MFM Wet Gas Meter

Technology Overview

Multiphase Flow Meter Wet Gas Meter comprises a standard venturi meter (as per ISO5167-4) with a recovery tapping. The mass rate is calculated from the standard Bernoulli equation assuming dry gas flow corrected for overreading due to the presence of the liquid phase. Liquid fraction required for the correction term can be estimated on-line by Multiphase Flow Meter WGM (from recovery pressure analysis – with proprietary Multiphase Flow Meter technology) and/or by means of tracer dilution technology.

Multiphase Flow Meter Wet Gas Meter (Venturi)

The dry gas flow equation across a differential device is given by:

 

Wet gas overreading correction correlation by de Leeuw is used to correct for overreading.

Where, X (the Lockhart-Martinelli Parameter) is defined as:

Where. Froude number is defined as:

Where, Usg is gas superficial velocity.

It is seen that de Leeuw correction requires a-priori knowledge of the liquid fraction. An estimate of the liquid fraction can be obtained from the recovery pressure (empiricial correlation giving liquid fraction as a function of recovery pressure as a fraction of pressure change across the venturi). Another techique, which is in favour is the tracer technique. If the objective of the measurement is just an accurate gas rate measurement we recommend the former as being quite adequate. We have analysed the relative contribution of the dry gas and wet-gas correction terms as described below

Liquid Fraction Error

As shown in the chart on the right, the wet-gas correction error (ie liquid fraction error) is relatively small. For example, at GVF=0.98, an increase in the liquid fraction error from 20% to 100% results in the doubling of the wet gas total measurement error from 3% to 6%.

 

 

Pressure and GVF Effect

The correction term is however quite sensitive to pressure. For example, consider the chart on the right. Under same measurement conditions and error margins, reducing the pressure from 60 bar to 15 bar results in increasing the error in the wet gas measurement by a factor of three.
 

Water Composition Measurement

Water composition measurement is not available with the venturi configuration but the cone configuration is capable of measuring watercut (limited to 50% water). Water composition is measured by means of capacitance technology. Further information is provided in Multiphase Flow Meter Water-inOil Meter brochure.

Multiphase Flow Meter Wet Gas Meter (Cone)

 

 

 

 

 

 

 

Tracer Dilution

PSL works with partners in providing tracer dilution measurements where this service is required.

 

 

 

 

 

 

Specification

Calibration Inputs (standing data)

• Gas composition or compressibility factor
• Liquid fraction (with tracer dilution option)
• Oil API gravity and water-cut

Outputs

The following outputs are provided:

• Gas flow rate (mass or volume)
• Liquid fraction
• Pressure
• Temperature

Operating Envelope

A sizing calculation will be made to suit given operating conditions. An example is shown on the right.

Limits

• Liquid fraction: up to 5 % by volume
• API gravity: No limitation (but must be specified a-priori)
• Water fraction: No limitation (but must be specificed a-priori).
• Ambient temperature: -40 to 85°C
• Process temperature: -40 to 120°C
• Process pressure: Maximum 100 bara

Mechanical and Electrical

• Pipe Diameter Customer specification
• Materials: Customer specification
• Flange connections: Customer specification
• Certification: EEx ia IIC T4/T6
• Power Supply: 24 VDC or 110/220 VAC

 

Transmitters

Multiphase Flow Meter WIO uses the following oil industry standard transmitters.

 

Flow Computer

The signals are processed in low power consumption computer installed on the flow line or an industrial PC in the safe area, Measurements can be transmitted via the SCADA interface

• Hazardous Area : Beckhoff CX1010 microprocessor in field enclosure Zone 1
• Safe area: 19” Rack mount industrial PC
• Software: Multiphase Flow Meter Wet Gas Metering Software
• Comms Protocol: Modbus, HART

 

Software

Multiphase Flow Meter Wet Gas is founded on a user friendly Windows based software package which handles all the data acquisition and measurement tasks. Measurements are displayed in real-time strip charts and saved in a database, Diagnostic and reporting functions are available. Measurements can also be transmitted in analog or digital form via Ethernet and serial ports under a number of protocols.