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Abstract

An apparatus and method for determining the phase volume fractions for a multiphase oil well effluent is disclosed. The apparatus measures multiple energy gamma ray attenuations through the effluent mixture, and the method determines the phase volume fractions from these measurements when the mixture is under inhomogeneous flow conditions. The apparatus includes a pipe section with a Venturi through which the mixture flows. A source of radiation transmits rays at two or more energy levels through the mixture. A solid state detector measures the transmitted attenuation count rates. A low absorption window of a truncated cone shape is preferably incorporated in lieu of the pipe wall in the area of the detector. The method comprises measuring ray attenuation, in the two-energy example, at one high energy emission line, to differentiate between the gas and liquid components, and at a relatively lower energy emission line, to differentiate between the oil and water phases within the liquid component. The attenuation count rates for one energy level are measured over short time intervals relative to the measurement period for the attenuation count rates at the second energy level. Through a series of calculations, the actual measured total count rates for each energy level are corrected to equivalent homogeneous count rates. The corrected count rates can then be used in homogeneous flow equations to determine the phase volume fractions. In this manner, the water, oil and gas volume fractions of the mixture are determined.

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