跨煤岩界面穿层压裂裂缝动态扩展特征试验研究  

Experimental study on dynamic propagation characteristics of fracturing crack across coal-rock interface

作　　者：李浩哲 姜在炳 范宗洋 庞涛[1,2] 刘修刚 LI Hao-zhe;JIANG Zai-bing;FAN Zong-yang;PANG Tao;LIU Xiu-gang(China Coal Research Institute,Beijing 100013,China;CCTEG Xi’an Research Institute(Group)Co.,Ltd.,Xi’an,Shaanxi 710077,China;College of Petroleum Engineering,China University of Petroleum(Beijing),Beijing 102249,China;College of Emergency Management and Safety Engineering,China University of Minim and Technology-Beijing,Beijing 100083,China)

机构地区：[1]煤炭科学研究总院,北京100013 [2]中煤科工西安研究院(集团)有限公司,陕西西安710077 [3]中国石油大学(北京)石油工程学院,北京102249 [4]中国矿业大学(北京)应急管理与安全工程学院,北京100083

出　　处：《岩土力学》2024年第3期737-749,共13页Rock and Soil Mechanics

基　　金：国家科技重大专项(No.2016ZX05045002);天地科技创新创业资金专项重点项目(No.2022-2-TD-ZD007)。

摘　　要：针对跨煤岩界面穿层压裂裂缝动态扩展过程,采用相似材料制作煤岩组合体试件,开展三点弯曲试验、真三轴水力压裂物理模拟试验,分别结合数字散斑技术、声发射监测技术,捕捉裂缝的动态扩展特征,分析裂缝扩展形态及影响因素。结果表明:三点弯曲试验中裂缝可从顶板直接进入煤层,裂缝在界面处未转向,增大预制裂缝长度试件断裂所需的峰值应力降低;真三轴水力压裂试验条件下,由于煤层塑性强,顶板内裂缝高度、长度均大于煤层,顶板内声发射事件比例高于煤层;在裂缝穿层扩展的前提下,增大水平井与煤层顶面距离会导致裂缝穿层扩展时间延长,提高压裂液注入排量可增大裂缝进入煤层的穿透深度,但是易导致缝高失控、缝长降低,提出采用变排量压裂施工,初期压裂液大排量注入促使裂缝纵向穿层,随后降排量促进裂缝在顶板和煤层内横向延伸;多裂缝同步起裂时缝间存在竞争扩展现象,部分裂缝可能无法穿层扩展。研究成果可为掌握裂缝跨煤岩界面穿层扩展特点、优化设计压裂施工参数提供理论支撑。To investigate the dynamic propagation process of the fracturing crack across the coal-rock interface,similar materials were used to prepare coal-rock combined specimens.Three-point bending tests and true triaxial hydraulic fracturing tests were carried out.By the digital speckle technology and the acoustic emission(AE)technology,the dynamic propagation characteristics of the fracturing crack were captured.The fracture pattern and its influencing factors were analyzed.The results show that in the three-point bending test,the crack can penetrate into the coal seam directly from the roof without changing direction at the interface.The peak stress required for the specimen fracturing is reduced while increasing the prefabricated crack length.In the true triaxial hydraulic fracturing test,due to the strong plasticity of the coal seam,the crack height and length in the roof are both larger than those in the coal seam,and the proportion of acoustic emission events in the roof is also higher than that in the coal seam.When the crack propagates across layers,increasing the distance between the horizontal well and the top surface of the coal seam will lead to the extension of the crack propagation time.Increasing the injection rate of the fracturing fluid can increase the penetration depth of the crack into the coal seam,but it is easy to cause the crack height to be out of control and the reduction of crack length.The fracturing method with variable injection rates was proposed.In the initial stage,the fracturing fluid injection with a large rate promotes the crack propagation across layers,and then the injection rate is reduced to promote the lateral propagation of the crack in the roof and coal seam.There is a competitive propagation phenomenon among cracks when multiple cracks are initiated synchronously,and part of the cracks can not propagate across layers.The research results can provide support for mastering the propagation characteristics of the crack across the coal-rock interface and optimizing the hydraulic fr

关 键 词：煤岩界面 穿层压裂 动态扩展 数字散斑 声发射 

分 类 号：TE355[石油与天然气工程—油气田开发工程]