Development of a Multiphase Flowmeter without Radioactive Source

Abstract

Abstract Development of a multiphase metering system, which measures unseparated oil, gas and water flow rates, is one of the key technologies to improve subsea production. Adopting a multiphase metering system benefits subsea oil and gas production. For example, subsea production wells can be directly and continuously monitored, and associated platforms can be downsized by omitting test separators. Most of the commercially available multiphase flowmeters have several technical problems. In view of this, Japan National Oil Corporation launched a 6-year joint project to develop a multiphase flowmeter in April 1995. Our multiphase flowmeter is safe for both personnel and the environment, because there is no radioactive source. Furthermore, it has no moving parts and therefore has minimal maintenance requirements. The flowmeter consists of two capacitance sensors and a venturi meter, and uses a measurement technique which is not affected by the flow patterns or the slip velocity between liquid and gas. The performance of this meter has been evaluated in a threephase flow of tap water, lubricating oil and air in a horizontal 2inch test line, mainly in slug flow and elongated bubble flow. Water flow rates up to 8.2 m3/h, oil flow rates to 8.2 m3/h and air flow rates to 6.5 Nm3/h were tested. Most of the test results show that the total muItiphase flow rate error (TM error : specified uncertainty of one phase / multiphase flow rate) of the oil phase is within +/-10%. Especially in fluid with high water cut, the performance is good. Introduction In the recent years, many oil-production countries have aggressively stepped up development of deepwater offshore hydrocarbon fields.1 Many oil and gas discoveries are expected in many promising deep water basins of the world, including Northwest Palawan located offshore of the Philippines, the Gulf of Mexico, Campos Basin of Brazil and the North Sea. In many of these area, subsea production systems are proposed for field development. For such systems, a key technology for their implementation is the use of multiphase metering to measure the flow rate of unseparated oil, gas and water. Adopting multiphase metering in a subsea system allows much simpler operations and lowers capital and operating expenses. The primary advantage is the flow from the individual wells is reliably and continuously monitored and the requirement for test separators and the extra piping involved is eliminated. In Europe several multiphase flowmeters are under development.2,3 Most of these are equipped with a static mixer or a T elbow to homogenize the multiphase flow, then the flow rate of each phase is measured using a combination of Gamma-ray densitometers, capacitance water cut meters, cross-correlation flow meters and so on.4 However, there are still a lot of technical problems in multiphase meters. In view of this, JNOC (Japan National Oil Corporation), Yokogawa Electric Corp., NKK Corp., Japan PetroleumExploration Co. and Ltd. Teikoku Oil Co., Ltd. launched 6-year joint project in April 1995. Our purpose is to make deepwater oil production more attractive by developing a new meter for measuring the multiphase flow from subsea production wells. The multiphase flowmeter under development is safe for both personnel and the environment, because use of a radioactive source is not required.