致密储层多尺度通道流体流动力学机制研究

In tight reservoirs, the multiscale channels are composed of matrix pores, natural fractures and hydraulic fractures at different sizes. Aimed at the engineering problem of low single-well production and fast decreasing rate after stimulation treatment, the long-term mechanism of fluid transport in multiscale channels is desired. This project focuses on fluid mechanics in multiscale channels to deeply analyze multiscale characteristics during fluid flow and establish three-dimensional dynamic flow models for multiphase fluids transport in multi-scale channels ao as to uncover the competition mechanism during fluid flow in multiscale channels. The numerical method for simulating fluid flow in 3D complex fracture networks is proposed to accurately analyze the flow characteristics in multiscale channels and uncover the progressive flow mechanism of reservoir fluids from matrix pores to the wellbore through fractures at different scales. The stress sensitivity of the multiscale channels is also studied to propose the optimization method of fracture networks with high productivity and long-term efficiency. The ultimate goal of this project is to provide scientific basis for hydraulic fracturing treatment and reservoir development, and also provide experimental method and theoretical reference for the development of similar reservoirs.

致密储层不同尺寸孔隙、天然裂缝和人工裂缝组成了多尺度油气流动通道。针对压裂后致密储层单井产量低、递减速度快的工程难题，急需探索多尺度通道长效流动机制。围绕多尺度通道流体流动力学行为问题，深入分析致密储层多尺度流动通道特征，建立多尺度通道多相流体三维流动力学模型，揭示多尺度通道流体流动的竞争机制；研究多尺度通道中三维交叉缝网流动的数值模拟方法，分析不同尺度流动通道的精细流动特征及影响规律，揭示流体由基质孔隙经不同尺度裂缝至井筒的逐级传输流动机理，获得多尺度通道应力敏感规律，提出长效缝网优化设计方法，为致密储层压裂与开发设计提供科学依据，同时也为类似油气藏开采的基础研究提供实验方法和理论借鉴。

近年来新增储量中 70%以上的深层油气藏都属于致密储层，低油价条件下如何实现油气藏的经济有效动用显得尤为重要。致密储层典型特征为低孔低渗、强非均质性和强各向异性，自然产能低，需要通过水力压裂来实现增产，压裂产生的复杂裂缝进一步加剧了流体在储层中流动的复杂性。本项目设计了一次开采岩石渗流模拟装置，采用人造岩心进行非稳态气体渗流模拟，发现了达西模型在拟合非稳态气体渗流实验数据方面精度低，不能准确反映一次开采气体依靠自身膨胀性的流动规律；建立了致密气藏气体自扩散流动模型，自扩散渗流方程反映了致密气藏一次开采是完全由气体的膨胀性驱动的物理本质，说明了自扩散是低孔低渗油气藏的主要流动机理，达西渗流模型并不适用于致密气藏一次开采过程。在自扩散流动模型基础上，发展了渗流场和温度场耦合的自扩散流动模型，分析了温度场变化对自扩散流动行为和单井气产量的影响；建立了页岩油自扩散两相流动数学模型，揭示了页岩油气在生产初期依靠自身膨胀性流动的本质规律。最后针对多尺度裂缝，提出了一种基于扩展有限元法和离散裂缝模型的全耦合模型，实现了断裂-流动-变形的全耦合，首次统一数值离散方法实现了压裂—生产的一体化模拟，为塔里木、四川盆地致密油气藏压裂设计提供了理论支撑。