Barite
Barite (or barytes) is barium sulphate, BaSO4 and it is the most commonly used weighting
material in the drilling industry. Barium sulphate has a specific gravity in the range of 4.20 -
4.60. The specific gravity of Most commercial barite contain impurities including quartz, chert,
calcite, anhydrite, and various silicates which slower its specific gravity. It is normally
supplied to a specification where the specific gravity is about 4.2. Barite is preferred to other
weighting materials because of its low cost and high purity. Barite is normally used when mud
weights in excess of 10 ppg are required. Barite can be used to achieve densities up to 22.0 ppg
in both water- based and oil -based muds. However, at very high muds weights (22.0 ppg), the
rheological properties of the fluid become extremely difficult to control due to the increased
solids content.
2. Iron Minerals
Iron ores have specific gravities in excess of 5. They are more erosive than other weighting
materials and may contain toxic materials. The mineral iron comes from several iron ores
sources including: haematite/magnetite, illmenite and siderite.The most commonly used iron
minerals are:
Iron Oxides: principally haematite, Fe2O3. Iron oxides have several disadvantages including:
magnetic behaviour which influences directional tool and magnetic logs, toxciticity an
difficulty in controlling mud properties.
Iron Carbonate: Siderite is a naturally occurring ferrous carbonate mineral (FeCO3).
Illmenite: The mineral illmenite, ferrous titanium oxide (FeTiO3).
3- Calcium Carbonates
Calcium carbonate (CaCO3) is one of the most widely weighting agents especially in non-
damaging drilling fluids. Its main advantage comes from its ability to react and dissolve in
hydrochloric acid. Hence any filter cake formed on productive zones can be easily removed
thereby enhancing production. It has a specific gravity of 2.60 - 2.80 which limits the
maximum density of the mud to about 12.0 ppg Calcium carbonate is readily available as
ground limestone, marble or oyster shells.
Dolomite is a calcium - magnesium carbonate with a specific gravity of 2.80 - 2.90. The
maximum mud density achieved is 13.3 ppg.
4- Lead Sulphides
Galena (PbS) has a specific gravity of 7.40 - 7.70 and can produce mud weights of up to 32
ppg. Galena is expensive and toxic and is used mainly on very high pressure wells.
5- Soluble Salts
Soluble salts are used to formulate solids free fluids and are used mainly as workover and
completion fluid. Depending on the type of salt used, fluid densities ranging from 9.0 - 21.5
ppg (sg =1.08 - 2.58) can be prepared.
B-VISCOSIFIERS:
The ability of drilling mud to suspend drill cuttings and weighting materials depends entirely
on its viscosity. Without viscosity, all the weighting material and drill cuttings would settle to
the bottom of the hole as soon as circulation is stopped. One can think of viscosity as a
structure built within the water or oil phase which suspends solid material. In practice, there are
many solids which can be used to increase the viscosity of water or oil. The effects of
increased viscosity can be felt by the increased resistance to fluid flow; in drilling this would
manifest itself by increased pressure losses in the circulating system.
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