Two-phase flow metering of heavy oil using a Coriolis mass flow meter: A case study

An aeroelastic model of Coriolis mass and density meters operating on aerated mixtures

There are large measurement errors in Coriolis mass flowmeter (CMF) when it is used to measure gas-liquid two-phase flow without compensation. In particular, the flowtube of CMF may stall when using analog transmitters and CMF cannot operate normally because of the high damping caused by gas-liquid two-phase. To solve above problems, a gas-liquid two-phase flow rig is developed to perform the two-phase flow experiments. A digital drive method using multiplying digital-to-analog converter and direct digital synthesizer is applied to CMF to maintain the flowtube oscillation under two-phase flow condition. A digital zero-crossing detection method based on Lagrange interpolation is adopted to calculate the frequency and phase difference of the sensor output signals in order to synthesize the digital drive signal and realize the flow measurement. The artificial neural network using back propagation algorithm is applied to correct measurement errors. A digital Coriolis mass flow transmitter is developed with a digital signal processor to control the digital drive, and realize the two-phase flow measurement and correction. By connecting the developed transmitter with a CMF025 type primary instrument, the gas-liquid two-phase flow experiments are conducted to validate the performance of the transmitter. The testing results show that the transmitter can maintain the flowtube oscillation and reduce the metering errors.

Gas–Liquid Two-Phase Flow Correction Method for Digital CMF

Density is an important physical property and its measurement has wide application in a vast number of industries including; oil and gas, petrochemical, pharmaceutical, brewing, food & beverage production and mining. Density is often required to be accurately measured either as a standalone property or in combination with other flow properties for the purpose of quality assessment, process control, and custody transfer. Given the increasing importance of density measurement, extensive research has been conducted over recent years to develop newer and more accurate density measurement sensors and to improve the accuracy of existing sensors.


This thesis describes the design and development of a novel, non-invasive, non-radioactive Vibrating Density Measurement System (VDMS) capable of measuring fluid density in both single phase and multiphase flows. The device is also capable of measuring mean in-situ phase volume fractions in two-phase flows. The VDMS comprises three sub-units; (i) a measurement unit which includes a straight length of sensing pipe with corrugated bellows at both ends, an actuator and relevant sensors; (ii) a signal conditioning and processing unit; and (iii) a data acquisition unit.


The thesis also reports the development of a novel mathematical density prediction model which is used in conjunction with the VDMS. It then goes on to report the results of static bench test experiments that were conducted on the VDMS using a bespoke test rig. These tests were performed (i) to obtain the mass of the sensing pipe, its stiffness constant and damping constant; (ii) to investigate the frequency response characteristics of the VDMS; (iii) to obtain the VDMS constant; (iv) to investigate the sensing pipe displacement pattern; (v) to investigate the capability of the VDMS to give accurate density measurements of static fluids and (vi) to define the optimal VDMS operating conditions. Computation of density was achieved using the VDMS, the density prediction model and a novel signal processing technique. This signal processing technique used the Discrete Fourier Transforms (DFTs) of the measured force, used to mechanically excite the sensing pipe at its centre, and the measured displacement at the sensing pipe centre.



Next, the thesis reports a novel computer based control system that was developed to ensure that the VDMS automatically operated at its optimal operating conditions, so that errors in the density measurement were minimised. The control system was also capable of providing online computation of the flow mixture density.


Results are reported of several experiments conducted by the author on the VDMS to measure the fluid density in a range of “water only” flows, “solids-in-water” flows and “air-in-water” flows. These flows were all vertically upward and were established in the working section of a multiphase flow loop. These multiphase flow experiments were subsequently extended to compute the mean in-situ phase volume fraction of the solids phase in “solids-water” flows and the gas phase in “air-water” flows. For the “water only” and “solids-water” flow experiments, the mean error in the predicted density was consistently within 0.5% of the reference density and the standard deviation of the error was less than 1%. For “air-in-water” flows the predicted density was within 1% of the reference density for flows where the air volume fraction in the mixture was less than 10%.


The mean in-situ volume fractions, measured by the VDMS, of the dispersed solids in “solids-in-water” flows and of the dispersed air in “air-in-water” flows were within 10% of the reference measurements for the vast majority of measurements taken.


Finally, the thesis describes a modified mathematical model, used with the VDMS, for predicting mixture density in “air-in-water” flows. This modified model is extended to make use of the predicted coupling stiffness between the VDMS sensing pipe and the multiphase mixture. The modified model gave density measurements with a higher order of accuracy than the earlier model which did not consider the effect of the flow compressibility on the coupling between the sensing pipe and the pipe contents.

Density Measurement of Multiphase Pipe Flows

High pressure measurement of mud density and flow rate for oil and gas well construction: Making the case for X-Ray metering

The largest problem users have with Coriolis flow meters is that they are sensitive to two phase fluids-primarily gas in liquids ('aeration'). 'Sensitive' means that they can convey the wrong mass flow and/or density reading, or, in the worst case, they could stop measuring all together. We explain this phenomenon in classical U-tube meters and give recommendations on how to handle such applications.

M. Seeger

Papers

Coriolis flow measurement in two phase flow