DUAL-MODALITY ELECTRICAL RESISTANCE AND CAPACITANCE PROCESS TOMOGRAPHY SYSTEM

Abstract

In the oil extraction and processing industry, it is of paramount importance to constantly assess the ratio of water, gas and oil being produced. This information allows to control the process and assess the economic viability of the well. Currently oil separators are used to estimate the production. Nonetheless, these are bulky and have a long settling time, in consequence, they cannot be used for on-line monitoring. multiphase flow meters (MPFM) based on the use of electrical tomography techniques have been developed as an alternative to oil separators. Taking advantage of the ability of electrical capacitance tomography (ECT) to distinguish between materials with different permittivity and electrical resistance tomography (ERT) to distinguish between materials with different conductivity. Nonetheless, MPFMs based in ECT are limited to imaging permittivity distributions, this is oil-continuous flow with water content less than 30\%. Conversely, ERT systems perform well only with mainly conductive distributions, this is water-continuous flow. Furthermore, although the ERT technique has been studied for several decades, its application for monitoring multiphase flows have been limited. To tackle the limitations of conventional ERT, electrical resistance tomography with voltage excitation (ERTv) has been developed. The use of a voltage excitation strategy, opposite to a current excitation one allows to successfully image stratified and highly bubbly flows. In this work, the effect of the contact impedance and the parasitic impedances is studied. The implementation of the four-terminal sensing strategy for ERTv is presented as a means to reduce the effect of the parasitic impedances. In addition, the effect of the parasitic capacitance of the CMOS switches in the multiplexing stage is assessed and the use of the four-terminal sensing strategy in ECT is used to reduce the effect of parasitic capacitances. In addition, the development of a four-terminal sensor structure is presented, featuring grounded guards and a ring-shaped terminal for voltage measurement, this shape guarantees the constant contact with the material for voltage measurement. Dual-modality tomography aims to solve the limitations of single ECT and ERT systems. Intended as a method for imaging materials in the whole range of compositions, form completely dielectric to entirely conductive. A dual-modality system featuring four-terminal sensing strategy for ECT and ERTv is presented. The use of a single-plane, single-set-of-electrodes sensor and a single data acquisition allows to simultaneously acquire capacitance and conductance. In addition, a model-based image reconstruction algorithm is presented, featuring the use of databases containing sets of solved-in-advance forward problems, this algorithm eliminates the need of heavy computational resources for solving the FEM model at each iteration, thanks to this and by the use of parallel processing GPU hardware, real-time high-quality parameter estimation is achieved.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Wuqiang Yang (Supervisor) & Wuliang Yin (Supervisor)