1.
n. [Drilling Fluids]
A class of polymers added to a drilling-grade
clay mineral during grinding, or added directly into a clay-based
mud system, to enhance the clay's
rheological performance. In concept, clay-extender polymers achieve the type of
rheology needed for fast drilling with fewer
colloidal solids and lower
viscosity at high
shear rate (at the
bit). This is the concept of a "
low-solids, nondispersed mud" system. Extenders are usually long-chain
anionic or nonionic polymers that link clay platelets together in large networks. Anionic polymers are highly effective but can be precipitated by hardness ions. Nonionic polymers are less effective but also much less sensitive to hardness ions. Excessively long, linear polymers may break up under mechanical shearing. Either by
precipitation or breakup, extender polymers can quickly become ineffective if poorly chosen and used improperly. A drilling-grade clay that has no extender is that which meets the standard for
API nontreated
bentonite. API bentonite and
OCMA-grade API bentonite usually contain extender polymers.