水压致裂煤层裂隙演化规律研究
发布时间：2019-04-13 21:30
【摘要】：水压致裂技术广泛应用于硬煤软化、坚硬顶板控制、煤层瓦斯抽采、冲击矿压防治以及大采高综采压裂节能等方面,研究压裂煤层裂隙演化是硬煤-硬厚煤层开采遇到的共性问题,对认识压裂煤层裂隙演化规律,实现煤层科学开采意义重大。对此,本文结合陕北侏罗纪5-2煤层利用水压预裂技术控制煤体有效破裂为工程背景,采用现场监测、理论分析与数值模拟相结合的方法,对水压致裂煤层裂隙演化规律展开研究,主要研究内容和结论如下:(1)通过MTS815电液伺服岩石力学试验系统,测定煤层和顶底板物理力学性质;通过监测煤层预裂裂隙扩展过程,分析了煤层复杂裂隙网络的形成过程,给出了钻孔水压预裂形成的裂隙类型。(2)基于线弹性断裂力学理论建立预裂裂隙起裂模型,分析预裂裂隙尖端单元体的应力状态及预裂裂隙的起裂条件,确定预裂裂隙的起裂位置。同时,提出适用于预裂裂隙起裂的“剪-拉-压”破坏机理,分析预裂裂隙在三个主应力状态和煤体特定参数条件下破裂所经历剪切屈服、张拉破坏、压裂贯通三个过程,确定预裂裂隙始裂的临界水压参数。研究表明:预裂裂隙长度、煤层硬度均影响预裂裂隙的起裂压力,且预裂裂隙长度与起裂压力呈正比关系,煤层硬度与预裂裂隙起裂压力呈反比关系。(3)基于断裂力学理论建立水压裂隙扩展的理论模型,并根据Irwin裂隙扩展准则,对水压裂隙进行分析,推导出水压裂隙分别在煤层、岩层中扩展的临界水压力,并判断水压裂隙在煤层、煤岩交界面的演化规律。研究表明:钻孔含有预裂裂隙的情况下,预裂裂隙长度在1倍孔径以内,裂隙一般沿最大主应力方向起裂,在扩展过程中受水压力和地应力的耦合作用,裂隙扩展呈曲折形态;预裂裂隙长度在2倍孔径以上,裂隙基本上沿水压裂隙尖端起裂,且最有利于钻孔起裂、扩展的预裂裂隙长度为3倍孔径。
[Abstract]:Hydraulic fracturing technology is widely used in hard coal softening, hard roof control, coal seam gas drainage, impact rock pressure prevention, and large mining height fully mechanized mining fracturing energy saving, and so on. The research on fracture evolution of fractured coal seam is a common problem in hard coal-hard thick coal seam mining, which is of great significance for understanding the law of fracture evolution of fractured coal seam and realizing scientific mining of coal seam. In this paper, combined with the engineering background of controlling the effective fracture of coal mass by hydraulic presplitting technology in Jurassic 5-2 coal seam in northern Shaanxi, this paper adopts the method of field monitoring, theoretical analysis and numerical simulation, and makes use of the method of field monitoring, theoretical analysis and numerical simulation. The main research contents and conclusions are as follows: (1) through the MTS815 electro-hydraulic servo rock mechanics test system, the physical and mechanical properties of coal seam and roof and floor are determined; In this paper, the formation process of complex fracture network in coal seam is analyzed by monitoring the propagation process of coal seam pre-crack fracture, and the type of fracture formed by drilling water pressure precrack is given. (2) based on linear elastic fracture mechanics theory, a fracture initiation model of pre-crack fracture is established. The stress state of the unit at the tip of the pre-crack and the initiation conditions of the pre-crack are analyzed, and the location of the initiation of the pre-crack is determined. At the same time, the "shear-tension-compression" failure mechanism suitable for pre-crack initiation is put forward, and the shear yield, tension failure and fracture penetration of pre-fracture under the conditions of three principal stress states and specific parameters of coal body are analyzed. The critical water pressure parameters of the prefracture initial fracture are determined. The results show that the pre-crack length and coal seam hardness all affect the initiation pressure of the pre-crack, and the length of the pre-crack is proportional to the initiation pressure. The hardness of coal seam is inversely proportional to the precrack initiation pressure. (3) based on the theory of fracture mechanics, the theoretical model of water pressure fracture propagation is established, and the hydraulic fracture is analyzed according to the Irwin fracture propagation criterion. The critical water pressure of water pressure fracture in coal seam and rock layer is deduced, and the evolution law of water pressure crack in coal seam and coal-rock interface is judged. The results show that in the case of pre-crack cracks, the length of the pre-crack cracks is less than 1 times of the pore diameter, and the cracks usually crack along the direction of the maximum principal stress. During the expansion process, the cracks are subjected to the coupling of the water pressure and the in-situ stress, and the fracture propagation is in the form of zigzag. The length of the pre-crack is more than 2 times of the pore diameter, and the crack basically begins to crack along the tip of the hydraulic fracture, and it is most favorable for drilling to crack, and the length of the expanded pre-crack is 3 times of the pore diameter.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD82
本文编号：2457961
[Abstract]:Hydraulic fracturing technology is widely used in hard coal softening, hard roof control, coal seam gas drainage, impact rock pressure prevention, and large mining height fully mechanized mining fracturing energy saving, and so on. The research on fracture evolution of fractured coal seam is a common problem in hard coal-hard thick coal seam mining, which is of great significance for understanding the law of fracture evolution of fractured coal seam and realizing scientific mining of coal seam. In this paper, combined with the engineering background of controlling the effective fracture of coal mass by hydraulic presplitting technology in Jurassic 5-2 coal seam in northern Shaanxi, this paper adopts the method of field monitoring, theoretical analysis and numerical simulation, and makes use of the method of field monitoring, theoretical analysis and numerical simulation. The main research contents and conclusions are as follows: (1) through the MTS815 electro-hydraulic servo rock mechanics test system, the physical and mechanical properties of coal seam and roof and floor are determined; In this paper, the formation process of complex fracture network in coal seam is analyzed by monitoring the propagation process of coal seam pre-crack fracture, and the type of fracture formed by drilling water pressure precrack is given. (2) based on linear elastic fracture mechanics theory, a fracture initiation model of pre-crack fracture is established. The stress state of the unit at the tip of the pre-crack and the initiation conditions of the pre-crack are analyzed, and the location of the initiation of the pre-crack is determined. At the same time, the "shear-tension-compression" failure mechanism suitable for pre-crack initiation is put forward, and the shear yield, tension failure and fracture penetration of pre-fracture under the conditions of three principal stress states and specific parameters of coal body are analyzed. The critical water pressure parameters of the prefracture initial fracture are determined. The results show that the pre-crack length and coal seam hardness all affect the initiation pressure of the pre-crack, and the length of the pre-crack is proportional to the initiation pressure. The hardness of coal seam is inversely proportional to the precrack initiation pressure. (3) based on the theory of fracture mechanics, the theoretical model of water pressure fracture propagation is established, and the hydraulic fracture is analyzed according to the Irwin fracture propagation criterion. The critical water pressure of water pressure fracture in coal seam and rock layer is deduced, and the evolution law of water pressure crack in coal seam and coal-rock interface is judged. The results show that in the case of pre-crack cracks, the length of the pre-crack cracks is less than 1 times of the pore diameter, and the cracks usually crack along the direction of the maximum principal stress. During the expansion process, the cracks are subjected to the coupling of the water pressure and the in-situ stress, and the fracture propagation is in the form of zigzag. The length of the pre-crack is more than 2 times of the pore diameter, and the crack basically begins to crack along the tip of the hydraulic fracture, and it is most favorable for drilling to crack, and the length of the expanded pre-crack is 3 times of the pore diameter.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD82
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