BAKER HUGHES - Drilling Fluids Reference Manual

TABLE OF CONTENTS
HYDRATE INHIBITION
Historically, most of the work on gas hydrate inhibition has been aimed at the prevention of hydrate
formation during the production and transportation phase of hydrocarbons.
Listed below are the three inhibitive mechanisms utilized:
• Thermodynamic inhibition
• Kinetic inhibition
• Prevention of hydrate agglomeration
Traditionally, hydrate suppression has been accomplished by a thermodynamic approach. High
concentrations of hydrate inhibitors such as salts, glycols or alcohols were added to the flow line. A
more modern approach is the use of low concentration inhibitors that time-delay or minimize the
amount of hydrate crystals formed (kinetic approach). The third approach, anti-aggregation, does not
stop the formation of hydrates but prevents the hydrates from agglomerating into large crystalline
masses or plugs. This effectively prevents a dramatic increase in the transported fluid’s viscosity.
It should be noted that many of the solutions employed in mitigating gas hydrate issues in
downstream operations are not applicable to drilling applications due to environmental constraints.
Thermodynamic Inhibition
In drilling fluids the principal method for hydrate inhibition is thermodynamic. As stated in the
previous section thermodynamic hydrate inhibition is extensively used in petroleum production.
These inhibitors which are added to the drilling fluid lower the chemical potential of the aqueous
phase. The hydrate equilibrium pressures and temperatures are measured for distilled water. When
the water is treated with the thermodynamic inhibitor, the phase boundaries are shifted to the left and
upward. Thus the inhibitor effectively reduces the temperature and increases the pressure at which
the hydrates are formed. The most common thermodynamic hydrate inhibitors are glycols, salts and
glycerol.
A typical phase equilibrium plot is given in the following figure.
Figure 13 - 7
Hydrate Phase Equilibrium Conditions
10000
With
Inhibitor
1000
Pure
Water
100
30 40 50 60 70 80 90
TEMPERATURE (°F)
• On a weight to weight basis, the hydrate suppression effectiveness (ΔT) of differing salts can
be expressed in the following order:
NaCl > KCl> CaCl 2 > NaBr>Na Formate> Calcium Nitrate
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 13-17