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A drilling fluid, or mud, is any fluid that is used in a drilling operation in which that fluid is circulated or pumped from the surface, down the drill string, through the bit, and back to the surface via the annulus.
Suspend cuttings (drilled solids), remove them from the bottom of the hole and the well bore, and release them at the surface. Control formation pressure and maintain well bore stability. Cool, lubricate, and support the drilling assembly Minimize reservoir damage Control corrosion etc
True foams contain at least 70% gas (usually N2, CO2, or air) at the surface of the hole. Aqueous drilling fluids are generally dubbed water-based muds (WBMs). while nonaqueous drilling fluids (NAFs) are often referred to as oil-based muds (OBMs) or synthetic-based muds (SBMs).
OBMs are based on NAFs that are distilled from crude oil; they include diesel, mineral oils, and refined linear paraffins (LPs). SBMs, which are also known as pseudo oil- based muds, are based on chemical reaction products of common feedstock materials like ethylene; they include olefins, esters, and synthetic LPs.
Compressed air is a very effective drilling fluid for drilling in dry formations in arid climates, in competent consolidated rock, or in frozen ground. When drilling frozen formations, refrigeration equipment may be required to chill the compressed air before it is pumped into the borehole, especially if the ambient temperature is warmer than about -5 deg C (23 deg F
Foam or mist may be added to compressed air to enhance its performance, especially when too much water is encountered when air drilling formations such as clays and shales. Foam will help keep the cuttings separated. assist in removing water from the drill hole.
Water is generally a cost-effective and efficient drilling fluid which has been used for numerous drilling operations. The drilling fluid is formed naturally by mixing clear water with cuttings of soil from the formation which is being drilled.
The most common additive to form a water- based mud is bentonite, although polymers have been developed and perform well for most drilling operations.
Until now, shale shaker is the most common cleaning method. With 60 mesh and 300 mesh filter screen in series 99% cuttings are removed.
Working with drilling fluids can be hazardous. Some shale and corrosion inhibitors and some oil-base mud emulsifiers tend to produce ammonia or other hazardous volatile amines. particularly in hot areas on a rig. Other products are flammable or combustible (flash point <140F), so that they too must be handled with caution. Thus, proper ventilation is vital in the mud pit areas and around the solids-control equipment.