BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
Flash Point
When using an oil based drilling fluid on HPHT wells, the flowline temperature can approach the
flash point of the base oil particularly when drilling deep 12 ¼” intervals. Usually bottom hole
temperatures are too low to cause a problem in 17 ½” hole and circulation rates in smaller hole
diameters allow the drilling fluid time to cool as it comes up the annulus. High return drilling
fluid temperatures can have adverse effects on elastomers, can produce undesirable volumes of
fumes and present a fire risk. Careful management of surface pits can facilitate cooling of the
drilling fluid, but the effect is usually minimal. Some operators advocate the use of mud coolers
(heat exchangers) and there is some evidence that, in the right application, this approach can
prove effective.
Symptoms and Remedial Action
Symptoms
Typical symptoms of problems associated with high temperatures are:
• High viscosity and gel strengths
• Increased filtrate
• Decreased alkalinity
These problems may manifest themselves as:
• Difficulty in breaking circulation
• Difficulty in running tools to bottom
• Difficulty in degassing circulated drilling fluid
• Differential sticking tendency
The first indications of thermal deterioration of the drilling fluid system will be seen in bottoms
up samples after trips. Trips tend to be lengthy on HPHT wells and the drilling fluid will have
been exposed to near bottom hole temperature for long periods. It is important that bottoms up
drilling fluid is tested and the results used as an indicator of future problems should remedial
treatment not be made.
Remedial Action – Water Based Drilling Fluid
• Increased Rheological Properties
• Add water – due to increased surface area of clays, increased downhole filtration and
surface evaporation drilling fluids at high temperature rapidly become dehydrated.
• Decrease solids content – reducing the percentage of low gravity solids in the drilling
fluid will facilitate the control of rheological properties and improve product
performance.
• Add deflocculants – If bottoms up samples indicate that the drilling fluid is becoming
excessively viscous it might be beneficial to increase the concentration of
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 7-49