BAKER HUGHES - Drilling Fluids Reference Manual

Fundamentals of Drilling Fluids
Chapter 1
A major component in drilling operation success is drilling fluid performance. The cost of searching
for hydrocarbon reserves becomes more expensive when drilling occurs offshore, in deep water, and
in hostile environments. These drilling environments require fluids that excel in performance.
Measuring fluid performance requires the evaluation of all key drilling parameters and their
associated cost. Simply stated, the effectiveness of a fluid is judged by its influence on overall well
cost. This chapter discusses the various fundamentals of drilling fluids and their performance in
assuring a safe and expeditious drilling operation at minimum overall cost.
Functions of Fluids
Promote Borehole Stability
A fluid helps establish borehole stability by maintaining a chemical and/or mechanical balance.
Mechanical Stability
The hydrostatic pressure exerted by the drilling fluid is normally designed to exceed the existing
formation pressures. The desired result is the control of formation pressures and a mechanically
stable borehole. In many cases, these factors must also be considered:
• Behavior of rocks under stress and their related deformation characteristics
• Steeply dipping formations
• High tectonic activity
• Formations with no cohesive (lack of proper grain cementation) strength
• High fluid velocity
• Pipe tripping speeds and corresponding transient pressures
• Hole angle and azimuth
Any of these factors may contribute to borehole instability. In these situations, a protective casing
string may be required, or hydrostatic pressure may need to be increased to values greater than the
anticipated formation pressure.
Chemical Stability
Chemical interactions between the exposed formations of the borehole and the drilling fluid are a
major factor in borehole stability. Borehole formation hydration can be the primary cause of hole
instability, or a contributing factor.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISED 2006 1-1