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Hydraulic conductivity changes and influencing factors in longwall overburden determined by slug tests in gob gas ventholes.

Authors
Karacan-CÍ; Goodman-G
Source
Int J Rock Mech Min Sci 2009 Oct; 46(7):1162-1174
NIOSHTIC No.
20035848
Abstract
This study presents the results of core-log analyses from the exploration boreholes, the analyses of face advance rates, and the results of downhole monitoring studies performed in gob gas ventholes for calculation of changes in hydraulic properties in the longwall overburden at a mine site in southwestern (SW) Pennsylvania section of Northern Appalachian Basin. In the first part of the study, coal measure rocks in overburden strata were analyzed and the locations where possible fractures and bedding plane separations would occur were evaluated. In the second part, the hydraulic conductivities were computed by two different slug test analyses methods using the water level changes measured in gob gas ventholes as longwall face approached. Hydraulic conductivities were analyzed with respect to the changes in overburden depth, the locations of the borehole, and mine face advance rates. These data were used to interpret the potential productivities of the gob gas ventholes as a result of fracturing and changes in hydraulic conductivities. The general results showed that the probability of fracturing and bedding plane separations in the overburden increase between strong and weak rock interfaces. Also, the probability of bedding plane separations increases as the interface is close to the extracted coal seam. Evaluation of slug tests showed that the hydraulic conductivity developments in the boreholes and their potential production performances are affected by the underground strata and the roof materials. In situations where the roof material is stiff and thick, the development of high permeability fractures around the borehole will be less. Results also indicated that borehole location with respect to face position affects the fracturing time and permeability evolution as well. Greater overburden depths generally cause earlier fracturing as longwall face approaches, but eventually result in lower hydraulic conductivities and potentially less effective boreholes. Increasing mining rates also resulted in generally lower hydraulic conductivities in the overburden. The results of this study were intended to improve the interpretation of gob gas venthole performance and to provide better siting of these boreholes.
Keywords
Mining-industry; Underground-mining; Longwall-mining; Coal-mining; Methane-control; Methane-drainage; Control-technology; Engineering-controls; Author Keywords: Longwall mining; Methane control; Gob gas ventholes; Slug tests; Hydraulic conductivity
Contact
C. Ozgen Karacan, National Institute for Occupational Safety and Health (NIOSH), Pittsburgh Research Laboratory, PO Box 18070, Pittsburgh, PA 15236, USA
CAS No.
74-82-8
Publication Date
20091001
Document Type
Journal Article
Email Address
cok6@cdc.gov
Fiscal Year
2010
NTIS Accession No.
NTIS Price
Issue of Publication
7
ISSN
1365-1609
NIOSH Division
PRL
Priority Area
Mining
Source Name
International Journal of Rock Mechanics and Mining Sciences
State
PA
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