应力敏感条件下的数字岩心微观渗流分析方法研究

In recent years, digital core technology has been used for studying micro pore structure, flow characteristic parameters, and fluid flow mechanisms in reservoirs. However, current digital core technology does not take into account the influences of the in-situ stress field variation on micro pore deformation and the flow field changes. It is a quite urgent and challenging issue to establish the digital core fluid flow analysis approach under the stress-sensitive condition in petroleum academics and industry. This project is going to conduct research from the macroscopic and microscopic points of view simultaneously. On one hand, we shall couple the common core analysis and triaxial stress-strain experiments to study the response relationship between stress and flow field variations. On the other hand, we shall combine the mesomechanics theory and digital core technology to some certain points, and study the internal nature mechanisms among stress value, stress path, stress rate, micro pore deformation and flow field variation by conducting digital rock imaging experiments under stress loading condition. Some modern mathematical theory such as symplectic geometry, polar decomposition and homeomorphism mapping methods will be used for describing micro pore deformations, and establish the stress, pore pressure and deformation model for micro pores, which will be further coupled into the microscale flow simulation in digital cores. By validating the microscale model with macroscopic experiment results and analysis, we could finally establish the digital core flow simulation analysis approach considering the micro pore deformation under stress-sensitive conditions. This research project could complement the digital core technology and provide theoretical basis for applying digital core technology in practical reservoir developments.

数字岩心技术已成为研究储层微观孔隙结构、渗流特征参数和渗流机理的新手段，但目前数字岩心技术未能考虑储层应力场变化对微观孔隙结构变形和渗流场的影响，建立应力敏感条件下的数字岩心渗流分析方法是石油工程学术界极具迫切性和挑战性的难题。本项目从宏观与微观两种研究角度出发，一方面通过宏观三轴应力应变渗流耦合实验，研究宏观渗流与应力变化响应关系；另一方面将细观力学理论与数字岩心技术相结合，通过应力加载条件下的岩心数字成像研究，探索应力敏感因素以及应力数值、应力路径、应力速率等与微观孔隙变形和流场变化的内在机理，应用辛几何、极分解和同胚映射等现代数学方法描述微观孔隙变形，建立应力、孔隙压力与孔隙变形的数学模型，并将其应用于数字岩心微观渗流模拟中，通过与宏观模型进行对比分析验证，建立考虑应力敏感、孔隙变形条件下的数字岩心渗流分析方法,进一步完善数字岩心研究方法和理论，为其应用于实际油气藏开发提供科学基础。

数字岩心技术已成为研究储层微观孔隙结构、渗流特征和渗流机理的新手段，但目前数字岩心技术未能考虑储层应力场变化对微观孔隙结构变形和渗流场的影响，建立应力敏感条件下的数字岩心渗流分析方法是石油工程领域极具迫切性和挑战性的难题。本项目从岩心高效数字化和微观岩心应力加载实验设计方法；微观孔隙应力与变形理论与模型研究；数字岩心考虑应力敏感、孔隙变形条件下的渗流模拟方法这三方面开展研究，取得了以下研究成果：（1）在岩心高效数字化方面提出页岩岩心双重区域重构模式，同时优化模拟退火法的初始模型，结合两点簇函数和预判方法加快重构速度；应用新的关联函数“互相关函数”分析并重构各类孔隙的空间分布情况，提升各类孔隙的各向异性分布特征的重构效果。（2）探索微米CT原位三维加载和扫描电镜与原位拉伸台相结合用于微观岩心应力加载的两种微观实验方法，针对致密砂岩和页岩两种岩心应用数字图像相关法对计算实时加载图像的位移和应变，得到兴趣区域的位移场和应变场，实验证明了孔隙微观尺度的弹性变形，同时也获得了各微观参数与应力之间的关系。（3）基于微米CT扫描成像实验统计孔隙结构微观特征参数并建立数字岩心孔隙结构的抽象模型，讨论数字岩心多孔弹性变形机理，建立应力与岩心孔隙结构变形的本构方程。（4）基于数字岩心真实孔隙结构模型利用有限元方法求解流固耦合控制方程，通过模拟孔隙尺度岩石变形耦合渗流特征，实现了从微观结构上来研究岩石变形性质，及其对渗流的影响及孔隙结构变形的演化规律。本项目研究成果进一步完善了数字岩心技术，使之更接近于油气藏开发实际条件，将来具有更多应用可能。