Theoretical and technological concepts of synergistic coal and natural gas extraction
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摘要:
我国存在大量的煤炭与天然气重叠赋存资源，出于对资源开采效率的要求，大量的煤与天然气重叠资源需要在同一时空内同步开采，传统的煤与天然气开采理论与技术难以满足协同开采出现的技术难题，煤与天然气协同开采的进程受到了严重制约。基于此，结合国内煤与天然气重叠赋存情况对煤与天然气协同开采进行了科学定义，总结了已有可借鉴的煤与天然气开采技术和相关理论。建立了天然气井近场岩体力学理论、天然气近场围岩耦合损伤理论、“围岩–水泥环–套管”耦合损伤理论、煤与天然气协同开采垂直场围岩耦合损伤理论，揭示了煤与天然气协同开采围岩的耦合损伤机理，为煤与天然气技术体系的构建提供了理论基础。提出了“煤与天然气协同开采技术”“煤炭开采通过废弃井技术”和“天然气近场小煤柱留设技术”3项技术以及“协同开采分区规划系统”“透明地质与生产信息动态监测系统”和“煤与天然气协同区安全监测与评价系统”三大系统，为煤与天然气协同开采提供技术支持，提高煤炭与天然气资源的开采效率。在此基础上，构建了煤与天然气协同开采的理论与技术体系，明确了煤与天然气协同开采未来的研究重点，提出了我国煤与天然气资源安全、绿色、高效协同开采的技术路径与研究方向。
Abstract:There are a large number of overlapping coal and natural gas resources in China, and due to the requirement of resource extraction efficiency, a large number of overlapping coal and natural gas resources need to be extracted synchronously in the same time and space, and the traditional coal and natural gas extraction theories and technologies are difficult to meet the technical problems arising from coordinated extraction, and the process of coordinated extraction of coal and natural gas has been seriously constrained. Based on this, a scientific definition of coal and natural gas synergistic mining is made based on the overlapping coal and natural gas resources in China, and the existing coal and natural gas mining technologies and related theories are summarised. We have established the near-field rock mechanics theory of natural gas wells, the coupled damage theory of natural gas near-field surrounding rock, the coupled damage theory of “surrounding rock-cement ring-casing”, and the coupled damage theory of vertical surrounding rock of coal and natural gas synergistic mining, which reveal the coupled damage mechanism of surrounding rock of coal and natural gas synergistic mining, and provide a theoretical basis for the construction of the technology system of coal and natural gas. It provides a theoretical basis for the construction of coal and natural gas technology system. The three technologies of “Coal and Natural Gas Cooperative Mining Technology”, “Coal Mining through Abandoned Wells Technology” and “Natural Gas Near-Field Small Coal Pillar Retention Technology” are proposed, as well as the “Coal and Natural Gas Cooperative Mining Zoning Planning Technology”. Three major systems, namely, “Coal and Natural Gas Cooperative Mining Zoning Planning System”, “Transparent Geological and Production Information Dynamic Monitoring System” and “Coal and Natural Gas Cooperative Zone Safety Monitoring and Evaluation System”, provide technical support for coal and natural gas cooperative mining, and improve the safety of coal and natural gas production. This system provides technical support for the synergistic mining of coal and natural gas and improves the mining efficiency of coal and natural gas resources. On this basis, the theoretical and technological system of coal and natural gas synergistic mining is constructed, the future research focus of coal and natural gas synergistic mining is clarified, and the technological path and research direction for the safe, green and high-efficiency synergistic mining of coal and natural gas resources in China are proposed.
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0. 引 言
对于煤矿充填采矿所用的胶结充填材料的强度、流动性等相关指标研究，煤炭行业学者充分借鉴混凝土标准测试方法、非煤矿山研究与实践经验，结合煤矿充填开采的特殊性，已探索形成了较为成熟完善的测试硬件、分析软件体系，逐步形成行业标准及国家标准，同时取得大量的学术成果[1-6]，为工业性应用提供了坚实的理论基础，也为本研究的开展提供了重要支持。同时为进一步提高充填材料的流动性、强度性能，大批学者从原材料的精细加工、骨料与粉料比例调整、辅助添加料创新等方向也进行了大量研究[7-10]。
晋陕蒙宁甘省域的许多煤矿井田范围内存在过去小煤窑采用高落式等落后采煤工艺开采遗留的局部空区（包括空硐区、老巷群及煤矸冒落堆积区），原有煤层的完整性受到了极大破坏，同时为瓦斯和水积聚、浮煤自燃等提供了潜在条件[11-14]。后续再进行上述区域的资源回收时，采场围岩变形控制、覆岩移动控制等异常困难。在采掘进行预充填来消除局部空区、重新再造相对完整的煤岩体结构可大幅度提高作业安全性系数[15-20]。煤矿现有充填材料主要以散体矸石、高水或膏体胶结充填材料等为主，用于预充填易导致洗选过程煤矸分离难，影响煤炭品质和价格。
与此同时，煤炭的洗选环节会产生大量终端产物−煤泥，煤泥粘性大、热量值低，传统的煤泥处理方式大多采用露天堆放，主要用于地销民用，销售价格低廉，煤泥价值利用不充分，而且现场环境脏乱，容易造成土壤和地下水污染。如何对煤泥进行无害化处理、资源化利用亦是诸多煤炭企业不得不面对的现实问题[21-23]。
鉴于此，本研究提出以煤泥为主料配制充填材料用于空区的预充填作业，实现回采前消除空区和资源化利用煤泥的双重目标。但截止目前，尚未系统性地开展研究并掌握煤泥基预充填材料的流动性及强度特性配比要素及作用机制，这极大限制了该材料的研制应用，亟待开展针对性研究。
1. 正交试验方案及测试结果
根据矸石膏体充填材料的制备经验，选择高水、水泥、粉煤灰这3种材料作为添加剂，与煤泥水共同制备胶结充填材料，其中水泥为42.5号普通硅酸盐水泥，粉煤灰为二级粉煤灰。经过数次配比调配试验，并参照已经开展前期研究[24]发现：当煤泥水质量分数（即煤泥占煤泥水的质量比）为28.75%～40.00%、高水材料质量、水泥质量、粉煤灰质量分别维持在煤泥基胶结充填材料总质量的2.4%～3.9%、3.3%～10%、3.3%～10%时，所制成的煤泥基胶结充填材料同时兼具较好的固结性、流动性与经济性。
结合试验矿井—彬长矿区水帘洞煤矿现场充填相关实际，设计4因素3水平正交试验表L9（34）进行方案设计，具体见表1。其中表中A表示煤泥水质量分数，B表示高水添加比例（高水添加质量/煤泥水质量），C表示水泥添加比例（水泥添加质量/煤泥水质量），D表示粉煤灰添加比例（粉煤灰添加质量/煤泥水质量）。
表 1 因素水平Table 1. Factor levels水平组数 A/% B C D 1 40.00 0.030 0 0.040 0 0.040 0 2 33.75 0.037 5 0.080 0 0.080 0 3 28.75 0.045 0 0.120 0 0.120 0 在室温25 ℃左右配置好材料，进行流动性测试以及试件制作；将试件放置在25 ℃、湿度90%的养护箱养护28 d，之后测试各试件的单轴抗压强度、单轴抗剪强度，测试结果见表2，极差分析结果见表3。需要说明的是：不同于水泥基材料，煤泥基充填材料强度较低无法使用维卡仪测量初凝时间，因而借鉴了高水材料的测试方法-将制备好的材料浆液置入烧杯中，静止一段时间后，将烧杯向一侧倾斜45°，当凝结无流动现象时认定为初凝（每隔1～2 min进行一次），该过程所历经时间即为初凝时间[25]。
表 2 正交试验结果Table 2. Summary of orthogonal test results试验组数 影响因素 试验结果 A/% B C D 初凝时间/min 扩散度/cm 抗压强度/MPa 抗剪强度/MPa 1 40.00 0.030 0 0.040 0 0.040 0 57.000 42.000 0.107 0.056 2 40.00 0.037 5 0.080 0 0.080 0 56.000 50.800 0.161 0.095 3 40.00 0.045 0 0.120 0 0.120 0 52.000 40.000 0.234 0.369 4 33.75 0.030 0 0.080 0 0.120 0 58.000 57.800 0.247 0.109 5 33.75 0.037 5 0.120 0 0.040 0 67.000 61.300 0.086 0.043 6 33.75 0.045 0 0.040 0 0.080 0 53.000 62.200 0.076 0.052 7 28.75 0.030 0 0.120 0 0.080 0 62.000 76.500 0.115 0.139 8 28.75 0.037 5 0.040 0 0.120 0 55.000 67.200 0.102 0.036 9 28.75 0.045 0 0.080 0 0.040 0 52.000 68.300 0.105 0.033 表 3 试验数据极差分析Table 3. Ranged analysis of test data因素 初凝时间/min 扩散度/cm A B C D A B C D k1 55.000 59.000 55.000 58.667 44.267 58.767 57.133 57.200 k2 59.333 59.333 55.333 57.000 60.433 59.767 58.967 63.167 k3 56.333 52.333 60.333 55.000 70.667 56.833 59.267 55.000 R 4.333 7.000 5.333 3.667 26.400 2.933 2.133 8.167 因素 抗压强度/MPa 抗剪强度/MPa A B C D A B C D k1 0.168 0.157 0.095 0.099 0.173 0.101 0.048 0.044 k2 0.136 0.116 0.171 0.117 0.068 0.058 0.079 0.095 k3 0.107 0.138 0.145 0.194 0.069 0.151 0.184 0.171 R 0.061 0.040 0.076 0.095 0.105 0.093 0.136 0.127 注：k为因素各个水平下指标总和的平均数；R为极差，表示因子对结果的影响幅度。 由表2可知：煤泥基充填材料初凝时间区间为52～67 min，扩散度为42.0～76.5 cm，抗压强度为0.076～0.247 MPa，抗剪强度为0.033～0.369 MPa，各参数分布范围较大。根据正交试验数据进行极差分析，得出4种因素对于试验结果的显著性排序，由表3可知：对于初凝时间，影响显著性有B>C>A>D；对于扩散度，有A>D>B>C；对于抗压强度，有D>C>A>B；对于抗剪强度，有C>D>A>B。
2. 流动性显著性分析
2.1 初凝时间影响因素
根据正交试验所得结果，所得多因素对初凝时间的影响关系如图1所示。由图1可知，各因素对初凝时间的影响程度存在差异，根据试验结果，将粉煤灰质量作为误差列，进行各水平的显著性检验，取显著性水平α=0.01、0.05、0.10、0.25。试验方差分析结果见表4。
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图 1 初凝时间与多因素的关系Figure 1. Relationship between initial setting time and multiple factors表 4 试验数据方差分析Table 4. Analysis of test data ANOVA变异来源 偏差平方和 自由度 方差 F值 Fa 显著水平 A 29.5319 2 14.766 1.187 F0.01(2,4)=18 — B 93.5319 2 46.7659 3.759 F0.05(2,4)=6.944 o C 53.5319 2 26.766 2.151 F0.1(2,4)=4.325 o 误差e1 20.2324 2 10.1162 0.813 F0.25(2,4)=2 修正误差e2 49.7643 4 12.4411 总和 196.828 注：Fa为F分布临界值；***表示影响极为显著；**表示影响较为显著；*表示影响一般显著；o表示有显著影响；—表示无显著影响。 由方差分析结果可知：B、C对初凝时间有一定影响，A和D的影响不显著，表明高水添加比例、水泥添加比例是影响初凝速度的主要因素，煤泥水百分浓度、粉煤灰添加比例影响不显著。根据F值：FB>FC，可以判断高水添加比例在设定水平内变化时所造成的影响高于水泥添加比例。
2.2 扩散度影响因素
根据正交试验所得结果，所得多因素对扩散度的影响关系如图2所示。由图2可知，各因素对扩散度的影响程度存在差异，根据试验结果分析，将水泥添加比例作为误差列，进行各水平的显著性检验，方差分析见表5。
表 5 试验数据方差分析Table 5. Analysis of test data ANOVA变异来源 偏差平方和 自由度 方差 F值 Fa 显著水平 A 1063.0560 2 531.528 99.466 F0.01(2,4)=18 *** B 13.3581 2 6.679 1.250 F0.05(2,4)=6.944 — D 107.1497 2 53.5749 10.026 F0.1(2,4)=4.325 ** 误差e1 8.0169 2 4.0085 0.750 F0.25(2,4)=2 修正误差e2 21.3750 4 5.3438 总和 1191.5810 由方差分析结果可知：A对扩散度有极为显著影响，D含量有高度显著影响，B与C基本无明显影响，表明煤泥水百分浓度、粉煤灰添加比例是影响扩散度的主要因素。
3. 强度显著性分析
3.1 抗压强度影响因素
根据正交试验所得结果，所得多因素对单轴抗压强度的影响关系如图3所示。由图3可知，各因素对抗压强度的影响程度存在差异，根据试验结果分析，将高水添加比例作为误差列，进行各水平的显著性检验，方差分析见表6。
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图 3 抗压强度与多因素的关系Figure 3. Relationship between compressive strength and multiple factors表 6 试验数据方差分析Table 6. Analysis of test data ANOVA变异来源 偏差平方和 自由度 方差 F值 Fa 显著水平 A 0.0055 2 0.0027 2.250 F0.01(2,2)=99 — C 0.0090 2 0.0045 3.750 F0.05(2,2)=19 o D 0.0154 2 0.0077 6.417 F0.1(2,2)=9 o 误差e1 0.0025 2 0.0012 1.000 F0.25(2,2)=3 总和 0.0320 由方差分析结果可知：C、D对抗压强度有一定影响，根据F值：FD>FC，可以判断粉煤灰添加比例在设定水平内变化时所造成的影响高于水泥，A与B基本无明显影响，表明水泥添加比例、粉煤灰添加比例是影响单轴抗压强度的主要因素。
3.2 抗剪强度影响因素
根据正交试验所得结果，所得多因素对单轴抗压强度的影响关系如图4所示。由图4可知，各因素对抗剪强度的影响程度存在差异，根据试验结果分析，将高水添加比例作为误差列，进行各水平的显著性检验，方差分析见表7。
表 7 试验数据方差分析Table 7. Analysis of test data ANOVA变异来源 偏差平方和 自由度 方差 F值 Fa 显著水平 A 0.0218 2 0.010 9 1.1010 F0.01(2,6)=10.925 — C 0.0303 2 0.015 2 1.5354 F0.05(2,6)=5.143 — D 0.0245 2 0.012 3 1.2424 F0.1(2,6)=3.463 — 误差e1 0.0132 2 0.006 6 0.6667 F0.25(2,6)=1.762 修正误差e2 0.0594 6 0.009 9 总和 0.09 由方差分析结果可知：在给定范围内，A、B、C、D这4个因素对抗剪强度均无明显影响。
4. 流动性与强度特性参数分析模型
4.1 单因素影响下特性参数变化
通过上述不同配比的试验，得出了各因素对材料流动性及强度的影响，分析结果如图5所示。由图5可知：初凝时间随着A、B的增加呈现先增加后减少的趋势，随着C的增加而逐渐增加，随着D的增加逐渐减少；扩散度随着A的增加而逐渐减少，随着B、D的增加先增大后减少，随着C的增加而增加；抗压强度随着A、D的增加而逐渐增大，随着B的增大先减少后增大，随着C的增大先增大后减少；抗剪强度随着A、C、D的增加而逐渐增大，随着B的增大先减少后增大。
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图 5 不同因素影响下材料流动性分析Figure 5. Analysis of material fluidity under the influence of different factors4.2 参数预测模型
对图5、图6中各影响因素与材料参数曲线进行拟合，可得到材料的煤泥水百分浓度、高水添加比例、水泥添加比例、粉煤灰添加比例与初凝时间、扩散度及抗压强度、抗剪强度的的关系式，具体见表8。
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图 6 不同因素影响下材料强度分析Figure 6. Material strength analysis under the influence of different factors表 8 拟合关系Table 8. Fitting relationship因素 指标 拟合关系式 拟合度R2 A 初凝时间 $ {t_1} = - 1\;150{A^2} + 778.5A - 72.47 $ 0.99 扩散度 $ {S_1} = 114.866 - 13.355{{\text{e}}^{A/0.24}} $ 0.99 抗压强度 $ {\sigma _{Y1}} = 0.33 - 0.497{{\text{e}}^{ - A/0.36}} $ 0.99 抗剪强度 $ {\sigma _{J1}} = {\text{15}}{\text{.22}}{A^2} - 9.537A + 1.553 $ 0.99 B 初凝时间 $ {t_2} = - 65\;190{B^2} + 4\;444B - 15.67 $ 0.99 扩散度 $ {S_2} = 59.89{{\text{e}}^{ - {{{\text{[(}}B - 0.035\;63{\text{)/}}0.040\;91{\text{]}}}^2}}} $ 0.99 抗压强度 $ {\sigma _{Y2}} = 551.1{B^2} - 42.53B + 0.936\;3 $ 0.99 抗剪强度 $ {\sigma _{J2}} = 1\;215{B^2} - 87.77B + 1.641 $ 0.99 C 初凝时间 $ {t_3} = {\text{54}}{\text{.976\;7}} + 0.023\;3{{\text{e}}^{(C - 0.04)/0.014\;7}} $ 0.99 扩散度 $ {S_3} = 59.328\;44 - 13.483\;77{{\text{e}}^{ - C/0.022\;05}} $ 0.99 抗压强度 $ {\sigma _{Y3}} = - 31.875{C^2} + 5.725C - 0.083 $ 0.99 抗剪强度 $ {\sigma _{J3}} = {\text{0}}{\text{.034\;95}} + 0.013\;1{{\text{e}}^{(C - 0.04)/0.032\;87}} $ 0.99 D 初凝时间 $ {t_4} = 67 - 6.944\;4{{\text{e}}^{D/0.219\;4}} $ 0.99 扩散度 $ {S_4} = 63.21\sin \left( {11.94D + 0.653\;6} \right) $ 0.99 抗压强度 $ {\sigma _{Y4}} = {\text{0}}{\text{.093\;8}} + 0.005\;5{{\text{e}}^{(D - 0.04)/0.027\;5}} $ 0.99 抗剪强度 $ {\sigma _{J4}} = - {\text{0}}{\text{.062\;8}} + 0.106\;8{{\text{e}}^{(D - 0.04)/0.101\;94}} $ 0.99 由表8可知，初凝时间与A、B成二次函数关系，与C、D均呈指数关系；扩散度与A、B、C均呈指数关系，与D呈三角函数关系；抗压强度与A、D均呈指数关系，与B、C呈二次多项式关系；抗剪强度与A、B呈二次多项式关系，与C、D均呈指数关系。
4.3 预测模型构建
由表8初凝时间、扩散度、抗剪强度及抗压强度与各因素的关系式，结合多元线性模型构建原则，可建立材料特性参数的综合预测模型，见式（1）。
$$ \left\{ \begin{gathered} t = {a_1}{t_1} + {a_2}{t_2} + {a_3}{t_3} + {a_4}{t_4} + {a_5} \\ S = {b_1}{S_1} + {b_2}{S_2} + {b_3}{S_3} + {b_4}{S_4} + b{}_5 \\ {\sigma _Y} = {c_1}{\sigma _{Y1}} + {c_2}{\sigma _{Y2}} + {c_3}{\sigma _{Y3}} + {c_4}{\sigma _{Y4}} + {c_5} \\ {\sigma _J} = {d_1}{\sigma _{J1}} + {d_2}{\sigma _{J2}} + {d_3}{\sigma _{J3}} + {d_4}{\sigma _{J4}} + {d_5} \\ \end{gathered} \right. $$ (1) 式中：t为4种因素共同影响下煤泥基胶结充填材料的初凝时间，s；S为4种因素共同影响下煤泥基胶结充填材料的扩散度，cm；σY为4种因素共同影响下煤泥基胶结充填材料的抗压强度，MPa；σJ为4种因素共同影响下煤泥基胶结充填材料的抗剪强度，MPa；a1、a2、a3、a4、a5、b1、b2、b3、b4、b5、c1、c2、c3、c4、c5、d1、d2、d3、d4、d5为系数。
根据大量的特性参数测试结果，对式（1）进行多元线性回归，可得到初凝时间、扩散度、抗剪强度及抗压强度与各因素的关系，见式（2）。
$$ \left\{ \begin{gathered} t = 0.167{t_1} + 0.898{t_2} + 0.831{t_3} + 0.942{t_4} - 106.076 \\ S = 0.966{S_1} + 0.355{S_2} + 0.232{S_3} + 1.465{S_4} - 119.329 \\ {\sigma _Y} = 1.068{\sigma _{Y1}} + 1.020{\sigma _{Y2}} + 1.058{\sigma _{Y3}} + 1.063{\sigma _{Y4}} - 0.436 \\ {\sigma _J} = 1.022{\sigma _{J1}} + 1.017{\sigma _{J2}} + 0.974{\sigma _{J3}} + 1.025{\sigma _{J4}} - 0.316 \\ \end{gathered} \right. $$ (2) 4.4 综合预测模型校验
对上述公式进行了校验，选取了3组配比（表9）配置充填材料浆液及试件，并进行初凝时间、扩散度、抗压强度、抗剪强度的实测，将根据预计模型得到预测值数据与试验值数据进行对比，对比表及误差见表10。
表 9 校验方案设计Table 9. Fitting relationship测试件编号 .煤泥水百分
浓度A/%高水添加
比例B水泥添加
比例C粉煤灰添加
比例DTEST-1 35.00 0.035 0 0.100 0 0.100 0 TEST-2 30.00 0.028 0 0.050 0 0.050 0 TEST-3 39.00 0.025 0 0.050 0 0.100 0 表 10 校验结果分析Table 10. Fitting relationship试件编号 材料 初凝时
间/min扩散
度/cm抗压强
度/MPa抗剪强
度/MPaTEST-1 预测值 57.290 60.200 0.173 0.056 试验值 60.010 63.980 0.159 0.062 误差/% 4.53 5.91 8.74 9.68 TEST-2 预测值 55.900 69.900 0.105 0.095 试验值 52.060 63.900 0.096 0.086 误差/% 7.38 9.39 9.69 10.47 TEST-3 预测值 50.910 51.330 0.241 0.370 试验值 48.330 53.710 0.263 0.411 误差/% 5.34 4.43 8.52 9.88 分析可知：根据该综合预测模型计算得到的参数与试验测试值较吻合，各项指标相对误差区间为4.43%～10.47% ，平均7.83% 。
5. 结 论
1）应用正交试验的方法，以煤泥水百分浓度、高水添加比例、水泥添加比例、粉煤灰添加比例为4个因素，每个因素设置3个水平，进行了流动性及强度特性正交测试后，分析得出煤泥基预充填材料的初凝时间分布在52～57 min，扩散度分布在42.0～76.5 cm，抗压强度分布在0.076～0.247 MPa，抗剪强度分布在0.033～0.139 MPa。
2）对于初凝时间，影响显著性排序为B>C>A>D，高水添加比例、水泥添加比例是影响初凝速度的主要因素；对于扩散度，影响显著性排序为A>D>B>C，表明煤泥水百分浓度、粉煤灰添加比例是影响扩散度的主要因素；对于抗压强度，影响显著性排序为D>C>A>B，水泥添加比例、粉煤灰添加比例是影响单轴抗压强度的主要因素；对于抗剪强度，影响显著性排序为C>D>A>B，且4种因素显著性均较低。
3）拟合出了A、B、C、D与流动性指标及强度指标的数学关系式，初凝时间与A、B成二次函数关系、与C、D均呈指数关系；扩散度与A、B、C均呈指数关系，与D呈三角函数关系；抗压强度与A、D均呈指数关系，与B、C呈二次多项式关系；抗剪强度与A、B呈二次多项式关系、与C、D均呈指数关系；构建初了4种原材料不同配比的特性参数综合预测模型，并进行了校验。
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图 1 近年煤炭与天然气消费总量及占比
Figure 1. Total consumption and proportion of coal and natural gas in recent years
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图 2 煤与天然气开采面临的挑战及解决途径
Figure 2. Challenges and solution of coal and natural gas extraction
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图 6 工作面与天然气井距离缩进时应力重叠情况
Figure 6. Stress overlap when distance between working face and natural gas well is indented
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图 7 “围岩–水泥环–套管”组合体耦合损伤模型
Figure 7. Stress overlap during workover and gas well distance indentation
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图 9 天然气井近场煤柱留设技术构想
Figure 9. Technical concept of small coal pillar retention in near field of natural gas well
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图 12 废弃井处理方法示意
Figure 12. Schematic diagram of the disposal method of the abandoned well
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图 15 透明地质示意与生产信息监测
Figure 15. Transparent geological diagram and production information monitoring map
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图 16 透明地质与生产信息动态监测系统构想
Figure 16. Concept of dynamic monitoring system for transparent geological and production information
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图 17 协同区安全监测系统构想
Figure 17. Concept of safety monitoring system in the coordination area
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图 18 煤矿工作面与天然气井位置示意
Figure 18. Schematic diagram of coal mine working face and gas well location
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图 19 煤炭工作面开采套管应力峰值变化
Figure 19. Peak stress variation in casing for coal working face mining
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图 20 天然气设施稳定性控制技术体系
Figure 20. Stability control technology system for natural gas facilities
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