BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
of addition of deflocculant and caustic soda should be increased along with an increase in
water dilution.
5. The API Filtrate is normally controlled with starch and/or CMC. Periodic additions of
MILGEL ® normally should be accompanied by treatments with a deflocculant.
6. After all chemicals have been added to the fluid system, a check should be made of fluid
properties. Minor adjustments can then be made on subsequent circulations with
additional lime, UNI-CAL ® , caustic, and a fluid loss control agent such as MIL-PAC ® .
7. The addition of lime and MILSTARCH ® , BIO-LOSE ® , BIO-PAQ ® or CMC
simultaneously through the hopper should be avoided because of drastic viscosity
increases.
8. Typical fluid properties after conversion and before weight-up are as follows.
Table 3-12
Typical Fluid Properties after Conversion and Before Weight-up
Fluid Weight
10.0 lbm/gal
Funnel Viscosity
40 to 44 sec/qt
Plastic Viscosity
18 cP
Yield Point 6 lb f /100 ft 2
Gels 0/0 lb f /100 ft 2
API Filtrate
6 to 12 cc/30 min
Calcium
75 to 200 mg/L
pH 11.5 to 12.0
Pf
1.0 to 2.0 ml
Pm
5.0 to 10.0 ml
Excess Lime
1.0 to 2.0 lbm/bbl (low
lime)
9. Occasionally, it is necessary to convert weighted fluids when dilution is not practical. In
this case, the fluid can be converted in the surface pits and displaced down the hole in
stages.
Maintenance of Lime Fluids
1. Lime fluid properties to be maintained should be determined and recorded; i.e., low-lime,
moderate-lime, or high-lime properties.
2. The P f and excess lime should be adjusted and maintained at near equal values. Low
excess lime with high P f or high excess lime with low P f tends to cause rheological
difficulties, i.e. the concentration of soluble calcium from lime is a function of pH, the
higher the pH the less soluble.
3. Caustic soda should be added to adjust the P f . The alkalinity of the filtrate affects the
solubility of added lime. As the filtrate alkalinity approaches 1.0 ml, the solubility of lime
decreases rapidly. After the 1.0 ml level is reached, solubility is only slightly affected.
Normal additions of lime to the fluid will maintain the alkalinity of the fluid and the
filtrate so that only small portions of caustic soda are required to maintain the desired
alkalinity level in the filtrate.
4. Lime is added to maintain the desired P m which controls the amount of excess lime.
Excess lime can be calculated by the formula.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-41