BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
Planning
The successful application of a fluid in an HPHT environment is greatly influenced by pre-job
planning. Prior to drilling an HPHT interval contingencies must be in place to ensure that the
potential fluid problems, common on HTHP wells, can be anticipated and corrected.
Drilling Fluid Selection
The type of drilling fluid that will be chosen for a particular application will depend very much
on factors other than just the ultimate bottom hole temperature.
The location of the well may have an influence on selection. If the well is to be drilled in a
particularly remote or environmentally sensitive area the use of a non-aqueous-based drilling
fluid, the commonly preferred option for high temperature applications, may be restricted.
The anticipated formations and contaminants are important factors in drilling fluid selection.
Highly dispersed water based drilling fluids may not, for example, be appropriate to drill reactive
shales or formations where CO 2 or brine flows are predicted. CO 2 can have dramatic negative
effects on water based drilling fluids that do not contain lime. However water based drilling
fluids, heavily treated with lime can be particularly difficult to stabilize at high temperatures.
Polymer based drilling fluids are subject to degradation by various means at high temperature.
It can be seen that neither clay nor polymer based fluids are ideal for high temperature
environments. However, by careful choice of materials, relative to the anticipated environment,
water based drilling fluids can be run, with some difficulty, on wells with BHT up to 500°F.
Non-aqueous-based drilling fluids have a distinct HSE disadvantage for HPHT applications in
that gas is soluble in these fluids under downhole conditions. Gas is not soluble in water based
drilling fluids.
Water based drilling fluids are much less effected by temperature and pressure than non-aqueousbased
drilling fluids. This makes hydraulic modeling and ECD control appreciably more
straightforward in water based fluids.
It is therefore essential that an appropriate drilling fluid system is selected for HPHT applications
and that, as part of the planning process, the formulation of the chosen system is optimized for the
anticipated downhole environment and contaminants.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 7-51