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, fueloil, selected crude oil or mineral oil. –wiki
“TRUE” OIL-BASE MUD
“True” Oil-base Mud contains a liquid phase with ninety to ninetyfive percent (90–95%) diesel oil and five to ten percent (5–10%) water
emulsified within the oil. These muds often use asphaltic type materials
suspended in the liquid for controlling viscosity and fluid loss. “True” oil-base muds provide good hole protection, especially in shale type formations, and also increase drill string lubrication.
INVERT EMULSION MUD
Invert Emulsion Mud is oil-base mud in which the liquid phase is sixty to ninety percent (60–90%) diesel oil with ten to forty percent (10–40%) water emulsified within the oil. An invert mud can be formulated with mineral oil or other low environmental risk oil substitutes when needed. In this mud, water and chemicals are used together to control viscosity and fluid loss. Invert emulsion muds provide good hole protection and are the most commonly used oil mud.
SYNTHETIC OIL MUDS
The term “Synthetic-Based Mud”, or SBM, describes any oil-base mud
that has a synthesized liquid base. Some common synthetic base fluids
include linear alphaolefins (LAO), straight internal olefins (IO), polyalphaolefins (PAO), vegetable oils, esters, and ethers. This base fluid is
then combined with viscosifiers, weighting material, and other additives
to produce a stable, useful drilling fluid.
SBMs share several advantages with traditional oil-base muds, including excellent wellbore stability, improved drilling rates, good hole cleaning, excellent cuttings integrity, and reduced torque. SBMs also provide additional health and safety benefits — higher flash points, lower vapor production, and reduced eye and respiratory irritation. The major benefit of SBMs over traditional OBMs is the reduced environmental impact of cuttings and liquid mud. Currently, SBMs and cuttings meet U.S. offshore
environmental requirements and may be discharged under WBM protocols.
SBMs are expensive, $200–400/bbl., depending on the oil/water ratio. Proper solids removal and liquid recovery techniques must be used to maintain desired fluid properties and drilling rate, and to control mud maintenance costs. The alternatives to mechanical solids control — dilution and whole SBM additions — are prohibitively expensive when compared to the cost of proper solids control equipment.