BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
Figure 3-21
Relative Inhibition of Tertiary Clay in KCl Solutions
MIL-PAC LV – Low viscosity polyanionic cellulose will provide a degree of polymer
encapsulation, but its principle function is in the control of the API filtrate. MIL-PAC LV as a
filtration control agent will impart minimal viscosity to the system. Concentrations will vary with
filtration rate desired and overall salinity of the fluid. Normally, a treatment level of 1.43 to 5.7
kg/m 3 (0.5 to 2.0 lbm/bbl) will provide the desired results.
MIL-PAC R – The regular grade polyanionic cellulose functions in a similar way to the low
viscosity version but will also impart viscosity. The ratio of MIL-PAC R to MIL-PAC LV will
control the degree of viscosity-to-filtrate control required. MIL-PAC R will impart a significant
level of high shear viscosity, but minimal gel strength.
Traditionally, the gel strengths in the system were provided in part by formation clays in a
conventional polymer system while drilling in a reactive area. However, the high level of
inhibition provided by AQUA-COL has led to minimal increase in gel strengths. On recent wells,
the concentration of MIL-PAC R has been decreased in favor of XAN-PLEX D polymer.
Improved hole cleaning is a direct result of this change. To reduce fluid loss or increase viscosity,
1.43 to 5.7 kg/m 3 (0.5 to 2.0 lbm/bbl) is normally required.
XAN-PLEX D– Xanthan gum used to increase viscosity and gel strengths, as well as to aid in
suspending weight materials and cuttings. Normal treatment is 2.85 kg/m 3 (1.0 lbm/bbl) to
achieve a funnel viscosity of 35 to 38 sec/qt.
NEW-DRILL – This is a PHPA polymer supplied in fine powder form. The high molecular
weight of this anionic polymer is designed to encapsulate and reduce drill cutting dispersal and
swelling. Addition of a PHPA polymer is a preventative measure and not a cure for high solids
induced mud rheological properties. If PHPA polymer is added to a system that is solids laden,
this will result in excessive viscosities. NEW-DRILL additions to new polymer fluid will result in
a viscosity hump, therefore, allow a minimum of four (preferably eight) hours mixing time. If the
drill-out formation is a clay, then it is recommended that a minimum of half the NEW-DRILL
concentration be added prior to displacement. The level of NEW-DRILL in the system can be
monitored using the Clapper Gas Train test. While this provides only approximate values, it will
clearly indicate an excess of the polymer in the system. A minimum excess of 1.0 lbm/bbl is
recommended.
Reference Manual
Baker Hughes Drilling Fluids
3-84 Revised 2006