Emerson’s Svein Erik Gregersen and John Goetz discussed oil & gas multiphase metering. Their abstract:
For over 20 years, Roxar has delivered innovative multiphase (oil, gas, and water) flow measurement solutions to offshore & subsea oil and gas customers. Over this period, multiphase flow technology has undergone an impressive evolution with meters becoming increasingly accurate, compact, and easy to use. Come learn the basics of multiphase metering along with an exciting look ahead at Emerson’s next generation products that include innovations from both Roxar and Rosemount.
Svein Erik opened with multiphase metering basics. These meters provide accurate, real-time flowrates for oil, gas, and water mixtures, which is vital information for managing reservoirs and processes. They detect critical conditions within subsea topside within the well such as water/gas breakthrough, hydrate formation, or increased sand production.
Oil & gas producers use multiphase meters to reduce the number of production stops to perform well tests which include test separator and time the well is diverted from production to test. For subsea installations, flowlines can be comingled subsea.
Svein Erik explained Gas Volume Fraction (GVF) – The gas volumetric flow rate, relative to the multiphase volumetric flow rate, at the pressure and temperature prevailing in that section. The GVF is normally expressed as a fraction or percentage.
Roxar Multiphase meters are designed for oil wells with increasing GVF over time.
Wetgas meters are designed for gas wells with decreasing GVF over time. Wetgas meters are available for subsea and surface applications.
The multiphase meter includes densitometer that determines the gas vs. liquid content. Capacitance and inductance electrodes measures the %liquid that is hydrocarbon vs. water. Differential pressure transmitters measuring across a Venturi provide the liquid flow rate. The time lag measured between separated capacitance and inductance electrodes determines the velocity of the gas. Finally, a flow computer is used to analyze the data quickly and compute flow rates for each phase. From the flow computer, data is output digitally.
The multiphase meter is designed to address challenges such as offshore platform size and weight considerations, changing field and flow conditions, increasing requirements for reliability and accuracy, and increasingly complex reservoirs.
Svein Erik described a new technology development for a subsea multiphase flowmeter that is capable of 15,000 psi at 180C. These meters incorporate an ultra-compact subsea Rosemount DP transmitter with remote seals. These meters can be applied in depths up to 3,000 meters (5,700 psi) and allow operators to distinguish injected H2O from reservoir H2O due to water breakthrough through salinity measurement.
John described how the Rosemount 3251 Subsea DP transmitters (expected 2015 release) have been designed for the increased pressure requirements of subsea applications up to 15,000 PSI. The heart of the sensor is the proven 3051S SuperModule which has had changes made to accommodate the subsea requirements.
Remote seals are used to isolate the sensors and electronics from the high process temperatures as well as hydrates forming in the high and low side pressure lines.
