Bjørn Tore Hjertaker

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.

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.

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.

A data acquisition and control system for high-speed gamma-ray tomography

A data acquisition and control system (DACS) for high-speed gamma-ray tomography based on the USB (Universal Serial Bus) and Ethernet communication protocols has been designed and implemented. The high-speed gamma-ray tomograph comprises five 500 mCi 241Am gamma-ray sources, each at a principal energy of 59.5 keV, which corresponds to five detector modules, each consisting of 17 CdZnTe detectors. The DACS design is based on Microchips PIC18F4550 and PIC18F4620 microcontrollers, which facilitates an USB 2.0 interface protocol and an Ethernet (IEEE 802.3) interface protocol, respectively. By implementing the USB- and Ethernet-based DACS, a sufficiently high data acquisition rate is obtained and no dedicated hardware installation is required for the data acquisition computer, assuming that it is already equipped with a standard USB and/or Ethernet port. The API (Application Programming Interface) for the DACS is founded on the National Instruments LabVIEW® graphical development tool, which provides a simple and robust foundation for further application software developments for the tomograph. The data acquisition interval, i.e. the integration time, of the high-speed gamma-ray tomograph is user selectable and is a function of the statistical measurement accuracy required for the specific application. The bandwidth of the DACS is 85 kBytes s−1 for the USB communication protocol and 28 kBytes s−1 for the Ethernet protocol. When using the iterative least square technique reconstruction algorithm with a 1 ms integration time, the USB-based DACS provides an online image update rate of 38 Hz, i.e. 38 frames per second, whereas 31 Hz for the Ethernet-based DACS. The off-line image update rate (storage to disk) for the USB-based DACS is 278 Hz using a 1 ms integration time. Initial characterization of the high-speed gamma-ray tomograph using the DACS on polypropylene phantoms is presented in the paper.

Flow imaging by high speed transmission tomography.

Fourth generation medical X-ray scanners using a gantry with a rotating X-ray source and a fixed circular detector array as sensor head, are too slow for imaging of the process dynamics for instance in multiphase flows. To avoid inconsistent measurements and motion blurring, all measurements need to be carried out in a short time compared to the time constants of the process dynamics. Two different high speed tomographic imaging systems are presented here demonstrating that image rates of several thousand images per second is possible.

Level measurement and control strategies for subsea separators

Level monitoring instrumentation is an essential part of hydrocarbon processing facilities, and has, together with separator technology, been widely addressed over the last decade. Key is- sues are production capacity, product enhancement, and well-flow control. The reliability and accuracy of the level instrumentation, and its ability to monitor all the interface layers of the separator, includ- ing the thickness of the foam and the oil-water emulsion, are par- ticularly important when considering the level instrumentation as the main sensing element in the automatic control of the separator ves- sel. Lately, industry focus has been placed on optimal automatic control to improve the quality of the production output, and to mini- mize the use of expensive and environmentally undesirable separa- tion enhancing chemicals. Recent developments in hydrocarbon production include subsea separation stations, where the con- straints placed on the reliability and accuracy of the level instrumen- tation are especially demanding. This paper presents level interface monitoring developments based on electrical, ultrasonic, thermal, and nucleonic physical principles for three-phase hydrocarbon separators, and introduces the notion of tomometry, meaning multi- point cross-sectional metering aiming to acquire information on the cross-sectional flow-component distribution in the process vessel intended for control purposes.

Static characterization of a dual sensor flow imaging system

Abstract A dual sensor flow imaging system based on electrical capacitance and gamma-ray tomography has been developed and tested at the Department of Physics, University of Bergen, Norway. The capacitance tomograph utilizes an eight-electrode sensor set-up, whilst the gamma-ray tomograph is configured in a setting of five radiation sources versus a total of 85 compact gamma-ray semiconductor detectors. The data acquisition system is based on transputer technology, whereas the reconstruction and image presentation processing system can be either a transputer-based network or a conventional state of the art processing engine. This paper presents the work that has been performed in relation to the static phantom characterization of the imaging system. The objective of the work has been to quantitatively evaluate the static imaging performance of the tomography system with respect to relative parameter and relative spatial measurement errors. The work shows that the dual sensor imaging system is feasible for acquisition of two and three phase tomograms, and accurate acquisition of process parameters. The difference in spatial accuracy of the soft field sensor tomograms (capacitance) from that of the hard field sensor tomograms (gamma-ray) is clearly demonstrated.

Dual-mode capacitance and gamma-ray tomography using the Landweber reconstruction algorithm

A dual-mode tomography system based on electrical capacitance and gamma-ray tomography has been developed at the Department of Physics and Technology, University of Bergen. The objective of the dual-mode tomograph is to acquire cross-sectional images, i.e. tomograms, of hydrocarbon flow comprising oil, water and gas constituents. The capacitance tomograph utilizes an eight-electrode sensor set-up mounted around a PVC pipe structure which is sensitive to the electrical permittivity ?r of the fluid. By using the capacitance tomograph, the produced water constituent can be separated from the gas and crude oil constituents, assuming that the liquid phase is oil continuous. The high-speed gamma-ray tomograph comprises five 500 mCi 241Am gamma-ray sources, each at a principal energy of 59.5 keV, which corresponds to five detector modules, each consisting of 17 CdZnTe detectors mounted around the same pipe section as the capacitance sensor. The gamma-ray tomograph discriminates between the gas and the liquid phase, since these have different photon attenuation properties. As a result, the gamma-ray tomograph is able to distinguish the gas phase from the liquid phase of the hydrocarbon flow. Consequently, the dual-mode capacitance and gamma-ray tomography set-up is able to distinguish the oil, water and gas constituents of hydrocarbon flow. This paper presents the work that has been performed related to static characterization of the dual-mode tomograph using the Landweber reconstruction algorithm on polypropylene phantoms. The objective of the work has been to quantitatively evaluate the static imaging performance of the dual-mode tomograph with respect to relative spatial measurement errors, i.e. root mean square errors of the reconstructed tomograms compared to that of the phantom. The work shows that dual-mode tomography using electrical capacitance and gamma-ray sensors is feasible on hydrocarbon flow components using a pixel-to-pixel fusion procedure on separately reconstructed tomograms based on the Landweber reconstruction algorithm.

The development of a dual mode tomography for three-component flow imaging

Abstract A dual mode tomograph for three-component flow imaging has been designed and is being built in a cooperative project between the University of Bergen, Christina Michelsen Research AS and Norsk Hydro AS. It is based on an eight-electrode capacitance tomography and a γ-ray tomograph with five radiation sources and 85 compact detectors. Embedded Transputers using memory-mapping ensure high speed data acquisition into the transputer-based reconstruction unit. The quality of the reconstructed imges from the capacitance system is improved by the use of new reconstruction algorithms. New efficient γ-ray detectors enable real-time flow imaging. The first tomograms from the capacitance tomograph demonstrate its good capability for flow regime identification. The first test results of the γ-ray detector system show a fairly good energy resolution (about 10 keV FWHM) even at high count rates (around 1 MC s−1).