This paper presents a study assessing potential factors and migration paths of methane emissions experienced in a room-and-pillar mine in Lower Kittanning coal, Indiana County, Pennsylvania. Methane emissions were not excessive at idle mining areas, but significant methane was measured during coal mining and loading. Although methane concentrations in the mine did not exceed 1% limit during operation due to the presence of adequate dilution airflow, the source of methane and its migration into the mine was still a concern. In the course of this study, structural and depositional properties of the area were evaluated to assess complexity and sealing capacity of roof rocks. Composition, gas content, and permeability of Lower Kittanning coal, results of flotation tests, and geochemistry of groundwater obtained from observation boreholes were studied to understand the properties of coal and potential effects of old abandoned mines within the same area. These data were combined with the data obtained from exploration boreholes, such as depths, elevations, thicknesses, ash content, and heat value of coal. Univariate statistical and principal component analyses (PCA), as well as geostatistical simulations and co-simulations, were performed on various spatial attributes to reveal interrelationships and to establish area-wide distributions. These studies helped in analyzing groundwater quality and determining gas-in-place (GIP) of the Lower Kittanning seam. Furthermore, groundwater level and head on the Lower Kittanning coal were modeled and flow gradients within the study area were examined. Modeling results were interpreted with the structural geology of the Allegheny Group of formations above the Lower Kittanning coal to understand the potential source of gas and its migration paths. Analyses suggested that the source of methane was likely the overlying seams such as the Middle and Upper Kittanning coals and Freeport seams of the Allegheny Group. Simulated ground-water water elevations, gradients of groundwater flow, and the presence of recharge and discharge locations at very close proximity to the mine indicated that methane likely was carried with groundwater towards the mine entries. Existing fractures within the overlying strata and their orientation due to the geologic conditions of the area, and activation of slickensides between shale and sandstones due to differential compaction during mining, were interpreted as the potential flow paths.

中文翻译：

---

下基坦宁煤矿甲烷排放的地质和水动力控制分析

本文介绍了一项研究，评估了宾夕法尼亚州印第安纳县下基坦宁煤矿的一个房柱式矿井中甲烷排放的潜在因素和迁移路径。闲置矿区的甲烷排放量并不超标，但在煤炭开采和装载过程中测量到了大量的甲烷。尽管由于存在足够的稀释气流，矿井在运营期间的甲烷浓度没有超过 1% 的限制，但甲烷的来源及其向矿井的迁移仍然是一个问题。在这项研究过程中，对该地区的结构和沉积特性进行了评估，以评估顶板岩石的复杂性和密封能力。下基坦宁煤的成分、含气量和渗透率，浮选试验结果，研究了从观测钻孔中获得的地下水的地球化学和地球化学，以了解煤炭的性质和同一地区旧废弃矿井的潜在影响。这些数据与从勘探钻孔中获得的数据相结合，例如深度、海拔、厚度、灰分和煤的热值。对各种空间属性进行了单变量统计和主成分分析 (PCA) 以及地质统计模拟和联合模拟，以揭示相互关系并建立区域范围的分布。这些研究有助于分析地下水质量并确定下基坦宁煤层的原位气体 (GIP)。此外，对下基坦宁煤层的地下水位和水头进行了建模，并检查了研究区域内的流动梯度。使用下基坦宁煤层上方的阿勒格尼组地层的构造地质解释建模结果，以了解潜在的天然气来源及其迁移路径。分析表明，甲烷的来源可能是上覆煤层，如阿勒格尼群的中、上基坦宁煤层和弗里波特煤层。模拟的地下水水位、地下水流梯度以及非常靠近矿井的补给和排放位置的存在表明，甲烷很可能随地下水一起流向矿井入口。由于该地区的地质条件，上覆地层内的现有裂缝及其方向，以及由于开采过程中的压实差异导致页岩和砂岩之间的滑层活化，