Techniques de débitmétrie polyphasique non intrusive. Revue bibliographique
Non Intrusive Multiphase Flow Measurement Techniques. Bibliographic Review
Institut Français du Pétrole
Cet article présente les différentes techniques de débitmétrie polyphasique non intrusive décrites dans la littérature du domaine public. Ces techniques sont considérées du point de vue de leur application dans le cadre de la production pétrolière sous-marine (mélange eau/huile/gaz). A partir d'une analyse des différentes méthodes physiques qui peuvent être utilisées, des perspectives d'avenir sont proposées.
Several operations in the oil reservoir exploitation industry call for flowmeters capable of delivering information on the quantity and rate of flow of the different phases (gas, oil, water, solids . . . ) present in a pipeline. Amongst these are the estimation of remaining reserves and of well performance, control of production units such as multiphase pumping systems and fiscal monitoring in the case of pipeline networking. Existing methods, based on phase separation, require separate test lines and thus tend to be cumbersome, give only intermittent values of flow parameters and need to be calibrated due to the intrusive nature of the measurements. These drawbacks are seen to be all the more critical in subsea production where the ideal flowmeter would be compact, require little maintenance and supply precise real time data for network and multiphase pump control. In recent years flow measurement in two or more phase systems has received increasing attention both in laboratory studies and for applications in a variety of industries (for example : nuclear power production and food processing as well as of course oil production). We review here the many methods considered for non-intrusive flow metering with two or more components from the point of view of an industrial (in particular subsea oil production) application. The situation is rendered delicate, in particular for density measurement, by the uncontrolled nature of the flow which may occur in any of several regimes with differing spatial distributions of the components. Parameters permitting the various phases to be discriminated are identified in order to evaluate the various techniques. The latter are classified in two major families of interaction for which a range of frequencies are explored : mechanical interactions from ultrasound to simple pressure and noisemeasurement and electromagnetic interactions from the use of gamma rays to the measurement of static electrical properties. Consideration is also given to two techniques of special interest falling outside this classification : the use of neutron bombardment and that of nuclear magnetic resonance (NMR). Most of the techniques considered give only partial responses to the question of measuring the quantites and velocities of each of the three major components : oil water and gas. Some, such as visible light or infrared spectroscopy, are eliminated entirely due to the local nature of the measurements in the system considered. Methods such as acoustic or pressure measurement, providing a rapid and simple means of detecting major events such as the passage of slugs and gas pockets and of measuring their velocity in favorable cases, may be incorporated into the final system. Little information is however furnished as to the flow rates of individual components. Four types of measurement have been selected as presenting particular advantages in all or part of the range of parameters for which information is required. Neutron based methods, particularly when coupled to induced gamma ray spectroscopy, promise to provide useful information on water/oil ratios and on salinity although the development of practical sources is as yet only in its earliest stage. NMR is potentially capable of providing independant measurements of both the quantity and velocity of the two liquid phases although the size of such a flowmeter would be prohibitive in the application envisaged. A restricted application (both in terms of size and in the number of measured parameters) may however be advantageous in combination with other techniques. Two regions of the electromagnetic spectrum are identified as of particular interest. The first is the hard X-ray to gamma ray region where the use of two energies would allow evaluation of three phases : oil water and gas. Velocity measurement is however intrinsically difficult and, for industrial applications, detector technology still has to be improved. In the microwave region (including high frequency capacitance and resistivity measurements) most of the necessary parameters appear to be attainable by combining absorption and reflection measurements with the easy tunability of sources. Although this technology is already used in a wide variety of applications from food processing to traffic control, the range of conditions for which it will be applicable in multiphase oil production is not yet clear. A successful industrial flowmeter may imply a combination of several of these techniques incorporating intelligent use of more classical measurements such as temperature and pressure for auto calibration. Further work on evaluating the range of attainable measurements in a compact, reliable and economic system is likely to further stimulate the development of subsea multiphase production systems.
© IFP, 1991