Page 234 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 210

[ ] Well Programming
2.5.5

LV, but starch can also be used. There is little point in using a filtration
control agent such as PAC (which is more expensive than CMC). In an
environment of 5 ppb of lignosulfonate, any encapsulating effect from
PAC can be forgotten.
Gypsum muds are stable up to 250˚F depending on the polymer
used for filtration control. Always add new volume to the system by
whole mud prepared to the specific formulation. Gypsum muds have
also been formulated in the nondispersed condition.
Lime lignosulfonate mud. The principles of low lime lignosul-
fonate mud are very similar to that of gypsum lignosulfonate mud. The
means of inhibition is the presence of filtrate calcium. In this case, the
filtrate calcium is derived from the addition of calcium hydroxide.
The pH of low lime lignosulfonate mud would normally be in the
range of 11.5 to 12.0. Excess lime is normally 1 to 2.5 ppb. Care should
be taken in breaking over to a lime mud because a viscosity hump will
occur. The order in which you add the chemicals is very important.
A high lime variant of a lime lignosulfonate mud exists. The excess
lime in such a case would be controlled in the range of 5 to 15 ppb.
Low lime lignosulfonate muds can withstand substantial carbonate
contamination. Low lime lignosulfonate muds are not commonly used
these days but some mud companies have their propriety variants.
They have been supplanted by lime polymer systems or gypsum ligno-
sulfonate muds.

2.5.5. Nondispersed or Polymer Water-Based Muds

A nondispersed mud is where the hydration and dispersion of a
drilled clay is minimized. There are a number of ways to achieve this.
The most common is to limit the amount of water that reacts with the
clay by encapsulating the clay with polymer as quickly as possible to
prevent further access of water to the clay. Such mud systems are
described as encapsulating polymer muds.
Nondispersed polymer systems in the drilling industry are mostly
based upon anionic and nonionic polymers. There are also some sys-
tems that have been developed which are based upon cationic and non-

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