Page 11 - Wind Waves and Weather

Petroleum Extension-The University of Texas at Austin

Offshore Operations

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he location and environment of an offshore drill site plays a Drilling Units
Tlarge role in the type of rig that an operating company
selects. The area’s wind, waves, currents, and other forces
determine what a rig needs to withstand. Offshore operators
broadly divide offshore drilling rigs into two categories: mobile
offshore drilling units (MODUs) and fixed, or stationary, drill‑
ing units. In general, MODUs drill exploration, or wildcat, wells,
which are wells drilled to determine whether oil and gas exist
in an offshore location. After a MODU drills a single well, the
company then moves it to another location where it drills an‑
other well. On the other hand, fixed drilling units are placed
in position over an offshore reservoir, drill several wells, and
are never moved from the location. (For more information
about offshore drilling units and offshore operations, obtain
the PETEX publication, A Primer of Offshore Operations. Log on
to www.utexas. edu/cee/petex.)

Today, operating companies and offshore drilling contractors Mobile Offshore
mainly use two types of MODUs: bottom-supported offshore drill- Drilling Units
ing rigs and floating offshore drilling rigs. With bottom‑supported
units, part of the rig is in contact with the seafloor during drill‑
ing. A bottom‑supported unit floats only when being moved
from one site to another. On the other hand, a floating rig not
only floats while it is being moved, but also it floats over the
site while it drills a well.

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