A drilling fluid, or mud, is circulated during drilling operations to carry cuttings to the surface, control formation pressure and maintain wellbore stability, cool and lubricate the drill bit, and minimize damage to the reservoir. There are three main types of drilling fluids: gaseous (such as air), aqueous (such as water-based muds containing clay or polymer), and non-aqueous (such as oil-based or synthetic-based muds). Cuttings are removed from the drilling fluid using various solids control equipment and processes at the surface. Working with drilling fluids requires safety precautions as some components can be hazardous if not properly handled.

1. Jefri Chandra Runanda

2.  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.

4.  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

5.  Gaseous : Air, Nitrogen
 Aqueous : Gasified-foam, clay, polymer,
emulsion
 Non-aqueous : oil or synthetic

6.  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).

7.  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.

10.  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

11.  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.

12.  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.

13.  The most common additive to form a water-
based mud is bentonite, although polymers
have been developed and perform well for
most drilling operations.

15.  Screening : Shale shaker, gumbo removal
devices
 Hydrocycloning : desander, desilter
 Centrifugation : scalping, and decanting
centrifuge
 Gravitational settling : sump, dewatering unit

17.  Until now, shale shaker is the most common
cleaning method.
 With 60 mesh and 300 mesh filter screen in
series 99% cuttings are removed.

19.  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.