Page 267 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 243

Drilling Fluids Program [ ]
2.5.10

ants of organ-clays by adding other materials to the clay before it goes
to the dryer.
As is the case with bentonite clay in a water-base mud, the presence
of organo-clay in an oil mud will have an effect on filtration control of
the mud. If the concentration of organo-clay becomes too low (e.g.,
less than 2.0 ppb), filtration control can become difficult. Such a low
concentration of organo-clay is not very common in an oil mud but
could be the case in an oil mud with an ultra low oil/water ratio.
Filtration control additives. It is possible in an invert emulsion
oil-base fluid to obtain filtration control without any fluid loss addi-
tives if the emulsion is strong enough. This is because the water phase
droplets can act as a solid and reduce filtration. Every time emulsifier
is added to the mud, it will be noticed that the HTHP filtration rate is
reduced to a certain extent.
It is, however, the case that filtration control additives can effec-
tively improve HTHP filtration. These are particularly relevant in
HTHP control at very high temperatures.
In some muds, asphalts, gilsonites, or various proprietary variants
are effective filtration control agents. In using these materials, the soft-
ening point temperatures in whatever base oil is used should be con-
sidered. These materials are relatively inexpensive and at normal tem-
peratures can perform effectively.
Organophylic lignites are used as filtration control agents, particu-
larly in high-temperature formulations. They are more expensive than
asphaltic or gilsonitic materials because they have been processed to be
organophylic. They are produced by the addition of a quaternary amine
salt as an adduct onto the lignite. This treatment, as in the case of
organophylic clays, makes the lignite dispersible in an oil. The same
factors that effect the dispersibility of the organo-clays also affect the
organo-lignites.
In addition to the filtration control agents mentioned, some
drilling fluid companies also provide liquid fluid loss agents. These
materials are proprietary and the particular mud company should be
contacted for further details.
Rheology modifiers. These are usually diamer or triamer salts
which, when added to an oil mud, can alter the low-shear rate rheolo-
gy or the thixotrophy (speed and strength of development of gel) of the
oil mud. These are usually system specific and their performance will

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