4th International SEA Hydrocarbon Flow Measurement Workshop 9th-11th March 2005 1 Three-Phase Flow Measurement Technique Using a Coriolis Flow Meter and a Water Cut Probe Dr. Robbie Lansangan, Robert E. Dutton, P.E., Invensys Foxboro Dr. Michael Tombs, Dr. Manus Henry, Dr. Mihaela Duta, University of Oxford ______________________________________________________________ 1 INTRODUCTION The ability to measure individual component flow rates of oil, water and free gas in commingled flow without separation presents numerous advantages for the oil and gas industry. This is apparent with the continuous deployment of inline multiphase meters (iMPM) in upstream production operations. The benefits and advantages of multiphase metering in production well testing, compared to separator-based measurement, are well documented [1,2,3]. While the industry has largely accepted the use of iMPM, the purchase price and cost of ownership of these devices are still considered relatively high. Efforts to develop low-cost multiphase meters have generally been based around the use of separation devices such as a compact cyclonic separator coupled with single-phase (conventional) meters. Acceptable performance of compact separation-based multiphase metering (csMPM) relies on the complete separation of the free gas from the liquid phase. While advancement in compact separation technologies has made this achievable, changing well conditions over the life of a field or severe slug flow, for instance, can pose problems. The robustness (and perhaps, large scale acceptability) of csMPM can be realized if accurate measurements can be made under partial separation conditions. The latter requirement, however, places the burden on conventional flow meters to have acceptable performance under what has been called trace or limited multiphase flow regimes. Coriolis mass flow meters are highly regarded for their precision, accuracy and simultaneous measurement of true mass flow, fluid density and temperature. However, the meter’s stability and operability under trace multiphase conditions (less than 5% gas void fraction [GVF]) has generally been considered the Coriolis meter’s Achilles’ heel. Under such conditions it can be difficult for the flowtubes to maintain oscillation, and even at low levels of gas void fraction severe errors may appear on the measurements. While techniques to alleviate the problem have been developed, such as performing background corrections while in trace multiphase conditions, the danger of the meter ceasing to operate at higher gas voids is a looming possibility. These problems with Coriolis measurement have been investigated for over 15 years in the Invensys University Technology Centre at the University of Oxford. A novel all-digital Coriolis mass flow transmitter has been developed which is able to maintain flowtube operation throughout an extended range of two-phase flow [4,5,6]. Invensys Foxboro has made this technology commercially available in the CFT50 product range. This paper presents a new technique in multiphase measurement that utilizes a Coriolis meter with two-phase flow measurement capability and a commercially available water cut probe. The water cut probe presents additional information to provide mathematical closure for the oil, water and free gas resolution. It is envisioned that the Coriolis meter-water cut probe approach can provide the performance requirement that will allow partial separation multiphase metering to be a viable alternative in production well testing. Furthermore, this technique offers the possibility of inline measurement without any separation, for production profiles that fit that upper GVF limit from the limited multiphase standpoint and the flow rates from the meter’s flow capacity, for the Coriolis meter-water cut probe implementation.