A compact low energy multibeam gamma-ray densitometer for pipe-flow measurements

A compact low-energy multibeam gamma-ray densitometer for oil/water/gas pipe-flow measurement has been built at the University of Bergen (UoB). The instrument consists of one Am-241 source and three detectors, all collimated and embedded in the pipe wall. Only the 59.5 keV radiation energy of the source is utilized. Two of the detectors measure transmitted radiation across the pipe flow, and one measure scattered radiation at a 90degrees angle. The purpose of the multibeam measurement geometry is to acquire flow regime information and to reduce the flow regime dependency of the gas volume fraction (GVF) measurements. The measurement of scattered radiation enables the dual modality densitometry (DMD) measurement principle to be exploited. Its basic principle is to combine the measurement of scattered and transmitted radiation in order to obtain salinity independent GVF measurements. The salinity dependency is otherwise strongly significant when using low-energy radiation. It is also possible to measure the salinity by using this principle. The instrument is a laboratory prototype, and it has been used for characterising the measurement principle and to test different detector alternatives. The testing of the instrument includes static tests on plastic phantoms, tests on simulated water/gas flow and three phase flow loop tests. Both the multibeam measurement principle and the DMD principle have been verified to provide valuable information. This paper presents the physics behind, experimental results and an evaluation of the system. (C) 2002 Elsevier Science B.V. All rights reserved.