Karacan C Özgen
NIOSH, Office of Mine Safety and Health Research, Pittsburgh, PA 15236, United States.
Int J Coal Geol. 2013 Jul 30;114:96-113. doi: 10.1016/j.coal.2013.02.011.
Coal seam degasification and its efficiency are directly related to the safety of coal mining. Degasification activities in the Black Warrior basin started in the early 1980s by using vertical boreholes. Although the Blue Creek seam, which is part of the Mary Lee coal group, has been the main seam of interest for coal mining, vertical wellbores have also been completed in the Pratt, Mary Lee, and Black Creek coal groups of the Upper Pottsville formation to degasify multiple seams. Currently, the Blue Creek seam is further degasified 2-3 years in advance of mining using in-seam horizontal boreholes to ensure safe mining. The studied location in this work is located between Tuscaloosa and Jefferson counties in Alabama and was degasified using 81 vertical boreholes, some of which are still active. When the current long mine expanded its operation into this area in 2009, horizontal boreholes were also drilled in advance of mining for further degasification of only the Blue Creek seam to ensure a safe and a productive operation. This paper presents an integrated study and a methodology to combine history matching results from vertical boreholes with production modeling of horizontal boreholes using geostatistical simulation to evaluate spatial effectiveness of in-seam boreholes in reducing gas-in-place (GIP). Results in this study showed that in-seam wells' boreholes had an estimated effective drainage area of 2050 acres with cumulative production of 604 MMscf methane during ~2 years of operation. With horizontal borehole production, GIP in the Blue Creek seam decreased from an average of 1.52 MMscf to 1.23 MMscf per acre. It was also shown that effective gas flow capacity, which was independently modeled using vertical borehole data, affected horizontal borehole production. GIP and effective gas flow capacity of coal seam gas were also used to predict remaining gas potential for the Blue Creek seam.
煤层瓦斯抽采及其效率与煤炭开采安全直接相关。黑勇士盆地的瓦斯抽采活动始于20世纪80年代初，当时采用的是垂直钻孔。虽然玛丽·李煤组中的蓝溪煤层一直是煤炭开采关注的主要煤层，但在上波茨维尔组的普拉特、玛丽·李和黑溪煤组中也完成了垂直钻孔，以对多个煤层进行瓦斯抽采。目前，蓝溪煤层在开采前2 - 3年采用煤层内水平钻孔进一步进行瓦斯抽采，以确保安全开采。本研究的地点位于阿拉巴马州塔斯卡卢萨县和杰斐逊县之间，曾使用81个垂直钻孔进行瓦斯抽采，其中一些钻孔仍在使用。当当前的长壁煤矿在2009年将其作业扩展到该区域时，还在开采前钻了水平钻孔，仅对蓝溪煤层进行进一步瓦斯抽采，以确保安全高效作业。本文提出了一项综合研究及一种方法，即利用地质统计模拟将垂直钻孔的历史拟合结果与水平钻孔的生产建模相结合，以评估煤层钻孔在减少原地瓦斯量（GIP）方面的空间有效性。本研究结果表明，煤层内钻孔的有效排水面积估计为2050英亩，在约2年的作业期间累计产甲烷6.04亿标准立方英尺。随着水平钻孔的开采，蓝溪煤层的原地瓦斯量从平均每英亩152万标准立方英尺降至123万标准立方英尺。研究还表明，利用垂直钻孔数据独立建模的有效瓦斯流动能力会影响水平钻孔的产量。煤层气的原地瓦斯量和有效瓦斯流动能力也被用于预测蓝溪煤层的剩余瓦斯潜力。
