2008-06-09_PERMIT FILE - C1980007 ‎(5)‎

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 6/9/2008
• Doc Name: Exhibit 79 Deer Creek Shaft and E Seam Methane Drainage Wells Project Final-August 2007
• Section_Exhibit Name: Exhibit 80 Drilling Activities - TR111
• Media Type: D
• Archive: No

Alternatives Considered but Eliminated from Detailed
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• It has been MCC's experience drilling
directionally in the B seam that directional
holes must be drilled such that the
producing part of the well above the wain
is vertical. This distance was
approximately 250 feet in the B seam
methane drainage wells and is projected to
be 150 feet minimum in the E seam
methane drainage wells. If such holes fail
to achieve vertical in this portion of the
well, they are subject to collapse and
ineffective as degas holes.
The ~naxi~nu~n safe angle of drilling
(above this ininiinuin vertical section) that
can be achieved by the drilling equipment
available is 45 degrees.
The drill mast is set at 45 degrees to begin
the holes. This angle must be gradually
corrected to vertical during the drilling
process.
The maximum allowable dog-leg in
directional drilling is 4 percent, in order to
be able to successfully install casing in the
hole.
Given the parameters of overburden depth,
as it relates to physical constraints of
directional drilling, MCC is unable to
reach the required methane drainage
targets from outside the roadless
boundary.
Based on preliminary plans these types of
boreholes alone are inadequate for proper
ventilation and efficient mine operations. These
methods are already used by MCC where
possible.
Directionally Drill MDWs from
Outside IRAs
Directional drilling is limited by the thickness
of overburden (or amount of rock) overlying
the coal E seam. This limited thickness of
overburden precludes the ability to drill
exclusively from outside the IRA boundaries
and hit the MDW targets needed in the
ventilation plan.
MCC expended a tremendous effort over a
three-year period in an attempt to find a means
to successfully accomplish degas drainage
using the in-mine horizontal drilling system.
These holes were drilled in the gateroads of the
1.4-17 panels and connected to a massive
collection system to exhaust the gases from. the
mine. The conclusion of this effort was that the
holes could not be drilled large enough, or stay
open long enough, to allow safe mining of the
coal (due to resulting high. methane
concentrations). They were simply very
inefficient collectors of minimal quality gas,
due to the limits of the drilling equipment in
this application and the location of the gas-
producing zones within the overlying strata.. In
MCC's previous experience in the B Seam
approximately 13 percent of total mine
methane was able to be vented horizontally
(extracted from BLM analysis, 2007). Any
attempt to degas the E seam via the horizontal
drilling system would have the same issues and
possibly more due to constraints of the
overlying strata.
Therefore, use of directional drilling
opportunities has been used as much as
possible, however because in places the
overburden is not thick enough that directional
drilling either from outside the IRA is practical
or possible, therefore some of the operations
must be placed in the IRA
Helicopter Drilling of IRA Sites
Regardless of how they are accessed, drill pads
still need to be constructed and large-diameter
boreholes would still need to be completed to
achieve effective methane drainage. Drill pad
construction would require the use of heavy
equipment such as a tracked dozer and a
backhoe to dig mud pits. Depending on the
terrain, a tracked backhoe may also be needed.
Large diameter drill-holes cannot be drilled by
the drill rigs typically flown in by helicopter.
Such rigs are normally used for drilling
exploration coreholes by an entirely different
drilling method than the air-foam rotary used to
drill large-diameter holes. Large-diameter holes
are necessary for the effective removal of
Deer Creek Ventilation Shaft and E Seam Methane Drainage Wells FEIS
47