WO2013122477A1

WO2013122477A1 - Apparatus and method for well testing

Info

Publication number: WO2013122477A1
Application number: PCT/NO2013/050026
Authority: WO
Inventors: Bjørn DYBDAHL; Sigve HAUGLAND; Roald Skjoldal
Original assignee: Petrotech As
Priority date: 2012-02-16
Filing date: 2013-02-12
Publication date: 2013-08-22
Also published as: NO20120163A1; NO335176B1

Abstract

An apparatus and a method of using it for collecting reservoir samples in a well (2) are described, in particular for use in connection with wells of the kind that is found in petroleum recovery, the apparatus including a combination tool (30) which is provided with one or more sampling devices including at least one sample chamber (42, 70) which is arranged to be put into fluid communication with fluid from the reservoir of the well (2), at least one of the at least one sample chamber (42, 70) being a tracer sample chamber (70) which is provided with an internal surface consisting of a material which is practically non-reactive relative to substances that are carried into the tracer sample chamber (70) from the well (2), so that tracers that have been carried into the tracer sample chamber (70) may be brought out of the tracer sample chamber (70) when the reservoir sample is being analysed.

Description

APPARATUS AND METHOD FOR WELL TESTING

This invention relates to an apparatus for testing a well and a method of using the apparatus. More particularly, the present invention relates to an apparatus and a method for collecting reservoir samples in a well, especially for use in connection with wells of the kind that is found in petroleum recovery, in which the apparatus includes a combination tool which is provided with one or more sampling devices that include at least one sample chamber which is arranged to be put into fluid communication with fluid from the reservoir of the well.

In the exploration phase of a petroleum well, it is necessary, in order to determine the reservoir properties, to measure many physical and chemical parameters relatively accurately. By reservoir properties are meant, here, both the properties of the fluids stored in the reservoir, the properties of the formation minerals and the prevailing fluidic properties, for example with respect to permeability, sand outflow, porosity and flow volume.

Typically, the exploration includes measuring the reservoir temperature and pressure, the density of the reservoir fluid by means of a gamma log, water saturation by means of a resistivity meter, porosity by means of a neutron measuring device, permeability and porosity by means of a nuclear magnetic resonance gauge. The chemical composition must also be examined. Further, measurements are carried out to determine the so-called saturation point (boiling point of oil, dew point of gas) of the well fluid. These measurements form the basis for the preparation of a so-called pressure-volume- temperature (PVT) diagram.

Mainly, two methods are used to collect information on the properties of a reservoir. The older method is the so-called "drill-stem test" (DST) which assumes that the well is provisionally completed, so that the reservoir fluid may flow to the surface where fluid samples are filled into compression tanks. Alternatively, a compression tank may be lowered into the underground fluid reservoir itself by means of a wireline, where the compression tank is filled up with fluid and then closed, after which it is transported to the surface for analysis locally or to be shipped to a laboratory.

The fluid flowing up from the well is burnt in a flare stack. The drill-stem test (DST) provides extensive and, for most types of samples, also reliable results. However, relatively much time and resources are spent to carry out testing in accordance with this method which may also imply considerable polluting of air and water. Another negative feature of the method is that the fluid samples must be taken to the surface, where the temperature is lower than in the reservoir. This also causes pressure and temperature differences relative to the reservoir conditions. When collecting data for the determination of the saturation point of the fluid, it is crucial in order to obtain a correct result that the testing is carried out at the pressure and temperature of the reservoir. Therefore, pressure and temperature must normally be increased before testing/analysis can be carried out, which means uncertainty with respect to the gas/oil shares, wax and asphaltenes in the oil of the reservoir.

Another method, the so-called Wireline Formation Testing and Sampling (WF /WFS) was adopted in the 1970s and involves the lowering of measuring equipment and a sample container by means of a cable/wireline into an uncased well which is full of drilling fluid (mud), where measurements are carried out. A smaller fluid sample may be brought to the surface. After continuous development, the method has been given an embodiment in which the apparatus that is lowered into the well is provided with remote-controlled instruments that communicate data to the surface while measuring. It is not possible to simulate a real production situation by means of this method because only very small amounts of reservoir fluid are extracted. It may also be difficult to make sure that drilling fluid (mud) does not affect the measuring results.

US patent 5,329,811 discloses a measuring tool for determining downhole fluid properties. While the tool is in the well, pressure versus volume-fluid data is measured at controlled volume variation of a sample chamber with well fluid.

US patent 5,635,621 discloses a method of determining well-fluid properties with a formation-testing tool based on downhole pressure, volume and temperature measurements of a trapped sample.

US patent 6,128,949 discloses a method of downhole fluid analysis. By means of a sampling tool with a pump unit, fluids may be drawn from the formation, circulated through the instrument for analysis and then pumped into the borehole.

From NO 312689B1, which belongs to one of the inventors of the present invention, an invention is known that has for its purpose to remedy the negative aspects of established techniques.

From the publication US 2010/0252258 Al, an apparatus for sampling reservoir fluids is known, in which a concentration component placed in a sample chamber may have a surface coated with an adsorption medium for temporarily binding tracers that are carried into the chamber.

From the publication WO 93/14295 Al, a sampling apparatus is known which has a sampling chamber which is provided with an internal surface which, chemically, is substantially non-reactive with substances in the fluid sample in the chamber. The apparatus is provided with a variable-volume sample chamber.

During drilling through a formation, a trace element or a so-called "tracer" may be added to the drilling fluid. By measuring the tracer content in the well, it may subsequently be determined when the tracer and thereby the drilling fluid have been removed from the measuring area. Alternatively, an analysis of the drilling fluid is done, which is then compared with the fluid of the well to determine when the drilling fluid has been removed. The method is known under the name of "the Finger-Print

Method".

In the preparations for testing, the drill pipe with the drill bit is pulled out of the well. A combination tool is attached to the free end portion of a drill pipe / production tubing / coiled tubing or wireline and lowered into the well. In what follows, this pipe is called production tubing. It is emphasized that the combination tool may also be lowered into the well by means of said wireline. At the location of exploration, the well may be open (an open hole) or provided with casing, wherein the casing is or will be perforated by so-called TCP (Tubing-Conveyed Perforation) in the zone that is to be tested. Dry seal plugs/elements isolate a zone from which there is going to be testing/production. The dry seal plugs/elements are attached to a drill stem / production tubing or to the combination tool (which is then functioning as a so-called "carrier") at intervals adjusted to the thickness of the reservoir zone(s). Possibly, the lower dry seal plug/element may be positioned before the combination tool is lowered into the well.

The combination tool should, as mentioned, also be able to be lowered on a wireline into an uncased or cased well and be operated downhole.

In operations in an uncased well, the dry seal plugs/elements seal directly against the well formation. In a so-called DST (Drill-Stem Test), the combination tool is placed as close to the lower test valve as possible. The flow out of the production tubing to a separator is controlled by means of a throttling valve on the surface, a so-called choke. The separator is arranged to be put into fluid communication with a burner. In connection with fluid communication from the formation into the production tubing being opened, for example by means of TCP, said choke is opened and the well fluid from the isolated zone flows through the combination tool into the separator. A portion of the fluid is carried to said burner.

An alternative method to what has been mentioned above is to run a batching pig / piston (called a batching pig in what follows) into the production tubing through a sluice at the surface and pump it down to the combination tool by means of pressure fluid. The fluid, usually drilling fluid, which is displaced by the batching pig as it is displaced downwards, flows through a circulation outlet valve in the combination tool, a valve in the upper dry seal plug/element and up through the annulus between the casing and the production tubing. A detergent may have been supplied to the production tubing before the batching pig is pumped downwards to wash the so-called filter cake in connection with the reservoir. Washing circulation may run in both directions. In one embodiment, the batching pig may be provided with a valve which is arranged to enable fluid circulation through the pig, possibly also with measuring equipment for, for example, temperature, pressure, fluid identification and position. The valve of the batching pig also enables circulation through the production tubing if the batching pig should get stuck in the production tubing. If desirable, the batching pig may also be provided with an electrically or hydraulically driven propelling device with position indication for increasing the accuracy of movement of the batching pig. Alternatively, the batching-pig position may be determined by means of so-called volume points.

The method according to NO 312689B1 comprises two typical alternative methods, called alternative "A" and alternative "B" in what follows, for treating the reservoir fluid contaminated with drilling fluid.

For both the methods A and B, a throttling valve or choke is opened in the production tubing at the surface, and reservoir fluid flows out of the reservoir through the reservoir-inflow valve of the combination tool. In the method according to alternative A, the batching pig is displaced up through the production tubing by the entering reservoir fluid contaminated with drilling fluid, while at the same time, fluid measurements are carried out in the combination tool to identify a tracer which was added to the drilling fluid in advance, alternatively by using the Finger-Print Method to determine when the area has been cleaned of drilling fluid. A reservoir-inflow valve may include one or more valves and ports. When the tracers are no longer traceable, or the drilling-fluid analysis can no longer be recognized, the reservoir-inflow valve in the combination tool is closed, whereby the contaminated fluid is shut in. The lower end portion of the combination tool is connected to the lower dry seal plug/element, and the valve of the lower dry seal plug/element is opened, so that the fluid column staying in the production tubing below the batching pig by means of fluid pressure against the top side of the batching pig, is pumped through the lower dry seal plug/element and down into an underlying chamber/well. The valve of the lower dry seal plug/element is closed. The reservoir-inflow valve of the combination tool is opened and reservoir fluid enters the production tubing / drill pipe, driving the batching pig upwards.

The climbing speed and thereby the production volume may be measured directly or calculated from displaced fluid volume flowing in front of the batching pig into a collector on the surface, provided with measuring equipment.

In alternative B, the reservoir fluid contaminated with drilling fluid flows through the valve of the batching pig and up through the production tubing. After the well has been cleaned of drilling fluid in the reservoir area, the valve of the batching pig is closed and the batching pig is moved upwards by the clean reservoir fluid.

In a further alternative that is described in NO 312689B1 the fluid column contaminated with drilling fluid is not pumped down into another chamber, but rises in the production tubing together with reservoir fluid when the reservoir fluid enters the production tubing.

Subsequently, a volume of reservoir fluid is produced, after which the reservoir-inflow valve in the inlet opening of the combination tool is closed, thus isolating this clean amount/sample of fluid from all other fluids in the well. It must be possible to carry out the production very slowly, in order not to disturb the state of the formation fluid by loss of pressure. By moving the batching pig/element upwards in a controlled manner, and, at the same time, reading and logging the temperature gradient of the shut-in sample chamber and also the volume, pressure and temperature of the sample, a volume-pressure-temperature diagram and a saturation-point curve for the reservoir fluid can be prepared without removing the reservoir fluid from the well. Other measurements, such as multiphase flow metering, mass flow, fluid identification, density, conductivity, pH, composition of hydrocarbon fluid and ionic composition of water, are performed by means of suitable measuring equipment in the combination tool. These measurements are known from said NO 312689 and will, for the sake of sim- plicity, also be called PVT measurements in what follows, even though the measurements could also include measurements beyond pressure, volume and temperature, as mentioned above.

In a well, there will also be tracers which are desirably to be measured. For example, the mercury level and hydrogen-sulphide content are measured to determine the quality of the reservoir fluid, possibly its corrosiveness.

During testing and analysis, smaller samples may be isolated in separate chambers which are designed to preserve the properties of the reservoir fluid all the way until the sample arrives at the laboratory on the surface or on shore. The details and operation of the sample chambers are explained in the specific part of the description.

The pressure on the top side of the batching pig/element is relieved and the reservoir- inflow valve is opened so that reservoir fluid flows into the production tubing. The batching pig is moved towards the surface by the entering reservoir fluid, and measurements for establishing understanding of the flow characteristics of the reservoir fluid in the reservoir rock may be carried out in the combination tool. Afterwards, the reservoir fluid may be pumped back into the same reservoir, or possibly another reservoir of the same well.

If the reservoir pressure should be too low so that the necessary parameters cannot be registered, fluid in the production tubing above the batching pig may be pumped out and replaced with nitrogen to lighten the pressure on the top side of the batching pig so that the batching pig/element rises. Possibly, the fluid above the batching pig/element may be replaced with a fluid of a lower specific gravity. As mentioned above, the batching pig may also be provided with propulsion machinery.

While NO 312689 is primarily directed towards said PVT measurements (with the additions mentioned above), the present invention is directed towards a sample chamber which is suitable for collecting samples which are to be analysed for, inter alia, tracers that are naturally present in the reservoir fluid. A person skilled in the art will know that such tracers may occur in very small concentrations and are typically measured in ppb (parts per billion). To achieve a satisfactory result, it is very important that the tracers that are carried into the sample chamber may also be liberated, to the greatest extent possible, from the chamber when the sample is to be analysed.

In what follows, the sample chamber in accordance with the present invention will be referred to as a tracer sample chamber, whereas a sample chamber which is primarily intended for the above-mentioned PVT measurements (again with the additions men- tioned above) will simply be referred to as a PVT sample chamber.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through features which are specified in the description below and in the claims that follow.

According to a first aspect of the present invention, an apparatus for collecting reservoir samples in a well has been provided, in particular for use in connection with wells of the kind that is found in petroleum recovery, the apparatus comprising a combination tool which is provided with one or more sampling devices which comprise at least one sample chamber which is arranged to be put into fluid communication with a space which is arranged to accommodate fluid from the reservoir of the well, at least one of the at least one sample chamber being a tracer sample chamber of fixed volume; the apparatus further comprising :

- a fluid line which extends between the space and an inlet portion of the tracer sample chamber; and

- at least one valve for controlling the fluid flow through the fluid line;

the tracer sample chamber, the fluid line and the at least one valve being provided with an internal surface consisting of a material which is practically non-reactive relative to substances that are carried from the space into the tracer sample chamber, so that tracers that are carried into the tracer sample chamber may be brought out of the tracer sample chamber when the reservoir sample is being analysed.

The effect of this is that the major part of any tracers present in the fluid sample may be brought out of the tracer sample chamber together with the fluid when the sample is analysed. The analytical results will thus be more reliable with respect to the content of tracers of the reservoir.

The combination tool may be connected to a pipe which connects the combination tool to the surface. Said combination tool and pipe may together constitute a closed, volume-adjustable space, as it is known from NO 312689. The reservoir sample which is carried into the at least one sample chamber may be taken from this space. Alternatively, the combination tool may be connected to a wireline extending from the surface down into the well.

Thus, to be able to control the inflow of reservoir fluid into the at least one sample chamber, each of the at least one sample chamber is connected to the reservoir of the well via a separately controlled filling valve. The apparatus may further include a PVT sample chamber arranged to collect samples as it is known from NO 312689, in which the P T sample chamber is provided with an upper partition piston and a lower partition piston, the space of the sample chamber located between the partition pistons communicating with the closed space of the combination tool via the filling valve.

The cavity present above the upper partition piston in the PVT sample chamber may be filled with pressure fluid and communicate with an air chamber via a choke/shut-off valve.

A person skilled in the art will know that, to date, there are no materials that are 100 % non-reactive with tracers that might be present in a formation fluid from a petroleum well. In order to prevent, to the greatest extent possible, tracers in the reservoir sample from binding to the practically non-reactive material of the tracer sample chamber, it may be an advantage to provide the tracer sample chamber with an adsorption medium which is much more reactive with the tracers that might be carried into the tracer sample chamber than the material of the tracer chamber.

Such an adsorption medium may be positioned inside the tracer sample chamber or in an inlet portion associated therewith. As mentioned, the purpose of the adsorption medium is to temporarily bind tracers that are carried into the camber. What type of adsorption medium is used, depends on what tracers are desirably to be adsorbed, but an adsorption medium made from gold, platinum or some alloy including one or both of these, has proved effective for use in connection with tracers that are normally found in a reservoir fluid in a petroleum well. When the sample is analysed, the adsorption medium is exposed to an agent that liberates the adsorbed tracers from the adsorption medium, so that the amount of tracers is determined. Such an agent may typically be heat.

In one embodiment, the tracer sample chamber is arranged to be put into fluid communication with a pressure-relief chamber so that an analysis of the collected reservoir fluid may be carried out in the well. The pressure-relief chamber is preferably made with an internal surface of the same material as or one corresponding to that of the tracer sample chamber so that tracers bind to / react with the internal surface of the pressure-relief chamber to the least possible extent. In one embodiment, the combination tool is provided with measuring instruments which are arranged to measure the physical and chemical properties of fluids.

According to a second aspect of the present invention, a method of collecting reservoir samples in a well is provided, in particular for use in connection with wells of the kind that is found in petroleum recovery, in which the reservoir sample is at least to be analysed for tracers that might be present in the reservoir sample, wherein the method includes providing a combination tool which is provided with one or more sampling devices including at least one sample chamber which is arranged to be put into fluid communication with fluid from the reservoir of the well, at least one of the at least one sample chamber being a tracer sample chamber which is put into fluid communication with the space by means of a fluid line and at least one valve for controlling the fluid flow through the fluid line; the tracer sample chamber, the fluid line and the at least one valve being provided with an internal surface consisting of a material which is practically non-reactive relative to the substances to be analysed, so that a tracer sample chamber is provided, wherein tracers that are carried into the tracer sample chamber may be brought out of the tracer sample chamber by a subsequent analysis of the reservoir sample.

The at least one sample chamber may be put into fluid communication with an amount of fluid trapped in a closed space in the well. In one embodiment, the volume of the space may be adjusted while, at the same time, measuring of physical/chemical/ thermodynamic quantities relating to the fluid shut in is performed .

In one embodiment, the well fluid flows into a space defined by a pipe and the combination tool together, the pipe connecting the combination tool to the surface, after which the space is shut off by means of a valve and a batching pig is gradually displaced within the pipe to alter the closed space while, at the same time, pressure and temperature in the space is being read, as it is known from NO 312689.

After the desired amount has been received, at least one of the at least one sample chamber may be shut off and then pressure-compensated.

After the desired amount has been received, at least one of the at least one sample chamber may be shut off and then temperature-controlled.

An adsorption medium arranged to temporarily bind tracers that are carried into the tracer sample chamber, may be positioned inside or in connection with an inlet portion of the tracer sample chamber before the combination tool is inserted in the well. When the sample is being analysed, the adsorption medium is exposed to an agent that liberates the adsorbed tracers from the adsorption medium so that the amount of tracers is determined. Such an agent may typically be heat. An adsorption medium may thus be used in connection with sampling for the determination of tracer content in a well fluid.

In what follows, a non-limiting example of a preferred embodiment is described, which is visualized in the accompanying drawings, in which :

Fig. 1 shows schematically a petroleum well which has been prepared for testing, wherein a lower dry seal plug/element, a combination tool, an upper dry seal plug/element and a batching pig have been lowered into the well;

Fig. 2 shows schematically the well of fig. 1 as reservoir fluid contaminated with drilling fluid is entering the production tubing ;

Fig. 3 shows schematically the well of fig. 1 as contaminated reservoir fluid is flowing down into a chamber below the lower dry seal plug/element;

Fig. 4 shows schematically the well of fig. 1 during volume-pressure- temperature testing;

Fig. 5 shows schematically the well of fig. 1 as clean reservoir fluid is pumped back into the reservoir;

Fig. 6 shows, on a larger scale, the configuration of the sample chambers in the non-filled state;

Fig. 7 shows, on a larger scale, configuration of the sample chambers in the filled state;

Fig. 8a shows the combination tool of fig. 7, but where the combination tool is further provided with a tracer sample chamber in accordance with the present invention, but where fluid communication between a well-fluid chamber and the tracer sample chamber is closed ;

Fig. 8b shows the same as fig. 8a, but after fluid communication has been established between the well-fluid chamber and the tracer sample chamber;

Fig. 9 shows an alternative embodiment of the tool of fig. 8a;

Fig. 10 shows the combination tool of fig. 8, but where the tracer sample camber is provided with an adsorption medium arranged to temporarily re- act with any tracers that might be carried into the tracer sample chamber; and

Fig. 11 shows the combination tool of fig. 8b, but where the tool is further provided with a pressure- relief chamber.

Figures 1-7 show the apparatus according to NO 312689, whereas figures 8a-l l show the apparatus according to the present invention which is provided with a tracer sample chamber 70.

The present invention may be used together with the apparatus according to NO 312689 as shown in figures 1-7, but the apparatus could also be used with only the tracer sample chamber 70, thus without the sample chamber 42 as it appears from the figures. Further, the apparatus shown in figures 8a-ll, and also figures 6-7, for that matter, may be attached to a free end portion of, for example, a production tubing 10 as shown in figures 1-5. But the apparatus may just as well be attached to a lower end portion of a wireline extending to the surface. The wireline is not shown in the figures but will be well known to a person skilled in the art.

In the drawings, the reference numeral 2 indicates a well that has been drilled into a petroleum reservoir 4. Arrows indicate flow paths and directions of movement. The well 2, see fig. 1, is provided with a casing 6 which is perforated through the reservoir 4. A lower dry seal plug/element 20, which is provided with a seal 22 sealing against the casing 6, a shut-off valve 24, a communication/battery part 26 and wire connections, not shown, between the valve 24 and the communication/battery module 26, shuts off an underlying well section which forms a chamber 8. A combination tool 30 including a reservoir-inflow valve 32, a circulation outlet valve 34, measuring instruments 36, a communication/battery part 38 with associated wire connections, not shown, has been sealingly attached to the lower end portion of a production tubing 10 and lowered into the well 2 and is in the reservoir 4. The combination tool 30 may be provided with one or more sample-collecting devices 39, see fig. 6, each typically including an air chamber 40 at atmospheric pressure, a sample chamber 42, an equalizing/nitrogen chamber 47 and a filling valve 45. A closed choke/shut-off valve 41 connects the air chamber 40 to the upper portion of the sample chamber 42. The sample chamber 42 is provided with an upper partition piston 43 and a lower partition piston 44. The space formed in the sample chamber 42 between the partition pistons 43 and 44 communicates with the closed space 14 of the combination tool 30 through a filling valve 45. The filling valve 45 is open. The cavity of the sample chamber 42 above the upper partition piston 43 is filled with oil or another suitable pressure fluid. The space of the sample chamber 42 that is below the lower partition piston 44 communicates with the upper portion of the equalizing chamber 47 via a shut-off valve 46. A partition piston 48 in the equalizing chamber 47 forms a boundary between a pressure fluid present above the partition piston 48 and a nitrogen gas which is present on the opposite side of the partition piston 48 and is, in the main, at the pressure level of the well. All partition pistons 43, 44 and 48 are provided with seals 49 sealing against the inside of the respective chambers. One or more partition pistons may be replaced by membranes.

The lower dry seal plug/element 20 may be fixedly connected to the combination tool 30, as it appears from the drawings, or it may form an independent unit. An upper dry seal plug/element 50 is positioned in the annulus 12 between the casing 6 and the production tubing 10. The upper dry seal plug/element 50 may be fixedly connected to the production pipe 10 at a fixed distance from the combination tool 30, or it may be pumped down to the desired position where, possibly, it is secured to the production tubing 10 and/or the casing 12 with a securing device, not shown. The upper dry seal plug/element 50 is provided with a seal 52 which seals against the casing 6, a seal 54 which seals against the production tubing 10, a valve 56, a communication/battery module 58 and wire connections, not shown, between the valve 56 and the communication/battery module 58. A batching pig 60 including a seal 62 that seals against the inner diameter of the production tubing 10, a valve 64 and a communication/battery module 66 with the associated wire connection, not shown, is pumped down the production tubing 10. A closed space 14 is thus formed between the batching pig 60 and the combination tool 30 when the valves 32, 34, 24 and 64 are closed. All the valves and measuring devices are remote-controlled from the surface by means of, for example, acoustic signal transmission in accordance with the prior art known per se.

A cleaning fluid may have been supplied to the well 2 before the combination tool 30 is lowered into the well 2, or the cleaning fluid may circulate from the annulus 12, through the valves 56, 34 and 64 to the production tubing.

In a typical method, called alternative A in the above, a valve, not shown, is opened at the surface for fluid to flow out of the production tubing 10. Said valve is placed at the upper end portion of the production tubing. Reservoir fluid flows together with remnants of drilling fluid through the reservoir-inflow valve 32 into the combination tool 30, displacing the batching pig 60 upwards while, at the same time, the inflowing fluid is measured with respect to added tracer, see fig. 2. When the reservoir section of the well has been cleaned of tracer and thereby drilling fluid, the reservoir-inflow valve 32 is closed, the shut-off valve 24 is opened, and the fluid present below the batching pig 60 in the production tubing 10 flows, by means of pressure on the top side of the batching pig 60, down into the chamber 8, see fig. 3. In alternative B of the method, the contaminated reservoir fluid flows through the valve 64 of the batching pig 60 to the surface. The shut-off valve 24 is closed and the reservoir-inflow valve 32 is opened, whereby the batching pig 60 is displaced upwards in the production tubing 10 by the entering reservoir fluid, in the same way as that shown in fig. 2. When there is a sufficient amount of clean reservoir fluid in the production tubing 10, the reservoir- inflow valve 32 is closed, see fig. 4. The batching pig 60 is then displaced gradually upwards by draining fluid from above the batching pig 60 while, at the same time, the reservoir fluid present in the production tubing 10 between the batching pig 60 and the combination tool 30 is measured with respect to volume, pressure and temperature. Other measurements, as they are described above, may be performed at the same time. After the measurements have been carried out, the reservoir fluid present in the production tubing 10 may possibly be pumped back into the reservoir by the reservoir-inflow valve 32, and possibly also the valve 64 in the batching pig, being opened, see fig. 5.

When, during testing, it is desirable to take a sample in one of the sampling devices 39, which is arranged to receive a minor amount of reservoir fluid and ensure that this is kept at constant pressure and/or temperature until it is subsequently to be analysed in a laboratory, the choke/shut-off valve 41 is operated into the open position, for example by means of an acoustic signal from the surface via receivers and actuators, not shown. The pressure oil present in the upper part of the sample chamber 42 will flow at a predetermined rate through the coke/shut-off valve 42 into the air chamber 40. The upper partition piston 43 is displaced upwards by the reservoir fluid entering through the filling valve 45.

As the upper partition piston 43 reaches its upper position by the sample chamber 42 having filled up, a sensor/switch/initiator, not shown, is operated, closing the filling valve 45 and opening the valve 46 via connections and actuators, not shown, whereby the pressure fluid within the equalizing chamber 47 may communicate with the volume below the lower partition piston 44 in the sample chamber 42. The pressure gas in the equalizing chamber 47 ensures that temperature variations during transport to a laboratory will not insignificantly affect the pressure of the sample.

In an alternative sampling device, the air chamber 40 and the sample chamber 42 with the choke/shut-off valve 41 are surrounded by an insulated and temperature- controlled container (thermos bottle). Temperature control may be performed by means of an accumulator-operated, thermostat-controlled heating foil, for example. Pressure compensation is not necessary with this solution.

The above-mentioned apparatus is known from NO 312689 and has turned out to function very satisfactorily for acquiring physical quantities relating to, for example, PVT (pressure, volume and temperature).

However, in a reservoir fluid, there may be so-called tracers which may occur in the order of ppb (parts per billion), but which it may be very important to identify as accurately as possible. Such tracers may be, for example, but are not limited to, mercury Hg (inorganic, organic, total), C0₂, H₂S, carbon oxide sulphide COS, RS-H and other individual sulphur components and tracers, radioactive isotopes or other components known within the art.

The sample chamber 42 discussed above includes, inter alia, seals 49 arranged to form a fluid-tight connection across the pistons 43, 44. The tracers which should desirably be identified by analysis may react with or bind to these seals 49, to a fluid film occurring between the seals 49 and the sample chamber 42, to the surfaces of the partition pistons 43, 44 and to the chamber 42 itself. Such a reaction implies that at least a portion of the tracers will not be liberated in an analysis. Thus, the analytical results could be severely misleading. Even if the tracers may occur in very small concentrations, the industry still has a strong need for achieving correct analytical results.

It is sought to solve or at least reduce the above-mentioned problems by means of the present invention.

Fig. 8a and fig. 8b show an example of an apparatus in accordance with the present invention, the apparatus including a combination tool 30 of the kind that has been explained above. The combination tool 30 is provided with two sampling devices 39 which, in the embodiment shown, include a first sample chamber 42 which is of the kind described above and takes care of PVT measurements, among other things, and a second sample chamber 70. For the sake of simplicity, in what follows, the first sample chamber 42 will be called a PVT fluid-sample chamber or just a PVT sample chamber 42, whereas the second sample chamber 70 will be called a tracer sample chamber 70, but might just as well have been called an "inert chamber" 70 or "noble chamber" 70, for example.

The tracer sample chamber 70 is provided with an internal surface consisting of a material which is practically non-reactive relative to substances that are carried into the tracer sample chamber 70 from the well 2. The purpose of such a non-reactive material is primarily that the tracers, among other things, that are carried into the tracer sample chamber 70 may also be brought out of the tracer sample chamber 70 when the fluid is to be analysed. Examples of materials that could be used are nickel-based alloys, for example of the types that are sold under the names of Inconel®, Incoloy®, Hastelloy® and titanium alloys. The entire tracer sample chamber 70 may be made of a material such as Hastelloy®, or only the internal surface of the tracer sample chamber 70 may be coated with such a material. The internal surface could alternatively or additionally be coated with a ceramic material, for example of the kind that is sold under the name of Sulfinert®. Other coatings of the ceramic thin-film type are known.

In fig. 8a, there is fluid communication between the closed space 14 and PVT sample chamber 42. The fluid communication may be controlled by adjusting the valve 45.

When the PVT sample chamber 42 has been filled with reservoir fluid as described above in the discussion of figures 6 and 7, it is closed by opening the valve 45 so that the partition piston 44 is moved somewhat upwards in consequence of the pressure in the nitrogen chamber 47. As a consequence of the reduced volume in the PVT sample chamber 42, this will be pressurized.

When the partition piston 44 is moved upwards, a fluid line 72 extending to the tracer sample chamber 70 via a valve 71 placed at the inlet of the chamber 70 may provide fluid communication between the space 14 in the combination tool 30 and the tracer sample chamber 70 so that reservoir fluid may enter the tracer sample chamber 70. This is shown in fig. 8b.

The tracer sample chamber 70 is initially at underpressure. The underpressure has been provided during the assembly of the combination tool 30. The purpose of the underpressure is two-fold. Firstly, there is a need for an initially empty tracer sample chamber 70 so that the reservoir fluid is allowed to enter it without another fluid, such as air, having to be evacuated. Secondly, air, for example, or any other fluid that might initially be present in the tracer sample chamber 70, could represent a contamination that could manifest itself in the analysis of the fluid collected in the tracer sample chamber 70.

To reduce the risk of tracers reacting with the pipes and valves 45, 71 of the fluid line 72 through which the reservoir fluid is flowing from the space 14 to the tracer sample chamber 70, these are preferably made of practically non-reactive materials, for example of the Hastelloy® type. For the same reason, the fluid line 72 preferably ex- flow, to the greatest extent possible, directly into the fluid line 72, thereby avoiding contact with the seals 49 of the partition piston 44. The materials of the pipes and valves of the fluid line may be of the types mentioned above in connection with the tracer sample chamber 70. Further, preferably, metal-metal valves are used without, for example, elastomer seals which are exposed to the reservoir fluid conveyed through them.

In fig. 9, an alternative embodiment of the apparatus shown in figures 8a and 8b is shown. The main difference between figures 8a and 9 is that, in fig. 9, a further chamber 73 defined between a lower partition piston 48' and an underlying partition piston 73' is arranged. Further, in fig. 9, the tracer sample chamber 70 is provided with a sample port or valve 45' of its own instead of a valve 45 shared by the PVT sample chamber 42 and the tracer sample chamber 70 as shown in figures 8a and 8b.

The purpose of the additional chamber 73 is to enable flushing of the inlet port / pipe channels that lead into the tracer sample chamber 70. When the first chamber 42 is closed and pressurized from the nitrogen chamber 47, the isolation valve piston 74 will open in a manner known per se andsaid inlet port / pipe channels are cleaned.

To provide a sufficient flushing of the inlet port / pipe channels, the volume of the dump chamber 73 is larger than the overall volume to be flushed. In one preferred embodiment, the volume is in the order of ten times said overall volume or more, but the volume could also be smaller than this.

Fig. 10 shows the apparatus of fig. 8a, but where the tracer sample chamber 70 is provided with an adsorption medium 75 to temporarily bind tracers that are carried into the tracer sample chamber 70. In the embodiment shown, the adsorption medium 75 is shown as "gold wool". When the fluid sample present in the tracer sample chamber 70 is being analysed, the adsorption medium is exposed to an agent that liberates the adsorbed tracers from the adsorption medium 75, so that the amount of tracers is determined. Such an agent may typically be heat.

Fig. 11 shows the apparatus of fig. 8b, but where a pressure-relief chamber 80 has been arranged to be put into fluid communication with the tracer sample chamber 70 by the opening of a valve 81. The purpose of the pressure relief is to reduce the pressure of the tracer sample chamber 70 so that the fluid sample may be analysed down- hole, for example by means of measuring instruments 36 that have been described in connection with the discussion of fig. 1. Alternatively, a measuring instrument 82 may be arranged for the tracer sample chamber 70 or the pressure-relief chamber 80 as shown in fig. 11. The pressure-relief chamber 80 is thus a dump chamber. The dump chamber 80 and the valve 81 between it and the tracer sample chamber 70 are preferably made from the same materials as the tracer sample chamber 70 and associated valves. The apparatus and method according to the present invention provide the possibility of greatly improved accuracy in the measuring of tracers that may be naturally present in a reservoir fluid, compared with apparatuses and methods known hitherto.

Claims

C l a i m s

An apparatus for collecting reservoir samples in a well (2), in particular for use in connection with wells of the kind that is found in petroleum recovery, the apparatus including a combination tool (30) which is provided with one or more sampling devices including at least one sample chamber (42, 70) which is arranged to be put into fluid communication with a space (14) which is arranged to hold fluid from the reservoir of the well (2), c h a r a c t e r i z e d i n that at least one of the at least one sample chamber (42, 70) is a tracer sample chamber (70) of fixed volume; and that the apparatus further includes:

- a fluid line (72) which extends between the space (14) and an inlet portion of the tracer sample chamber (70); and

- at least one valve (45, 71) for controlling the fluid flow through the fluid line (72);

the tracer sample chamber (70), the fluid line (72) and the at least one valve (45, 71) being provided with an internal surface consisting of a material which is practically non-reactive relative to substances that are carried from the space (14) into the tracer sample chamber (70), so that tracers that have been carried into the tracer sample chamber (70) may be brought out of the tracer sample chamber (70) when the reservoir sample is being analysed.

The apparatus in accordance with claim 1, wherein the apparatus further includes a PVT sample chamber (42), the PVT sample chamber (42) being provided with an upper partition piston (43) and a lower partition piston (44), the space of the sample chamber (42), which is between the partition pistons (43, 44), communicating with the closed space (14) of the combination tool (30) via the valve (45).

The Apparatus in accordance with claims 1 and 2, wherein, in its cavity located above the upper partition piston (43), the PVT sample chamber (42) is filled with pressure fluid and communicates with an air chamber (40) via a choke/shut-off valve (41) .

The apparatus in accordance with one or both of the claims 2 and 3, wherein the cavity of the PVT sample chamber (42) that is below the lower partition piston (44) communicates with a pressure-fluid-filled part of an equalizing chamber (47) via a shut-off valve (46).

5. The apparatus in accordance with one or more of claims 3-4, wherein the air chamber (40), the PVT chamber (42) and the choke/shut-off valve (41) are in a surrounding temperature-compensated chamber releasable from the combination tool (30)

6. The apparatus in accordance with claim 5, wherein the surrounding temperature-compensated chamber is heated by a battery-operated thermostat- controlled heating foil.

7. The apparatus in accordance with claim 1, wherein an adsorption medium is positioned inside the tracer sample chamber (70) to temporarily bind tracers that are carried into the chamber (70).

8. The apparatus in accordance with claims 7, wherein the adsorption medium is selected from the group consisting of gold, platinum or a mixture thereof.

9. The apparatus in accordance with any one of the preceding claims, wherein the tracer sample chamber (70) is arranged to be put into fluid communication with a pressure-relief chamber (80).

10. The apparatus in accordance with claim 9, wherein the pressure-relief chamber (80) is made with an internal surface of the same material as, or one corresponding to that of, the tracer sample chamber (70).

11. The apparatus in accordance with any one of the preceding claims, wherein the combination tool (30) is provided with measuring instruments (36, 82) that are arranged to measure the physical and chemical properties of fluids.

12. A method of collecting reservoir samples in a well (2), in particular for use in connection with wells of the kind that is found in petroleum recovery, in which the reservoir sample is at least to be analysed for tracers that might be present in the reservoir sample, c h a r a c t e r i z e d i n that the method includes providing a combination tool (30) which is provided with one or more sampling devices including at least one sample chamber (42, 70) which is arranged to be put into fluid communication with fluid from the reservoir of the well (2), at least one of the at least one sample chamber (42, 70) being a tracer sample chamber (70) which is put into fluid communication with the space (14) by means of a fluid line (72) and at least one valve (45, 71) to control fluid flow through the fluid line (72); the tracer sample chamber (70), the fluid line (72) and the at least one valve (45, 71) being provided with an internal surface consisting of a material which is practically non-reactive relative to the substances to be analysed, so that a tracer sample chamber (70) is provided, wherein tracers that have been carried into the tracer sample chamber (70) may be brought out of the tracer sample chamber (70) by a subsequent analysis of the reservoir sample.

13. The method in accordance with claim 12, wherein, after a desired amount of fluid has been received, at least one of the at least one sample chamber (42, 70) is shut off and then pressure-compensated.

14. The method in accordance with claim 13, wherein, after the desired amount has been received, at least one of the at least one sample chamber (42, 70) is shut off and then temperature-controlled.

15. The method in accordance with claim 12, wherein an adsorption medium (75) arranged to temporarily bind tracers that are carried into the tracer sample chamber (70) is positioned inside or in connection with an inlet portion of the tracer sample chamber (70) before the combination tool (30) is inserted in the well.