STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Muds and Completion Fluids 681
b. Bactericides reduce the bacteria count. Paraformaldehyde, caustic soda,
lime, and starch are commonly used as preservatives.
c. Calcium removers are chemicals used to prevent and to overcome the
contaminating effects of anhydride and gypsum, both forms of calcium
sulfate, which can wreck the effectiveness of nearly any chemically treated
mud. The most common calcium removers are caustic soda, soda ash,
bicarbonate of soda, and certain polyphosphates.
d. Corrosion inhibitors such as hydrated lime and amine salts are often added
to mud and to air-gas systems. Mud containing an adequate percentage
of colloids, certain emulsion muds, and oil muds exhibit, in themselves,
excellent corrosion inhibiting properties.
e. Defoamers are products designed to reduce foaming action, particularly that
occurring in brackish water and saturated saltwater muds.
f. Emulsifiers are used for creating a heterogenous mixture of two liquids.
These include modified lignosulfonates, certain surface-active agents,
anionic and noionic (negatively charged and noncharged) products.
g. Filtrate, or fluid loss, reducers such as bentonite clays, CMC (sodium
carboxymethyl cellulose), and pregelatinized starch serve to cut filter loss,
a measure of the tendency of the liquid phase of a drilling fluid to pass
into the formation.
h. Flocculents are used sometimes to increase gel strength. Salt (or brine),
hydrated lime, gypsum, and sodium tetraphosphates may be used to cause
the colloidal particles of a suspension to group into bunches or “floos,”
causing solids to settle out.
i. Foaming agents are most often chemicals that also act as surfactants
(surface-active agents) to foam in the presence of water. These foamers
permit air or gas drilling through water-producing formations.
j. Lost circulation materials (LCM) include nearly every possible product used
to stop or slow the loss of circulating fluids into the formation. This loss
must be differentiated from the normal loss of filtration liquid, and from
the loss of drilling mud solids to the filter cake (which is a continuous
process in an open hole).
k. Extreme pressure lubricants are designed to reduce torque by reducing the
coefficient of friction, and thereby increase horsepower at the bit. Certain
oils, graphite powder, and soaps are used for this purpose.
1. Shale control inhibitors such as gypsum, sodium silicate, chrome lignosulfonates,
as well as lime and salt are used to control caving by swelling
or hydrous disintegration of shales.
m. Surface-active agents (surfactants) reduce the interfacial tension between
contacting surfaces (e.g., water-oil, water-solid, water-air, etc.); these may
be emulsifiers, deemulsifiers, flocculents, or deflocculents, depending upon
the surfaces involved.
n. Thinners and dispersants modify the relationship between the viscosity and
the percentage of solids in a drilling mud, and may further be used to
vary the gel strength, improve “pumpability,” etc. Tannins (quebracho),
various polyphosphates, and lignitic materials are chosen as thinners or
as dispersants, since most of these chemicals also remove solids by precipitation
or sequestering, and by deflocculation reactions.
0. Viscosifers such as bentonite, CMC, attapulgite clays, subbentonites, and
asbestos fibers (all colloids) are employed in drilling fluids to assure a high
viscosity-solids ratio.
p. Weighting materials, including barite, lead compounds, iron oxides, and
similar products possessing extraordinarily high specific gravities, are used