Abstract:
The accurate measurement of multiphase flows of oil/water/gas is a critical element
of oil exploration and production. Thus, over the last three decades; the development
and deployment of in-line multiphase flow metering systems has been a major focus
worldwide. Accurate measurement of multiphase flow in the oil and gas industry is
difficult because there is a wide range of flow regimes and multiphase meters do not
generally perform well under the intermittent slug flow conditions which commonly
occur in oil production.
This thesis investigates the use of Doppler and cross-correlation ultrasonic
measurements made in different high gas void fraction flow, partially separated
liquid and gas flows, and homogeneous flow and raw slug flow, to assess the
accuracy of measurement in these regimes.
This approach has been tested on water/air flows in a 50mm diameter pipe facility.
The system employs a partial gas/liquid separation and homogenisation using a T-Y
junction configuration. A combination of ultrasonic measurement techniques was
used to measure flow velocities and conductivity rings to measure the gas fraction. In
the partially separated regime, ultrasonic cross-correlation and conductivity rings are
used to measure the liquid flow-rate. In the homogeneous flow, a clamp-on
ultrasonic Doppler meter is used to measure the homogeneous velocity and combined
with conductivity ring measurements to provide measurement of the liquid and gas
flow-rates. The slug flow regime measurements employ the raw Doppler shift data
from the ultrasonic Doppler flowmeter, together with the slug flow closure equation
and combined with gas fraction obtained by conductivity rings, to determine the
liquid and gas flow-rates.
Measurements were made with liquid velocities from 1.0m/s to 2.0m/s with gas void
fractions up to 60%. Using these techniques the accuracies of the liquid flow-rate
measurement in the partially separated, homogeneous and slug regimes were 10%,
10% and 15% respectively. The accuracy of the gas flow-rate in both the
homogeneous and raw slug regimes was 10%. The method offers the possibility of
further improvement in the accuracy by combining measurement from different
regimes.
