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Drainage Against Gravity: Factors Impacting the Load Recovery in Fractures

机译:引流防止重力:影响裂缝中负荷回收的因素

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Horizontal wells in the tight reservoirs are stimulated using multistage hydraulic fracturing. The fracturing fluid used in this operation is generally water based. A very low percentage of fracturing water is recovered during the flowback operation. Non-recovered water can block the gas flow and damage the reservoir. The water recovery in propped fractures is controlled by microscopic displacement efficiency and fracture areal sweep efficiency. Microscopic displacement efficiency is mainly controlled by capillarity, and has been studied extensively. Areal sweep efficiency during water drainage in propped fractures is controlled by mobility ratio and displacement direction relative to gravity direction, which needs further investigation. This paper reports various fracture drainage experiments to understand the effect of gravity, surface properties, and viscosity on fracture sweep efficiency and total load recovery. A visual cell was built to model a propped fracture. Glass beads were packed in the space between two glass plates, and the pack was then saturated with the fracturing fluid. This simulates the initial conditions before opening the well for flowback. For simulating the water drainage against gravity, representing a fracture element below the horizontal well, the gas was injected at the bottom of the cell. Four sets of experiments were conducted to study the effect of injection pressure, interfacial tension, wettability, and fluid rheology on sweep efficiency and load recovery. Glass beads were chemically treated to alter their wettability from hydrophilic to hydrophobic. For each test, normalized fluid recovery was obtained by measuring the mass of produced fluid and using the material balance. The cell was kept in a dark room in front of a light box, and pictures were taken at regular time intervals. These images were later used to compare the drainage patterns. The results suggest that water recovery in an upward displacement very low mainly due to poor sweep efficiency. Increasing the injection pressure does not improve water recovery. Reducing surface tension and using treated hydrophobic sand improves the sweep efficiency and in turn the load recovery.
机译:使用多级液压压裂刺激紧密水库中的水平孔。该操作中使用的压裂流体通常是水的。在流量操作期间,回收了非常低的压裂水。不回收水可以阻挡气体流动并损坏储层。通过微观位移效率和裂缝面积扫描效率来控制预裂缝中的水回收。微观位移效率主要由毛细血管控制,并已广泛研究。在额外的裂缝中排水期间的区域横扫效率由相对于重力方向的迁移率和位移方向控制,这需要进一步研究。本文报告了各种骨折引流实验,了解重力,表面性质和粘度对骨折扫描效率和总负荷回收的影响。构建了一个视觉池以模拟额外的骨折。将玻璃珠包​​装在两个玻璃板之间的空间中,然后用压裂液饱和。这在打开井以进行流动之前模拟初始条件。为了模拟重力的排水,代表水平井下的断裂元件,气体被注入细胞底部。进行了四组实验,以研究注射压力,界面张力,润湿性和流体流变效果对扫描效率和负荷回收的影响。化学处理玻璃珠子以改变它们从亲水到疏水的润湿性。对于每个测试,通过测量产生的流体的质量并使用材料平衡来获得归一化流体回收。将该电池保持在灯箱前面的暗室中,并且以规则的时间间隔进行图片。这些图像后来用于比较排水模式。结果表明,水恢复在向上位移非常低,主要是由于扫效差。增加注射压力不会改善水回收。减少表面张力和使用经过处理的疏水性砂,提高了扫描效率,然后转动负荷回收。

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