Geology Reference
In-Depth Information
SIDEBAR 5.2 HIGH-FREQUENCY SEISMIC CASE HISTORY
In some cases it is possible to infer the presence of mines from
decreased signal strength of seismic reflections from layers beneath the
coal, which in this instance is about 550 feet deep. The vertical axis is in
seconds of two-way reflection time, and the coal reflection is present at
about 0.13 seconds. In contrast to the Pittsburg, Kansas, example
( Sidebar 5.3 ), it is not possible to distinguish individual rooms and pillars
in this figure. It is possible to see the general location of the mined area
and to define the mine boundaries to within about 65 feet (Waters, 1987).
The location of the mine near the center of the seismic section is indicated
by a “faded” area except where the coal reflection is present. The coal
reflection also has a lower frequency appearance in the mined area than
in the unmined area.
Seismic detection of mine works at 548-foot depth. Courtesy of
CONOCO, Inc.
HYDRAULIC TESTING
A potential technique that may aid in determining the extent of a coal
outcrop barrier or coal seam is to test a questionable area hydraulically. This is
accomplished by conducting hydraulic packer tests in boreholes drilled into the
coal (Harlow and LeCain, 1991; Minus, 1993). Tested intervals where the
permeability of the coal is significantly higher than the statistical range for
confined coal seams would be suspected of having void space within the
smaller surface volume of unconfined coal. The increased stress could result
Search WWH ::




Custom Search