BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
solution is a function of the specific polyglycol used, its concentration and the presence of
other dissolved materials, especially electrolytes.
The CPT for a given polyglycol and aqueous phase forms a locus of CPT’s with concentration,
or CPT curve, as shown in the figure below. Below the curve the polyglycol forms a single
solution in water, but if the temperature of the solution is increased above the curve the
solution will separate into two disticnt phases. The composition of the two phases is defined
strictly by the temperature of the system and is given by the temperature of an isotherm (any
horizontal line in the figure below) with the curve at the two points.
250
Cloud Point Temperature, F
Temperature, Degrees F
200
165-
150
135-
100
50
5% Glycol at 165F
2% in solution 3% out of solution
5% in solution 0% out of solution
5% Glycol at < 135F
0
2% 5%
0 1 3 4 6 7 8
Glycol content, Weight weight %
Polyglycol
, volume %
Figure 7 - 6 Phase Conditions of Cloud Point Formation
Baker Hughes Drilling Fluids’ proprietary software GLY-CAD will perform CPT calculations
and is the recommended tool for designing CPT glycol fluids.
The significance of the CPT is somewhat controversial, as the exact mechanism by which
polyglycols stabilize clays and shales is debated. Polyglycols form complexes with clays. This
fails to account for the wide variability in efficiency seen in various polyglycols. Most of the
laboratory studies showing efficient and effective shale stabilization as well as the successful
field applications have used polyglycol solutions at or near their CPT. This clearly suggests
that the CPT is important, but the exact mechanism is elusive. Laboratory studies eventually
provided insight into the importance of CPT and provided a mechanism by which chameleonic
or TAME polyglycols provide highly efficient shale stabilization.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 7-18