MULTIPHASE FLOWMETER FOR OIL, WATER AND GAS IN PIPELINES BASED ON GAMMA-RAY TRANSMISSION TECHNIQUES

A multiphase flowmeter (MFM) has been developed to determine the mass flow rates of oil, water and gas in pipelines. It is based on two specialized gamma-ray transmission gauges mounted on a pipe carrying the full flow of oil, water and gas. One gauge uses single energy gamma-ray transmission and the other dual energy gamma-ray transmission (DUET). Pressure and temperature are also measured. Calculations show that the DUET gauge determines the mass fraction of oil in the liquids, and the volume fractions of oil, water and gas, with an accuracy sufficient for most multiphase flow applications. The velocity of flow is determined by cross-correlation of the outputs of the two gauges, one mounted downstream of the other. The two gauges were tested on flows in a water/air loop, the flow rates of water and air were determined to better than 5% relative. The MFM has been tested in trials on an offshore oil platform. The y-ray transmission gauges were mounted about a pipeline connecting the test manifold to the test separator. Gamma-ray measurements were made on the full, and on reduced flows of oil/water/gas mixtures from each of nine single wells, and on five combined flows of different sets of two wells. The r.m.s. difference between the flow rates determined by the MFM and by the separator output meters was determined by least squares regression. The ratio of r.m.s. difference to mean flow rate was 8.9% for oil, 5.6% for water, 8.2% for gas and 5.2% for total liquids for flows in the vertical pipeline and somewhat larger for flows in the horizontal pipeline.