BAKER HUGHES - Drilling Fluids Reference Manual

HORIZONTAL AND EXTENDED REACH DRILLING
from a horizontal well, one should examine a core plug from both the horizontal and vertical
planes.
Recommended Fluid Parameters
• Velocity – One of the major obstacles to overcome in horizontal and ERD drilling is hole
cleaning. In vertical holes, cuttings have room to settle without causing problems. In
horizontal wells, cuttings only have to settle 4+ inches to form a cuttings bed. Research and
practical experience has shown that cuttings bed formation is analogous to sand dunes on an
ocean beach. The bed moves in a wave fashion up the hole. If sufficient annular velocity is
not present, the bed thickens until it reaches equilibrium, which usually occurs when
turbulent flow conditions exist. With water, turbulent flow is easily obtained since viscosity is
in the denominator of the turbulent flow equation, and water has a viscosity of 1. Fluids other
than water require more pump output to approach turbulent flow conditions. Practical
experience in other industries has proven that materials can be transported in water slurries if
the fluid velocity is between 3 and 7 ft/sec.
• Rheological Properties – Ideally one would want a true thixotropic fluid to drill horizontally.
In effect, two different conditions exist simultaneously. One occurs in the vertical portion of
the hole where larger diameter casing may be set, or wash-outs in the open hole occur. In that
case, a fluid having a high Yield Stress, or if the fluid is visco-elastic, the initial gel strength
needs to be elevated. The opposite is needed in the horizontal section from a hole-cleaning
point of view. Here one wants water for the reasons pointed out earlier. Compromises are the
result. If casing is set into the zone of interest, or if formations up-hole are not a problem,
then water may be possibly combined with occasional sweeps.
• Surface Apparatus – Special attention must be placed on the solids removal equipment at the
surface. Solids removal efficiency must be continually monitored so that unwanted
particulate material is not retained in the fluid system that may negatively affect fluid weight
or filter cake quality, resulting in lost circulation or increased torque and drag. The cost of
problems that may occur due to not doing this correctly may far outweigh the cost of
equipment needed.
• Common Fluid Utilized – Table 11 - 2 is a comparison of drilling fluids utilized in horizontal
wells which can vary depending upon the area in question, historical preference,
environmental constraints, fluid company experience, and operator. Types have included gel
and water, oil based fluids, polymers, and in some cases, sized-salt systems. Combinations of
the above, as well as other fluids have been tried.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006. 11-24