Page 230 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 206

[ ] Well Programming
2.5.3

Not all dispersants are deflocculants. Sodium hydroxide in water is
a powerful dispersant but has no deflocculating effect. The various lig-
nosulfonates and lignites can be strong deflocculants that result in full
dispersion. Examples of other deflocculants are some polyacrylates.

2.5.3. Mud Types Available

There are three mediums in use today as makeup fluids for drilling
mud: water, oils (hydrocarbon liquids), and air/gas.
The most commonly used medium is water and the resultant
drilling mud may be described as water-based mud. There is a sub-
stantial variety of water-based fluids that may be used in the drilling
industry and these types may be classified in many different ways. One
common classification of water-based mud types is to divide them into
two groups, dependent on the state of the clay that is present in the
mud (see the previous topic). Thus, a drilling mud can be described as
either dispersed or nondispersed (see the subsequent topics). Oil, air,
and miscellaneous systems will be discussed later.
There are a substantial variety of mud types and special applications
available in drilling. It is beyond the scope of this book to cover them
all. However, outlined below are some mud types that have been (or are
being) commonly used. Although they have been classified on the basis
of dispersed and nondispersed systems, attention is drawn to the vary-
ing ways in which inhibition of shales is achieved; e.g., potassium sys-
tems, calcium systems, silicate systems, etc. The mechanism of inhibi-
tion varies with each. The type of mechanism to use can best be select-
ed on the basis of the type of shale being drilled. In many cases, the idea
that there are closely defined mud systems (particularly with water-
based muds) should be dispelled. As can be seen from some of the
examples shown below, one type of mud blends into another type of
mud in the same way that one type of shale might vary into another.

2.5.4. Dispersed Water-Based Muds

An uninhibited dispersed mud is where any clay present has been
allowed to hydrate and expand (disperse), or has had a chemical such

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