GB2252296A - Fluid sampling systems - Google Patents

Abstract

When sampling the fluids issuing from the geological formations into which a well, such as an oil well, has been drilled, it is highly desirable to bring the formation fluid to the surface in its original monophasic state. Various mechanical sampling arrangements have been proposed to ensure that this happens, and safely, but so far none have been entirely satisfactory. Both to keep the original state of the sample and to meet the requirements of avoiding the container bursting, there is required an arrangement that is in some way pressure compensated, so that as the container is lifted to the surface, and the ambient pressure and temperature drop, firstly the sample itself is sealed off to prevent it expanding (and separating) under the reducing pressure, and secondly the original ambient sample pressure is actually positively maintained despite any temperature change seeking to cause a corresponding pressure change (so that temperature-induced pressure drop and phase separation is avoided) even as there is provided the effect of a temperature-induced pressure-increase-absorbing gas cap without the actuality. This end, is attained by a sampler wherein the sample chamber (11), in which the sample itself is received and stored, is sealingly closed at one end by a movable partition (21) to the other side of which is applied either directly or indirectly (via a buffer fluid) a source of suitably pressurised gas. <IMAGE>

Description

SamDl ina Svstems This invention relates to sampling systems, and concerns more particularly such systems as are pressure compensated - that is, maintain a desired sample within a chosen pressure range whilst conditions external to the sample vary.

There are many circumstances wherein it is necessary to sample a fluid material, whether as a gas, a liquid, or a mixture of the two, and determine its nature - for example, its physical and chemical composition - to learn something useful about the body of fluid from which the sample was taken. On some of these occasions the sample may be obtained under one set of ambient conditions - of pressure and temperature, say - and thereafter removed to a quite different set for analysis such that, if unprotected, the sample's state its physical and chemical form, maybe - may change during this removal until it is no longer sufficiently representative of the original fluid. One typical example of this situation occurs when sampling the fluids issuing from the geological formations into which a well, such as an oil well, has been drilled.At the bottom of the well, which may be several miles deep, the pressure and temperature are high - possibly several hundred atmospheres, and in the low hundred degrees Celsius - and whilst the formation fluid may under the ambient conditions be a single phase fluid nevertheless a sample of this fluid raised to the quite different ambient conditions of the surface (specifically of pressure and temperature, often referred to as NAP, Normal Atmospheric Pressure, or as NTP, Normal Temperature and Pressure), where it is to be analysed to reveal useful information about the well, may easily separate into two or more distinct phases - for example1 a liquid phase, a gas phase (originally dissolved in the liquid), and a solid phase (originally suspended in the liquid).As such, the separated sample is no longer truly representative of the original ambient fluid - or, at least, not in an easily-understood way - and so has lost much of its value.

One possible way to deal with this problem is to attempt in the laboratory to reconstitute the original monophasic fluid by increasing the separated sample's pressure until it equals that pertaining at the downhole formation from which the sample was taken, but in fact either it is often not possible to "re-combine" the phases in this way or, if it is, the result is subtly different from the original sample. In either case the situation is unsatisfactory, and so in order to solve the problem attempts have been made to ensure that the downhole sample is retrieved in its original monophasic state, and is not allowed to separate out into a biphasic, or even triphasic, form.To achieve this it has been suggested that the sample be obtained using a pressure-resistant container (a surface, or a subsurface or bottomhole, sampler) that is sealed closed after receiving the sample therein, and so prevents any change in sample pressure, and hence any phase separation.

Unfortunately, this somewhat simplistic view overlooks -two important factors. Firstly, if the sample's temperature drops significantly, as with the drop in ambient temperature as a bottomhole sample is removed from the well, then separation may occur anyway as the corresponding decrease in volume of the sample Der se results in an associated reduction in pressure within the sampler. Secondly, if the reverse happens - if the sample's temperature increases, as it might - then the result in the liquid within the sealed container will be a very substantial pressure rise that might possibly cause at best the seals to fail and at worst the whole container to explode.For the latter reason the regulations regarding the provision and transport of (well) samples under pressure in sealed containers require that the liquid be "in equilibrium" with a small volume of gas - a gas "cap" - to absorb any temperaturecaused sample volume increase, and in practice this is normally achieved by deliberately increasing the effective volume of the container, once the sample has been taken, so as to reduce the sample pressure to the point where some slight phase separation occurs and such a gas cap is formed naturally.

What, then, is needed, both to keep the original state of the sample and to meet the requirements of avoiding the container bursting, is an arrangement that is in some way pressure compensated, so that as, for instance, the container is lifted to the surface, and the ambient pressure and temperature drop, firstly the sample itself is sealed off to prevent it expanding (and separating) under the reducing pressure, and secondly the original ambient sample pressure is actually positively maintained despite any temperature change seeking to cause a corresponding pressure change (so that temperature-induced pressure drop and phase separation is avoided) even as there is provided the effect of a temperature-induced pressure-increaseabsorbing gas cap without the actuality.

The invention proposes a novel way of attaining this end. More particularly, the invention suggests a sampler wherein the sample chamber (in which the sample itself is received and stored) is sealingly closed at one end by a movable partition to the other side of which is applied either directly or indirectly (via a buffer fluid) a source of suitably pressurised gas.

Such an arrangement means that the sample itself is sealed in the chamber, one effective end of which is the movable partition, and so cannot expand beyond its original volume (at the downhole ambient conditions), but even though its temperature, and hence its volume, may drop nevertheless its pressure - and thus its phase nature - is maintained by the pressurising gas acting on the partition to move it to "re-compress" the sample.

Moreover, the pressurising gas moving into the chamber behind the partition constitutes the required gas cap, so that the sample is safe despite still being a monophasic liquid.

In one aspect, therefore, the invention provides a container for holding a sample of a fluid that is, in its original ambient conditions; at a greater-thannormal pressure, which container has a reservoir for a gas pressurised to somewhat greater than the expected original ambient pressure of the sample liquid, and has, connectable to that reservoir, a chamber for the sample, and wherein the sample chamber is sealingly divided into two portions by a partition movable therewithin to adjust the effective size of each portion, one such portion (the sample portion) having valved port means to allow the ingress of the liquid to be sampled, and the other (the buffer portion) being connectable to the pressurised gas reservoir so that in operation the pressure of the gas therein is transferred across the partition to the contents of the sample portion, whereby the pressure of the sample liquid is maintained at or above its original ambient pressure.

The sampling container of the invention may be of various kinds, used for various purposes. The following description discusses for the most part a sampler which is a subsurface, or bottomhole, sampler, and is intended to be lowered (typically on a wire, but also perhaps as part of a downhole test string) down a well bore, opened and then closed (to allow the formation fluid to enter, and then to retain it therein), and then pulled back up to the surface, but the same concept can be used on the surface to transfer/transport a thus-retrieved sample from the well head to a testing laboratory, when the sampling container is generally known as a sample cylinder or bottle. As will become apparent, the details of construction of the inventive sampler may differ depending upon whether it is a subsurface sampler or a sample bottle.

The sampler of the invention may be used for any purpose where it is required to obtain a fluid sample which may be a liquid or gaseous sample - under pressure conditions greater than NAP and then bring it into an environment where NAP conditions prevail. It is especially useful for taking samples of formation fluids in oil wells, though, and is for the most part so described hereinafter.

The sampler may take any physical form suitable to the circumstances in which it is to be used. When it is a bottomhole sampler, to be lowered down the bore of a well, it is naturally of an appropriate shape - a long cylinder, with its various components (the sample chamber, the gas reservoir, and so on) arranged sequentially along the cylinder's main axis - and size to fit within the bore (or within any piping within the bore).

The sampler is in effect a container including a gas reservoir and a ported sample chamber sealingly divided into two by a movable partition across which may be applied the gas pressure.

The gas, which may be of any sort, but is very preferably a reasonably inert (non-combustible and noncorrosive) gas such as oxygen-free nitrogen, is, when present, under a pressure somewhat greater than the pressure expected at the depth the sample is to be taken. It is often not easy accurately to determine the actual ambient pressure at the relevant depth, and an approximate value, rather more than the actual value, is generally satisfactory. For example, if the actual pressure is 3,000 lbs/sq in (in the field of oil well technology pressures are still measured in US/Imperial units rather than in metric/SI units, but this is about 200 atmospheres, 15,000 kg/sq cm, or 20,700 Pascals), then an initial gas pressure of this plus 50% (about 4,500 lbs/sq in) should be sufficient, when applied, to prevent the sample separating as it progresses up the well bore to the surface.

The size of the reservoir, coupled (of course) with the pressure of the gas therein, determines how much of a potential volume (and pressure) reduction of the sample can be compensated for, though another factor is obviously the size of the sample itself. For an average size sample - about 35 to 40 in3, or 600 to 700 cc operating at about 10,000 to 15,000 lbs/sq in, a satisfactory volume for the gas reservoir is around 10 in3, or 150 cc.

The gas reservoir is connectable to the sample chamber so that, when it is thus connected, the pressure in the former is transferred to the liquid in the sample portion of the latter across the movable partition. The connection may be direct - the gas actually contacts the partition - or indirect - transfer is made via an intermediate member - and the mechanism by which the act of connecting is effected may take any suitable form.

In the bottomhole sampler discussed hereinafter with reference to the accompanying Drawings the pressurised gas is brought into actual physical contact with the partition, and so its pressure is transferred directly, whereas in the surface cylinder also described hereinafter with reference to the Drawings the gas pressure is transferred indirectly, via a layer of a buffer fluid which itself bears directly on the partition. The way in which the connection is enabled in which the actual act of connection is effected could be by way of some simple mechanical switch or valve triggered by any of the conventional ways of causing downhole equipment to act. For example, in a bottomhole sampler it could involve briskly lifting and dropping the sampler, or applying a pulse of pressure to the well bore, or it could be electrically actuated by a relay device.Preferably, however, it is a conceptually simple pressure-operated switch, or valve, conveniently of the spindle variety, enabled (when the sample chamber is full) to make the required connection when the pressure in the gas reservoir exceeds some other pressure - in the sample, in the borehole mud, or (and preferably, as described hereinafter) in a buffer fluid.

The matter is discussed further hereinafter.

The sample chamber is sealingly divided into two portions (the sample portion and the buffer portion) by a movable partition. To a certain extent the actual shape and nature of the chamber go hand in hand with the shape and nature of the partition. Thus, while the chamber could be fairly flat and wide, like a drum, and fitted with an (elastically) deformable partition sealing mounted across the drum between the ends, so that it can be deformed to one end or the other, the preferred chamber, for fitting down an oil well bore, is a long, relatively narrow cylindrical space, and an appropriate partition therefor is a floating co-axial piston (preferably sealingly mounted for sliding movement along a co-axial piston rod) freely movable along the cylinder between its ends.Such an arrangement, in which movement of the piston along the cylinder adjusts the sizes of the two portions (one getting larger, the other getting correspondingly smaller), is shown in the accompanying Drawings. It will be noted that in the described embodiment the sampler starts off with the piston at one end of the cylindrical chamber, that as the fluid being sampled is allowed in at that one end so the piston moves to the other end of the chamber (displacing buffer fluid, about which more below), and that it is at that second end, and to the "outside" face of the piston, that the pressurised gas is applied to drive the piston back towards the first end and so re-pressurise the fluid in the sample.

The sample chamber is divided by the partition into two portions, and the sample-portion one of these is provided with a (valved) port - or, indeed, a plurality of ports - through which the formation fluid to be sampled is permitted tc enter (when the valve is open).

Where the chamber is the preferred elongate cylinder, as just described, then conveniently the port is at one end thereof, specifically in the wall adjacent the chamber's end face. The valve for the port may take any appropriate form, and it may be its operation that actually initiates ingress of the sample fluid.

However, in the particularly preferred example discussed hereinafter with reference to the Drawings this is not the case (and it is not this valve that controls the ingress of the fluid). Instead, the valve is neither such as can be opened and shut at will, nor even a nonreturn valve, but rather a "one-time" valve that starts open (to allow fluid to flow through the port into the sample chamber) and is then "irreversibly" closed to secure the fluid within the chamber once the chamber is full. And to control fluid ingress there is employed a quite different mechanism, as is discussed hereinafter.

The reason for using a "one-time" valve is to ensure that, no matter what pressure and temperature changes may occur after the sample fluid has been allowed to fill the chamber, none of it is able to leak out via the ingress port. An example of a valve mechanism having the required characteristics is one that is physically actuated by movement of the partition into contact with the end of the non-sample portion (so that as the sample portion becomes full so the last part of the partition's movement closes the valve to seal the port), while an example of an "irreversible" valve is one in which the moving part of the valve, the valve member, is associated with a detente that acts, when that member has reached some predetermined position, to prevent the member moving back. In the preferred embodiment of the Drawings the valve is a piston (the valve member) moving within a cylinder to cover over a port (or ports) into the cylinder (this port is, indeed, the same port referred to above). This piston contains within it outwardly-directed spring-loaded detent bars, or lugs, and is operatively.linked, by the piston rod guiding the floating piston partition, to a collapsible structure mounted immediately adjacent the sampledistant end of the buffer portion of the chamber.As more sample fluid flows into the sample chamber, and the floating piston moves along the chamber into contact with collapsible structure, further movement of the piston collapses and compresses that structure away from the sample end, so that the piston rod, and thus the valve member piston, is moved with it, the movement of the valve member piston being sufficient to cover over, and so block, the chamber entry port. And at the limit of the piston's port-covering movement the spring-loaded lugs become aligned with matching shallow recesses in the chamber wall, whereupon the lugs are partly driven out thereinto (by their springs), and latch the piston irreversibly into place, so locking the valve shut.

Using the port, the sample is obtained by allowing formation fluid to flow into the chamber. As it does so, this fluid pushes the movable partition further and further out of the way, until eventually the partition can move no further, and the.sample-containing portion is now effectively the full size of the chamber, the buffer portion having no significant volume (in the case of the preferred embodiment of a floating piston within a cylinder, the piston is now hard up against that end of the cylinder distant from the ported end).The medium taking up the space on the buffer side of the partition may be any that is convenient, and may even be a gas (such as nitrogen) at some suitable pressure), though it is most advantageously a non-compressible "buffer" liquid (such as a synthetic oil, preferably of the synthetic hydrocarbon variety (typified by that available under the name MOBIL 1 RALLY FORMULA3 for a bottomhole sampler, and an aqueous glycol solution for a surface sampler). A gaseous medium may simply be compressed, but a liquid medium must be displaced out of the buffer portion, and whilst it might be ejected into the ambient borehole fluid it is best to transfer it into a storage space elsewhere in the container.This latter system is that used in the embodiment of the Drawings, in which the container includes an air space into which is transferred the buffer fluid displaced out of the sample chamber by the moving piston on entry of the well formation fluid.

Entry of formation fluid into the sample chamber of a bottomhole sampler naturally needs to be controlled so that the sample is only taken when the sampler container is in the correct position down the well bore. Although this control could be exercised using a valved port wherein the valve is initially shut (when the sampler is lowered into the bore) but can be opened when required, in fact this is not preferred. Instead, and with the embodiment employing a normally-open one-time valve in combination with a liquid buffer medium in the buffer portion of the sample chamber, as previously discussed, what is actually controlled is the flow of buffer liquid out of the chamber and into the air space for storage therein.More specifically, the passageway between the buffer portion of the sample chamber and the air space is valved, conveniently using a needle valve, and at the appropriate moment this valve is opened to allow the buffer liquid originally in the former to transfer into the latter. The valve itself may be actuated in any suitable way, but one already used in present-day samplers, and found very satisfactory (and shown in the Drawings), is to mount the needle at the end of a spring-loaded rod bearing on a stop carried by a lever riding on a clockwork-driven cam (as the clockwork drives the cam round, so one end of the lever drops into a slot in the cam surface, the other end moves until the stop no longer restrains the needle-carrying rod, and the rod is then driven both by its spring and by the ambient pressure to lift the needle and so open the valve and permit the transfer of buffer liquid). The clockwork mechanism, incidentally, may either be started as the sampler is readied for being dropped down the bore, it taking a known, and sufficient, time to actuate the controlling valve, or it may be coupled to a triggering mechanism the action of which is initiated once the sampler is at the appropriate position down hole (perhaps by some mechanical manipulation of the sampler, such as a sharp rise and fall).

As observed hereinbefore, the connection of the sample chamber to the pressurised gas reservoir is by a pressure-operated valve, conveniently of the spindle variety, enabled to make the required connection when the pressure in the gas reservoir exceeds the pressure in the buffer liquid. Using a spindle valve where each end of the spindle itself constitutes a needle valve, the buffer liquid is supplied via one needle valve to the corresponding spindle face while the pressurised gas is supplied via the other to the other face.While the buffer liquid's pressure is the higher its valve remains open (and the gas's valve remains shut), and buffer liquid can pass along to the air space for storage therein, but when - after the sample fluid ingress port is closed - the buffer liquid pressure necessarily drops, and the gas pressure becomes the higher, so the gas's valve opens, allowing the gas to pressurise the sample, and the buffer liquid's valve shuts, preventing both the liquid from returning from its reservoir and the gas from "leaking" into the liquid.

Once the sample has been secured, and brought up to the surface, it will usually be desirable to transfer it to a sample-cylinder version (see below) of the sampler of the invention for onwards transport to the desired destination. To assist in this the bottomhole sampler is very preferably formed in at least two parts, one of which contains the sample chamber and the other of which contains the pressurised gas reservoir, the two being sealingly but detachably joined by some suitable jointing mechanism (preferably a screw joint of some variety, with appropriate sealing gaskets and 0-rings) in association with a valve allowing the two parts to be separated while still retaining the contents of the sample chamber in the required high pressure state.

Such a system, an embodiment of which is described hereinafter with reference to the Drawings, permits the sample chamber of the bottomhole sampler to be detached from the rest of the sampler and then to be sealingly attached via its own sample input port to the sample input port end of a sample cylinder suited for transporting the sample, actual sample transfer being achieved by pumping buffer fluid into the sampler's sample chamber buffer portion to drive back the movable partition and force the sample fluid in the sample portion of the chamber out and into the sample cylinder's sample chamber portion against the counterpressure of the buffer fluid in the cylinder's chamber's buffer portion (which is allowed to flow out through a constricting valve).

For the most pet the invention has been described in terms of X '7i:tc-.^holr sampler but, as observed hereinbefore. it Lay also find use as a surface sampler, more specifically as a container - a sample cylinder or sample bottle - for transporting an obtained sample from one site to another, such as from the well head to the laboratory, or for obtaining a surface sample (e.g., from the well head, a separator, or a production process point). In such a case the inventive container takes its more simple form, and is in essence merely the partitioned sample chamber and the gas reservoir connectable thereto. An example of such a sample cylinder is shown in the Drawings.

The materials used in the construction of the container of the invention may be any considered appropriate, bearing in mind the conditions of temperature, pressure and general mechanical harshness of the intended operating environment, and need little discussion here. Even so, it is perhaps worth noting that the bottomhole sampler is conveniently made of 17/4 PH stainless steel, CA 104 aluminium bronze, and/or silver steel, with metal-to-metal sealing surfaces backed up by fluorocarbon polymer O-rings, oxygen-free nitrogen as the pressurised gas, and a synthetic oil of the synthetic hydrocarbon plus additives variety such as MOBIL 1 RALLY FORMULA as the buffer fluid, while the sample cylinder is conveniently made of 17/4 PH stainless steel, with metal-to-metal sealing surfaces backed up by fluorocarbon polymer O-rings, oxygen-free nitrogen as the pressurised gas, and a 2::1 water/ethyleneglycol mixture as the buffer fluid.

As will be appreciated from the foregoing, the invention may, in its bottomhole sampler aspect, be summarised as a sampling tool for sampling fluid from a downhole well, said sampling tool comprising: sample chamber means having valve means actuatable to be opened when the tool is at a desired depth to admit well fluid to fill said sample chamber, piston means moveable within said sample chamber, one side of said piston means defining a surface of said sample chamber and the other side of the piston means being coupled to elastic fluid reservoir means; said pistcn being moveable in said sample chamber in response to admitted well fluid to force said piston along said chamber and to compress said elastic fluid reservoir, said valve means being closable once said sample chamber is filled;; the elastic fluid reservoir providing a force which acts on said piston to maintain the sample in a monophasic state as the tool is raised in the well, said piston being moveable in the sample chamber to expel said sample from the sample chamber once the sampling tool is removed from the well.

Similarly, in its surface sampler aspect the invention may be summarised as a sample bottle for receiving a monophasic sample of well fluid for storing the sample in a monophasic state, said sample bottle comprising: a sample chamber for receiving said monophasic sample; piston means forming a wall of said sample chamber, said piston means being moveable within said sample chamber as said sample is admitted; gas reservoir means located within said bottle containing gas under pressure, and means for applying said gas to said piston to maintain said sample in the monophasic state.

Moreover, the use of these samplers, and specifically of the bottomhole sampler, may be defined in terms of a method of obtaining a sample of well fluid from a well and maintaining the sample in a monophasic state, the method comprising the steps of: lowering a sampling tool with a sample chamber into said well; at a predetermined depth admitting a sample of well fluid into said sample chamber; applying pressure to the sample in the chamber from a gas reservoir via a moveable piston sufficient to maintain the sample in the monophasic state as the tool is raised to the surface; and removing the monophasic sample from the sample chamber by applying pressure to said piston to move said piston and expel said sample from the sample chamber.

Furthermore, there is also disclosed a method of providing mercury-free transfer of a monophasic sample from a sample chamber in a sampling tool to a sample bottle and storing the sample in said bottle in a monophasic condition, said method comprising the steps of: coupling the sample bottle to the sampling tool to provide fluid communication between said sample chamber in said tool and a sample storage chamber in said bottle; applying non-mercury fluid pressure to said sampling tool to move a piston in said sampling chamber to expel said sample into said sample storage chamber; sealing the sample in said sample storage chamber; and applying pressure to said sample via a gas reservoir acting directly or indirectly on a moveable piston within said sample chamber and forming a wall of said sampling chamber to maintain the sample within the sample storage chamber in said monophasic condition.

An embodiment of the invention is now described, though by way of illustration only, with reference to the accompanying Drawings in which: Figures 1A to 1G show a sequence of overlapping axially-parallel sectional views of a bottomhole sampler according to the invention; Figures 2(1)A to (1)C, 2(2), 2(3)A to (3)C, 2(4)A to (4)C and 2(5) are a set of five overlapping section sequences and part sequences (like those of Figure 1, but diagrammatic) showing a bottomhole sampler in the various stages it goes through as the sample is taken; Figures 3A & 3B are part axial sections of the sample portion end of a bottomhole sampler similar to that of Figure 1, showing respectively the unlocked and locked states of the portion's port valve system; and Figures 4A & 4B show a sequence of overlapping axially-parallel sectional views of a surface sampler - a sample cylinder - of the invention.

Figure 1 shows a complete bottomhole sampler (bottom end to the left, as viewed) according to the invention. The sampler is a long cylindrical tube. It may notionally be split into five main sections, these being: the sample chamber (11), with its lockable valve assembly (generally 12), of Figures 1A and lB; the pressurised gas control valve assembly (generally 13), of Figure 1C; the pressurised gas reservoir (14), of Figure 1C; the buffer liquid storage space (15) and the choke assembly (generally 16) leading thereto, of Figure lE; and the clockwork-driven trigger assembly (generally 17), of Figure 1F.

The sample chamber (11) is a cylindrical space containing a floating piston (21) sealed therein by suitable O-rings. At one end (the bottom/left as viewed) there is a plurality of ports (22, 22a) arranged in a ring in the cylinder wall, allowing (when open) communication between the sampler's surroundings and the inside of the sample chamber 11. The piston 21 is born on a piston rod (23) attached at one end (the bottom left as viewed) to a piston-like valve member (24) sealed (by O-rings) into what is in effect an extension of the chamber 11 and able, when suitably pulled (to the right as viewed) by the piston rod 23 to move to block off the ports 22, 22a and so prevent egress of the sample already in the chamber. This valve member 24 is part of the one-time locking mechanism employed, and the assembly is described in more detail hereinafter.

The piston rod 23 is attached, at its other end (the top/right as viewed) to a telescopicallycollapsible structure (generally 31) consisting of an outer tubular member (32) sliding over and along an inner rod member (33), the two connected by one or more shearable links (as 34). The piston rod 23 is attached to the outer member 32, and will move with it as, the links 34 having been sheared, the outer member slides along over the inner rod 33. This is described in more detail hereinafter.

When the sampler is set into operation the floating piston is, as shown in Figure 1A, all the way to the bottom/left (as viewed). The chamber space to the left of the piston, which is the sample portion, is practically nothing, while the chamber space to the right, which is the buffer portion, is practically the whole of the chamber. To start with, this buffer portion is full of buffer liquid, and this buffer liquid communicates, along a variety of passageways (35) through the sampler, with the buffer storage space 15 (Figure 1E), which is initially full of air at NAP save that this communication is via an initially-closed valve actuated by the trigger assembly (Figure 1F).

These passageways 35 are; 35a through the collapsible structure 31; 35b past an open isolation valve (59); 35c to the gas control valve assembly 13; 35d and 35e past that assembly; 35f in a coiled tube through the gas reservoir 14; 35g to and through a flow control regulator (choke assembly 16); 35h to and through another coiled tube in the buffer liquid storage space 15; and finally 35i to, past and back from the trigger assembly valve and debauching into the space 15.

The isolation valve 59 is in a removable body (60) sealingly mounted at the end of the collapsible structure 31 portion and having the gas control assembly 13 mounted onto it to make a continuous arrangement. By "breaking" the arrangement across the joint (61; the joint just above the valve 59, to the right thereof as viewed) so the sample-containing chamber may be readied for the transfer of its contents to a sample cylinder, as described in more detail hereinafter.

Up (to the right as viewed) along the sampler from the collapsible structure 31 is the gas control valve 13, and beyond that is the pressurised gas chamber 14. This chamber is initially full of pressurised gas (nitrogen), and this gas can communicate with the buffer portion of the sample chamber 11 via the control valve 13 along a number of passageways 41.

These are: 41a from the gas reservoir to and past the control valve 13t and 35c, 35b and 35a (as before, but in the reverse direction). Whether the buffer liquid or the pressurised gas can flow past the control valve depends on the position of the O-ring-sealed spindlelike valve member (36; Figure 1C). It will be clear (from an examination of the valve as shown in Figure lC, that it has a floating piston-like spindle 36 with a needle (37, 38) at each end co-operating with a corresponding valve seat. The two needles control the flow of liquid through the valve; if the one (37) on the left (as viewed) is open while that (38) on the right (as viewed) is closed then only the buffer liquid can pass through the valve, while if it is the other way round (37 closed, 38 openj then only pressurised gas can pass through.Which happens depends on the relative pressures of the buffer liquid and the gas, for it will be seen that each is fed independently to its side of the piston in such a way as to act to push the piston away and thus open that particular valve. Now, in the initial stages of operation of the sampler, where there is an (incompressible) liquid in the buffer portion, the pressure on the buffer liquid side will be the higher, and the piston will always be biassed towards the right (as viewed), keeping valve 37 open and valve 38 closed.

However, once all the buffer liquid has been pushed out of the buffer portion into the air space 15 then the liquid pressure will drop to below that of the pressurised gas in reservoir 14 - in fact, and though it may not be clear from the Figure, in this embodiment the relevant areas against which the pressures act are such that the pressure on the pressurised gas reservoir side must be four times that of the buffer fluid pressure to actuate the valve - and the gas's pressure against piston 36 will drive it to the left (as viewed), closing valve 37 and opening valve 38 - and allowing gas into the buffer portion. This is discussed further hereinafter.

Almost at the very top (the right as viewed) of the sampler is the clockwork-driven trigger mechanism 17 that not only operates the valve controlling the flow of buffer liquid into the space 15 but also, by so doing, controls the entire operation of the sampler. This mechanism includes a clockwork-driven cam (51) with a deep cut-out (52) therein. Against the cam is biassed a pivotally-mounted lever arm (53), such that as the cam rotates and the arm falls into the cut-out it (the arm) moves sharply to one side.The arm carries a pin (54) projecting therefrom, and axially biassed against this pin "unstably" is the free end of a rod-like extension (55) of the "needle" valve member (56) of the trigger mechanism's valve (in actual fact the valve member proper is little more than the other end of the rod 55, which in operation moves axially into and out of sealing co-operation with an annular seal (57) in passageway 35i). When seated against the pin 54 the rod is prevented from moving so as to open the valve.

However, when the lever 53 moves to one side the pin can no longer prevent this, the rod is urged by its bias to slide past the pin, and its valve member end 56 moves axially away from the valve seals, so opening the valve.

The operation of the sampler can best be understood with reference to both Figure 1 and the sequence of Figure 2.

To start with, the air space into which the buffer fluid is to be transferred is checked to ensure that it contains no buffer fluid, only air. The sampler Is subsequently assembled in the correct manner, ensuring the integrity of all springs on the main tubular connections, and the unit is then primed to the appropriate pressure - buffer fluid is forced into the buffer portion of the sample chamber, driving the floating piston 21 fully down (to the left as viewed) to meet the piston-like valve member 24, thus expressing all contents of the sample portion of the chamber. This pressurised buffer fluid is also allowed to contact the balanced piston valve 36 via the passageways 41a and 35d at 37, thus locking the valve 36 into the initial position. Control valve 58 is subsequently opened. and the oxygen-free nitrogen from the chamber 14 (previously filled to the appropriate pressure pertinent to the subsurface conditions prevailing) permitted to contact the reverse side of the valve 36 at 38.

The clockwork trigger mechanism is then assembled with the valve rod 55 restrained by the pin 54, and the lever arm resting on the main part of the cam surface 51, and connected to the chamber, then set to the necessary time period and initiated. Finally, the whole assembly is then lowered into the well at an appropriate rate to allow at least a half-hour stationary period at the required sampling depth. This is the situation shown in Figure 1 and Figure 2(1).

As the cam 51 rotates, eventually the lever arm 53 drops into the cut-out 52, the arm's sideways movement frees the valve rod 55 from the pin 54, and the valve member 56 retracts from its seals to open the valve.

This permits buffer liquid to pass along passageway 35 from the buffer portion of sample chamber 11 to the storage space 15, and immediately formation fluid can flow into the sample portion, on the other side of floating piston 21, by way of the ports 22, 22a. As it does so, the floating piston is pushed further and further along the sample chamber (to the right as viewed), sweeping the buffer liquid out ahead of it.

This is the situation shown in Figure 2(2), where the piston 21 is depicted about halfway along.

Eventually the piston reaches the collapsible structure 31, and further movement causes progressive deformation and collapse of that structure. At the same time the piston rod 23 is driven up (to the right as viewed), and it takes with it the valve member piston 24, gradually closing off the ports 22, 22a. And as the floating piston finally reaches the end of its movement so the port 22 is completely closed. At this stage spring-loaded lugs (as 25) are pushed out of recesses in the valve member piston 24 and into corresponding recesses (as 26) in the wall of the valve seat, so locking the valve member into place and preventing the valve opening (and thus ensuring that, whatever happens, the sample cannot be discharged through the ports 22, 22a to the surroundings). This situation is shown in Figure 2(3).

Although, at this stage, the floating piston 21 cannot move any further, the size of the air space 15 is large enough that the buffer liquid can still "expand" into it. As a result, the pressure in the buffer liquid - and thus on the liquid's side of the spindle valve mechanism 13 - drops until it is below that of the pressurised gas in the reservoir 14. At this point the spindle piston 36 is urged away from valve seat 38 and toward valve seat 37 (this is the situation in Figure 2(3), and shortly after this the original state of the spindle valve assembly 13 is reversed, with valve 37 closed (isolating the buffer liquid in the storage space 15) and valve 38 open (allowing pressurised gas to feed past the valve into the buffer portion of the sample chamber 11.To start with the situation is as shown in Figure 2(4), but in time the dynamic equilibrium set up across the floating piston 21 between the sample pressure and the gas pressure leads to a situation shown, perhaps exaggeratedly, in Figure 2(5), where the gas literally provides the desired "gas cap" for the sample fluid, albeit one physically separated from the fluid by the floating piston 21.

In summary, the clockworkdriven valve assembly 17 allows the buffer liquid to flow into the storage space 15, the sample then enters the sample portion, pushing the buffer liquid out ahead of the partitioning floating piston 21, and eventually the valve assembly 12 associated with the port 22 is locked closed, and the gas control valve operates to allow the pressurised gas to act upon the floating piston 21 and so pressurise the sample.

Some details of the "one-time" non-reversible valve assembly are shown in Figure 3 (which is a slightly different version from that shown in Figure 1), where Figure 3A shows the situation before the collapsible structure 31 is crushed as the piston 21 drives the outer tube member 32 in front of it, taking the piston rod 23 with it and so pulling up the valve member piston 24 to close off the ports 22, 22a, while Figure 3B shows the situation afterwards.As can be seen, as the piston rod 23 moves upwards (while the collapsible structure 31 is progressively collapsing) so an extension (63) of that rod projecting from the bottom (left, as viewed) side of the valve piston 24 pulls up a pair of spring-loaded sleeve members (65), which eventually reach, and expand into, the recess (66), so preventing the whole piston/rod assembly from being driven back down again, and so ensuring that the ports 22, 22a stay closed.

Once the sample has been brought up the bore to the surface, it is transferred into a surface sampler. Such a sampler is shown in Figure 4. It is a cylindrical container holding within itself a cylindrical sample chamber (generally 111), divided into two portions (a sample port Ion, to the right as tiewed, and a buffer portion, to the left as viewed) by a floating piston (121), and a pressurised gas reservoir (114).At the right (as viewed) end of the sample chamber sample portion there is a valved inlet port (122), and at the left (as viewed) end of the sample chamber buffer portion there is a passageway (135) communicating with both the gas reservoir 114 and, via a valve assembly (generally 201; this assembly also includes valve means allowing both the filling of the gas reservoir and the manipulation of the sample subsequent to transfer), to the outside world.

In broad terms the sample cylinder of Figure 4 is very similar to the bottomhole sampler of Figure 1. In operation, buffer fluid is allowed to exit the buffer portion of the sample chamber 111 (to the left of the floating piston 121, as viewed) as the sample is introduced - as upon transfer from a bottomhole sampler, for instance (pressure is maintained during such an operation by means of the restricting action of the buffer fluid exit valve at the end of passageway 135, as is discussed further hereinafter) - into the sample portion of the sample chamber (to the right, as viewed, of the floating piston).Once this introduction is complete, and the buffer fluid exit valve in passageway 135 is closed, pressurised gas from the reservoir 114 is allowed into the sample chamber buffer port-ion via valve assembly 201 and passageway 135 to maintain the sample at or above its original pressure, so keeping it in its original state.

The actual transfer of a sample from the bottomhole sampler to the sample cylinder is a mercury-free transfer carried out in the following manner.

Once the bottomhole sampler has been retrieved from downhole, and reaches the surface, valve 59 in passageway 35b/35c is closed to isolate the buffer fluid portion of the sample chamber from the pressurised gas reservoir 14, and the reservoir is also isolated from the air chamber 15 by a valve (62) between the two passageways 35f and 35q. Then, following a number of safety operations not relevant to the invention per se, the sample chamber part of the whole apparatus is separated from the rest at joint 61 (just above valve 59).

The "exposed" main tubular connection to the sample chamber is then connected to an (air activated multiplying) pump containing buffer fluid, and this buffer fluid is pumped therefrom into the sample chamber connection, pressurised to a pressure equal to or greater than that of the pressurising gas remaining in the chamber's sample portion (and in passageway 35b leading thereto), and allowed into contact with this remaining gas by opening valve 59.

With the sample chamber suitably pressurised, the bottomhole sampler is now attached to the sample cylinder for transfer of the former's contents into the latter, this involving a connection between a valve (122) in the sample cylinder communicating with the cylinder's chamber's sample portion (on the right, as viewed) and (via port 22a) a needle valve assembly (generally 301, and possibly best seen in Figure 3B) within the body of floating piston 24. Buffer fluid is then pumped into the buffer portion of the bottomhole sampler's sample chamber, pushing back the partitioning piston 21 and forcing the sample itself out of the sample portion, via needle valve 301, and thence through valve 122 into the sample cylinder chamber's sample portion against the counter pressure of the sample cylinder's buffer fluid being displaced out through valved passageway 135.

Claims (21)

1. A container for holding a sample of a fluid that is, in its original ambient conditions, at a greaterthan-normal pressure, which container has a reservoir for a gas pressurised to somewhat greater than the expected original ambient pressure of the sample liquid, and has, connectable to that reservoir, a chamber for the sample, and wherein the sample chamber is sealingly divided into two portions by a partition movable therewithin to adjust the effective size of each portion, one such portion (the sample portion) having valved port means to allow the ingress of the liquid to be sampled, and the other (the buffer portion) being connectable to the pressurised gas reservoir so that in operation the pressure of the gas therein is transferred across the partition to the contents of the sample portion, whereby the pressure of the sample liquid is maintained at or above its original ambient pressure.

2. A sampler as claimed in Claim 1 for use as a bottomhole sampler, and taking the shape of a long cylinder, with its various components (the sample chamber, the gas reservoir, and so on) arranged sequentially along the cylinder's main axis, and sized to fit within the bore (or within any piping within the bore).

3. A sampler as claimed in either of the preceding Claims, wherein when present and ready for use the pressurised gas is under a pressure roughly 50% greater than the pressure expected at the depth the sample is to be taken.

4. A sampler as claimed in any of the preceding Claims, wherein the size of the reservoir is around 10 in3 (150 cc).

5. A sampler as claimed in any of the preceding Claims, wherein the gas reservoir is indirectly connectable to the sample chamber so that, when it is thus connected, the pressure in the former is transferred to the liquid in the sample portion of the latter across the movable partition via an intermediate member.

6. A sampler as claimed in any of the preceding Claims, wherein the way in which the connection is made is by a pressure-operated switch, or valve, of the spindle variety, enabled (when the sample chamber is full) to make the required connection when the pressure in the gas reservoir exceeds some other pressure.

7. A sampler as claimed in any. of the preceding Claims, wherein the sample chamber is a long, relatively narrow cylindrical space, the partition therefor being a floating co-axial piston sealingly mounted for sliding movement along a co-axial piston rod and freely movable along the cylinder between its ends.

8. A sampler as claimed in any of the preceding Claims, wherein the sample chamber's sample portion is provided with a (valved) port (or ports) through which the formation fluid to be sampled is permitted to enter (when the valve is open), and where the chamber is an elongate cylinder then the port is at one end thereof, in the wall adjacent the chamber's end face.

9. A sampler as claimed in Claim 8, wherein the input port valve is a one-time valve that starts open (to allow fluid to flow through the port into the sample chamber) and is then irreversibly closed to secure the fluid within the chamber once the chamber is full.

10. A sampler as claimed in Claim 9, wherein the one-time valve mechanism is one that is physically actuated by movement of the partition into contact with the end of the non-sample portion (so that as the sample portion becomes full so the last part of the partition's movement closes the valve to seal the port), the moving part of the valve, the valve member, being associated with a detente that acts, when that member has reached some predetermined position, to prevent the member moving back.

11. A sampler as claimed in Claim 10, wherein the valve is a piston (the valve member) moving within a cylinder to cover over a port (or ports) into the cylinder, this piston containing within it outwardly-directed springloaded detent bars, or lugs, and being operatively linked, by the piston rod guiding the floating piston partition, to a collapsible structure mounted immediately adjacent the sample-distant end of the buffer portion of the chamber, such that, as more sample fluid flows into the sample chamber, and the floating piston moves along the chamber into contact with the collapsible structure, further movement of the piston collapses and compresses that structure away from the sample end, so that the piston rod, and thus the valve member piston, is moved with it, the movement of the valve member piston being sufficient to cover over, and so block, the chamber entry port, and such that at the limit of the piston's port-covering movement the springloaded lugs become aligned with matching shallow recesses in the chamber wall, whereupon the lugs are partly driven out thereinto-(by their springs), and latch the piston irreversibly into place, so locking the valve shut.

12. A sampler as claimed in any of the preceding Claims, wherein in use the buffer portion of the sample chamber contains a non-compressible "buffer" liquid, which liquid is displaced out of the buffer portion into a storage space elsewhere in the container.

13. A sampler as claimed in any of the preceding Claims, wherein, in any embodiment employing a normallyopen one-time valve in combination with a liquid buffer medium in the buffer portion of the sample chamber, entry of formation fluid into the sample chamber is controlled by controlling the flow of buffer liquid out of the chamber and into the storage space.

14. A sampler as claimed in Claim 13, wherein the passageway between the buffer portion of the sample chamber and the storage space is valved, and in use at the appropriate moment this valve is opened to allow the buffer liquid originally in the former to transfer into the latter.

15. A sampler as claimed in any of the preceding Claims, wherein there is employed a buffer liquid, and the connection of the sample chamber to the pressurised gas reservoir is by a pressure-operated valve of the spindle variety, enabled to make the required connection when the pressure in the gas reservoir exceeds the pressure in the buffer liquid, and there is employed a spindle valve where each end of the spindle itself constitutes a needle valve, the buffer liquid being supplied via one needle valve to the corresponding spindle face while the pressurised gas is supplied via the other to the other face, such that while the buffer liquid's pressure is the higher its valve remains open (and the gas's valve remains shut), and buffer liquid can pass along to the storage space, but when - after the sample fluid ingress port is closed - the buffer liquid pressure necessarily drops, and the gas pressure becomes the higher, so the gas's valve opens, allowing the gas to pressurise the sample, and the buffer liquid's valve shuts, preventing both the liquid from returning from its reservoir and the gas from leaking into the liquid.

16. A sampler as claimed in any of the preceding Claims, which is formed in at least two parts, one of which contains the sample chamber and the other of which contains the pressurised gas reservoir, the two being sealingly but detachably joined by some suitable jointing mechanism.

17. A sample container as claimed in any of the preceding Claims and substantially as described hereinbefore.

18. A sampling tool for sampling fluid from a downhole well, said sampling tool comprising: sample chamber means having valve means actuatable to be opened when the tool is at a desired depth to admit well fluid to fill said sample chamber, piston means moveable within said sample chamber1 one side of said piston means defining a surface of said sample chamber and the other side of the piston means being coupled to elastic fluid reservoir means:: said piston being moveable in said sample chamber in response to admitted well fluid to force said piston along said chamber and to compress said elastic fluid reservoir, said valve means being closable once said sample chamber is filled; the elastic fluid reservoir providing a force which acts on said piston to maintain the sample in a monophasic state as the tool is raised in the well, said piston being moveable in the sample chamber to expel said sample from the sample chamber once the sampling tool is removed from the well.

19. A method of obtaining a sample of well fluid from a well and maintaining the sample in a monophasic state, the method comprising the steps of: coupling the sample bottle to the sampling tool to provide fluid communication between said sample chamber in said tool and a sample storage chamber in said bottle; lowering a sampling tool with a sample chamber into said well; at a predetermined depth admitting a sample of well fluid into said sample chamber; applying pressure to the sample in the chamber from a gas reservoir via a moveable piston sufficient to maintain the sample in the monophasic state as the tool is raised to the surface; and removing the monophasic sample from the sample chamber by applying pressure to said piston to move said piston and expel said sample from the sample chamber.

20. A sample bottle for receiving a monophasic sample of well fluid for storing the sample in a monophasic state, said sample bottle comprising: a sample chamber for receiving said mnophasic sample; piston means forming a wall of said sample chamber, said piston means being moveable within said sample chamber as said sample is admitted; and gas reservoir means located within said bottle containing gas under pressure1 and means for applying said gas to said piston to maintain said sample in the monophasic state.

21. A method of providing mercury-free transfer of a monophasic sample from a sample chamber in a sampling tool to a sample bottle and storing the sample in said bottle in a monophasic condition, said method comprising the steps of: coupling the sample bottle to the sampling tool to provide fluid communication between said sample chamber in said tool and a sample storage chamber in said bottle; applying non-mercury fluid pressure to said sampling tool to move a piston in said sampling chamber to expel said sample into said sample storage chamber; sealing the sample in said sample storage chamber; and applying pressure to said sample via a gas reservoir acting directly or indirectly on a moveable piston within said sample chamber and forming a wall of said sampling chamber to maintain the sample within the sample storage chamber in said monophasic condition.