超深储层裂缝剪切变形及裂缝面磨损的三维离散元模拟

3D discrete element method modelling of shear deformation and face wear of irregular fractures in ultradeep reservoirs

摘要

为揭示超深油气储层中不规则裂缝在高法向应力条件下的剪切变形、裂缝开度变化与裂缝面磨损特征,基于离散元方法(DEM)建立三维数值模型。模型中的裂缝面积为63 mm×63 mm,具有不规则的几何形态,裂缝两侧离散元颗粒采用光滑节理接触模型模拟裂缝面在变形中的滑移,并使用基于颗粒替代的破碎算法来模拟剪切过程中产生的局部磨损。研究不同法向应力下裂缝的剪切应力应变关系、开度分布、法向剪胀剪缩特征与裂缝区域中的力链演化规律。结果表明:高法向应力显著提高了裂缝峰值剪切强度并延缓了软化;引入颗粒破碎机制后的模型可以模拟剪切破坏造成的裂缝界面粗糙度降低、剪胀效应减弱,界面形成细颗粒润滑层减小剪切模量等效应;颗粒破碎与力链集中具有明显空间对应关系,表明裂缝面磨损主要发生在强接触和嵌锁区域。结合不规则裂缝形态与颗粒破碎机制的离散元模型能有效揭示超深储层裂缝的剪切演化特征,为超深油气储层裂缝导流渗透能力研究提供数值分析框架和细观力学基础。

Abstract

In order to reveal the shear deformation, aperture evolution and surface wear of irregular fractures in ultradeep reservoirs under high normal stress, a three-dimensional numerical model was established based on the discrete element method (DEM). The fracture area in the model is 63 mm×63 mm, with irregular geometry. The discrete element particles on both sides of the fracture use the smooth joint contact model to simulate the slip of the fracture surface in the deformation, and use the particle replacement-based crushing algorithm to simulate the local wear generated during the shear process. The shear stress-strain response, aperture distribution, normal dilation/contraction, and force-chain evolution within the fracture zone were investigated under different normal stresses. The results indicate that high normal stress significantly increases the peak shear strength and delays softening stage of the fracture. The model after introducing the particle breakage mechanism can simulate the effects of shear failure, such as reducing the roughness of the fracture interface, weakening the dilatancy effect, and forming a fine particle lubrication layer at the interface to reduce the shear modulus. A clear spatial correlation is observed between particle breakage and force chain concentration, indicating that fracture surface wear predominantly occurs in regions of strong contact and interlocking. These findings demonstrate that the DEM model combining irregular fracture morphology and particle breakage mechanism can effectively characterise the wear evolution behaviour of fractures in ultradeep reservoirs, providing a numerical framework and micromechanical basis for subsequent research on fracture conductivity and permeability in ultradeep reservoirs.

关键词

超深油气储层 / 三维不规则裂缝 / 离散元模拟 / 剪切变形 / 裂缝面磨损

Key words

ultradeep reservoir / 3D irregular fracture / discrete element method (DEM) / shear deformation / fracture face wear

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基金资助

国家自然科学基金卓越研究群体项目A类(52288101)