Analysis of gob gas venthole production performances for strata gas control in longwall mining

Abstract

Longwall mining of coal seams affects a large area of overburden by deforming it and creating stress-relief fractures, as well as bedding plane separations, as the mining face progresses. Stress-relief fractures and bedding plane separations are recognized as major pathways for gas migration from gas-bearing strata into sealed and active areas of the mines. In order for strata gas not to enter and inundate the ventilation system of a mine, gob gas ventholes (GGVs) can be used as a methane control measure. The aim of this paper is to analyze production performances of GGVs drilled over a longwall panel. These boreholes were drilled to control methane emissions from the Pratt group of coals due to stress-relief fracturing and bedding plane separations into a longwall mine operating in the Mary Lee/Blue Creek coal seam of the Upper Pottsville Formation in the Black Warrior Basin, Alabama. During the course of the study, Pratt coal's reservoir properties were integrated with production data of the GGVs. These data were analyzed by using material balance techniques to estimate radius of influence of GGVs, gas-in-place and coal pressures, as well as their variations during mining. The results show that the GGVs drilled to extract gas from the stress-relief zone of the Pratt coal interval is highly effective in removing gas from the Upper Pottsville Formation. The radii of influence of the GGVs were in the order of 330–380 m, exceeding the widths of the panels, due to bedding plane separations and stress relieved by fracturing. Material balance analyses indicated that the initial pressure of the Pratt coals, which was around 648 KPa when longwall mining started, decreased to approximately 150 KPa as the result of strata fracturing and production of released gas. Approximately 70% of the initial gas-in-place within the area of influence of the GGVs was captured during a period of one year.

Grade Distribution Modeling within the Bauxite Seams of the Wachangping Mine, China, Using a Multi-Step Interpolation Algorithm

“…Longwall mining technology, a widely-used method for mechanized continuous and large-scale extraction of underground coal [21][22][23][24][25][26], was progressively introduced for extracting an underground mineral seam, for example, a bauxite seam [27,28]. In the longwall mining panel, in general, the two roadways at both sides of the panel, called the tail roadway and the head roadway, are excavated to provide ventilation and transportation for mining operations.…”

Numerical Simulation of Parameters Optimization for Goaf Gas Boreholes

“…Many foreign scholars have done a lot of research about gas disaster prevention, gas drainage in coal mine goaf, etc [9][10][11][12][13][14][15][16]. Many other scholars have also examined the effects of ground boreholes [17][18][19][20].…”

Parametric Analysis of Slotting Operation Induced Failure Zones to Stimulate Low Permeability Coal Seams

“…Gas emission and flow patterns in thick seam mining have been investigated through extensive field measurements and numerical simulations, which provides essential guidance for gas drainage design in ultra-thick coal seams (Si 2015;Si et al 2015a, b). In the US, goaf gas venthole production was found to be largely enhanced due to stress-relief fracturing and bedding plane separation during the period of longwall face advance (Karacan 2015).…”