WO1992010732A1

WO1992010732A1 - Method and apparatus for measuring of leakage especially over wellhead valves and annular space sealings

Info

Publication number: WO1992010732A1
Application number: PCT/NO1991/000141
Authority: WO
Inventors: Jens Myklebust
Original assignee: Jens Myklebust
Priority date: 1990-12-14
Filing date: 1991-11-14
Publication date: 1992-06-25
Also published as: NO174567C; NO174567B; AU9038291A; NO905406D0; NO905406L

Abstract

The invention relates to a method for measuring leakage across potential leakage sources such as valves, particularly wellhead valves (10, 10'), and annulus seals or packoffs (production packers) (7, 8) in oil and/or gas wells. In order to achieve more accurate metering results than hitherto, by means of a simplified and rapid measuring method, one establishes at a potential leakage place or at each potential leakage place (7, 8, 10, 10'), respectively, a metering offtake (11, 9, 9'), whereafter one, at closed valve (10, 10') and/or operative production packers (7, 8), respectively, over a predetermined period admit the entire leakage medium amount at the respective leakage place into a measuring apparatus (14) adapted for direct measuring of the leakage gas amount and/or leakage liquid amount. The invention also relates to an apparatus adapted to accommodate a certain amount of leakage medium per time unit from the respective leakage place, said apparatus being equipped with the necessary metering instruments (21, 25-27) for determining the amount of leakage medium per time unit.

Description

METHOD AND APPARATUS FOR MEASURING OF LEAKAGE ESPECIALLY OVER WELLHEAD VALVES AND ANNULAR SPACE SEALINGS This invention relates to a method 'and an apparatus for measuring a leak over especially wellhead valves and annulus seals/packoffs (production packers) in oil and/or gas wells.

Such measurements are being conducted i.a. to form the basis for an evaluation whether or not wellhead valves/annulus seals should be overhauled or replaced. The sealing surfaces in wellhead valves and production packers will after some time of use be weared and weakened so that they no longer secure full tightness. The price of such a wellhead valve is in the order NOK 1.000.000,- whilst replacement of the lower production packer may amount to ten times this sum. Therefore, it amounts to- enormous additional costs to replace such valve or packer, respectively, prior to this replacement being absolutely necessary. Moreover, it would involve an obvious advantage to be able to replace valve/ packer with a planned production stoppage, so that one avoids to stop the production merely because of the replacement operation. The method and apparatus will also ^•be useable in order to measure possible leakage in- pipes between annulus seals.

API-specification 14H establishes criterions for allowed amount of leakage per time unit for valve/packer prior to rapair/replacement must be effected. With smaller -leakages, valve/packer is considered as acceptably operative.

Therefore, it is of the utmost importance to be capable of achieving a measurement as accurate as possible, so that one may postpone the overhaul/replacement to the point of time most suitable, namely with a planned production stoppage, provided, of course, that allowed amount of leakage per time unit is not exceeded prior to said stoppage of operation.

With today's technique, the necessary accuracy in leakage measurements cannot be achieved. When one is to test if a wellhead valve or an annulus seal (production packer) leaks (too much), the valve in question is closed (full pressure upstream said valve) together with all valves incorporated within the pipe system downstream the valve being tested. As a consequence thereof, the pressure will increase within the closed pipe system and, according to prior art technique, thiε increase is utilized as a basis for the determination of the amount of leakage. Then, one calculates the internal volume of the closed pipe system and finds, thereafter, the amount of gas leakage by means of a relatively complex calculation wherein pressure increase and temperature are considered.

The pressure increase is often measured by means of a manometer and a pressure printer. Usually, the measurement takes one hour.

This known measuring method as well as the apparatus serving for its carrying out, give inaccurate and uncertain results, substantially due to partially difficulties in determining accurately the internal volume of the closed pipe system because of branching, valves, possibly accumulated liquid, etc. , partially in that the liquid portion of the amount of leakage cannot be determined. If portions of said volume are filled with liquid, the result will be a larger building-up of pressure than expected and, consequently, erroneous measurement results. Further, one cannot neglect errors of calculation. Often, decisions are made from personal evaluations and will vary from one person to another.

The object of this invention is to provide a method for measuring leakage over valves, particularly wellhead valves, as well as annulus seals in oil and/or gas wells wherein, simply and rapidly, very accurate measurement results are provided. Likewise, the invention aims at providing an appropriate apparatus adapted to carry out this method.

Said object is realized through the features appearing from the following claims .

Thus, the invention consists substantially in arranging the conditions such that the amount of leakage (gas and/or liquid) at a potential place of leakage in its entirety is let into a measuring apparatus adapted for direct measurement of both the gas and liquid amount.

Thus , the method according to the invention is completely independent on internal volume of a closed pipe system, constituting a source for a simple and reliable readout of amounts of leakage. The amount of gas may be read off in relation to a previously made calibrated curve based on thermometer and manometer readouts. The method in accordance with the invention is rapid, a readout time of five to ten minutes usually being sufficient in order to achieve the final result of the leakage amount measurement. This results in a minimum time of production stoppage during the test.

The method and apparatus according to the invention may also be used for testing other valves than wellhead valves, and method as ..well as appaatus are independent on the nature of the leakage medium, two-phase leakages as well as pure liquid _E≤ s>x-._t_-€_- _Ss-_; -Leskages toeing -fc ress-t. _.a. wά_-_fc__h the same ease.

An example of an embodiment of the invention is further explained in the following in association with the accompanying drawing, the single figure thereof in side elevational view showing an apparatus of the invention in connection to an oil/gas well, the apparatus and well not being drawn on the same scale, the illustration being exclusively diagrammatic.

In the figure of the drawing, reference numeral 1 denotes a wellhead, 2 and 3 indicating production casing and tubing, respectively, the intermediate annulus being denoted 4.

The level of the platform deck is indicated at 5 and the seabed at 6.

7 and 8 denote bottom and top annulus packoff or production packer, respectively.

E.g. two metering offtakes 9 and 9' are provided for testing wellhead valves 10 and 10' with respect to leakage, as well as a corresponding metering offtake 11 for testing the annulus seals or packoffs 7 and 8. Other valves, not shown, may be assigned similar metering offtakes.

In the measuring situation shown, the metering offtake 9' of the wellhead valve 10' is coupled to a flexible pipeline or hose 12 leading to an inlet valve 13 of an apparatus 14 according to the invention, and which is assigned a safety valve 15. Inlet valve 13 and safety valve 15 are provided on a pipe 16, one end thereof being connected to the hose 12, the other end terminating into the container 17 of the apparatus 14, a distance above the rounded bottom end Dortion 17' of the container. The container 17 is adapted to separate liquid and gas, and comprises a droplet separator 18. Uppermost, the container 17 is terminated with a blind flange 19 and an overlying safety valve 15' .

Immediately above the droplet separator 18, a first pipeline 20 leads from the container 17 to an orifice meter and differensial pressure meter 21, from where the pipeline 20 leads to a second pipeline 22 coupled to the bottom 17' of the separator container 17. Between first pipeline's 20 connection point at second pipeline 22 and the connection point of the latter at the container bottom 17' , an outlet valve 23 is incorporated.

A third pipeline 24 is coupled to the discharge pipe line 22 of the container 17 and to a point at the container 17 below the droplet separator 18, and is^' provided with a manometer 25 and a level indicator 26.

Immediately below the droplet separator 18, a thermometer 27 is provided.

From the interconnection point of the pipelines 20 and 22, a second hose 12' leads to a closed discharge 28.

By .means of the apparatus shown, the measuring method is carried out as follows: The valve 10' to be tested is closed (full well pressure upstream valve). The flexible hose 12 is coupled to the outtake 9' downstream the valve, whereafter the pressure here is relieved to 0 - 3 bar (approximately atmosphere pressure). The hose 12 is coupled to the inlet 13 of the test apparatus 14, where the apparatus by means of the second hose 12' is coupled to a closed discharge system 28, in order to prevent όil/gas from the experiments from escaping into the surroundings. Thereafter, the inlet valve^' 13 is opened whilst the outlet or discharge valve 23 is closed so that the leakage gas (the leakage oil, the leakage oil/gas mixture) flows through the pipeline 20 and orifice meter 21 to discharge 28.

The differensial pressure across the orifice meter is read on the differensial pressure meter 21, the pressure within the container 17 being read on the manometer 23 and the temperature on the thermometer 27. The amount of gas can be read on a curve, not shown.

The amount of- leakage liquid can be read directly on the graduation of the level indicator 26.

When the test iε completed, the outlet valve 23 is opened and the amount of liquid blown to discharge 28.

Claims

C l a i m s

1. A method for measuring leakage across potential leakage sources such as valves, particularly wellhead valves (10, 10' ), and annulus seals or packoffs (production packers) (7, 8) in oil and/or gas wells, c h a r a c t e r i z e d i n that one at a potential leakage place or at each potential leakage place (7,8,10,10' ), respectively, establishes a (closeable) metering offtake (11,9,9' ), and with closed valve (10,10' ) and/or with operative annulus seals (7,8), over a predetermined period admit the entire amount of leakage at the respective leakage place into a measuring apparatus ( 14 ) , which is adapted for direct measuring of the amount of leakage gas and/or liquid.

2. A method as set forth in claim 1, c h a r a c t e r i z e d i n that one measures the temperature (27) and pressure (25) of the leakage amount as well as the pressure difference across an orifice meter (21), and that the gas portion of the leakage amount is read on a previously made, calibrated curve, based on thermometer (27) and manometer readings.

3. An apparatus for carrying out the method as set forth in claim 1 or 2, c h a r a c t e r i z e d i n that said apparatus comprises a container (17) having a closeable inlet (13) and a closeable outlet (23), e.g. in the form of shut-off valves (13,23), said container (17) being dimensioned to accommodate a certain leakage amount (two- phase leakage, pure gas leakage or pure liquid leakage) over a certain period, said container (17) being equipped with at least one thermometer (27) and at least one manometer (25) for metering the temperature and pressure of the leakage medium.

4. An apparatus as set forth in claim 3, c h a r a c t e r i z e d i n that said container (17) is a separator adapted to separate liquid and gas of the leakage medium, said separator (17) comprising a droplet separator (18) and being assigned a level indicator 26 and an orifice meter and differensial pressure meter (21).

5. An apparatus as set forth in claim 3 or 4, c h a r a c t e r i z e d i n that the outlet (23) of the (separator) container (17) is coupled to a closed discharge circuit (28) .