An investigation into gas drainage performance of long-reach directional boreholes in underground longwall coal mining
File(s)
Author(s)
Yuan, Xuehao
Type
Thesis
Abstract
The presence of coal seam gas presents a longstanding risk for mining safety and production efficiency in underground coal mines. The increase of formation pressure and gas content with increasing mining depth further intensifies this challenge.
In European coal mines, drilling cross-measure boreholes, targeting seams above, has been implemented with some effectiveness. The current technical solutions applied in drainage strategy are not capable of providing the increase in methane extraction that is needed in many mines. It is, therefore, necessary to develop new methane drainage strategies. The application of long reach underground directional boreholes drilled into seams above the mined coal seams provides a potential alternative for gas drainage practices at coal mines.
The objective of this PhD research was to investigate the drainage performance of long-reach directional boreholes drilled in the strata above producing longwall coal faces stimulated by undermining, and further optimise the borehole configuration.
A comprehensive review of gas drainage methods used in longwall mining and the theories on stress and permeability changes around a working longwall face was carried out first. The state-of-the-art coupled geomechanical and flow model developed earlier at Imperial College was then used to assess the methane drainage performance of long-reach directional boreholes drilled underground.
The results suggested that gas captured by each borehole from the overlying seams is controlled by the prevailing local permeability as well as the distance to the mined seam. The peak drainage rate occurs when the borehole is about 30 m behind the face-line, corresponding to the maximum permeability enhancement.
The performance of the long reach horizontal boreholes was also compared with that of different variants of cross measure boreholes commonly used by the industry. The results have suggested that long reach boreholes achieve a greater drainage efficiency and utilisation rate of the borehole overall.
In European coal mines, drilling cross-measure boreholes, targeting seams above, has been implemented with some effectiveness. The current technical solutions applied in drainage strategy are not capable of providing the increase in methane extraction that is needed in many mines. It is, therefore, necessary to develop new methane drainage strategies. The application of long reach underground directional boreholes drilled into seams above the mined coal seams provides a potential alternative for gas drainage practices at coal mines.
The objective of this PhD research was to investigate the drainage performance of long-reach directional boreholes drilled in the strata above producing longwall coal faces stimulated by undermining, and further optimise the borehole configuration.
A comprehensive review of gas drainage methods used in longwall mining and the theories on stress and permeability changes around a working longwall face was carried out first. The state-of-the-art coupled geomechanical and flow model developed earlier at Imperial College was then used to assess the methane drainage performance of long-reach directional boreholes drilled underground.
The results suggested that gas captured by each borehole from the overlying seams is controlled by the prevailing local permeability as well as the distance to the mined seam. The peak drainage rate occurs when the borehole is about 30 m behind the face-line, corresponding to the maximum permeability enhancement.
The performance of the long reach horizontal boreholes was also compared with that of different variants of cross measure boreholes commonly used by the industry. The results have suggested that long reach boreholes achieve a greater drainage efficiency and utilisation rate of the borehole overall.
Version
Open Access
Date Issued
2023-08-22
Date Awarded
01/12/2023
License URL
Advisor
Durucan, Sevket
Shi, Ji-Quan
Cao, Wenzhuo
Sponsor
Research Fund for Coal and Steel
Grant Number
847338 — DD-MET — RFCS-2018/RFCS-2018
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)