Oil and gas production handbook An introduction to oil and gas production

101 kPa
10 °C
20 MPa
100 °C
40 MPa
200 °C
Reservoir hydrostatic pressure 
pushes oil and gas upwards.
Gas expands 
and pushes oil 
downwards

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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.  
 
The main components of the 
drilling rig are the derrick, floor, 
drawworks, drive and mud 
handling. 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. 
Photo: Puna Geothermal Venture
 
 
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 above 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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27 
 
As the well is sunk into the ground, the weight of the drill string increases 
and might reach 500 metric tons or more for a 3,000 meter deep well. The 
drawwork and top drive must be precisely controlled so as not to overload 
and break the drill string or the cone. Typical values are 50kN force on the 
bit and a torque of 1-1.5 kNm at 40-80 RPM for an 8-inch cone. Rate of 
penetration (ROP) is very dependent on depth and could be as much as 
20m  per hour for shallow sandstone and dolomite (chalk), and as low as 1m 
per hour on deep shale rock and granite.  
 
Directional drilling is 
intentional deviation of a 
well bore from the vertical. 
It is often necessary to drill 
at an angle from the 
vertical to reach different