Developmental Research on Cutting a Notch in Deep Borehole for Hydraulic Fracturing with High Speed Waterjets

为了明确高速水射流技术在水力压裂深孔开缝中的适用性，首先制作了试验装置，模拟了2000m深水岩石的开缝切割，然后研究了驱动压力、开缝距离、喷嘴直径、穿越速度等各种切割参数对切割深度的影响。在驱动压力为100 MPa、流量为801 /min的条件下，研究了白川焊凝灰岩的槽宽和比能。本研究的主要结果总结如下：1)随着周向水压的增大，切割深度迅速减小，但在10 MPa左右时，切割深度基本保持不变。白川焊凝灰岩在水压20 MPa下最大切割深度为32.2 mm。2)较小空化数< 0.05时，切削机制以空化侵蚀为主，较大空化数时，其他机制占主导地位。3)在切深依赖于环向水压和不依赖于水压的情况下，提出了切深的经验公式。4)从能耗角度看，存在最优水压力和最优隔水距离。5)槽宽随着水压的增大而迅速增大，直至接近恒定值。6)高速水射流可用于水力压裂深孔开缝。

In order to clarify the applicability of high speed waterjets technology to making a slit in deep borehole for hydraulic fracturing, the testing apparatus was manufactured first to simulate the slot cutting of rock in deep water up to 2000m and then, the effects of various cutting parameters such as driving pressure, standoff distance, nozzle diameter and traverse rate on the depth of cut, the slot width and the specific energy were investigated for Shirakawa welded tuff using the driving pressure up to 100 MPa and flow rate of 80 1/min.The main results obtained in this study are summarized as follows;1) Although the depth of cut rapidly decreases with circumferential water pressure, if finally becomes almost constant at about 10 MPa of water pressure. Maximum depth of cut was 32.2 mm under water pressure of 20 MPa for Shirakawa welded tuff.2) Main cutting mechanism is cavitation errosion for the smaller cavitation number less than 0.05, and for larger cavitation number other mechamisms predominate.3) Empirical formulae on the depth of cut were proposed for both regions where the depth of cut depends on circumferential water pressure and where it is independent of water pressure.4) It is found that there exists an optimum water pressure and optimum standoff distance from the view point of energy consumption.5) The width of slot rapidly increases with water pressure until it reaches almost constant value.6) High speed waterjets can be applied to making a slit in deep borehole for hydraulic fracturing.