Page 317 - Advanced Mine Ventilation

294 Advanced Mine Ventilation

Figure 17.7 Horizontal well completion in deep coal seams.

coal seams or shale, the horizontal laterals are hydrofracked every 250e1000 ft to
enhance gas production.
A typical drill site is 4e5 acres in area and has a drill platform for the drill rig, a
compressor station for compressed air to get the cuttings out, and a large pond to
dump drill cuttings and recover water for reuse. A temporary office is created on-
site to provide communications, food, and other facilities for the workers on site. A
typical drilling and hydrofracking procedure for a coal seam 8000 ft deep is described
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here. The coal seam is 60 ft thick and has a gas content of 500 ft /ton. It is advisable to
complete drilling to the target without any interruptions.

17.4.3.2 Drilling Procedure
A smaller drill rig, such as a Speedstar 185 with top drive and a hook load capacity of
185,000 lbs, is moved to the site and properly anchored.
Fig. 17.8 shows a typical well bore schematic.
First, a 20-in. diameter surface casing is set in place to a depth of 30e40 ft. Then, a
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17 / 2 -in. diameter well is drilled to a depth of about 600 ft (below all known aquifers),
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1
and a 13 / 8 -in. casing is set with class A cement. Next, a 12 / 4 -in. borehole is drilled to
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a depth of 3000 ft and the borehole is logged for any mineable coal seams. A 9 / 8 -in.
casing is set in the well.
Next, the Speedstar rig is moved away from the site and a heavier rig, such as an
IDECO Model H-44 double, capable of handling 318,000 lbs hook load is moved
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to the site. It also has a top drive. A 5000 lbs, 9 / 8 -in. casing head is mounted, and a
blowout preventer is installed.
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Next, drilling starts with an 8 / 4 -in. polycrystalline diamond (PCD) bit with 6 / 2 -in.
drill collars (rods). The well and flow lines are pressure tested and all safety protocols
are completed. The production well is drilled to a target depth well below the target