Tomography for multi-phase flow measurement in the oil industry

Electrical capacitance tomography (ECT) was one of the techniques which were firstly developed for process tomography (PT) Two types of capacitance measuring circuits are the most suitable for the use in ECT systems - the charge/discharge circuit and the AC-based circuit - because of their immunity to stray capacitance Since the standing capacitances involved are relatively large and the capacitance changes to be measured are very small, the standing values need to be cancelled by DC offset compensation or AC feedback compensation Alternatively, the capacitances can be measured by high-accuracy self-balancing circuits without standing value compensation In this paper different designs of sensing electronics for ECT systems are presented and the advantages and disadvantages compared

https://iopscience.iop.org/article/10.1088/0957-0233/7/3/003/pdf

Hardware design of electrical capacitance tomography systems

The design of the sensor electronics for a tomographic imaging system based on electrical capacitance sensors is described. The performance of the sensor electronics is crucial to the per- formance of the imaging system. The problems associated with such a measurement process are discussed and solutions to these are described. Test results show that the present design has a resolution of 0.3 femtofarad (For a 12-electrode system imaging an oil/gas flow, this represents a 2% gas void fraction change at the centre of the pipe) with a low noise level of 0.08 fF (rms value), a large dynamic range of 76 dB and a data acqui- sition speed of 6600 measurements per second. This enables sensors with up to 12 electrodes to be used in a system with a maximum imaging rate of 100 frames per second, and thus provides an improved image resolution over the earlier 8- electrode system and an adequate electrode area to give sufficient measurement sensitivity.

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Design of sensor electronics for electrical capacitance tomography

In this paper the general principles of capacitance tomography are explained. Recent developments in the design of the primary sensor, the sensor electronics and the reconstruction are shown as well as future trends identified. Industrial and research applications of capacitance tomography are given.

Recent developments and industrial/research applications of capacitance tomography

Capacitance electrode systems for the measurement of the volumetric concentration of two-phase flows have inherently non-uniform sensitivity distributions over the pipe cross section and therefore have different responses to different flow regimes (eg core, annular and stratified flows) In processes with varying flow regimes, this can lead to significant measurement errors An electrode system which has a uniform sensitivity distribution and consequently a response independent of flow regime is therefore desirable The system performance parameters of surface electrode systems used with stray-immune measurement transducers have been characterised quantitatively using a two-dimensional finite-element model The electrode system design parameters have also been identified and their effects on system performance parameters have been investigated As a result, optimum electrode designs are proposed, with responses to different flow regimes having a minimum deviation from linearity

https://iopscience.iop.org/article/10.1088/0957-0233/1/1/012/pdf

Design of capacitance electrodes for concentration measurement of two-phase flow

A stray-immune capacitance measuring instrument based on the charge transfer principle is described. It has a programmable measurement frequency up to several megahertz and is inexpensive and suitable for integration onto a single chip. The effects of stray capacitances, including those of the switching components, have been eliminated by using a special switching arrangement, resulting in a baseline drift of 0.02 pF (at 1-MHz measurement frequency) over a 12-h period. >

R.G. Green

Papers

A high frequency stray-immune capacitance transducer based on the charge transfer principle