STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

662 Drilling and Well Completions
Alkalinity and Lime Content. The whole mud alkalinity test procedure is a
titration method which measures the volume of standard acid required to react
with the alkaline (basic) materials in an oil mud sample. The alkalinity value is
used to calculate the pounds per barrel unreacted “excess” lime in an oil mud.
Excess alkaline materials, such as lime, help to stabilize the emulsion and also
neutralize carbon dioxide or hydrogen sulfide acidic gases.
To approximately 20 ml of a 1:l mixture of toluene (xy1ene):isopropyl alcohol,
add 1 ml of oil-base mud and 75 to 100 ml of distilled water. Add 8 to 10 drops
of phenolphthalein indicator solution and stir vigorously with a stirring rod (the
use of a Hamilton Beach mixer is suggested). Titrate slowly with H,SO, (N/lO)
until red (or pink) color disappears permanently from the mixture. Report the
alkalinity as the number of ml of H,SO, (N/10) per ml of mud. Lime content
may be calculated as
Lime, ppb = ( 1.5)(H,S04, ml)
Calcium Chloride [25]. Calcium chloride estimation is based on calcium
titration. To 20 ml of 1:l mixture of toluene (xy1ene):isopropyl alcohol, add a
1-ml (or O.l-ml, if calcium is high) sample of oil-base mud, while stirring.
Dilute the mixture with 75 to 100 ml of distilled water. Add 2 ml of hardness
buffer solution and 10 to 15 drops of hardness indicator solution. Titrate
mixture with standard versenate solution until the color changes from winered
to blue. If common standard versenate solution (1 ml = 20 g calcium
ions) is used, then
CaCl,, ppb = (0.4)(standard versenate, ml)
If strong standard versenate solution (1 ml = 2 g calcium ions) is used, then
CaCl,, ppb = (4.0)(strong standard versenate, ml)
Sodium Chloride [25]. Sodium chloride estimation is based on sodium titration.
To 20 ml of a 1:l mixture of toluene (xy1ene):isopropyl alcohol, add a 1-ml sample
of oil-base mud, stirring constantly and 75 to 100 ml of distilled water. Add 8-10
drops of phenolphthalein indicator solution and titrate the mixture with H,SO,
(N/lO) until the red (pink) color, if any, disappears. Add 1 ml of potassium
chromate to the mixture and titrate with 0.282N AgNO, (silver nitrate, 1 ml =
0.001 g chloride ions) until the water portion color changes from yellow to
orange. Then
NaCl, ppb = (0.58)(AgNO,, ml) - (l.OG)(CaCl,, ppb)
Some other procedures for CaCl, and NaCl content determination are used
by mud service companies. Although probably more accurate, all of them are
based on calcium filtration for CaCl, detection and on chlorides filtration for
NaCl detection.
Total Salinity. The salinity control of oil-base mud is very important for
stabilizing water-sensitive shales and clays. Depending upon the ionic concentration
of the shale waters and of the mud water phase, an osmotic flow of
pure water from the weaker salt concentration (in shale) to the stronger salt
concentration (in mud) will occur. This may cause a dehydration of the shale
and, consequently, affect its stabilization.