Page 234 - Introduction to Petroleum Engineering

OFFSHORE FACILITIES 221
TABLE 11.1 Producer‐to‐Injector Ratios for Common Well Patterns
Well Pattern Producer‐to‐Injector Ratio

Four‐spot 2
Five‐spot 1
Direct line drive 1
Staggered line drive 1
Seven‐spot 1/2
Nine‐spot 1/3

Intelligent wells can be found in an intelligent field (i‐field). An i‐field is an
integrated operation that uses improved information and computer technology to
operate a field. The operation uses supervisory control and data acquisition (SCADA),
which is computer technology designed to monitor the field. Operators are able to
use the technology to respond to changing conditions in real time. Capital investment
in i‐field technology can be larger than in fields without i‐field technology, but a
good design can result in a decrease in operating expenses by increasing automation
of a field and allow remote control of a field in a difficult environment. The desired
result is less direct human intervention.

11.7 OFFSHORE FACILITIES

Hydrocarbon production using offshore drilling rigs in shallow water began in the
early twentieth century. Today there are many types of offshore platforms as shown
in Figure 11.10. Drilling jack‐up rigs can be installed in varying depths of water.
Jack‐up rigs can be floated to drilling locations where the legs are lowered to the
seabed. Fixed platforms are set on steel jackets that sit on the seabed. Pilings ham-
mered into rock beneath the seafloor can be used to support the jacket and platform.
A compliant tower has a platform set atop a scaffold. A bottom‐setting platform in
dry dock is shown in Figure 11.11. The platform has a derrick and must be used in
relatively shallow water.
Wellheads can be installed on the seabed. Fluid produced through subsea well-
heads is routed to either a platform or through flowlines in a riser to a floating rig or
ship. If well depths are beyond the reach of human divers, remotely operated vehicles
(ROVs) must be used to install and maintain equipment.
The definition of deep water for classifying production of oil and gas in
deepwater conditions depends on the operator. Seitz and Yanosek (2015) defined
deepwater production as production in water depths greater than 450 m ( 1500ft).
Subsea completions can be used in deep water. Subsea facilities in deep water are
maintained using ROVs.
A key factor in selecting an offshore platform is water depth. Gravity‐based plat-
forms can be used in up to 1000 ft of water. Steel jacket platforms are typically used
in up to 1500 ft of water depth. Compliant towers can be used at up to 3000 ft. Tension
leg platforms can be used at depths of up to 5000 ft. Production spars can be used at