BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
Total Volume = (35 bbl + 10 bbl) = 45 bbl
• Materials to mix 45 bbl slurry
Water = 26.9 × 45 = 1121 gal = 29 bbl
SAPP = 0.5 × 29 = 14.5 lb
Caustic Soda = as needed
Barite = 5.3 × 45 = 239 sacks
Total Slurry Volume = 239 × 0.189 = 45 bbl
A non-settling barite plug using lignosulfonate as a thinner has been recommended by some.
The materials required are listed below. One advantage of lignosulfonate is that it can be used
in either fresh or sea water. It is recommended that the plug be non-settling and designed to
provide a hydrostatic kill. The reasoning is that it is more reliable than a barite plug designed to
settle. A settling plug can also be formulated if desired.
Field Mixing Procedure for Barite Plugs (Nonsettling)
(1 bbl of 21 lb m /gal Density)
1. Prepare mix water equal to 54% of final volume.
2. Mix,
• Water (fresh or sea), 0.54 bbl
• Lignosulfonate, 15 lb
• Caustic Soda, 2 lb
• XANPLEX D, 1 lb
• Defoamer, if needed
For settling pill, omit XANPLEX D Polymer
3. Add barite to mix water to prepare the final slurry.
A 21 lb m /gal slurry will require 700 lb of barite per finished bbl.
Gas Kicks in Invert Emulsion Fluids
Detection of gas kicks while drilling with an invert emulsion fluid is made more difficult
because of the solubility of gas in oil. The amount of solubility is dependent on (1)
composition of the formation gas, (2) composition of the oil used in the fluid, (3) pressure, and
(4) temperature. Even a low volume influx that goes undetected will rapidly expand when it
reaches the surface and cause unloading of fluid from the hole. This reduces bottomhole
pressure, allows additional gas influx, and an uncontrolled situation (blowout) can develop.
The key to well control in oil fluids is quick detection and proper shut-in procedures.
The problem lies in that the normal surface responses to gas kicks in oil fluids are dampened
because of the solubility of the gas in the oil. The rig crews must be aware of the differences in
responses to gas kicks in oil fluids and be prepared to detect small changes in pit levels, flow
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-37