8
Right was in an area of thick shale roof, a 20 to 30 ft thick
layer. These evaluations will be expanded to other longwall
panels at the site.
The GGV production evaluations can be made on the
basis of cumulative gas production per unit time. Typically,
with a slower rate of advance, gas emissions will bleed off
and diminish gas production from GGVs on the panel. The
wider face on 1 South compared to 31 Right (1000 ft com-
pared to 705 ft) can advance at a slower rate to produce the
same quantity of coal.
The high gas emission rates on panel 31 Right were
focused on the first half of the panel being mined. The
down-dip mining direction was a function of the regional
geologic structure. As the mine progresses, the workings
will advance towards an anticline that is producing a more
pronounced dip in the Pocahontas No. 3 coal bed similar to
what was experienced in the mining of panel 31 Right. This
portion of the panel also contained a very thick sequence of
Pocahontas No. 3 coal, increasing the capacity for gas stor-
age. As depicted in Figure 7, gas contents tend to be greater
in this southeast portion of the mine property, although the
data density can be quite sparse in portions of the southern
region. These contour plots (Figure 7) do not address the
gas distribution in the coal beds within the overburden or
in the floor.
The results of the FLAC3D analysis indicated that the
gas emission zone above the longwall panels can reach up
to 970 ft. Karacan (2023) also stated that the gas emissions
zone (GEZ) at the mine site is expected to reach a height of
700–900 ft. above the mining interval. In the overburden
geology, which is interpreted from the core hole shown in
Figure 10, the main gas sources are the coal beds within the
mining interval Pocahontas No.3 and the other major coal
beds in the GEZ, including the Horsepen coals, Pocahontas
No.4 and No.7 (Fig 10).
Karacan (2023) indicated that the GEZ above the min-
ing interval could extend up to the mid of the headgate
and tailgate on the horizontal axis, approximately +150 ft
beyond either side of the panels. FLAC3D simulations pre-
dicted GEZ extends +140 ft beyond tailgate side and +90 ft
beyond headgate side for the panel 31 Right (R31). The
mining-induced zone of influence depends on the mining-
induced overburden strata deformations and stress redis-
tributions. Mining induced stresses and displacements of
the overburden strata above the tailgate of panel 31 Right
(R31) are higher than the headgate. The difference in the
vertical stress distribution over the tailgate and headgate
pillars of panel 31 Right (R31) can be seen in Figure 3. The
peak stress on the headgate side found to be lower than the
peak stress on the tailgate side and closer to the edge of the Figure 11. Geometry of the model domain
Figure 12. Gob properties used for modeling airflow in gob area (A) porosity and (B) permeability
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