BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
2CH
3COOH
+ 2 Na → 2CH
3COONa
+ H
2
↑
Acetic acid + sodium → Sodium acetate + hydrogen
In both cases, the products are a salt and hydrogen gas. The number of hydrogen atoms that are
available to be replaced is known as the basicity of the acid. Both hydrochloric acid and acetic
acid are monobasic, since only one hydrogen is replaceable. Sulfuric acid is dibasic, as both of
the hydrogen atoms can be replaced.
Dibasic salts and tribasic acids can form salts in which not all of the hydrogen atoms are replaced.
These are generally acidic in nature, as further replacement of hydrogen is possible. Examples
Are: NaHCO 3 ,– sodium hydrogen carbonate, also called sodium bicarbonate, or bicarbonate of
soda; NaH 2 PO 4 – sodium dihydrogen phosphate; and Na 2 HPO 4 – disodium hydrogen phosphate.
Bases and Alkalis
A base is a compound that will react with an acid to form a salt and water only. A base that is
soluble in water is called an alkali.
Bases are either oxides or hydroxides of metals. Alkalis are exclusively hydroxides of
electropositive metals. Thus CuOH – copper (I) hydroxide and Fe 2 O 3 – iron (II) oxide are both
bases, since they are both insoluble. NaOH – sodium hydroxide (caustic soda) and NH 4 OH –
ammonium hydroxide, are both soluble and are alkalis. The reaction of an acid with a base and
an alkali is illustrated by the following equations:
FeO + HCl → FeCl + 2
H
2O
Iron (II) oxide + hydrochloric acid → iron (II) chloride + water
NaOH + HCl → NaCl + H
2O
Sodium hydroxide + hydrochloric acid → sodium chloride + water
Both acid and base are said to be neutralized as the resulting solution is neutral, in other words,
neither acidic (containing an acid) nor alkaline (containing an alkali).
Other compounds react with acids to produce a salt and water, but are not strictly bases, as other
compounds are formed in the reaction. Thus all carbonates and hydrogen carbonates are
decomposed by acids, liberating carbon dioxide as a gas. For example:
pH
CaCO3 + 2 HCl → CaCl2
+ CO2
+ H
2O
Calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water
This equation describes the reaction that occurs when acidizing a limestone reservoir rock to
increase the flow of oil. A strong solution of hydrochloric acid is pumped down the well and
reacts with the limestone (mainly calcium or magnesium carbonate), thus enlarging the fissures
and pores in the rock and allowing the oil to flow more freely.
Water itself is very slightly ionized under ordinary conditions. Thus a very small number of
hydrogen and hydroxide ions exist free in solution and in equal numbers.
H2O ↔ H+ + OH⎯
Water ↔ hydrogen ion + hydroxide ion
Reference Manual
Baker Hughes Drilling Fluids
3-18 Revised 2006