Continuing on from my previous article, lets put a few numbers in:
- Density of crude: 700 kg/m3
- Density of water: 1000 kg/m3
Case 1
- 99 kg crude, 1 kg H2O.
- Mass fraction: 99% crude, 1% H2O (no surprises here)
- Volume fraction: 99.3% crude, 0.7% H2O
Case 2
- 70 kg crude, 30 kg H2O.
- Mass fraction: 70% crude, 30% H2O (again, no surprises)
- Volume fraction: 77% crude, 23% H2O
Now, what does this mean? Well, if you measure the volumetric fraction of water, and assume that it is the same as the mass fraction, you will understate the mass of water in your sample. If your transactions are on a mass basis, than the amount of crude sold is overstated.
Engineering moral: not only are units important, the basis of measurement is important as well.
I’ll attach a short PowerPoint presentation that restates the numbers used above.
Posted by Wata 
Wata - Malaysian Oil and Gas Engineer 