复杂裂缝中支撑剂运移铺置规律数值模拟

Numerical simulation of proppant migration and distribution in complex fractures

裂缝型储层压裂过程中易沟通天然裂缝形成复杂缝网,而压裂裂缝中支撑剂的铺置严重影响压后增产效果。采用考虑精确捕获颗粒运动的CFD-DEM耦合方法,建立复杂裂缝三维模型,探究注入流速、压裂液黏度、支撑剂密度对复杂裂缝(分支缝位置、角度和级数)中支撑剂运移铺置规律的影响。结果表明分支缝的位置和角度决定进入分支缝支撑剂的比例;注入时间相同,位于主裂缝1/3处分支缝砂堤面积是2/3处分支缝的2倍,30°分支缝砂堤面积是150°分支缝的3.2倍;对于多级分支缝,二级裂缝中砂堤形态多为抛物线形,三级裂缝为三角形;裂缝复杂程度越高,分支缝总分流效应越大,主缝中砂堤平衡高度越高;将优于支撑剂输送的参数与优于支撑剂沉降的参数进行再组合,较高流速(大于0.4 m/s)+线性胶+低支撑剂密度(小于2000 kg/m^(3))和较低注入流速(0.2 m/s)+滑溜水+高支撑剂密度(3000 kg/m^(3))的施工方式既能有效提高裂缝远端及分支缝的铺置效果,也能保证近井筒区域的充填。

In the fracturing process of reservoirs with natural fractures,it is easy to form complex fracture networks after the main fracture connected with the natural microfractures,which can make the placement of proppants difficult and will seriously affect the performance of the fracturing.In this study,a three-dimensional model of complex fractures was established using a CFD-DEM coupling method considering precisely captured particle movement.The effects of injection velocity,fracturing fluid viscosity and proppant density on proppant migration and placement in complex fractures were investigated,in which branching fractures with various positions,angle and progression were considered.The simulation results show that the position and angle of the branch fracture determines the proportion of proppant entering the branch fracture.For the same injection time,the area of sand embankment located at the 1/3 section of the main fracture is twice that of the 2/3 section of the main fracture,and the area of sand embankment located at 30°branch fracture is 3.2 times that of 150°branch fracture.For multi-stage branch fracturing,the shape of the sand embankment in the second level fractures is parabola,and the shape of the sand embankment in the third level fractures is triangle.The higher the fracture complexity,the greater the total diverging effect of the branch fractures,and the higher the balance height of the sand embankment in the main fractures.The results of fracturing process optimization considering proppant transport and settlement show that combinations of high flow rates(greater than 0.4 m/s),linear glue,low proppant density(less than 2000 kg/m^(3)),low injection flow rate(0.2 m/s),slick water and high proppant density(3000 kg/m^(3))can ensure a good proppant displacement at near wellbore fractures and increase the placement area in the distal and branch fractures.