WO2016019825A1 - 一种低透气性煤层水力相变致裂强化瓦斯抽采方法 - Google Patents

一种低透气性煤层水力相变致裂强化瓦斯抽采方法 Download PDF

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WO2016019825A1
WO2016019825A1 PCT/CN2015/085652 CN2015085652W WO2016019825A1 WO 2016019825 A1 WO2016019825 A1 WO 2016019825A1 CN 2015085652 W CN2015085652 W CN 2015085652W WO 2016019825 A1 WO2016019825 A1 WO 2016019825A1
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water injection
hole
freezing
coal seam
phase change
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PCT/CN2015/085652
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English (en)
French (fr)
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翟成
林柏泉
彭深
向贤伟
汤宗情
武世亮
余旭
倪冠华
李全贵
杨威
许彦明
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翟成
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Priority to AU2015299587A priority Critical patent/AU2015299587B2/en
Publication of WO2016019825A1 publication Critical patent/WO2016019825A1/zh

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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E21B43/261—Separate steps of (1) cementing, plugging or consolidating and (2) fracturing or attacking the formation
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
    • E21F7/00—Methods or devices for drawing- off gases with or without subsequent use of the gas for any purpose

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  • the invention relates to a method for extracting gas, in particular to a method suitable for high-gas low permeability coal seam hydraulic phase transformation cracking enhanced gas drainage.
  • Coal is the basic energy source of China. With the increase of mining depth, gas has become a major factor that seriously threatens the safe production of coal mines. More than 90% of mines in China are mined, and high gas and coal and gas outburst mines, which account for 51% of the total number of mines, are accompanied by a large amount of gas in the mining process. The threat of gas explosion and gas outburst is also becoming more serious. Gas disasters have become the most important factor restricting the development of high-efficiency intensive mining technology and safe production. Since most of China's coal seams belong to high gas and low permeability coal seams, the main measure to solve the gas problem in the mining process of high gas and low permeability coal seams is pre-implementation of coal seam gas drainage.
  • the conventional gas drainage method has a small effective impact range.
  • the hole spacing is 0.5 ⁇ 2m.
  • the drilling face construction work volume is large, the extraction efficiency is low, and some mine extraction time is up to one year or even several years. It still can't reach the national gas drainage standard, and it has low gas permeability for high gas.
  • Coal seams are difficult to achieve.
  • the high gas and low permeability coal seam pressure relief and anti-reflection measures are artificially preliminarily loosened the original coal body to improve the gas permeability of the coal seam.
  • the main methods are deep hole loose blasting, water jet slitting technology and hydraulic punching technology.
  • underground coal seam hydraulic fracturing technology Deep hole loose blasting, water jet slitting technology and hydraulic punching technology have problems such as small effective impact of drilling, large workload and complicated construction process.
  • Conventional downhole hydraulic fracturing technology can relatively achieve a large range of coal seam pressure relief. Due to the high flow rate of high pressure water injection, high pressure water is affected by the coal body stress distribution and the main coal seam crack, which cannot control the crack expansion direction. The coal body is relieved of pressure, and some coal bodies are concentrated in stress. At the same time of pressure relief, high stress concentration areas are easily generated. The concentrated stress can reach about 3 to 4 times of the original stress, and it is difficult to form a regional overall pressure relief and anti-reflection.
  • the object of the present invention is to provide a new method for gas drainage of high gas and low gas permeability coal seam for high gas and low gas permeability coal seam, and combine the coal seam water injection technology with refrigeration technology by utilizing the phase change principle of water.
  • the coal seam is cracked by the phase change of water, and a complex fracture network is formed in the coal body, thereby increasing the gas flow passage in the coal seam.
  • the method for hydraulic phase change cracking and enhanced gas drainage of the low permeability coal seam of the present invention comprises the following steps:
  • a phase change cracking unit is arranged along the bedding layer in the coal seam roadway, each phase change cracking unit includes a water injection hole, two freezing holes and two temperature measuring holes, and the implementation process is as follows: firstly, according to conventional techniques Construction hole depth in the coal seam It is a water injection hole of 80 to 200 m, and then a freezing hole parallel to the water injection hole is constructed at a distance of 5 to 10 m on both sides of the water injection hole, and a temperature measurement is respectively constructed between the two freezing holes and the water injection hole.
  • the distance N between the hole, the temperature measuring hole and the water injection hole is 3 m, the hole diameter of the temperature measuring hole is 75 mm, and the hole depth is 30 m;
  • the feeding depth is not less than 20m, and then the injection of the temperature measuring hole
  • the length of the sealing section is not less than 12m; the freezing tube is fed into the two freezing holes respectively, and the feeding depth is not less than 80% of the depth of the freezing hole, and then the grouting is sealed;
  • the temperature sensors disposed in the two temperature measuring holes respectively pass through the data line.
  • the temperature signal in the coal seam is transmitted to the digital temperature display device, and the temperature of the coal seam in the two temperature measuring holes is monitored in real time by the digital temperature display device.
  • the temperature of the coal seam in the two temperature measuring holes reaches -3 ° C, it is judged that The coal seam in the phase change cracking unit has been frozen; the coal seam is cracked by the phase transformation of water, and a complex fracture network is formed in the coal body, thereby increasing the gas flow passage in the coal seam;
  • the freezing system After completing the phase change cracking, the freezing system is closed, and the frozen coal layer gradually absorbs the underground heat and begins to melt.
  • the digital temperature display shows that the temperature in both temperature measuring holes is greater than 3 °C, the phase change is considered to be caused.
  • the water in the frozen coal seam in the crack range is completely converted from solid to liquid, completing the phase change cracking process of one unit;
  • the phase change cracking unit can be repeatedly filled with water and frozen to enhance the permeability of the coal seam in the phase change cracking zone to achieve enhanced gas. The effect of the extraction.
  • the coal seam water injection technology is combined with the refrigeration technology by using the phase change principle of water, and the coal seam is cracked by the phase transformation of water, and the coal body affected by the freezing influences the expansion force, forcing The larger cracks in the coal seam expand and connect, and promote the formation and gradual opening of micro-cavity cracks, forming a new regenerated fracture network, providing gas flow channels in the coal seam, changing the mechanical properties of the coal body and improving the permeability of high gas coal seams.
  • Sexuality improves the flow of gas in the coal seam.
  • the influence radius of drilling gas drainage can reach 10 ⁇ 40m.
  • the effective radius of single hole extraction is increased by 5 ⁇ 20 times, and the number of gas drainage holes is reduced by 20% ⁇ 60%.
  • the secondary fractures generated by the hydraulic phase change in the coal seam are continuously generated and expanded.
  • the flow channels of the coal seam gas in the frozen area can be effectively increased from the macroscopic and microscopic levels, and the permeability coefficient of the coal seam can be increased by 30 to 200 times.
  • the average extraction volume of Kongvas can reach 0.8m 3 /min, the concentration of gas drainage can reach 30 ⁇ 90%, and the gas extraction rate of mining face can reach more than 50%, which solves the low gas drainage efficiency of high gas permeability coal seam.
  • the problem is that the extraction period is long and the influence range of the extraction drilling is small.
  • the method has the advantages of simple method, convenient operation, good implementation effect, high safety, strong coal seam applicability, and wide practicality in the technical field.
  • Figure 1 is a schematic view showing the horizontal direction of the working surface of the present invention
  • Figure 2 is a schematic view showing the vertical direction of the A-A working surface of Figure 1;
  • Figure 3 is a cross-sectional view of the B-B water injection hole connection system of Figure 1;
  • Figure 4 is a cross-sectional view of the C-C freezing hole connection system of Figure 1;
  • Figure 5 is a cross-sectional view of the D-D temperature measuring hole connection system of Figure 1.
  • Phase change cracking units are arranged along the bedding layer to the coal seam 1 in the coal seam roadway.
  • Each phase change cracking unit comprises a water injection hole 2, two freezing holes 3 and two temperature measuring holes 4, and the implementation process is as follows: Firstly, according to the conventional technology, a water injection hole 2 having a hole diameter of 75 to 130 mm and a hole depth of 80 to 200 m is applied to the coal seam 1, and then a water separation hole 2 is constructed in parallel with a distance L of 5 to 10 m on both sides of the water injection hole 2.
  • the freezing hole 3, a temperature measuring hole 4 is respectively constructed between the two freezing holes 3 and the water injection hole 2, the distance N between the temperature measuring hole 4 and the water injection hole 2 is 3 m, and the diameter of the temperature measuring hole 4 is 75 mm, and the hole depth is 30m;
  • the high-pressure water injection pipe 5 is fed into the water injection hole 2, and the water-filling hole 2 is sealed by the capsule sealing device 6 used in the conventional technique, and then the temperature sensor 7 is fed into the temperature measuring hole 4, and the feeding depth is not less than 20m, after grouting and sealing the temperature measuring hole 4, the length of the sealing section 10 is not less than 12m; respectively, the freezing tube 11 is fed into the two freezing holes 3, and the feeding depth is not less than 80 of the depth of the freezing hole 3. %, then grouting and sealing;
  • the high-pressure water injection pipe 5 is connected with the high-pressure water injection pump 12, and the high-pressure water injection pipe 5 is injected into the water injection hole 2 with a pressure of 3-15 MPa of high-pressure water, so that the normal temperature water is injected into the coal seam through the borehole 2, and the coal surrounding the water injection hole 2 is injected. Seepage on the wall When the pressure of the water injection or the water injection pressure suddenly decreases or the continuous water injection pressure does not change significantly, the shut-off valve 13 of the orifice of the water injection hole 2 is closed; the water injection is stopped, and the injected water remains in the coal seam and continues to seep into a smaller crack;
  • the freezing tube 11 in the freezing hole 3 is connected with the underground freezing system 14, and the water injected into and around the borehole of the coal seam is frozen by the refrigeration freezing technique, and the free water in the coal seam crack is gradually converted from the liquid state to the solid state during the freezing process.
  • the volume of water will expand by about 9.1%, causing expansion damage to the coal body, promoting the generation and expansion of internal cracks in the coal body; freezing the coal seam 1 through the freezing pipe 11
  • Phase change cracking, phase change cracking process the temperature sensor 7 disposed in the two temperature measuring holes 4 respectively transmits the temperature signal in the coal seam 1 to the digital temperature display device 9 through the data line 8, through the digital temperature display device 9 real-time monitoring of the temperature of the coal seam in the two temperature measuring holes 4, when the temperature of the coal seam in the two temperature measuring holes 4 reaches -3 ° C, it is judged that the coal seam in the phase change cracking unit has been frozen;
  • the freezing system 14 is closed, and the frozen coal seam 1 gradually absorbs the underground heat and begins to melt, and further increases the pore penetration and crack expansion of the coal body during the melting process, and enhances the effect of phase transformation cracking.
  • the digital temperature display device 9 indicates that the temperatures in the two temperature measuring holes 4 are both greater than 3 ° C, it is considered that all the water in the frozen coal seam 1 in the phase change cracking region is converted from a solid state to a liquid state, and a phase change of one unit is completed.
  • the high-pressure water injection pipe in the water injection hole 2 is connected with the gas drainage pipeline, and the gas extraction is carried out in the unit after the phase transformation cracking according to a conventional technique, and may also be in the phase change cracking affected zone.
  • Inward coal seam 1 is constructed with multiple gas drainage holes for gas drainage to improve the efficiency of gas drainage;
  • the phase change cracking unit can be repeatedly filled with water and frozen to enhance the permeability of the coal seam in the phase change cracking zone to achieve enhanced gas.
  • the effect of the extraction; the abnormal situation includes the flow of gas, the concentration suddenly decreases, and the flow rate decays to a lower level ( ⁇ 0.005m 3 /min) in a short time ( ⁇ 10 days);

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Abstract

一种低透气性煤层水力相变致裂强化瓦斯抽采方法，将常温的水通过钻孔注入煤层（1），注水结束后关闭阀门；然后通过制冷冻结技术对注水孔（2）周围煤层进行冻结，冻结过程中煤层裂隙中的自由水逐渐由液态转化为固态，对煤体产生膨胀破坏，促进煤体内部裂隙的产生和扩展；冻结结束后，煤层吸收井下环境热量逐渐融解，融解过程中进一步提高煤体孔隙贯通和裂隙的扩展，增强相变致裂的效果；冻融结束后将注水孔与瓦斯抽采管路连接进行瓦斯抽采、或者在相变致裂区域向煤层实施瓦斯抽采钻孔进行瓦斯抽采。抽采过程中，根据瓦斯抽采效果变化，可以对钻孔进行重复水力相变致裂，达到提高煤层透气性和高效抽采瓦斯的目的。

Description

一种低透气性煤层水力相变致裂强化瓦斯抽采方法 技术领域
本发明涉及一种抽采瓦斯方法，尤其是一种适用于高瓦斯低透气性煤层水力相变致裂强化瓦斯抽采的方法。
技术背景
煤炭是我国的基础能源，随着开采深度的增加，瓦斯已成为严重威胁煤矿安全生产的主要因素。我国90％以上的矿井为井工开采，占矿井总数51％的高瓦斯和煤与瓦斯突出矿井在开采过程伴随着大量的瓦斯涌出，瓦斯爆炸和瓦斯突出的威胁也越来越严重，因此，瓦斯灾害已成为制约高效集约化开采技术发展和安全生产的最重要因素。由于我国大多数煤层均属于高瓦斯低透气性煤层，解决高瓦斯低透气性煤层开采过程中的瓦斯问题的主要措施是预先实施煤层瓦斯抽采，常规的瓦斯抽采方法有效影响范围小，钻孔间距0.5～2m，工作面钻孔施工工程量大，抽采效率低，有的矿井抽采时间长达一年甚至数年，仍然达不到国家瓦斯抽采标准，对于高瓦斯低透气性煤层难以起到理想效果。若要做到抽采达标，消除煤层瓦斯灾害，需要采取增透的方法，扩大单个钻孔有效影响范围，提高瓦斯抽采效果。目前采用的高瓦斯低透气性煤层卸压增透措施是采用人为方法预先松动原始煤体，提高煤层的透气性，主要采取的方法有深孔松动爆破、水射流割缝技术、水力冲孔技术和井下煤层水力压裂技术等。深孔松动爆破、水射流割缝技术、水力冲孔技术存在单个措施钻孔有效影响范围小、工作量大、施工工艺复杂等问题。常规的井下水力压裂技术相对来说能够实现大范围的煤层卸压，由于采用大流量高压注水，高压水受到煤体应力分布和煤层主裂隙的影响，无法控制裂隙扩展方向，这样会导致部分煤体卸压，部分煤体应力集中，在卸压的同时也容易产生高应力集中区，集中应力能达到原始应力的3～4倍左右，难以形成区域性整体卸压增透。
发明内容
技术问题：本发明的目的是针对高瓦斯低透气性煤层，提供一种新的高瓦斯低透气性煤层强化瓦斯抽采的方法，利用水的相变原理，将煤层注水技术与制冷技术相结合，通过水的相变对煤层进行致裂，在煤体内形成复杂裂隙网，从而增加煤层内瓦斯流动通道。
技术方案：本发明的低透气性煤层水力相变致裂强化瓦斯抽采方法，包括以下步骤：
a.在煤层巷道内沿顺层向煤层方向布置相变致裂单元，每个相变致裂单元包括一个注水孔、两个冻结孔和两个测温孔，实施过程如下：首先按常规技术向煤层内施工孔深 为80～200m的注水孔，然后在注水孔两侧间隔距离L为5～10m位置处分别施工一个与注水孔相平行的冻结孔，在两个冻结孔与注水孔之间分别施工一个测温孔，测温孔与注水孔的距离N为3m，测温孔的孔径为75mm、孔深为30m；
b.向注水孔中送入高压注水管，采用胶囊封孔器对注水孔进行封孔，然后向测温孔内送入温度传感器，送入深度不小于20m，之后对对测温孔进行注浆封孔，封孔段的长度不小于12m；分别在两个冻结孔内送入冻结管，送入深度不小于冻结孔深度的80％，之后进行注浆封孔；
c.将高压注水管与高压注水泵连接，通过高压注水管向注水孔中注入压力为3-15MPa高压水，待注水孔周围煤壁出现渗水现象或注水压力突然降低时或持续注水压力无明显变化时停止注水；
d.将冻结孔内的冻结管与井下冻结系统相连接，通过冻结管对煤层进行冻结相变致裂，相变致裂过程中，设在两个测温孔内的温度传感器分别经数据线将煤层内的温度信号传输给数字温度显示仪，通过数字温度显示仪实时监测两个测温孔内煤层的温度，当两个测温孔内煤层的温度达到-3℃时，则判断出该相变致裂单元内的煤层已经冻结；通过水的相变对煤层进行致裂，在煤体内形成复杂裂隙网，从而增加煤层内瓦斯流动通道；
e.完成相变致裂之后，关闭冻结系统，冻结后的煤层逐渐吸收井下环境热量开始融解，当数字温度显示仪显示两个测温孔内的温度均大于3℃时，则认为相变致裂范围内冻结煤层中的水全部从固态转化为液态，完成一个单元的相变致裂过程；
f.将注水孔与瓦斯抽采管路相连，按常规技术在相变致裂后的单元内进行瓦斯抽采；
g.重复步骤a、b、c、d、e、f，进行下一单元的相变致裂和瓦斯抽采，周而复始，直至完成所有单元内的相变致裂和瓦斯抽采。
当相变致裂区域进行瓦斯抽采过程中，瓦斯浓度、流量变化异常时，可对该相变致裂单元重复进行注水、冻结，增强相变致裂区域内的煤层透气性，达到强化瓦斯抽采的效果。
有益效果：由于采用了上述技术方案，利用水的相变原理，将煤层注水技术与制冷技术相结合，通过水的相变对煤层进行致裂，冻结影响区域煤体受到膨胀力的作用，迫使煤层中的较大裂隙扩展联通，并促使微小孔裂隙形成和逐渐张开，形成新的再生裂隙网，提供瓦斯在煤层中的流动通道，改变了煤体力学性质，提高了高瓦斯煤层的透气性，改善了煤层中的瓦斯流动状态。钻孔瓦斯抽采影响半径可达10～40m，与普通抽采钻孔相比，单孔有效抽采影响半径扩大5～20倍，瓦斯抽采钻孔数减少20％～60％。同时，水力 相变在煤层中产生的次生裂隙不断的产生和扩展，从宏观和微观层面都能有效的增加冻结区域煤层瓦斯的流动通道，煤层的透气性系数可以提高30～200倍，单孔瓦斯抽采量平均可达0.8m3/min，瓦斯抽采浓度可达30～90％，回采工作面瓦斯抽采率达到50％以上，解决了高瓦斯地透气性煤层瓦斯抽采效率低、抽采周期长、抽采钻孔影响范围小的问题。其方法简单，操作方便，实施效果好，安全性高，具有较强的煤层适用性，在本技术领域内具有广泛的实用性。
附图说明
图1是本发明的工作面水平方向施工示意图；
图2是图1的A－A工作面垂直方向施工示意图；
图3是图1的B－B注水孔连接系统剖面图；
图4是图1的C－C冻结孔连接系统剖面图；
图5是图1的D－D测温孔连接系统剖面图。
图中：1－煤层，2—注水孔，3-1—冻结孔，3-2—冻结孔，4-1—测温孔，4-2—测温孔，5—高压注水管，6—胶囊封孔器，7—温度传感器，8—数据线，9—数字温度显示仪，10—注浆封孔段，11—冻结管，12—高压注水泵，13—截止阀，14—冻结系统。
具体实施方式
下面结合附图对本发明的一个实施例作进一步的描述：
本发明的低透气性煤层水力相变致裂强化瓦斯抽采方法，具体步骤如下：
a.在煤层巷道内沿顺层向煤层1方向布置相变致裂单元，每个相变致裂单元包括一个注水孔2、两个冻结孔3和两个测温孔4，实施过程如下：首先按常规技术向煤层1内施工孔径75～130mm，孔深为80～200m的注水孔2，然后在注水孔2两侧间隔距离L为5～10m位置处分别施工一个与注水孔2相平行的冻结孔3，在两个冻结孔3与注水孔2之间分别施工一个测温孔4，测温孔4与注水孔2的距离N为3m，测温孔4的孔径为75mm、孔深为30m；
b.向注水孔2中送入高压注水管5，采用常规技术使用的胶囊封孔器6对注水孔2进行封孔，然后向测温孔4内送入温度传感器7，送入深度不小于20m，之后对对测温孔4进行注浆封孔，封孔段10的长度不小于12m；分别在两个冻结孔3内送入冻结管11，送入深度不小于冻结孔3深度的80％，之后进行注浆封孔；
c.将高压注水管5与高压注水泵12连接，通过高压注水管5向注水孔2中注入压力为3-15MPa高压水，使常温的水通过钻孔2注入煤层，待注水孔2周围煤壁出现渗水现 象或注水压力突然降低时或持续注水压力无明显变化时，关闭注水孔2孔口的截止阀13；停止注水，注入的水存留在煤层中并持续渗流进入更微小的裂隙；
d.将冻结孔3内的冻结管11与井下冻结系统14相连接，通过制冷冻结技术将注入煤层钻孔中及周围的水冷冻，冻结过程中煤层裂隙中的自由水逐渐由液态转化为固态，发生相变变化，在相变的过程中，水的体积会膨胀增加约9.1％，对煤体产生膨胀性破坏，促进煤体内部裂隙的产生和扩展；通过冻结管11对煤层1进行冻结相变致裂，相变致裂过程中，设在两个测温孔4内的温度传感器7分别经数据线8将煤层1内的温度信号传输给数字温度显示仪9，通过数字温度显示仪9实时监测两个测温孔4内煤层的温度，当两个测温孔4内煤层的温度达到-3℃时，则判断出该相变致裂单元内的煤层已经实现冻结；
e.完成相变致裂之后，关闭冻结系统14，冻结后的煤层1逐渐吸收井下环境热量开始融解，融解过程中进一步提高煤体孔隙贯通和裂隙的扩展，增强相变致裂的效果。当数字温度显示仪9显示两个测温孔4内的温度均大于3℃时，则认为相变致裂范围内冻结煤层1中的水全部从固态转化为液态，完成一个单元的相变致裂过程；
f.完成冻融之后，将注水孔2内的高压注水管与瓦斯抽采管路相连，按常规技术在相变致裂后的单元内进行瓦斯抽采，也可在相变致裂影响区域内向煤层1施工多个瓦斯抽采钻孔进行瓦斯抽采，以提高瓦斯抽采的效率；
当相变致裂区域进行瓦斯抽采过程中，瓦斯浓度、流量变化异常时，可对该相变致裂单元重复进行注水、冻结，增强相变致裂区域内的煤层透气性，达到强化瓦斯抽采的效果；异常情况包括瓦斯的流量、浓度突然降低，流量在短时间(<10天)衰减至较低水平(<0.005m3/min)；
g.重复步骤a、b、c、d、e、f，进行下一单元的相变致裂和瓦斯抽采，周而复始，直至完成所有单元内的相变致裂和瓦斯抽采。

Claims (2)

  1. 一种低透气性煤层水力相变致裂强化瓦斯抽采方法，其特征在于，包括以下步骤：
    a.在煤层巷道内沿顺层向煤层(1)方向布置相变致裂单元，每个相变致裂单元包括一个注水孔(2)、两个冻结孔(3)和两个测温孔(4)，实施过程如下：首先按常规技术向煤层(1)内施工孔深为80～200m的注水孔(2)，然后在注水孔(2)两侧间隔距离L为5～10m位置处分别施工一个与注水孔(2)相平行的冻结孔(3)，在两个冻结孔(3)与注水孔(2)之间分别施工一个测温孔(4)，测温孔(4)与注水孔(2)的距离N为3m，测温孔(4)的孔径为75mm、孔深为30m；
    b.向注水孔(2)中送入高压注水管(5)，采用胶囊封孔器(6)对注水孔(2)进行封孔，然后向测温孔(4)内送入温度传感器(7)，送入深度不小于20m，之后对对测温孔(4)进行注浆封孔，封孔段(10)的长度不小于12m；分别在两个冻结孔(3)内送入冻结管(11)，送入深度不小于冻结孔(3)深度的80％，之后进行注浆封孔；
    c.将高压注水管(5)与高压注水泵(12)连接，通过高压注水管(5)向注水孔(2)中注入压力为3-15MPa高压水，待注水孔(2)周围煤壁出现渗水现象或注水压力突然降低时或持续注水压力无明显变化时停止注水；
    d.将冻结孔(3)内的冻结管(11)与井下冻结系统(14)相连接，通过冻结管(11)对煤层(1)进行冻结相变致裂，相变致裂过程中，设在两个测温孔(4)内的温度传感器(7)分别经数据线(8)将煤层(1)内的温度信号传输给数字温度显示仪(9)，通过数字温度显示仪(9)实时监测两个测温孔(4)内煤层的温度，当两个测温孔(4)内煤层的温度达到-3℃时，则判断出该相变致裂单元内的煤层已经冻结；
    e.完成相变致裂之后，关闭冻结系统(14)，冻结后的煤层(1)逐渐吸收井下环境热量开始融解，当数字温度显示仪(9)显示两个测温孔(4)内的温度均大于3℃时，则认为相变致裂范围内冻结煤层(1)中的水全部从固态转化为液态，完成一个单元的相变致裂过程；
    f.将注水孔(2)与瓦斯抽采管路相连，按常规技术在相变致裂后的单元内进行瓦斯抽采；
    g.重复步骤a、b、c、d、e、f，进行下一单元的相变致裂和瓦斯抽采，周而复始，直至完成所有单元内的相变致裂和瓦斯抽采。
  2. 根据权利要求1所述的低透气性煤层水力相变致裂强化瓦斯抽采方法，其特征在于：当相变致裂区域进行瓦斯抽采过程中，瓦斯浓度、流量变化异常时，可对该相变致裂单元重复进行注水、冻结，增强相变致裂区域内的煤层透气性，达到强化瓦斯抽采的效 果。
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