支撑剂在滑溜水中沉降规律探讨

Discussion on Proppant Settlement Regularity in Slickwater Fracturing Fluid

支撑剂在压裂液中的沉降计算多采用单颗粒支撑剂在静止液体中的Stokes公式,没有考虑压裂液输送支撑剂是一个动态过程。同时,支撑剂在低粘滑溜水压裂液中的沉降运移规律不同于以往的高粘压裂液。对此,修正了单颗粒Stokes沉降公式,并且考虑支撑剂沉降所形成砂堤的稳定性,给出了动态沉降计算方法。对影响临界速度和沉降速度的主要因素计算分析后,认为裂缝高度或过流高度越大、支撑剂粒径越小和密度越大,临界流速越大,形成的砂堤也就越稳定。通过与相关室内实验结果对比后,表明所用理论方法比较可靠。计算结果表明,加砂设计时应逐渐降低排量,这与目前所采用的保持排量不变的加砂方式不同,提供了新的压裂设计思路。

The proppant settlement in fracturing fluid is mainly calculated by Stokes formula, which is based on the single particle settling in static fluid, without considering dynamic transportation of proppants. Meanwhile, the transportation and settling principles of proppant in slick water are different with the high-viscosity fracturing fluid. In this paper, the Stokes formula was revised, and the calculating method about dynamic settling was proposed, considering the stability of sand bank in fractures. The main factors affecting critical velocity and settling velocity were analyzed. The results show that the fracture height or flow height is higher, the diameter is lower and proppant density is higher, the critical velocity will become higher, and sand bank will be more stable. These conclusions have been verified with the experiments done by others, so the theoretical method is reliable. The calculating results demonstrate that pump rate can be decreased step by step during sand fracturing treatment, which is different to the current method of keeping pump rate as constant, thus a new fracturing design idea is presented.