The Design, Development, and Field Testing of a Water-Cut Meter Based on a Microwave Technique

Abstract

This paper will describe a new and unique instrument to accurately determine the water-cut of an oil-water emulsion. The basic principle of the measurement is based on a novel technique, commonly called oscillator load-pull, which detects the microwave characteristic of the emulsion. This measurement technique will be described simply and concisely. The design and development of the measurement pipe section and the necessary microwave oscillator source and control electronics will be discussed. Laboratory calibration data for the microwave water-cut meter will be presented. Installation of the instrument at a presented. Installation of the instrument at a production facility will be described and field test production facility will be described and field test results will be presented. Performance of the microwave water-cut meter will be compared to other water-in-crude determination methods including distillation and centrifugal separation. Introduction The measurement of water content in crude oil is an important and widely encountered practice in all aspects of oil industry operations — crude oil production, processing, transportation, and refining. production, processing, transportation, and refining. The water-cut measurement is used to help determine production rates, custody transfer, and pipeline oil production rates, custody transfer, and pipeline oil quality control. Also, the separation efficiency of production operations may be optimized by monitoring production operations may be optimized by monitoring water-cut at various points throughout the processing facility. There are three separate categories of water-cut measurement in the oil industry — low water-cut (0–3% range), high water-cut (0–100%), and produced water quality (ppm of oil in water). The measurement technique developed in this project is capable of performing all three categories of measurement, but performing all three categories of measurement, but this paper will be focusing on the design and development of the meter for the low water-cut range. At Prudhoe Bay, ARCO Alaska, Inc. has a strict requirement of water-cut prior to sending the oil to the Trans Alaska Pipeline System. The pipeline specification for the water content in the crude is 0.35% maximum to prevent hydrate and corrosion problems. This strict requirement creates the need for problems. This strict requirement creates the need for the producer to find the most reliable and accurate method to continuously monitor the water-cut during the separation process before sending the "dry" crude oil to the pipeline. The present practices used for water-cut measurement in the oil industry can be divided into two classes: on-line continuous monitoring; and laboratory test methods. Several manufacturing companies offer a commercial device to measure the water-cut on line. The laboratory test methods include centrifugal separation, Dean-Stark distillation, and Karl-Fischer titration. Several commercial water-cut measurement units have been used to monitor water-cut at Prudhoe Bay, but none has proved to be satisfactory to the operation. These meters are either unstable or lack the required measurement resolution. The laboratory methods are used periodically to check the water-cut, but their results are invariably questioned due to each one's inherent sampling error. Another disadvantage of most laboratory methods is that they are too slow to respond to the occasional water spike situation. By the time the result comes back from the laboratory, the water slug may be downstream of the separation facility. Also, the laboratory methods do not measure the water-cut of all the fluids and there may be long time intervals between sample gatherings. For the case of custody transfer, the industry is primarily using either the distillation or centrifuge primarily using either the distillation or centrifuge method. These methods usually include the use of a composite sampler which draws a small portion of liquid into a "jug" whenever a fixed amount of oil passes by. The water-cut of the "jug" sample is then passes by. The water-cut of the "jug" sample is then determined by one of the laboratory methods. P. 775

Properties of Crude Oil-in-Water and Water-in-Crude Oil Emulsions: A Critical Review

“…For heavy crude oils, the use of microwave sensors are considered a better choice since water and oil absorb microwave energy differently and such a property is not affected by the oil density. − …”

Optimised mode selection in electromagnetic sensors for real time, continuous and in-situ monitoring of water cut in multi-phase flow systems

“…Consequently, the potential to carry out non-intrusive, online measurements of water-cut in oil-water flows, led to microwave sensors gradually attracting the attention of scientists and engineers and have been proposed in a number industrial applications for multiphase flow measurements [12]. Yang et al [13] described an oscillator load-pull system to accurately determine the water-cut of an oil-water emulsion and presented the installation of the instrument and the field test results, but the watercut range was limited between 0-3% . Avila et al [14] determined water fraction from 0 to 100% by the frequency shift of the first resonant peak in a non-intrusive way based on a radio frequency resonant cavity sensor, however did not provide any details under flow conditions.…”

“…These early application efforts produced promising results but also highlighted a number of areas requiring further study in order to understand the advantages and limitations of microwave sensors when used to monitor multiphase flow systems. The limitations/industrial drivers identified are related to: utilising the sensors during continuous flow and different flow regimes [13][14][15], the ability to accurately determine low water cuts [16], expansion of the measurement technique to non-homogenous systems [17], the large experimental errors resulting from certain configurations [18], the need to perform volumetric measurements [19] and the consideration of the influence of parameters such as temperature and salinity that can affect the measurements [20].…”

Study of hysteresis effects and emulsion properties in watercut measurement using high speed multi-frequency impedance sensor

“…In the watercut meter industry, different methods have been in use such as near-infrared technique (NIR) [12], microwave method [13][14][15], gamma tomography [16], and impedance measurements [17]. The impedance measurement method uses the impedance variation of the oil-water mixture for different water contents to obtain the watercut.…”