Page 26 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

allow up to 70%. Reservoirs can be quite complex, with many folds and
several layers of hydrocarbon-bearing rock above each other (in some areas
more than 10). Modern wells are drilled with large horizontal offsets to reach
different parts of the structure and with multiple completions so that one well
can produce from several locations.

3.3 Exploration and drilling

When 3D seismic investigation
has been completed, it is time to
drill the well. Normally, dedicated
drilling rigs either on mobile
onshore units or offshore floating
rigs are used. Larger production
platforms may also have their own
production drilling equipment.
Photo: Puna Geothermal Venture

The main components of the
drilling rig are the derrick, floor,
drawworks, drive and mud
handling. The control and power can be hydraulic or electric.

Earlier pictures of drillers and roughnecks working with rotary tables (bottom
drives) are now replaced with top drive and semi-automated pipe handling
on larger installations. The hydraulic or electric top drive hangs from the
derrick crown and gives pressure and rotational torque to the drill string. The
whole assembly is controlled by the drawworks.

The drill string is assembled from pipe segments about 30 meters (100 feet)
long normally with conical inside threads at one end and outside at the other.
As each 30 meter segment is drilled, the drive is disconnected and a new
pipe segment inserted in the
string. A cone bit is used to dig
into the rock. Different cones
are used for different types of
rock and at different stages of
the well. The picture shows
roller cones with inserts (on the
left). Other bits are PDC
(polycrystalline diamond
compact, on the right) and
diamond impregnated. Photo:
Kingdream PLC

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