Abstract
Considerable methane resources exist in abandoned coal mines. However, methane extraction from abandoned mines in China is still in the exploratory stage. This study presents technologies and engineering practices suitable for the extraction of gob methane from abandoned mines using surface vertical wells, including methane drainage systems, well bottom locations, and an intermittent drainage method. Seven surface wells in the Yongan abandoned mine in China were selected for gob methane extraction. Field results showed that the methane volumetric flow rate of a well whose bottom was close to the gob bottom was 2.5 times greater than that of a well with a bottom located in the gob fractured zone. Moreover, intermittent extraction can enable a well to extract methane cyclically at a high volumetric flow rate. A well drilled mistakenly into a coal pillar can be reused through hydraulic fracturing. The overall maximum methane volumetric flow rate, average concentration, and extraction span were 210 m3/h, 83%, and 1100 days, respectively.
Highlights
Coal mines are abandoned when they complete their useful economic life, and abandoned underground mines can be found in every country that has coal resources [1]
Before intermittent extraction A er intermittent extraction. This suggests that the intermittent extraction method, that is, extraction-pause-extraction, can enable the well to continue extracting at a high methane volumetric flow rate and significantly reduce energy consumption, thereby improving the efficiency of the well
It is necessary to extract the methane from abandoned gobs, which can contain considerable methane resources
Summary
Coal mines are abandoned when they complete their useful economic life, and abandoned underground mines can be found in every country that has coal resources [1]. Minable Partially minable Partially minable directional boreholes for methane drainage in adjacent seams during mining These studies have all focused primarily on the efficient extraction of stress-relief methane with surface wells. Existing studies did not consider some unique characteristics of abandoned mines in China, such as residual methane pressure, overlying strata development, and aquifers. This paper presents and describes in detail the technologies of the methane extraction of abandoned mines using surface wells, especially considering those unique characteristics of abandoned mines in China. These technologies were verified with a field engineering trial at the Yongan abandoned mine in China
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