Karacan C Özgen, Olea Ricardo A, Goodman Gerrit
NIOSH, Office of Mine Safety and Health Research, Pittsburgh, PA, United States.
USGS, Eastern Energy Resources, Reston, VA, United States.
Int J Coal Geol. 2012 Feb 1;90-91:50-71. doi: 10.1016/j.coal.2011.10.010.
Determination of the size of the gas emission zone, the locations of gas sources within, and especially the amount of gas retained in those zones is one of the most important steps for designing a successful methane control strategy and an efficient ventilation system in longwall coal mining. The formation of the gas emission zone and the potential amount of gas-in-place (GIP) that might be available for migration into a mine are factors of local geology and rock properties that usually show spatial variability in continuity and may also show geometric anisotropy. Geostatistical methods are used here for modeling and prediction of gas amounts and for assessing their associated uncertainty in gas emission zones of longwall mines for methane control. This study used core data obtained from 276 vertical exploration boreholes drilled from the surface to the bottom of the Pittsburgh coal seam in a mining district in the Northern Appalachian basin. After identifying important coal and non-coal layers for the gas emission zone, univariate statistical and semivariogram analyses were conducted for data from different formations to define the distribution and continuity of various attributes. Sequential simulations performed stochastic assessment of these attributes, such as gas content, strata thickness, and strata displacement. These analyses were followed by calculations of gas-in-place and their uncertainties in the Pittsburgh seam caved zone and fractured zone of longwall mines in this mining district. Grid blanking was used to isolate the volume over the actual panels from the entire modeled district and to calculate gas amounts that were directly related to the emissions in longwall mines. Results indicated that gas-in-place in the Pittsburgh seam, in the caved zone and in the fractured zone, as well as displacements in major rock units, showed spatial correlations that could be modeled and estimated using geostatistical methods. This study showed that GIP volumes may change up to 3 MMscf per acre and, in a multi-panel district, may total 9 Bcf of methane within the gas emission zone. Therefore, ventilation and gas capture systems should be designed accordingly. In addition, rock displacements within the gas emission zone are spatially distributed. From an engineering and practical point of view, spatial distributions of GIP and distributions of rock displacements should be correlated with in-mine emissions and gob gas venthole productions.
确定瓦斯排放区的大小、区内瓦斯源的位置，尤其是这些区域内滞留的瓦斯量，是在长壁采煤中设计成功的瓦斯控制策略和高效通风系统的最重要步骤之一。瓦斯排放区的形成以及可能迁移到矿井中的原地瓦斯量（GIP）是当地地质和岩石特性的因素，这些因素通常在连续性上表现出空间变异性，并且也可能表现出几何各向异性。本文采用地质统计学方法对长壁矿井瓦斯排放区的瓦斯量进行建模和预测，并评估其相关不确定性，以进行甲烷控制。本研究使用了从北阿巴拉契亚盆地某矿区匹兹堡煤层地表至底部钻取的276个垂直勘探钻孔获得的岩芯数据。在确定了瓦斯排放区的重要煤层和非煤层之后，对来自不同地层的数据进行了单变量统计和半变异函数分析，以确定各种属性的分布和连续性。序贯模拟对这些属性进行了随机评估，如瓦斯含量、地层厚度和地层位移。随后，对该矿区长壁矿井匹兹堡煤层垮落带和裂隙带的原地瓦斯量及其不确定性进行了计算。采用网格消隐法将实际采场上方的体积与整个建模区域隔离开来，并计算与长壁矿井瓦斯排放直接相关的瓦斯量。结果表明，匹兹堡煤层、垮落带和裂隙带的原地瓦斯量以及主要岩石单元的位移表现出空间相关性，可以用地质统计学方法进行建模和估计。本研究表明，原地瓦斯量每英亩可能变化高达300万标准立方英尺，在多采场区域，瓦斯排放区内的甲烷总量可能达到90亿立方英尺。因此，应相应地设计通风和瓦斯捕获系统。此外，瓦斯排放区内的岩石位移是空间分布的。从工程和实际角度来看，原地瓦斯量的空间分布和岩石位移的分布应与井下瓦斯排放和采空区瓦斯钻孔产量相关联。
