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A bit of an explanation about drill rigs might be useful. These are classified into
offshore rigs and land rigs. Offshore rigs operate on platforms above the water that
either stand on the bottom of the ocean or float. Platforms that stand on the bottom
are known as jack-ups, and are used in shallow water. Deep water drilling requires
a stable, floating platform. These come in two varieties: semi-submersibles and drill
ships. Semi-submersibles are basically a floating raft anchored tightly to the bottom.
The anchor cables pull the vessel partly underwater, and the buoyancy of the platform trying to rise back to the surface holds the cables in tension. These so-called
“tension leg” platforms are very stable and can operate in water that is kilometers
deep. They are expensive to move, however, requiring deep-diving submersibles
with specialized crews to access the anchors. The deployment of tension leg platforms led the major oil companies to support advances in directional drilling technology so multiple wells could be drilled without moving the platform (refer back
to Chap. 2). Drill ships are used in very deep water or other locations where anchoring to the bottom is not feasible. They employ a process called “station keeping”
where constant adjustments from small directional propellers are used hold the ship
in one spot. Although many offshore wells are fracked to improve conventional
production, offshore rigs are not being used for unconventional oil and gas development in a significant way (at least not yet) so the remainder of this discussion will
focus on land rigs.
Land rigs come in several different sizes from small, truck-mounted affairs to
large modular units that are brought out to a drilling location in pieces and assembled on-site. Land rigs are described by the number of lengths of drill pipe they can
pull from the ground in a single lift. Drill pipe and well casing both come in standard lengths of 30 feet (10 m), and each length is called a joint. Single rigs can pull
one joint at a time, and are used for shallow water wells and seismic survey boreholes. Double rigs can pull two joints, and are larger, capable of drilling into oil and
gas reservoirs at moderate depths. These are often employed as “workover” rigs to
replace casing or repair cement in existing wells. The largest land-based rigs are
triples that can pull three joints at a time. The rig shown in Fig. 7.1 is a triple; a close
look at the stands of drill pipe stacked in the derrick reveals that they consist of three
joints each.
Triple rigs are used for unconventional oil and gas drilling because they are able
to construct deep boreholes with long laterals. Many gas shales are quite deep, and
although some formations may be reachable with smaller rigs, continuing a vertical
borehole into a lateral that may need to extend several kilometers horizontally is
beyond their capability. Triple rigs are robust enough to drill record-setting wells
like the Outlaw C11 H, constructed in the Utica Shale of Ohio by Eclipse Resources
in 2017 (Soeder and Borglum 2019). According to a company news release, the
lateral has a length of approximately 19,500 feet (5.9 km or 3.7 miles) with a total
borehole length from the surface to the end of the lateral of about 27,750 feet
(8.5 km or 5.25 miles). These extremely long wells are said to be very efficient, paying for the extra drilling costs with substantial returns. They also benefit the landscape, because longer laterals allow for greater well spacing on the surface.
7.1 Bulldozers Running Amok
A bit of an explanation about drill rigs might be useful. These are classified into
offshore rigs and land rigs. Offshore rigs operate on platforms above the water that
either stand on the bottom of the ocean or float. Platforms that stand on the bottom
are known as jack-ups, and are used in shallow water. Deep water drilling requires
a stable, floating platform. These come in two varieties: semi-submersibles and drill
ships. Semi-submersibles are basically a floating raft anchored tightly to the bottom.
The anchor cables pull the vessel partly underwater, and the buoyancy of the platform trying to rise back to the surface holds the cables in tension. These so-called
“tension leg” platforms are very stable and can operate in water that is kilometers
deep. They are expensive to move, however, requiring deep-diving submersibles
with specialized crews to access the anchors. The deployment of tension leg platforms led the major oil companies to support advances in directional drilling technology so multiple wells could be drilled without moving the platform (refer back
to Chap. 2). Drill ships are used in very deep water or other locations where anchoring to the bottom is not feasible. They employ a process called “station keeping”
where constant adjustments from small directional propellers are used hold the ship
in one spot. Although many offshore wells are fracked to improve conventional
production, offshore rigs are not being used for unconventional oil and gas development in a significant way (at least not yet) so the remainder of this discussion will
focus on land rigs.
Land rigs come in several different sizes from small, truck-mounted affairs to
large modular units that are brought out to a drilling location in pieces and assembled on-site. Land rigs are described by the number of lengths of drill pipe they can
pull from the ground in a single lift. Drill pipe and well casing both come in standard lengths of 30 feet (10 m), and each length is called a joint. Single rigs can pull
one joint at a time, and are used for shallow water wells and seismic survey boreholes. Double rigs can pull two joints, and are larger, capable of drilling into oil and
gas reservoirs at moderate depths. These are often employed as “workover” rigs to
replace casing or repair cement in existing wells. The largest land-based rigs are
triples that can pull three joints at a time. The rig shown in Fig. 7.1 is a triple; a close
look at the stands of drill pipe stacked in the derrick reveals that they consist of three
joints each.
Triple rigs are used for unconventional oil and gas drilling because they are able
to construct deep boreholes with long laterals. Many gas shales are quite deep, and
although some formations may be reachable with smaller rigs, continuing a vertical
borehole into a lateral that may need to extend several kilometers horizontally is
beyond their capability. Triple rigs are robust enough to drill record-setting wells
like the Outlaw C11 H, constructed in the Utica Shale of Ohio by Eclipse Resources
in 2017 (Soeder and Borglum 2019). According to a company news release, the
lateral has a length of approximately 19,500 feet (5.9 km or 3.7 miles) with a total
borehole length from the surface to the end of the lateral of about 27,750 feet
(8.5 km or 5.25 miles). These extremely long wells are said to be very efficient, paying for the extra drilling costs with substantial returns. They also benefit the landscape, because longer laterals allow for greater well spacing on the surface.
7.1 Bulldozers Running Amok