In the oil industry, barytes is chiefly added to the drilling mud to
increase the specific gravity of the latter. Rotary drilling is generally adapted for the
development of oil fields in which circulation of drilling fluid or mud is a main feature. As
the drill bit of the oil rig grinds its way through the rocks in search of oil, mud is pumped
down the hollow drill rod. It passes into the drill hole through openings in the bit and rises to
the surface through the space between the wall of the hole and the drill rod. The main
functions of the drilling mud are:
(a) to cool the drilling bit and drilling string;
(b) to remove cuttings from the bits and to transport them to the surface;
(c) to have thixotropic or gelling properties so that in the event of a pump failure, the
mud will gel and hold all the cuttings in suspension;
(d) to seal the open wall of the well to counteract any tendency for a loose formation to
cave into the well;
(e) to counter and confine the pressure of oil and gas in the well and to prevent them
from blowing out of the hole and from causing hazards; and
(f) to lubricate the space between the rod and the wall.
24 Kaulir Kisor Chatterjee
So, the main criteria for using barytes are its high specific gravity — 4.5 for pure barytes,
low oil absorption (thus causing minimal loss of oil flowing into the well) and also its
chemical inertness. The specific gravity will, however, tend to be slightly less because of
impurities. A high BaSO4-content will automatically ensure less impurities. There has to be a
balance between grade and cost.
Amongst the deleterious constituents are SiO2, Al2O3, Fe2O3 and clay because all of them
tend to reduce the specific gravity of the barytes. In addition, silica in the form of grits will
have an abrasive effect on the drilling rod, although quartz of certain specifications is added
in some special cases (see chapter on silicon). Water solubility has to be low because the
barytes particles along with the mud are to remain in suspension in the drilling fluid and not
in solution. To help the barytes particles to remain in suspension, they must be in very fine
size so as to expose as large a surface area as possible.
The industries generally prefer barytes with specific gravity 4.15 (min) and containing
94% (min) BaSO4, 1.5% (max) SiO2, 0.15% (max) Al2O3 and Fe2O3 each, 0.02% (max)
water-soluble matter and as low as possible clayey matter. In 1984, the Bureau of Indian
Standards (BIS) has prescribed specifications as: 90% (min) BaSO4, 4.15 (min) specific
gravity, 4.2% (max) SiO2+Al2O3, 0.02% (max) water soluble matter, less than 53 micron
particle size.