A study on the affect of sulfur and a change in the API gravity on the Phase Dynamics' water-cut system is outlined below. Eight samples of different crude oils with varying gravity and sulfur were supplied by ARCO Pipeline for this evaluation. The gravity varied from API 22 to API 40 and the sulfur from 0.343 to 2.17%.
The test procedure included the following steps:
1.) Measure API gravity and correct for temperature.
2.) Load a flow loop which includes a Phase Dynamics system with a sample of oil and circulate.
3.) Pull a representative sample and determine the water-cut by distillation.
4.) Inject at a constant rate from the initial water cut to 4% total volume of water into the loop while measuring the apparent water-cut with the Phase Dynamics system.
Figure 1 shows the calibration factor required to zero out the water-cut change vs. API gravity and a best fit straight
line. From this data a factor of -0.174% change in water-cut offset per +1 degree API gravity can be determined. The
sulfur data deviation from a straight line vs. sulfur content appeared to be statistically randomly scattered. It can be
concluded that the sulfur content is not a function of water-cLd error. The calibration factor mentioned above is used as
an offset from a single point Karl Fischer or distillation where the crude oil API gravity is also known. With this single
point calibration, when another crude oil with a known API is to be measured, the correct calibration offset can be
determined for accurate readings.
For example; A single point calibration was performed and gave a 0.25% water-cut and a API gravity of 30. If the
water-cut read on the Phase Dynamics system was 0.3% when the calibration sample was pulled, then an offset of
-0.05% is placed into the memory. If the next crude type comes on line and its API is 22 then:
(Cal AP I - New AP 1) * (-0. 174% factor) + (Cal offset) = New Offset
(30-22) * (-0.174%) + (-0.05%) = -1.34% New Offset
The Phase Dynamics Analyzer can be corrected for varying API gravities once a calibration for a given crude is performed. Other crude oils of known API gravity are easily corrected by entering a water-cut offset using the above equation. Sulfur content has no effect on the system.