Measuring and testing – Volume or rate of flow – Of selected fluid mixture component
Patent
1997-07-08
1998-04-21
Dombroske, George M.
Measuring and testing
Volume or rate of flow
Of selected fluid mixture component
G01F 174
Patent
active
057419787
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for determining the flow rate in a fluid flow, particularly in a two-phase flow comprising oil/water/gas from a production well offshore.
BACKGROUND
Measuring of multi-phase flows in oil wells and pipelines including other different flow systems is a serious unsolved problem within the petroleum industry. A complete measurement of a multi-phase flow in e.g. an oil well comprises the three phases gas, oil and water.
In measurements of gas/liquid one has to determine the means flow rate of the composition and the mean density. The total flow rate can then be determined.
In general, it is more convenient to determine the composition density than its flow velocity by means of the known measuring methods for gas/liquid. According to these methods, the density is usually obtained by means of a gamma ray meter. Methods which are under development for measuring multi-phase and gas/liquid employ metering of the water fraction substantially based upon dielectric properties of the hydrocarbon/water composition.
In a multiphase hydrocarbon/water composition, when the multi-phase total density has been obtained by means of a gamma ray meter and the water fraction, the oil fraction and water fraction can be estimated. The apparatus for metering of water fraction usually has a simple and robust construction, and can therefore be implemented on production platforms offshore and possibly in installation below sea level.
However, gamma ray meters are expensive and can not be modified at a low cost to enable them to be used reliably in the harsh conditions existing on production platforms offshore and installations below sea level for commercial metering of well head fluids or fluids in pipelines. Moreover, the radioactive gamma ray source requires strict security regulations.
Capacitance methods are being developed to detect the quantities of hydrocarbons and water flowing in a pipe. This method is however sensitive to water; e.g., the method measures the quantity of waterflowing, whereby the remaining flow is constituted by hydrocarbons. However, this method cannot differentiate between liquid hydrocarbons and gaseous hydrocarbons. The capacitance method is also influenced by the gas/liquid ratio, which calls for a correction of the measuring results in view of an independent measuring result for a gas/liquid fraction, provided from e.g., a gamma ray meter.
Techniques using microwaves are being developed. Microwaves are absorbed by water, and as with the capacitance meter the remainder of the medium is assumed to be hydrocarbons. The microwave technique (and the capacitance method) are also influenced by the gas/liquid ratio. Therefore, calibration is required. On the other hand it is possible to use the microwave technique in cross-correlation, but because of the large volume of the measuring technique, only special features of the multi-phase flow in a large scale are detectable.
While the capacitance method and the microwave technique do in general have the same field of use they also have the same limitations.
In connection with research activity and with commercial activity development is proceeding on metering equipment consisting of two meters: a gamma ray meter and a capacitance or a microwave meter, in which one provides the gas/liquid ratio, and the other the water quantity. However, methods of this type are limited to narrow gas/liquid fractions, particular flow regimes or other particular conditions. These methods can therefore not provide reliable measurements of the flow velocity in multi-phase systems over a wide range of conditions.
An alternative metering method for use with multi-phase systems is described in NO Patent No. 174643. This patent describes a method for metering of flow velocity and quantity or mass ratio between different phases in pipes and wells in which the flowing medium comprises several phases, particularly two-phase systems of the natural gas and oil type. A pressure pulse generator arranged in or adjacent to the pipe or the well produces a lo
REFERENCES:
patent: 3523454 (1970-08-01), Rusnak
patent: 4312234 (1982-01-01), Rhodes et al.
patent: 4364413 (1982-12-01), Bersin et al.
patent: 5099697 (1992-03-01), Agar
Dombroske George M.
Thompson Jewel V.
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