压裂支撑剂在迂曲微裂缝中输送与分布规律

支撑剂在水力裂缝中的分布是影响压裂井产能的重要因素。通过对任意长度、孔隙度、迂曲度和方位角微裂缝的二维重构,利用COMSOL Multiphysics中的自由与多孔介质流动耦合模型,对压裂液在微裂缝中流动及向基质中滤失的情况进行模拟,在考虑支撑剂与压裂液相互作用的基础上,分析了支撑剂颗粒在输送过程中的受力情况,研究了不同砂比和支撑剂密度的情况下,支撑剂在迂曲微裂缝中的分布。研究结果表明,与规则裂缝相比,由于迂曲微裂缝壁面不规则,支撑剂不会均匀推进;在高砂比情况下,支撑剂大部分堆积在迂曲裂缝端部,无法有效支撑深部裂缝;降低砂比可以有效改善单条裂缝的支撑剂分布;不同砂比和支撑剂密度的组合可以改善相交裂缝的支撑剂分布,但是对于单条裂缝的作用不明显。

Transportation and distribution laws of proppants in tortuous micro-fractures

The distribution of proppants in hydraulic fractures has great influences on the productivity of the fractured reservoir. Using the MATLAB program self-developed by authors, this study achieves the two-dimensional reconstruction of any micro-fracture with different arbitrary length, porosity, tortuosity and azimuth. Then the free and porous medium flow coupling model in COMSOL Multiphysics is applied to simulate the flow of fracturing fluid in micro-fractures and filtering into matrix. Based on the consideration of the interaction between proppants and fracturing fluid, this paper analyzes the force condition of proppant particles during the transport process, and studies the distribution of proppant in the tortuous micro-fractures under different sand ratios and proppant densities. The results show that compared with the regular fractures, the proppant cannot be uniformly propelled due to the irregular wall surface of tortuous micro-fractures. In the case of high sand ratio, most of the proppant accumulates at the entrance of tortuous fracture, unable to effectively support the deep part of fractures. The reduction of sand ratio can effectively improve the proppant distribution in single fracture; the combination of different sand ratios and proppant density can improve the proppant distribution in intersecting fractures, but has no obvious effect on a single fracture.