Measuring and testing – Gas analysis
Reexamination Certificate
2000-04-17
2001-11-20
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas analysis
C073S025010, C073S025050, C073S031040
Reexamination Certificate
active
06318149
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and to a device for measuring Joule-Thomson coefficients of fluids.
2. Description of the Prior Art
The Joule-Thomson coefficient &mgr; measures the temperature variation of a fluid subjected to a pressure drop in an isenthalpic situation.
μ
=
(
∂
T
∂
T
)
H
This isenthalpy condition is precisely the one that is encountered during expansion of a fluid in a valve or in a line provided that the energy which is dissipated from the fluid can be disregarded.
Precise measurement of the Joule-Thomson coefficient finds applications in many fields where carrying fluids in pipes leads to changes of state that affect the proper circulation thereof, notably in the field of high-pressure/high-temperature (HP-HT) hydrocarbon reservoir production. This measurement allows determination of the << thermal profile>>in all the energy dissipative elements.
According to the temperature and pressure conditions, the Joule-Thomson coefficient &mgr; can be positive or negative, as shown in FIG.
1
. In the case of a positive coefficient (&mgr;>0), the gas cools down during an expansion whereas a negative coefficient (&mgr;<0) leads to warming through expansion. The positive range of the coefficient is separated from the negative range by inversion curve IC. It can be seen that, under the HP-HT conditions prevailing in a well at a great depth, coefficient &mgr; is negative: the fluid warms up through expansion. This is observed at the present time in reservoir production wells situated at a relatively great depth, notably in certain wells in the North Sea producing condensate gases where the HP-HT conditions cause an inversion of the Joule-Thomson coefficient.
The sign and the value of the Joule-Thomson coefficient are therefore important for dimensioning of a production well since it influences the thermal profile of the production facilities. In the case of a negative coefficient, it is imperative to know the warming reached through expansion: selection of the building materials depends thereon. This coefficient can also be used for dimensioning gas lines, for the same reasons. It is also necessary to know the sign and the value of this coefficient in order to assess the risks of hydrate or paraffin formation in case of a temperature decrease through expansion, so as to be able to select the suitable technique allowing prevention of the formation of deposits in the lines.
There are many reference books in the literature showing how to calculate the inversion curve IC(P,T) of the Joule-Thomson coefficient by means of equations of state conventionally used in the petroleum industry. One can notably refer to:
Kortekaas W. G., et al; Joule-Thomson Expansion of High-Pressure-High-Temperature Gas Condensates, in Fluid Phase Equilibria, 139, 1997, p.207-218.
However, this approach is difficult to exploit in practice for lack of the necessary experimental data which are scarcely disclosed. Furthermore, measuring the Joule-Thomson coefficient &mgr; is delicate because very low absolute values of the order of some tenths ° C./bar (some ° C./MPa) are assessed. Good determination of the inversion curve IC requires great precision because the observable temperature difference is very close to 0.
There are different types of experimental devices allowing determination of the Joule-Thomson coefficient by measuring the temperature variation of a fluid flowing through an element.
According to a first embodiment, this element consists of a porous medium causing a pressure drop that is a function of its permeability and of the fluid flow rate. Such a device has many drawbacks insofar as the Joule-Thomson effect is dispersed in the whole porous volume that is difficult to insulate thermally, and it has a certain thermal inertia, which requires a large amount of fluid in order to reach the state of thermal equilibrium during measurement.
According to a second embodiment, the element causing a pressure drop consists of a valve. This is an advantageous solution because, in this case, the pressure difference between the inlet and the outlet of the device can be readily varied. Furthermore, the Joule-Thomson effect is rather localized, but the various parts of the device such as the seat, the needle, etc., however form a thermal mass producing thermal losses that are difficult to prevent.
Assurance of a good thermal insulation and of a good localization of the Joule-Thomson effect are the key factors of a good measurement. These are the qualities of the device according to the invention.
SUMMARY OF THE INVENTION
The method according to the invention allows determination of the Joule-Thomson coefficient of a fluid by combination of measurements of concomitant pressure and temperature variations of a circulating fluid. It comprises injecting this fluid at a determined temperature into a thin tube containing a temperature detector leading to a pressure drop for this fluid, measuring, by means of this detector, the temperature variation of the fluid in relation to its injection temperature, measuring the pressure drop undergone by the fluid and determining the Joule-Thomson coefficient by combination of the pressure drop and temperature variation measurements of the fluid. The fine tube is preferably thermally confined in order to avoid heat losses.
The device according to the invention allows determination of the Joule-Thomson coefficient of a fluid under pressure. It comprises a tube, means for injecting the fluid into the tube at a determined temperature, a first detector in the tube creating a pressure drop and suited to measure the temperature variation of the fluid that has undergone this pressure drop, pressure detectors upstream and downstream from the tube for measuring the pressure drop, a second detector for measuring the temperature of the fluid injected, and a calculation means allowing determination of the Joule-Thomson coefficient of the fluid from this pressure drop and from this temperature variation.
The device preferably comprises confinement means for thermal insulation of the fine tube, comprising for example a confinement tube containing the fine tube, this confinement tube being provided with terminal parts at the two opposite ends thereof defining a sealed enclosure therewith, channels in the terminal parts allowing communication of the inside of the tube with the fluid injection means, the inside of the confinement tube with means for evacuating the tube, and the tube with the pressure means.
According to an embodiment, the confinement means further comprise an intermediate tube between the fine tube and the confinement tube. At least one of the tubes around the fine tube is provided with a reflective coating on the inner wall thereof in order to prevent heat losses through radiation.
The device preferably comprises a unit intended for temperature conditioning of the fluid prior to the injection thereof.
The temperature detectors are preferably identical thermocouples connected in opposition so as to detect slight temperature variations.
Using a flow valve for controlling the outgoing flow allows checking that measurement of the Joule-Thomson coefficient is really independent of the flow rate.
Highly localized measurement at the end of the pressure drop zone in the fine tube, preferably combined with good confinement of the fine tube substantially prevents any heat loss in the measurement zone, guarantees very high accuracy.
REFERENCES:
patent: 5415024 (1995-05-01), Proffitt et al.
patent: 5980102 (1999-11-01), Stulen et al.
patent: 0070188 (1983-01-01), None
patent: 1732191 (1983-03-01), None
patent: 777557 (1981-11-01), None
Derwent Abstract No. 1982-B4643E of SU 827866B to Tsvetnov.*
Atkins, P. W. Physical Chemistry. Oxford University Press, 1986, pp. 66-67.
Moracchini Gerard
Mougin Pascal
Peumery Roxane
Sanchez Jose
Antonelli Terry Stout & Kraus LLP
Cygan Michael
Institut Francais du Pe'trole
Larkin Daniel S.
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