BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
GLYCOL Systems
Glycol Chemistry
Polyols (the term “polyol” includes glycols glycerols, polyalkylene glycols and alcohol
ethoxylates) are well established shale inhibitors for water-base fluids. These compounds are
typically added to water-base fluids at concentrations between 3% and 10% by volume. They are
most commonly used in conjunction with a KCl/polymer-base fluid, but have also been added to
a wide range of systems from fresh water to salt saturated fluids.
Glycols are compounds containing two hydroxyl groups attached to separate carbon atoms in an
aliphatic chain. Although there are a few exceptions, nearly all glycols consist solely of carbon,
hydrogen, and oxygen. Simple glycols are those in which both hydroxyl groups are attached to an
otherwise un-substituted hydrocarbon chain as represented by the general formula, CnH2n(OH)2.
Note:
The more complex glycols are given the name polyglycols and are distinguished by
intervening ether linkages in the hydrocarbon chain, as represented by the general formula
CnH2nOx(OH)2.
A common method of manufacturing these simple glycols is by hydrolysis of the epoxides. These
epoxides are polymerized in the presence of other compounds and initiators (glycols, amines,
acids, or water) that contain active hydrogen. The end result is a vast range of products with
varying molecular weights and characteristics. The glycols are characterized by the way in which
the basic building blocks are arranged. The specific glycol products show a wide range of
properties depending on the molecular weight and the composition of the polymer. In general,
increasing molecular weights result in the following:
• lower water solubility
• higher viscosity
• higher flash point
• lower cloud point.
Prior to considering their field application, some key aspects of glycols are discussed below.
Simple Polyhydric Alcohols
Glycols are dihydric alcohols containing two hydroxyl groups and are members of the general
chemical class of polyhydric alcohols. Two commercially important glycols are ethylene glycol
(commonly used for automotive antifreeze) and propylene glycol (a food additive). A related
trihydric alcohol is glycerol (present in all vegetable oils and animal fats as glyceride esters).
Other polyhydric alcohols include sugar alcohols, sorbitol, and mannitol.
Polyglycols and Polyglycerols
Polyglycols and polyglycerols are oligormeric or polymeric forms of the simple glycols and
glycerols. The size and molecular weight of the polyglycols and polyglycerols increase as the
degree of polymerization or number of repeating units in the oligomers or polymers increases.
The properties of polyglycols and polyglycerols depend primarily on the molecular weight,
chemistry of the repeating units, and the chemistry of the starting material. Viscosity, flash point,
and pour point/freezing point all typically increase with increasing molecular weight, while
biodegradability and toxicity typically decrease.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-67