oil base mud
•Water in oil emulsion
•Diesel or crude oil forms its continuous phase
•Sometimes called invert emulsion
•Water droplets are emulsified in oil
•Water is used for gel strength and barite content
•Soaps are used as emulsifiers
•Soups are made from monovalent ion (Na+) or divalent ion
•(Ca++)
•The soap molecule bridge together oil and water interfaces
•Agitation is required to break the water into small droplets
•Oil/water ratio determine the final properties
Oil-based muds generally use hydrocarbon oil as the main liquid component with other materials such as clays or colloidal asphalts added to provide the desired viscosity together with emulsifiers, polymers and other additives including weighting agents. Water may also be present, but in an amount not usually greater than 50 volume percent of the entire composition. If more than about 5% volume water is present, the mud is often referred to as an invert emulsion, i.e., water-in-oil emulsion
ADVANTAGES:
(1) performs all the functions of a water-base mud or permits an acceptable
substitute for these functions;
(2) has most of the desirable properties of a water-base mud;
(3) does not hydrate and disperse cuttings;
(4) will not dissolve salt or other water-soluble formation deposits and can be
used to core such sections
(5)exhibits good penetration rates
(6) protects productive horizons
(7) does not increase the interstitial water of cores; and
(8) is not affected by contaminants such as cement, anhydrite, salt or shale, and
can tolerate contamination with water and raw crude.
Higher oil water increases resistance to contamination and
temperature stability
Used to drill hole with severe stability
More stable at high temperature
An excellent to drill pay zone; reduce formation damage and
preserve original permeability
Disadvantages:
• Contaminate the environment
• Flammability hazards
• Difficult removal of drilled solids due to high plastic PV
• Difficult electric logging
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