基于CFD-EDEM耦合考虑壁面滤失与摩阻的致密储层复杂裂缝内支撑剂铺置规律研究

Volume fracturing is the main technical measure for efficient and economic development of compact reservoirs by creating branch fractures or communicating natural fractures to form complex fracture networks. Effective support of complex fractures is the key to successful volume fracturing. At present, the influence factors of proppant placement in complex fractures mostly do not consider the influence of secondary fracture angle, fracture wall filtration and friction and other reservoir factors. It is difficult to establish an accurate proppant placement model, which can not effectively guide the design of volume fracturing construction scheme. This project intends to use the newly built visual simulation device for proppant placement in large and complex cracks to determine the factors affecting proppant placement in complex cracks. Modeling the proppant placement model affected by reservoir parameters (including secondary fracture angle, fracture wall filtration and friction), construction parameters (including displacement, proppant size and sand ratio, fracturing fluid viscosity, etc.); A mathematical model of fracturing fluid diversion in main and secondary fractures in complex fractures is established by using theoretical method and material model experimental data; Based on the established mathematical model of proppant placement and fracturing fluid diversion, CFD-EDEM numerical simulation method is used to carry out numerical simulation of proppant placement law in complex fractures, and to improve the study of proppant placement influencing factors in complex fractures. Finally, combined with theoretical analysis, experimental research and numerical simulation results, the proppant placement law in complex fractures of tight reservoir considering wall filtration and friction resistance is revealed, which provides strong support for effective guidance of efficient and economic development of tight reservoir.

体积压裂通过制造分支缝或沟通天然裂缝形成复杂裂缝网络，是致密储层高效经济开发的主要技术措施，而复杂裂缝得到有效支撑是体积压裂成功的关键。目前复杂裂缝中支撑剂铺置影响因素研究大多未考虑次级缝夹角、裂缝壁面滤失与摩阻等储层因素的影响，难以建立准确的支撑剂铺置模型，无法有效指导体积压裂施工方案设计。本项目拟使用新建立的大型复杂裂缝支撑剂铺置模拟可视装置，确定影响复杂裂缝中支撑剂铺置的各影响因素，构建受储层参数、施工参数影响的支撑剂铺置模型；运用理论方法，结合物模实验数据建立复杂裂缝中压裂液在主次裂缝中的分流数学模型；基于建立的支撑剂铺置与压裂液分流数学模型，运用CFD-EDEM数值模拟方法开展复杂裂缝中支撑剂铺置规律数值模拟，完善复杂裂缝中支撑剂铺置影响因素研究。最终结合理论、实验及数值模拟，揭示考虑壁面滤失与摩阻的致密储层复杂裂缝内支撑剂铺置规律，为有效指导致密储层高效经济开发提供有力支撑。

体积压裂造就的复杂裂缝中支撑剂的充填铺置状态直接决定了压后效果，要实现复杂裂缝中支撑剂的有效铺置，明确其运移铺置规律至关重要。通过大型可视化复杂裂缝支撑剂运移铺置模拟实验装置首先开展了复杂裂缝中支撑剂运移铺置规律实验研究，进而建立了复杂裂缝中支撑剂的运移铺置数学模型，基于此利用CFD-EDEM软件二次开发手段开展了复杂裂缝中支撑剂运移铺置规律数值模拟研究，明确了储层参数、压裂施工参数与压裂材料参数等对复杂裂缝中支撑剂运移铺置规律的影响。.研究结果表明：储层参数、压裂施工参数与压裂材料参数对单一主裂缝中支撑剂的运移铺置均产生影响，部分参数影响结果如下：分支缝的存在使得单一主裂缝中砂堤高度增加，砂堤高度增加幅度为33%~101.8%。单一主裂缝中对支撑剂运移铺置的影响由高至低分别为：排量、支撑剂粒径、砂比、支撑剂密度、压裂液粘度和滤失系数；考虑支撑剂颗粒间的相互作用建立了砂浓度修正系数，考虑缝宽较小及壁面粗糙建立了壁面效应修正系数，考虑裂缝壁面滤失建立了滤失修正系数，综合考虑上述三点建立了单一主裂缝中支撑剂沉降数学模型。建立了考虑分支缝角度、分支缝与主缝缝宽比的复杂裂缝携砂液分流模型；利用数值模拟方法研究了各因素对不同类型裂缝中支撑剂运移铺置的影响规律，对单一裂缝而言，较大携砂液排量、较小粒径支撑剂、较低密度支撑剂、较高砂比、较大密度压裂液及较大粘度压裂液均是有利于支撑剂长距离输送的人为可控因素；对复杂裂缝而言，较小粒径支撑剂、较大携砂液排量、较低密度支撑剂、较大砂比、较高粘度压裂液及较大密度压裂液均是有利于支撑剂在分支缝中有效铺置的人为可控因素，在压裂设计时应考虑在施工条件允许范围内按照上述顺序选择合理的施工参数以确保单一及复杂裂缝压裂时支撑剂的有效铺置。论文结合实验研究、理论分析和数值模拟手段，明确了复杂裂缝中支撑剂的运移铺置规律，对指导压裂施工方案设计具有重要意义。