了裂缝扩展和生产动态预测相脱节的问题；通过耦合智能优化算法和页岩油多机理数值模拟器，以最大化经济效益为目标，建立了页岩油井网-缝网-工作制度耦合优化设计方法，通过压裂施工参数和工作制度的智能协同优化设计实现了页岩油储层的最大化有效动用。研究成果已在大庆、新疆和胜利等油田成功应用，为我国陆相页岩油高效开发提供了重要的理论指导和方法借鉴。