Gob gas ventholes (GGVs) are used to control methane inflows into a longwall mining operation by capturing the gas within the overlying fractured strata before it enters the work environment. Using geostatistical co-simulation techniques, this paper maps the parameters of their rate decline behaviors across the study area, a longwall mine in the Northern Appalachian basin. Geostatistical gas-in-place (GIP) simulations were performed, using data from 64 exploration boreholes, and GIP data were mapped within the fractured zone of the study area. In addition, methane flowrates monitored from 10 GGVs were analyzed using decline curve analyses (DCA) techniques to determine parameters of decline rates. Surface elevation showed the most influence on methane production from GGVs and thus was used to investigate its relation with DCA parameters using correlation techniques on normal-scored data. Geostatistical analysis was pursued using sequential Gaussian co-simulation with surface elevation as the secondary variable and with DCA parameters as the primary variables. The primary DCA variables were effective percentage decline rate, rate at production start, rate at the beginning of forecast period, and production end duration. Co-simulation results were presented to visualize decline parameters at an area-wide scale. Wells located at lower elevations, i.e., at the bottom of valleys, tend to perform better in terms of their rate declines compared to those at higher elevations. These results were used to calculate drainage radii of GGVs using GIP realizations. The calculated drainage radii are close to ones predicted by pressure transient tests.

中文翻译：

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长壁采空区瓦斯通风孔速率下降参数的连续高斯联合模拟

采空区瓦斯通风孔 (GGV) 用于控制甲烷流入长壁采矿作业，方法是在气体进入工作环境之前捕获上覆断裂地层内的气体。本文使用地质统计联合模拟技术绘制了整个研究区域（阿巴拉契亚盆地北部的一个长壁矿）的速率下降行为参数。使用来自 64 个勘探钻孔的数据进行了地质统计原位气体 (GIP) 模拟，并将 GIP 数据绘制在研究区的断裂带内。此外，使用递减曲线分析 (DCA) 技术分析了从 10 辆 GGV 监测到的甲烷流量，以确定递减率参数。地表高程对 GGV 产生的甲烷影响最大，因此用于使用正态评分数据的相关技术研究其与 DCA 参数的关系。使用顺序高斯联合模拟进行地统计分析，表面高程作为次要变量，DCA 参数作为主要变量。主要 DCA 变量是有效百分比下降率、生产开始率、预测期开始率和生产结束持续时间。呈现联合仿真结果以在区域范围内可视化衰减参数。与位于较高海拔的井相比，位于较低海拔（即山谷底部）的井在其速率下降方面往往表现更好。这些结果用于使用 GIP 实现计算 GGV 的排水半径。计算的排水半径与压力瞬变试验预测的接近。