径向井复合脉动水力压裂煤层气储层解堵和增产室内实验

针对煤层气钻采过程中普遍存在的储层伤害解除不彻底的问题,提出了有助于解堵和增产的径向井复合脉动水力压裂技术思路:水力喷射多分支径向井,利用高导流径向孔眼进行适度的脉动水力压裂改造,从而在主井筒附近一定区域内最大限度地冲击、破碎煤层,形成高导流通道与裂缝网络相结合的大范围卸压增透区。为了验证其技术原理,设计并开展了径向井复合脉动水力压裂室内实验,采用声发射仪与脉冲伺服疲劳试验机等实验装置,围绕径向水平井复合压裂形成裂缝时的声发射响应特征与煤岩的破裂程度、宏观裂缝形态之间的关系开展了室内研究。结果表明:(1)实验条件下,径向水平井复合脉动水力压裂达到常规压裂峰值压力的1/3~1/4下即可起裂,声发射事件数是常规压裂的1.38~7.07倍;(2)径向水平井复合脉动水力压裂中获得强烈的声发射信号响应,产生宏观破裂的峰值压力较低,相同条件下更易获得较大范围的缝网;(3)径向井分支数、井眼长度、动载频率及振幅等参数是影响径向水平井复合脉动水力压裂效果的重要因素。结论认为,径向水平井复合脉动水力压裂方法提供了一种煤层气解除储层堵塞和高效开发的新思路,可实现煤层气井的有效解堵和增产。

Laboratory experiments on blockage removing and stimulation of CBM reservoirs by composite pulsating fracturing of radial horizontal wells

It is a common phenomenon during CBM drilling and production that reservoir damage is not eliminated completely. In view of this, a technical idea of composite pulsating fracturing of radial horizontal wells which is conducive to blockage removing and stimulation was put forward in this paper. Speaking of the hydraulic jetting in a multi-branch radial well, it is to conduct pulsating hydraulic fracturing moderately through a high-diversion radial hole, so as to crush and break coal beds near the main hole to the uttermost. Thus, an extensive pressure relief and permeability increase area where high-diversion pathways are combined with fracture networks is formed. Then, to verify its technical principles, laboratory tests on pulsating hydraulic fracturing of radial wells were designed and carried out. Besides, the relationships of the features of acoustic emission (AE) response during the formation of fractures by composite fracturing of radial horizontal wells vs. coal breaking degree and macro fracture morphology were experimentally studied by using a pulse servo fatigue testing machine and an acoustic emission detector. And the following research results were obtained. First, under experimental conditions, fractures initially occur when the pressure of composite pulsating hydraulic fracturing of radial horizontal wells is 1/3–1/4 of the peak pressure of conventional fracturing, and the amount of its AE events is 1.38–7.07 times that of conventional fracturing. Second, when composite pulsating hydraulic fracturing of radial horizontal wells is conducted, AE emission signals respond strongly, the peak pressure for macro fracturing is lower and a larger fracture network can be generated more easily under the same condition. Third, radial laterals amount, borehole length, dynamic loading frequency and amplitude are the important factors affecting the effect of composite pulsating hydraulic fracturing of radial horizontal wells. In conclusion, composite pulsating hydraulic fracturing of radial horizontal wells provides a new idea of removing the blockages in CBM reservoirs and developing CBM efficiently, realizing effective blockage removing and stimulation of CBM wells.