水平井压裂单缝和多分支缝中携砂液流动规律数值模拟

压裂过程中携砂液的注入是为了防止地应力将已压裂出的裂缝重新闭合,裂缝中携砂液的流动是典型的固液两相流。关于垂直井裂缝中携砂液的流动已有众多学者对其进行了研究,然而关于水平井单裂缝和分支缝中携砂液流动的二维或三维数值模拟几乎未见研究。采用混合物湍流计算模型,对携砂液在二维水平井单裂缝和三维水平井分支缝中的流动进行了模拟计算。模拟结果得出:水平井单裂缝中的铺砂形态与垂直井单裂缝中明显不同,水平井单裂缝中的铺砂前缘会形成一个"砂包"向前推进,并且在入口处向缝内展布的铺砂浓度不会快速地下降。在保持其他参数不变的情况下,随着携砂液入口速度的增大,裂缝中的铺砂高度逐渐增大;携砂液入口颗粒浓度越大其他位置的铺砂浓度也越大;携砂液颗粒密度越大铺砂分布范围越小,而铺砂浓度大小基本相同。楔形裂缝中的携砂液相较于矩形裂缝更容易填充满整个裂缝;楔形裂缝中向前推进的"砂包"比矩形裂缝较低。分支缝主缝中砂堤区厚度大于单缝中的厚度,而分支缝主缝中悬浮区的厚度远小于单缝中的厚度。随着支缝与主缝夹角的增大,分支缝主缝中铺砂范围逐渐减小。当夹角为90°、120°时,沙粒在支缝与主缝的连接处产生堆积,导致主缝在第一个连接处后方区域的铺砂浓度明显减小。

Numerical Simulation of Proppant-Laden Fluid Flow in Single Fracture and Branch Fractures of Horizontal Well

In the process of fracturing, the injection of proppant-laden fluid is to prevent the ground stress from re-closing the cracks that have been fractured. The flow of proppant-laden fluid in the fracture is a typical solid-liquid two phase flow. Many researchers have studied the flow of proppant-laden fluid in fractures of vertical wells. However, there are few researches on the two-dimensional or three-dimensional numerical simulation of proppant-laden fluid flow in single fracture and branch fractures of horizontal well. In this paper, the mixture turbulence model is used to simulate the flow of proppant-laden fluid in single fracture in two-dimensional space and branch fractures of horizontal well in three-dimensional space. It is concluded that the shape of sand in the single fracture of horizontal well is obviously different from that in the single fracture of vertical well. A "sand pack" is formed and pushed forward in the single fracture of horizontal well. The sand concentration does not decrease rapidly at the entrance. As the inlet speed increases, the height of the sand in the fracture gradually increases. The greater the inlet particle concentration, the greater the sand concentration at other locations. The larger the particle density, the smaller the spreading range of sand. There is no significant relationship between sand concentration and particle density. The proppant-laden fluid in the wedge fracture is easier to fill the entire fracture than that in the rectangular fracture. The position of "sand pack" in the wedge fracture is lower than that in the rectangular fracture. The sand embankment thickness in the main fracture of branch fractures is bigger than the thickness in the single fracture. While the thickness of the suspension zone in the main fracture of branch fractures is much smaller than the thickness in the single fracture. With the increase of the angle between the branch fracture and the main fracture of branch fractures, the scope of the sand in the main fracture gradually decreases. When the angle is 90°and 120°, the sand accumulates at the junction of the branch fracture and the main fracture, which leads to a significant decrease of sand concentration in the area behind the first joint of the main fracture.