BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
Figure 3-19
Cloud Points for Various Polyols in KCl Solutions
The great variety of cloud point temperatures seen indicates that one polyol may not be suitable
for all applications. Additionally, the polyol will have to be selected based upon its cloud point at
a specified salinity. Alternatively, the cloud point of the polyol can be adjusted by altering the
salinity of the liquid phase. Varying the polyol type and system salinity has afforded Baker
Hughes Drilling Fluids effective control of the cloud point over a wide operating range.
Cloud point is modified at the wellsite using the software program (available through Baker
Hughes Drilling Fluids TITAN group) GLY-CAD ® which models the downhole behavior of all
of drilling fluids water-soluble glycol products. With this program, the concentrations of salt and
glycol can be engineered to match the operational needs of the drilling fluid. Depending on
downhole conditions, such as formation temperature, the optimum blend of glycols and salts is
determined to achieve the most effective cloud point for shale inhibition.
Shale Inhibition and Drilling Performance
Baker Hughes Drilling Fluids has conducted studies to examine the benefits of cloud point
behavior on drilling performance and shale stability. The results have shown distinct performance
benefits both above and below cloud point. Improvement in inhibition seen over a wide range of
temperatures is directly related to the cloud point of the glycol. Cloud point is the transition point
or start of phase separation at which the glycol changes from being water soluble to water
insoluble.
Explanation
Research carried out by other investigators (SPE 28960) concluded that the glycol is adsorbed by
the clay. During the adsorption process, water is displaced from the clay surface and ordered
structures of polyols are formed. A weak attachment is postulated because of the observation that
there is no rapid depletion of the polyol in the drilling fluid system. For this to be the case, there
must be some mechanism of association and disassociation of the polyol in the circulating
system. The nature of these structures and their stability in aqueous fluids is strongly controlled
by the presence of potassium cations with certain polyols.
• Under most conditions, a single polyol layer forms on the clay in the presence of potassium.
The resulting complexes are stable in water.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-75