煤岩层分段水力压裂裂缝扩展与应力演化特征实验研究  

Experimental study on fracture propagation and stress evolution characteristics of segmented hydraulic fracturing in coal strata

作　　者：马兴莹 成小雨 程成 MA Xingying;CHENG Xiaoyu;CHENG Cheng(China Coal Energy Research Institute Co.,Ltd.,Xi’an 710054,China)

机构地区：[1]中煤能源研究院有限责任公司,陕西西安710054

出　　处：《实验技术与管理》2024年第9期47-53,共7页Experimental Technology and Management

基　　金：国家重点研发计划(2023YFF0615404);国家自然科学基金联合重点项目(U23B2093)。

摘　　要：随着我国煤层开采深度不断增加,由于煤层低渗透性导致的瓦斯抽采效率问题愈发严重,常规的瓦斯抽采措施已经不能满足现状。结合煤层瓦斯地质赋存条件和定向钻进技术特点,开展了分段水力压裂煤层增透技术,可有效解决上述问题,其关键在于水力压裂在岩层中所产生的新生裂缝能否顺利进入煤层并提供瓦斯抽采通道。该研究以沁水煤田某矿煤层顶板特征为背景,开展了地应力差、煤岩界面和泵注排量条件下的分段水力压裂实验,分析了分段水力压裂过程中试样生成裂缝发育规律及应力变化规律。研究结果表明:分段水力压裂过程中,第二段压裂效果受到第一段压裂所产生的裂缝影响,且泵注排量的增加会显著提高新生裂缝的发育扩展及连通度,有效改善了煤层透气性;整个压裂过程中应力变化曲线可以分为Ⅰ憋压阶段、Ⅱ裂缝扩展阶段、Ⅲ应力恢复阶段,其煤岩界面强度越高,越有利于岩层中新生裂缝扩展到煤层中。研究揭示了在地应力、煤岩界面和泵注排量影响下分段水力压裂过程中诱导应力的作用规律和裂缝扩展机制,实验结果对分段水力压裂煤岩层增透机理及其施工工艺参数设计具有一定的借鉴意义。[Objective]With the increasing mining depth of coal seams in China,issues related to gas extraction efficiency owing to local seam permeability have become increasingly severe.Conventional gas extraction methods are no longer sufficient.Hydraulic fracturing technology offers a promising solution to improve coal seam permeability and enhance gas extraction.However,crushed soft coal seams in China present challenges such as low strength,low permeability,significant gas content,and significant gas pressure,which result in poor drilling outcomes and limit control over gas disasters.Standard hydraulic fracturing techniques often result in short pressure cracks.To address this,long drilling stage hydraulic fracturing technology is used to create fractures that extend from the coal seam roof into the coal seam,forming a complex fracture network that improves gas migration channels and gas control.[Methods]To investigate the development and expansion of fracture networks during segmented hydraulic fracturing,a physical similarity simulation experiment was conducted using triaxial coal and rock assemblages.Acoustic emission monitoring technology was used to monitor the dynamic process of fracture expansion,and strain bricks were embedded in samples to monitor stress during and after fracturing.The study focused on understanding the fracture development and stress change laws of samples generated during subsection hydraulic fracturing under varying ground stress conditions,coal–rock interface characteristics,and the effect of pump displacement on the formation of new fractures.The goal was to determine whether new cracks generated in the roof rock stratum during segmented hydraulic fracturing can smoothly enter the coal seam and provide efficient gas extraction channels to increase the efficiency of gas extraction in the coal seam.[Results]The research results show that,in the process of segmented hydraulic fracturing of coal strata,the hydraulic fracturing effect of the second stage is affected by the fracture network g

关 键 词：瓦斯灾害防治 分段水力压裂 裂缝扩展 应力特性 煤层渗透性 

分 类 号：TD713[矿业工程—矿井通风与安全]