Effects of Gas on the Phase Dynamics System

Gas carry over in two or three phase separators can occur if the flow rate is too high to give enough residence time or if the separator is partially filled with sand or silt. Another case which will release gas from solution is where there is a pressure drop large enough to cause flashing of the light ends. In these instances, the entrained gas can be carried over into the measurement instrumentation and the effect of this free gas needs to be evaluated.


In the Phase Dynamics system, the measurement is made using the microwave permittivity of the gas, oil, and water, which are 1.0, 2.5 and 70 respectively. Since the gas and oil have low permittivity, the gas looks like extra oil and therefore, the effect at lower water cuts is to reduce the measured water content. As the water percentage goes above 50% the gas effect is increased since the gas is replacing a volume in the fluids of which water is a great part. As the fluids enter the water continuous phase (typically between 60% and 90% water content) , the error in water cut due to the gas is approximately equal to the volume content of gas.

 

Actual Water % Gas Volume Percent Approx. Phase Dynamics Measured Water % Error Percentage (%)

20%
20%
20%
20%
20%

50%
50%
50%
50%

90%
90%
90%
90%

0%
2%
5%
10%
20%

2%
5%
10%
20%

2%
5%
10%
20%

20.0%
19.8%
19.5%
19%
18%

49.5%
49%
48%
47%

88%
85%
80%
70%

0%
0.2%
0.5%
1.0%
2.0%

0.5%
1%
2%
3%

2%
5%
10%
20%