BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
Thus to remove 100 kg of calcium requires (53/20.05) x 100 kg of sodium carbonate giving 264
kg as before
In some calculations, milliequivalents are used. This is simply 1/1000 of the equivalent weight.
Thus 1 milliequivalent (1 me) is the equivalent weight in milligrams.
Techniques of Chemical Analysis
In order that a drilling fluid may function correctly, it is important to monitor its chemical
composition. If the chemical composition varies from that required for optimum performance,
then this variation will be detected and corrections can be made.
Chemical analysis is nearly always done on the filtrate rather than on the drilling fluid itself. The
reason for this is that the viscosity, solids content and even the color of the drilling fluid make
analysis difficult or may interfere with the analysis itself. The filtrate can be used because, with
the exception of polymers which are rarely analyzed for, it contains the same concentration of
dissolved substances as the drilling fluid.
Methods of Testing for Dissolved Ions
The most common method is to take a solution of known strength (often called a standard
solution) of a compound which reacts with the particular ion to be measured. This solution is
added gradually to a known volume of the filtrate until the reaction is just complete. Then,
knowing the volume of solution added, its concentration and the chemistry of the reaction that
occurs, it is possible to work out how much of the ion under test is in the filtrate. This is the
titration method of chemical analysis.
This technique requires an accurate measure of the volumes of filtrate and standard solution and
an accurate method for determining the “end point” of the reaction. This end point is the exact
point at which all of the ions being tested for have reacted with the standard solution.
Measurement of Volumes
An accurate measurement of volumes is accomplished by using pipettes and burettes. These are
glass or plastic tubes which are calibrated on the outside to measure liquid volumes. (See Figure
3-14.
Reference Manual
Baker Hughes Drilling Fluids
3-26 Revised 2006