Investigation of hydraulic jet multistage cavitycompletion in coalbed methane horizontal wells
YANG Ruiyue，HUANG Zhongwei，LI Gensheng，CHEN Jianxiang，WEN Haitao，QIN Xiaozhou
我国煤层气资源丰富，但是“ 单井产量低” 长期难以改变。 提出了煤层气水平井水力喷射 分段造穴的新思路，旨在大范围释放储层应力、提高渗透率，从而提高单井产量。 首先介绍了水平 井水力喷射分段造穴的优势:灵活调控洞穴形状和尺寸、定点喷射、精准分段、多簇卸压、构建体积 缝网、符合煤炭原位流态化开采的科学构想。 然后，采用有限元-离散元耦合方法(Finite-Discrete Element Method)建立了水平井造穴诱导煤层应力演化流-固耦合模型，计算了多段洞穴形成的应 力释放区域，描述了穴周、穴间应力干扰区诱导形成的裂缝分布特征，阐释了水平井分段造穴应力 释放开采煤层气的原理。 其次，开展了淹没条件下磨料直射流和旋转磨料射流喷射煤岩的室内实 验，研究了磨料射流喷射煤岩的成孔形态和破坏模式及天然裂隙对破坏作用的影响，发现磨料射流 冲击下，层裂是煤岩重要的破裂机制。 接着，介绍了裸眼井、筛管井、套管井、顶底板间接改造井等 不同水平井完井方式下水力喷射分段造穴的井下核心工具、工艺流程和煤粉返排方式。 最后，探讨 了该技术的地质储层适应性和应用前景，有望在构造煤、深部煤、煤系薄互层及压裂造缝效果欠佳 或无法实现分支井眼重入的松软煤层等推广应用。
China is rich in coalbed methane resource. However，a low production rate is the longtime bottleneck problem. In this paper，an innovative proposal of creating multistage cavities by hydraulic jet(abrasive jetting)in coalbed methane horizontal wells is presented. First，the advantages of horizontal cavity completion by hydraulic jet were discussed. Flexibility in achieving any cavity shape and size，pinpoint jetting，precise segmentation，multistage pressurerelief，creating complex networks and meeting the demand of insitu fluidized mining of underground coal resources are the major benefits. Subsequently，the FDEM method was implemented to calculate the stressrelief area and describe the fracture generation characteristics around the cavities，and then illuminate the production enhancement mechanisms. Then，the laboratory experiments of abrasive round jetting and rotating jetting on various types of coals under submerged conditions were conducted. Shapes of jetted holes，rockbreaking modes and impacts of natural fractures were investigated. The results indicated that the stratification cracking along the weak planes was the most important coalbreaking mechanism. Next，the critical downhole tools，technological processes and coal particles flowback related to different completion methods such as open hole，slotted liner，casingperforated and roof indirect stimulated wells were introduced and discussed. Finally，the application prospects and geological adaptability of the proposed method were illustrated. The proposed technique can be applied in tectonic coal，deep coal，coal measuredstrata，soft coal beds where hydraulic fracturing is ineffective or multilateral boreholes are difficult to reentry.
coalbed methane；hydraulic jet；horizontal well cavity completion；stress relief；abrasive water jet；natural fractures