BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
lb m /bbl Lime = .26( P m – F 1 P f )
where,
F l = percent retort water, or can be estimated by,
lb
m /bbl excess Lime
=
P m – P f
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4
5. Fluid loss control should be maintained with CMC, BIO-LOSE, and MILSTARCH, as
needed.
6. Solids concentration should be kept at a minimum; otherwise, the additions of lime and
fluid loss control materials such as starch or CMC cause undue increases in flow
properties and gel strengths.
7. Small additions of MILGEL to maintain proper colloidal distribution in the lime fluid is
often necessary for maximum filtration control.
8. Lime fluids are considered to be ideal rheological condition when they possess zero initial
and 10-minute gels and when lime additions do not cause flow property increases. Flow
properties are easily controlled under normal conditions with sufficient amounts of water
and/or chemicals.
Treatment of Contamination in Lime Fluids
1. Salt – Lime fluids will tolerate salt contamination up to 50,000 mg/L if the fluid is in
proper condition. Since an increase in salt increases the solubility of the calcium ion, the
lime fluid should be treated with large concentrations of caustic soda to maintain a high P f
which will limit the level of soluble calcium. UNI-CAL should be added as needed to
control the rheological properties during salt contamination.
2. Gypsum and Anhydrite – Under normal conditions, drilling of gypsum or anhydrite has
little or no effect on a properly-treated lime fluid. However, when large quantities are
drilled, the lime fluid may exhibit increases in flow properties and gel strengths, as well as
increased API Filtrate. Caustic soda can be used as a pretreatment or a post-treatment to
maintain the P f at the desired level. Lime additions are not necessary when gypsum is
encountered until the P m begins to decrease. UNI-CAL should be added to the fluid to
help restore and maintain flow properties. MIL-PAC, MILSTARCH, BIO-LOSE, or CMC
should be used for filtrate control depending upon the severity of the contamination.
3. Cement – Cement has very little effect on properly-conditioned lime fluids. If the solids
content is in balance and sufficient UNI-CAL has been added to the fluid, little or no
change will occur. However, when large quantities are drilled, the fluid alkalinity
increases and calculates out as additional excess lime. This is not normally detrimental
unless the cement concentration becomes so high that the total solids content is increased,
in which case proper use of solids control equipment is necessary.
4. Temperature – High-temperature gelation and solidification is a major problem with lime
fluids. Higher alkalinity along with high-lime content of this system causes it to be more
difficult to control when subjected to excessive temperature. Depending upon the
concentration of low specific gravity solids and the amount of excess lime and alkalinity,
solidification may occur at a temperature as low as 275°F. The degree of gelation or
solidification depends upon the concentration of solids, alkalinity of the fluid, and amount
Reference Manual
Baker Hughes Drilling Fluids
3-42 Revised 2006