BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
For a compound, the equivalent weight equals:
MolecularWt.
equiv . wt.
=
TotalValency of " cations"
Common equivalent weights are listed in Table 3-8.
It can now be seen that a one normal solution contains the equivalent weight of the solute in
grams dissolved in one liter of solution.
For compounds of valency one, a 1M solution is identical to a 1N solution. If the valency is two,
then a 1M solution is twice the strength of a 1N solution.
Sulfuric acid (H 2 SO 4 ) has a molecular weight of 98 (a 1 M solution is 98 g/l) and “valency” 2.
Thus its equivalent weight is 49 (a 1 N solution is 49 g/l). Thus, 1M H 2 SO 4 is 98 g/l. This
compares with hydrochloric acid, HCl, where a 1M and 1N solution both contain 36.5 g/l.
Calculation of Reacting Weights
There are two methods:
1. Write down the chemical formulas of the reactants and products and balance the equation
which describes the reaction, bearing in mind the valences of the ions involved. This
gives the ratios in which the molecules combine. Multiplying by the molecular weights
thus gives the ratios of weights, which combine.
An example calculation is given below.
Calculate the weight of sodium carbonate needed to completely remove calcium from 100m 3 of a
drilling fluid containing 1000 mg/l Ca + .
The reaction of sodium carbonate with calcium is:
Na 2 CO 3 + Ca 2+ → CaCO 3 + 2Na +
from this equation, we know that 1 mole Na 2 CO 3 reacts with 1 mole of Ca 2+
Na 2 CO 3 molecular weight = 106 (Table 3-8)
Ca 2+ molecular weight = 40.1 (Table 3-8)
Thus, 106 g Na 2 CO 3 always reacts with 40.1 g of calcium. 100m 3 of drilling fluid, with Ca 2+ at
1000 mg/l, contains 1000 x 100 mg Ca 2+ , or 100 kg Ca 2+
Units conversion
1000 mg/L x 1000L/m 3 x 1 Kg/1,000,000 mg x 100 m 3 = 100 Kg
Therefore, weight of sodium carbonate needed is:
(106 / 40.1) x 100 kg = 264 kg
3. This method involves the use of equivalent weights. The equivalent weights of
elements always combine on a 1:1 basis, since the “balancing of the equation” has
already been taken into account when dividing molecular weight by valency to
obtain the equivalent weight.
Referring to the previous example, sodium carbonate has equivalent weight 53, while calcium has
equivalent weight 20.05. Therefore, when these combine, they will do so in the ration 53g
sodium carbonate to 20.05g calcium. It is not necessary to know the formula of the reactants, nor
of the products (or even what reaction occurs).
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-25