Measuring and testing – Borehole or drilling – Fluid flow measuring or fluid analysis
Reexamination Certificate
1999-03-22
2001-09-11
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Borehole or drilling
Fluid flow measuring or fluid analysis
C073S152420, C073S152210, C073S061470, C073S061440, C073S861630, C073S861620
Reexamination Certificate
active
06286367
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of evaluating the effluent of a hydrocarbon well by means of a multiphase flowmeter. The invention also relates to an installation implementing such method.
When operating an oil well, it is necessary to monitor a large number of parameters concerning the multiphase fluid that flows out from the well. Such parameters vary over time, and the operating conditions must be adapted to take into account such variation.
The flow rates of the various phases contained in the fluid (e.g. a gas phase constituted by gaseous petroleum and two liquid phases constituted by water and liquid petroleum) are among the parameters to be monitored. Such monitoring may be performed either continuously, or periodically, e.g. every two or three months.
A first known technique for measuring the flow rates of the various phases of the fluid flowing out from an oil well consists in measuring the flow rates separately once the various phases of the fluid have been separated. In which case, the fluid passes successively through a plurality of separators in which gravity is used to separate the gas phase from the liquid phases, and then to separate the liquid phases from each other. The flow rates of each of the phases can thus be measured separately at the corresponding outlets of the separators.
In such existing flow-rate measurement installations, valves are placed downstream from the flowmeters provided to measure the separate flow rates of the various phases, in the outlet piping of the separators. Such valves serve to regulate the level of the interface between the phases to be separated inside the separator, and to regulate the pressure in the separator to a reference value.
That type of installation suffers from the drawback of taking up a particularly large amount of space because of the large dimensions of the separators.
For that reason, research and experimentation is being done with a view to measuring the flow-rates of the various phases of the oil well effluent by means of a multiphase flowmeter placed directly in the piping via which the fluid flows out from the well. Such flowmeters take up significantly less space, thereby enabling them, in particular, to be moved from one well to another to perform periodic measurements on each of them.
There are numerous types of multiphase flowmeters. By way of example, mention may be made of the flowmeters described in French patent applications No 2 764 065 and 2 767 919.
When such a multiphase flowmeter is used, the pressure in the flowmeter is controlled entirely by the conditions at the wellhead, i.e. immediately at the outlet of the oil well, and by the conditions much further downstream in the production line, at the place where the various phases of the fluid are finally separated.
SUMMARY OF THE INVENTION
There is provided according to the invention a method of evaluating the effluent of a hydrocarbon well by means of a multiphase flowmeter connected to the well, comprising the step of adjusting the pressure in the flowmeter so that the respective flow rates of the liquid phases and of the gas phase of the fluid lie within the measurement domain of the flowmeter.
The pressure in the flowmeter can be varied independently of the conditions that prevail at the outlet of the oil well and downstream from the flowmeter, where the various phases of the fluid are finally separated.
Thus, when the flow rates of the liquid phases and of the gas phase of the fluid are situated outside the measurement domain of the flowmeter, it is possible to bring these flow rates into said measurement domain by adjusting the pressure in the flowmeter.
In addition, adjusting the pressure in the flowmeter enables measurements to be taken for various values of said pressure, and enables an optimum separation pressure to be established.
Furthermore, it is possible, by taking appropriate measurements, to verify that the pressure drop induced in this way in the piping at the flowmeter does not result in the flow of the fluid becoming critical. If the flow does become critical, then the flow-rate measurements might be erroneous under normal operating conditions, i.e. once the measurement installation has been removed.
When a venturi flowmeter is used, the pressure is adjusted so that the pressure drop in the venturi lies between a maximum pressure drop and a minimum pressure drop that are acceptable for the flowmeter.
Regardless of the flowmeter used, die pressure is adjusted so that the ratio between the flow rates of the gas phase and of the liquid phase; is lower than a maximum ratio that can be measured by the flowmeter,
In a preferred embodiment of the invention, the pressure is adjusted by means of an adjustable back-pressure valve mounted in the piping at the outlet of the flowmeter.
Preferably, the back-pressure valve defines a flow section that is adjustable between a non-zero minimum section having its flow properties above the minimum acceptable flow characteristics for the flowmeter, allowing a limited flow of fluid to pass through, and a maximum section in the vicinity of the section having its flow properties below the maximum acceptable flow characteristics for the flowmeter of the piping,
The back-pressure valve may in particular be a cage valve or a needle valve.
In the preferred embodiment of the invention, the back-pressure valve is removably mounted in a T of the piping.
The invention also provides an installation for the evaluation of the effluent of a hydrocarbon well, comprising a multiphase flowmeter placed downstream from the well and upstream from a region in which there is a determined pressure, and means for adjusting the pressure in the flowmeter so that the restrictive flow rates of the liquid
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Jeffery Brigitte L.
Larkin Daniel S.
Ryberg John J.
Schlumberger Technology Corporation
Wiggins David J.
LandOfFree
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