BAKER HUGHES - Drilling Fluids Reference Manual

Contamination of Water Based Fluids
Hydrogen Sulfide (H2S) Contamination
Hydrogen sulfide as a contaminant will be briefly discussed here since, in a practical sense, safety
is the paramount issue in dealing with H 2 S. Certainly, H 2 S can have adverse effects on a drilling
fluid, i.e., viscosity, filtration control, and fluid chemistry, but its detection at any level should be
determined immediately and the safety issue addressed first. High pH fluids and H 2 S scavengers
have proven effective in controlling H 2 S concentration even at very high concentrations. The
Garrett Gas Train is necessary to accurately determine soluble sulfides. Chemical treatment
should maintain flow properties and filtration properties as required. See Chapter 8, Corrosion,
for guidelines to the treatment of H 2 S contamination.
Temperature Flocculation / Deterioration
Many water-base fluids have a temperature limit of ±300°F. This can often be exceeded with the
addition of temperature stabilizing additives such as MIL-TEMP ® , ALL-TEMP ® , or
CHEMTROL ® X, etc. In planning the fluid to be used in high temperatures, an estimation of
bottom hole temperature (BHT) should be used to make sure temperature has a minimal effect on
the fluid.
If the following issues are not addressed:
• treatment to address temperature stability
• adequate control of type, distribution, and amount of low specific gravity solids
• provision to counter contaminants as discussed above,
A flocculated, thick fluid off bottom can result which can lead to hole or drilling problems.
Hot rolling and static oven testing a fluid at estimated wellsite BHST should be used to
supplement suction pit and flowline fluid checks to counter the effects of high temperatures.
A fluid program that addresses wellbore temperatures at all times in a given well will help in
preventing temperature flocculation and deterioration of a fluid. Knowing product temperature
limits and how to apply products in high temperature environments is imperative.
Solids Contamination
Throughout this chapter on chemical contamination, severity of fluid contamination is predicated
on amount, type, and particle size distribution of solids. Fluids with an unacceptable
concentration of low specific gravity solids are more likely to have a severe reaction to chemical
contaminants. Solids should be kept to a minimum at all times. Any complete fluids program
should include recommendations for solids control equipment and mud dilution. Solids control is
discussed in greater detail in Chapter 10, Mechanical Solids Control.
Oil / Gas Contamination
In elemental composition, crude oils are mainly carbon and hydrogen with lesser and varying
proportions of oxygen, nitrogen, and sulfur. The hydrocarbons in crude oils are generally
categorized as aromatics, naphthenes, and paraffins, but include various hybrids. The aromatics
are generally referred to as unsaturated with six carbon atoms in each structural ring. Asphaltic
type crudes contain asphaltenes and resins. Crude oils can contaminate a water-base drilling
fluid, affecting density and possibly viscosity. With high concentrations of crude in a water-base
fluid, approved disposal of that fluid could be the appropriate action to take. The fluid properties
Baker Hughes Drilling Fluids
Reference Manual
4-14 Revised 2006