Page 281 - Advanced Mine Ventilation

258 Advanced Mine Ventilation

For liquid flow, Eq. (15.4) becomes:

0.03976 kh ðp p Þ
w
e
Q ¼ (15.5)
m lnðr e =r Þ
w
where Q is in CF/day and m is liquid viscosity.
For example,
Calculate gas and water flow from a well producing steadily under the following
conditions:
k ¼ 0.003 darcy (3 md)
h ¼ 40 ft
m ¼ 0.02 cp
z ¼ 0.90

T ¼ 60 F(þ460)
r e ¼ 1000 ft
r w ¼ 0.25 ft
p e ¼ 500 psi
p w ¼ 50 psi
Using Eq. (15.4),

2 2
707:8 ð0:003Þ40 500 50
Q ¼
1; 000
0:9 520 ð0:02Þ ln
0:25
¼ 270.9 MCFD

The above conditions describe a typical well drilled into a thick seam with good
permeability. The well is produced at a constant pressure of 50 psi. Similarly, using
Eq. (15.5), the water flow can be calculated as 46.2 bbl/day.

15.3 Application of In-Mine Horizontal Drilling

First application of this technique was reported by Thakur [3,4] in 1978. A 1200 ft
long borehole was drilled ahead of a development section from the return side of
the section as shown in Fig. 15.7. It produced about 500 MCFD of methane.
The borehole was connected to a vertical borehole with pipes, and gas was safely
discharged on surface. The impact of degasification was noted as follows:
1. The greatest impact of degasification was in the face area where methane concentration drop-
ped to 0.25% in course of two to 3 months from an initial value of 0.95%.
2. The methane concentration in the section return (at the last open crosscut) fell to 50% of its
original value indicating a methane capture ratio of 50%.
3. The immediate influence of those boreholes was felt up to a radius of 400 ft. This indicated
that only one borehole drilled in the outermost airway of a section can adequately degas the