基于CFD-DEM粗糙缝内支撑剂流动数值模拟研究

Numerical Simulation Study of Proppant Flow in Rough Fractures Based on CFD-DEM

摘要

针对传统光滑平板模型忽略粗糙度对支撑剂运移影响的不足, 基于分形理论, 利用实测岩样轮廓修正Weierstrass-Mandelbrot函数, 构建符合储层粗糙特征的裂缝模型, 并通过计算流体力学与离散元（CFD-DEM）耦合方法模拟支撑剂运移与返排过程, 重点研究注入孔数、砂比及粒径组合的影响。结果表明：单孔注入能量集中, 砂堤平衡高度最高达3.25 cm, 返排率最低；砂比由8%升至11%时, 砂堤高度由2.60 cm增至3.28 cm, 出砂率随之降低；70/140目、40/70目与20/40目按质量比1∶6∶3组合时, 砂堤平衡高度3.28 cm, 支撑剂留存率达97.64%。粗糙壁面起伏可诱导局部涡流区, 增加颗粒沉降阻力并促进颗粒间力链形成, 从而显著提升砂堤稳定性与近井带铺置效率。该分形修正模型与耦合方法能有效反映壁面起伏对颗粒运移的非线性作用, 为页岩油压裂支撑剂工艺优化提供理论支撑。

Abstract

To address the limitation of conventional smooth parallel-plate models, namely neglecting the influence of roughness on proppant transport, this study establishes a fracture geometry model based on fractal theory to embody actual reservoir roughness characteristics, where the Weierstrass-Mandelbrot function is modified using measured rock-wall profile data. The coupled computational fluid dynamics and discrete element method （CFD-DEM） is employed to simulate proppant migration and post-fracturing flowback, with a focus on the effects of the injection port number, proppant concentration, and particle size combination. The results indicate that in the case of single-port injection, fracturing fluid energy is concentrated to deliver a maximum equilibrium proppant bank height of 3.25 cm and the lowest flowback rate. When the proppant concentration increases from 8% to 11%, the proppant bank height rises from 2.60 cm to 3.28 cm, accompanied by a corresponding decrease in the flowback rate of proppants. For a particle size combination of 70/140 mesh, 40/70 mesh, and 20/40 mesh at a mass ratio of 1：6：3, the equilibrium proppant bank height reaches 3.28 cm, and the proppant retention rate reaches 97.64%. It is revealed that rough-wall undulations induce localized vortex zones, increase the resistance to particle settling, and promote the formation of inter-particle force chains, thereby significantly enhancing proppant bank stability and near-wellbore placement efficiency. The proposed fractal-modified fracture model and the CFD-DEM coupling approach effectively capture the nonlinear effects of wall undulations on particle transport, providing theoretical support for optimizing proppant placement strategies in shale oil hydraulic fracturing.

关键词

水力压裂 / CFD-DEM / 粗糙裂缝 / 支撑剂运移 / 分形理论

Key words

hydraulic fracturing / CFD-DEM / rough fracture / proppant transport / fractal theory

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基金资助

国家自然科学基金项目“页岩层系组构单元划分与力学耦合竞争控制水力压裂造缝行为研究”(52474036)

国家自然科学基金项目“页岩油层交替混合压裂诱导及竞争耦合造缝与参数调控机制研究”(52174022)

黑龙江省自然科学基金联合基金重点项目“古龙页岩油SC-CO₂立体井网压裂造缝与排采参数调控机制研究”(ZL2024E008)

黑龙江省自然科学基金联合引导项目“页岩油脉动压裂造缝缝网演化声发射信号时空表征研究”(LH2024E008)

黑龙江省“揭榜挂帅”科技攻关项目“古龙页岩油油藏工程理论、CO₂提产机理及合理排采制度研究”(DQYT-2022-JS-758)

2024年度科技创新领军人才团队“页岩油地质工程一体化压裂与防控技术创新团队”(CYCX24015)