Drilling for oil involves penetrating through various layers of the earth surface to reach, deposits of hydrocarbons. Drilling goes on both below the subsoil on land or below the seabed.
Operations in drilling:
Rotary movement: Depending on the type of well the rotary movement is generated mainly by three methods.
- Transmission of rotary motion by a pipe, called Kelly generated at surface by rotary table.
- By a power swivel connected directly to the last drill pipe
- By a drilling turbine or engine at the bottom of the well itself. (turbo-drilling)
Circulating Drilling mud: During drilling mud is circulated in the well. Drilling mud is pumped, using mud pump, through the core of drill-string and comes out to the surface passing through the space between drill pipes and the well.
Drilling mud performs these five essential functions.
- Cleans the bottom of the well.
- Cools the drilling bit.
- Lubricate the drilling bit.
- Consolidate the walls of the well-bore.
- Exercise pressure such as to contain the flow of oil, gas or water from a drilled formation.