【摘要】：水壓致裂技術(shù)廣泛應(yīng)用于硬煤軟化、堅硬頂板控制、煤層瓦斯抽采、沖擊礦壓防治以及大采高綜采壓裂節(jié)能等方面,研究壓裂煤層裂隙演化是硬煤-硬厚煤層開采遇到的共性問題,對認識壓裂煤層裂隙演化規(guī)律,實現(xiàn)煤層科學(xué)開采意義重大。對此,本文結(jié)合陜北侏羅紀5-2煤層利用水壓預(yù)裂技術(shù)控制煤體有效破裂為工程背景,采用現(xiàn)場監(jiān)測、理論分析與數(shù)值模擬相結(jié)合的方法,對水壓致裂煤層裂隙演化規(guī)律展開研究,主要研究內(nèi)容和結(jié)論如下:(1)通過MTS815電液伺服巖石力學(xué)試驗系統(tǒng),測定煤層和頂?shù)装逦锢砹W(xué)性質(zhì);通過監(jiān)測煤層預(yù)裂裂隙擴展過程,分析了煤層復(fù)雜裂隙網(wǎng)絡(luò)的形成過程,給出了鉆孔水壓預(yù)裂形成的裂隙類型。(2)基于線彈性斷裂力學(xué)理論建立預(yù)裂裂隙起裂模型,分析預(yù)裂裂隙尖端單元體的應(yīng)力狀態(tài)及預(yù)裂裂隙的起裂條件,確定預(yù)裂裂隙的起裂位置。同時,提出適用于預(yù)裂裂隙起裂的“剪-拉-壓”破壞機理,分析預(yù)裂裂隙在三個主應(yīng)力狀態(tài)和煤體特定參數(shù)條件下破裂所經(jīng)歷剪切屈服、張拉破壞、壓裂貫通三個過程,確定預(yù)裂裂隙始裂的臨界水壓參數(shù)。研究表明:預(yù)裂裂隙長度、煤層硬度均影響預(yù)裂裂隙的起裂壓力,且預(yù)裂裂隙長度與起裂壓力呈正比關(guān)系,煤層硬度與預(yù)裂裂隙起裂壓力呈反比關(guān)系。(3)基于斷裂力學(xué)理論建立水壓裂隙擴展的理論模型,并根據(jù)Irwin裂隙擴展準則,對水壓裂隙進行分析,推導(dǎo)出水壓裂隙分別在煤層、巖層中擴展的臨界水壓力,并判斷水壓裂隙在煤層、煤巖交界面的演化規(guī)律。研究表明:鉆孔含有預(yù)裂裂隙的情況下,預(yù)裂裂隙長度在1倍孔徑以內(nèi),裂隙一般沿最大主應(yīng)力方向起裂,在擴展過程中受水壓力和地應(yīng)力的耦合作用,裂隙擴展呈曲折形態(tài);預(yù)裂裂隙長度在2倍孔徑以上,裂隙基本上沿水壓裂隙尖端起裂,且最有利于鉆孔起裂、擴展的預(yù)裂裂隙長度為3倍孔徑。
[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.
【學(xué)位授予單位】：西安科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TD82

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