Geir Anton Johansen

Recent developments in three-phase flow measurement

The problem of how to meter oil - water - gas mixtures has been a significant one in the oil industry since the early 1980s. Since then, considerable research has been conducted into the development of a three-phase flowmeter suitable for use in an offshore environment. This work discusses why three-phase flow measurement is important, the principal strategies and technologies which may be used to meter three-phase flows, and reviews the status of some currently available solutions.

Three-phase flow measurement in the petroleum industry

The problem of how to accurately measure the flowrate of oil–gas–water mixtures in a pipeline remains one of the key challenges in the petroleum industry. This paper discusses why three-phase flow measurement is still important and why it remains a difficult problem to solve. The measurement strategies and principal base technologies currently used by commercial manufacturers are described, and research developments that could influence future flowmeter design are considered. Finally, future issues, which will need to be addressed by manufacturers and users of three-phase flowmeters, are discussed.

A dual sensor flow imaging tomographic system

A dual sensor tomograph for three-component flow imaging has been built at the University of Bergen in cooperation with Christian Michelsen Research AS and Norsk Hydro AS. It utilizes an eight-electrode electrical capacitance tomograph and a -ray tomograph with five radiation sources and 85 compact detectors. Embedded transputers using memory-mapped I/O ensure high-speed data acquisition into an Alpha AXP-based on-line processing unit. The first results demonstrate that three-component flow regime identification is possible at rates of about 30 frames per second, provided that sufficient computing capability is available.

Determination of void fraction and flow regime using a neural network trained on simulated data based on gamma-ray densitometry

This paper describes low-energy gamma-ray densitometry using a 241Am source for the determination of void fraction and flow regime in oil/gas pipes. Due to the reduced shielding requirements of this method compared to traditional gamma-ray densitometers using 137Cs sources, the low-energy source offers a compact design and the advantage of multi-beam configuration. One of the aims of this investigation was to demonstrate the use of a neural network to convert multi-beam gamma-ray spectra into a classification of the flow regime and void fraction, as well as to determine which detector positions best serve this purpose. In addition to spectra obtained from measurements on a set of phantom arrangements, simulated gamma-ray spectra were used. Simulations were performed using the EGS4 software package. Detector responses were simulated for void fractions covering the range from 0 - 100%, and the simulations were performed with homogeneous, annular and stratified flows. Neural networks were trained on the simulated gamma-ray data and then used to analyse the measured spectra. This analysis allowed determination of the void fraction with an error of 3% for all of the flow regimes, and the three types of flow regime were always correctly distinguished. It has thus been shown that multi-beam gamma-ray densitometers with detector responses examined by neural networks can analyse a two-phase flow with high accuracy.

Salinity independent measurement of gas volume fraction in oil/gas/water pipe flows

Dual mode densitometry is presented as a novel method of measuring the gas volume fraction in gas/oil/water pipe flows independent of the salinity of the water component. The different response in photoelectric attenuation and Compton scattering to changes in salinity is utilized. The total attenuation coefficient is found through traditional transmission measurements with a detector positioned outside the pipe wall diametrically opposite the source. The scatter response is measured with a second detector positioned somewhere between the source and the transmission detector. The feasibility of the method is demonstrated for homogeneously mixed flows.

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 90° 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.

Improved void fraction determination by means of multibeam gamma-ray attenuation measurements

Abstract Gamma-ray densitometry is a frequently used non-intrusive method for determining void fraction in two- and multi-phase gas liquid pipe flows. The traditional gamma-ray densitometer using a 137 Cs source and a scintillation PMT detector has proved itself reliable and robust. This paper presents a method using a low energy source ( 241 Am), which offers the advantages of reduced size due to reduced shielding requirements, compact detectors, and lesser dependence on flow regime, due to its multibeam measurement configuration. These are important aspects with regard to future subsea and down-hole fluid flow measurement applications. The performance of single-beam and the compact multi-beam low-energy gamma-ray measurement principles was compared. Consideration of the measurement volume, defined by the detector area and the radiation beam, demonstrated the flow regime dependency of single-beam gamma-ray measurement principles. With the multi-beam low-energy gamma-ray measurement principle, the dependence on flow regime is negligible when several detector responses are combined. Use of phantoms and one movable detector verified the multi-beam gamma-ray measurement principle. The detector responses at several positions around the pipe were obtained for different flow regimes and void fractions.

Multimodality tomography for multiphase hydrocarbon flow measurements

Multimodality sensing is used for monitoring of multiphase hydrocarbon flow where there is a need to measure the quantity of oil, water and gas in a cross section of a pipe originating from an oil well. Information on the flow regime, i.e., the physical distribution of the hydrocarbon production constituents in the pipe cross section, is demanded. Expedient information concerning the productivity of the well, i.e., the quantity of oil, water and gas produced, the transport of multiphase flow and the upstream separation process can be provided by tomographic information. A dual modality tomograph (DMT), consisting of capacitance and gamma-ray sensors, has been developed at the University of Bergen. Characterization of the DMT has demonstrated feasibility in relation to the hydrocarbon flow application, but also shortcomings mainly relating to the performance of the capacitance sensor in water continuous phase, and the salinity dependence of the gamma-ray measurements. Research work has been conducted to further develop the DMT for hydrocarbon multiphase flow. The new developments include dual modality densitometry (DMD), where both mixture density and salinity are measured, and a water-cut independent high-frequency magnetic field sensor.

Operational characteristics of an electron-bombarded silicon-diode photomultiplier tube

Abstract An electron-bombarded silicon-diode photomultiplier tube (EDPMT) has been constructed and the first experimental data on operational characteristics are presented. The signal multiplication of this tube is, in contrast to the traditional PMT, not accomplished by multiplying the number of photo-generated electrons, but by increasing each electrons energy 3–4 orders of magnitude. The relative simplicity of design properties make this type of tube an attractive alternative for many applications. This tube has small size, low mass, it is robust and it incorporates a low cost electron multiplier. Also, it only requires a single negative high voltage connection, without a voltage-divider, and a low voltage diode reverse-bias connection, which greatly reduces the power supply requirements for large scale operations such as those at CERN, Fermilab, and the Superconducting Supercollider.

Multiphase flow regime identification by multibeam gamma-ray densitometry

Multibeam gamma-ray densitometry can be applied to identify flow regimes in hydrocarbon multiphase oil, water and gas pipe flows. The acquired flow regime information can be used for improved measurement accuracy on gas volume fractions, and as complementary information for other types of flow instrumentation, in order to enhance their accuracy. The work presented in this paper includes both theoretical calculations and experimental work on three-phase flow using multibeam gamma-ray densitometry. It is demonstrated that a fan beam geometry with one radiation source and several collimated detectors is sufficient to provide information on the liquid-gas distribution of the pipe flow. In order to perform testing on deviated multiphase oil, water and gas flows, a special tilt section was designed and built. Several different flow regimes were successfully identified from the acquired experimental measurement data. The work presented in this paper was conducted as a part of a project aiming to develop technology for improved multiphase hydrocarbon metering, along with joint project partners Roxar Flow Measurements AS and Christian Michelsen Research AS.