Oil-based mud
type of drilling fluid
Oil-based mud is a drilling fluid used in drilling engineering. It is composed of oil as the continuous phase and water as the dispersed phase in conjunction with emulsifiers, wetting agents and gellants. The oil base can be diesel, kerosene, fuel oil, selected crude oil or mineral oil.
Requirements and composition
The requirements are a gravity of 36–37 API, a flash point of 180 °F (82 °C), fire point of 200 °F (93 °C) and an aniline point of 140 °F (60 °C).
Emulsifiers are important to oil-based mud due to the likelihood of contamination. The water phase of oil-based mud can be freshwater, or a solution of sodium or calcium chloride. The external phase is oil and does not allow the water to contact the formation. The shales don't become water wet.
Poor stability of the emulsion results in the two layers separating into two distinct layers.
Advantages
The advantages are:
high drilling rates
lowered drill pipe torque and drag,
less bit balling and
reduction in differential sticking.
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