软煤层逐级跃升水力压裂增渗技术研究

Study on Increasing Permeability of Soft Coal Seams by Step-by-Step Hydraulic Fracturing Technology

水力压裂作为一种高效瓦斯抽采及瓦斯灾害防治技术得到了广泛的应用,现有的水力压裂技术大多采用高压脉冲或者低压水力对钻孔周围煤体进行压裂。这种方式在硬煤层中能够取得较好的效果,但在软煤层中,大流量的高压水很大程度上破坏钻孔周围煤岩体,致使软煤层在次生裂隙没有完全充分发育的情况下就遭到破坏、甚至闭合,致使水力压裂效果不显著,甚至造成煤体压出或突出危险。针对软煤层若采用低压水力压裂,一方面影响范围小,不容易形成压差,裂隙无法充分扩展;另一方面,压裂施工时间较长,用水量较大,存在排水困难,增加瓦斯治理成本和难度。因此,针对软煤层,如何有效使煤岩体在裂隙充分发育的情况下得到逐步延伸,首次提出了一种煤层逐级跃升水力压裂增渗方法。

Hydraulic fracturing has been widely used as a high-efficiency gas extraction and gas disaster prevention technology.The existing hydraulic fracturing technology mostly uses high-pressure pulse or low-pressure hydraulic to fracturing the coal around the borehole.This method can achieve good results in hard coal seam,but in soft coal seam,high-pressure water with large flow largely destroys the coal and rock mass around the borehole,which makes the soft coal seam destroyed or closed when the secondary cracks are not fully developed.Therefore,the application effect of hydraulic fracturing in soft coal seam is not significant,and even easy to cause the risk of coal extrusion or outburst.In the application of low-pressure hydraulic fracturing technology in soft coal seam,there are two main problems:one is that the influence scope is small,it is not easy to form differential pressure,and the fracture cannot be fully expanded;the other is that the fracturing construction time is long,the water consumption is large,and the drainage is difficult,which increases the cost and difficulty of gas control.On this issue,aimed at how to effectively extend the coal and rock mass in soft coal seam under the condition of fully developed cracks,a method of step-by-step jump fracturing hydraulic pressure and increasing coal seam permeability is put forward for the first time.