Coal seam degasification and its success are important for controlling methane, and thus for the health and safety of coal miners. During the course of degasification, properties of coal seams change. Thus, the changes in coal reservoir conditions and in-place gas content as well as methane emission potential into mines should be evaluated by examining time-dependent changes and the presence of major heterogeneities and geological discontinuities in the field. In this work, time-lapsed reservoir and fluid storage properties of the New Castle coal seam, Mary Lee/Blue Creek seam, and Jagger seam of Black Warrior Basin, Alabama, were determined from gas and water production history matching and production forecasting of vertical degasification wellbores. These properties were combined with isotherm and other important data to compute gas-in-place (GIP) and its change with time at borehole locations. Time-lapsed training images (TIs) of GIP and GIP difference corresponding to each coal and date were generated by using these point-wise data and Voronoi decomposition on the TI grid, which included faults as discontinuities for expansion of Voronoi regions. Filter-based multiple-point geostatistical simulations, which were preferred in this study due to anisotropies and discontinuities in the area, were used to predict time-lapsed GIP distributions within the study area. Performed simulations were used for mapping spatial time-lapsed methane quantities as well as their uncertainties within the study area.The systematic approach presented in this paper is the first time in literature that history matching, TIs of GIPs and filter simulations are used for degasification performance evaluation and for assessing GIP for mining safety. Results from this study showed that using production history matching of coalbed methane wells to determine time-lapsed reservoir data could be used to compute spatial GIP and representative GIP TIs generated through Voronoi decomposition. Furthermore, performing filter simulations using point-wise data and TIs could be used to predict methane quantity in coal seams subjected to degasification. During the course of the study, it was shown that the material balance of gas produced by wellbores and the GIP reductions in coal seams predicted using filter simulations compared very well, showing the success of filter simulations for continuous variables in this case study. Quantitative results from filter simulations of GIP within the studied area briefly showed that GIP was reduced from an initial ∼73 Bcf (median) to ∼46 Bcf (2011), representing a 37 % decrease and varying spatially through degasification. It is forecasted that there will be an additional ∼2 Bcf reduction in methane quantity between 2011 and 2015. This study and presented results showed that the applied methodology and utilized techniques can be used to map GIP and its change within coal seams after degasification, which can further be used for ventilation design for methane control in coal mines.

中文翻译：

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使用基于过滤器的多点地统计模拟，对煤层的Mary Lee组中的甲烷量进行时移分析。

煤层脱气及其成功对控制甲烷，从而对煤矿工人的健康和安全至关重要。在脱气过程中，煤层的性质发生变化。因此，应通过检查随时间变化以及田间主要异质性和地质不连续性来评估煤储层条件和就地瓦斯含量的变化以及排入煤矿的甲烷的潜力。在这项工作中，阿拉巴马州黑武士盆地的新城堡煤层，玛丽·李/蓝溪煤层和贾格尔煤层的随时间推移的储层和流体储藏特性，是根据天然气和水的生产历史匹配以及垂直井的产量预测确定的。脱气井筒。将这些属性与等温线和其他重要数据相结合，以计算就地气体（GIP）及其在井眼位置随时间的变化。通过使用这些点数据和TI网格上的Voronoi分解，生成了与每种煤和日期对应的GIP和GIP差异的延时训练图像（TIs），其中包括断层作为Voronoi区域扩展的不连续性。基于过滤器的多点地统计模拟，由于该区域的各向异性和不连续性，在本研究中被优先采用，用于预测研究区域内随时间推移的GIP分布。进行的模拟用于绘制研究区内甲烷随时间推移的空间量及其不确定性。本文介绍的系统方法是文献中首次将历史记录匹配，GIP的TI和过滤器模拟用于脱气性能评估和评估GIP的采矿安全性。这项研究的结果表明，使用煤层气井的生产历史记录匹配来确定延时的储层数据，可以用来计算空间GIP和通过Voronoi分解产生的代表性GIP TI。此外，使用逐点数据和TI执行过滤器模拟可用于预测经过脱气的煤层中的甲烷量。在研究过程中，结果表明，使用过滤器模拟预测的井筒产生的气体的物质平衡和煤层的GIP降低比较好，展示了此案例研究中连续变量过滤器仿真的成功。来自研究区域内GIP过滤器模拟的定量结果简要表明，GIP从最初的约73 Bcf（中位数）降低至约46 Bcf（2011），代表减少了37％，并通过脱气而在空间上变化。预计2011年至2015年间，甲烷量将再减少约2 Bcf。该研究和结果表明，所应用的方法和所采用的技术可用于绘制脱气后煤层中的GIP及其变化图，可进一步用于煤矿的甲烷控制通风设计。来自研究区域内GIP过滤器模拟的定量结果简要表明，GIP从最初的约73 Bcf（中位数）降低至约46 Bcf（2011），代表减少了37％，并通过脱气而在空间上变化。预计2011年至2015年间，甲烷量将再减少约2 Bcf。该研究和结果表明，所应用的方法和所采用的技术可用于绘制脱气后煤层中的GIP及其变化图，可进一步用于煤矿的甲烷控制通风设计。来自研究区域内GIP过滤器模拟的定量结果简要表明，GIP从最初的约73 Bcf（中位数）降低至约46 Bcf（2011），代表减少了37％，并通过脱气而在空间上变化。预计2011年至2015年间，甲烷量将再减少约2 Bcf。该研究和结果表明，所应用的方法和所采用的技术可用于绘制脱气后煤层中的GIP及其变化图，可进一步用于煤矿的甲烷控制通风设计。