GB2230802A

GB2230802A - Well control apparatus

Info

Publication number: GB2230802A
Application number: GB9006586A
Authority: GB
Inventors: Jeffrey Charles Edwards; Ray Johns; Robert Donald Buchanan
Original assignee: Exploration and Production Services North Sea Ltd
Current assignee: Exploration and Production Services North Sea Ltd
Priority date: 1989-04-28
Filing date: 1990-03-23
Publication date: 1990-10-31
Anticipated expiration: 2010-03-23
Also published as: NO914200L; CA2053245A1; WO1990013731A2; US5193619A; EP0470160B1; GB9006586D0; GB2230802B; DK0470160T3; WO1990013731A3; GB8909892D0; EP0470160A1; CA2053245C; NO914200D0; NO302253B1

Description

1 Well Control Ap12aratus This invention relates to well control

apparatus, and concerns in particular that apparatus employed in discontinuing a well testing procedure, especially an oil well testing procedure.

Whether at sea or on land, the first stages in the production of a new hydrocarbon well - an oil well - are the drilling of the well bore itself through the various formations within the earth's crust beneath the drilling rig, followed by "casing" (the introduction and cementing into position of piping which will serve to support and line the bore) and the placing in the bore, at the depth of a formation of interest, of a device known as a packer, into which inner tubing (of smaller diameter than the casing) can subsequently be lodged.

The next work carried out is normally some programme of testing, for the purpose of evaluating the production potential of the chosen formation. The testing procedure usually involves the measurement of downhole temperatures and pressures, in both static and flow conditions (the latter being when fluid from the relevant formation is allowed to flow into and up the well), and the subsequent calculation of various well parameters. To collect the necessary data there is lowered into the well a test string - a length of tubing containing the tools required for testing. The flow of fluid from the formation of interest into the well bore and thus to the test tools is controlled by a valve known as a sub- surface control valve.

The operation of the various tools included in the downhole test string can be effected using one of three main types of mechanism. These types are those actuated by reciprocal motion of the pipe string (the inner tube, of which the test string constitutes a part), by rotational motion of the pipe string, or by changes in the pressure differential between the tubing and the annular space which surrounds it In the well hereinafter referred to simply as "the annulus". Test strings wherein the tools thereof are actuated by changes in annulus pressure are at present much in vogue, and it is this type of actuation mechanism that is to be employed with the apparatus of the invention.

A mechanism of the annulus pressure-responsive type requires the provisiorr and maintenance of a fixed &$reference" pressure within the tool. This, used in conjunction with an adjustable (and higher) annulus pressure, allows the establishment of the chosen pressure differential necessary to control the operation of the appropriate component of the test string. The achievement of such a fixed reference pressure is the subject of our copending British Patent Application No. 89107,098.1 (Publication No:; FN P1049).

Following completion of the well testing procedure, It Is necessary safely to "shut down" the test tools, and then to remove the test string from the packer assembly and pull it to the surface. These operations do, however, require careful control and planning. In the case of pressuredifferential-actuated test tools, for example, the string will, at the end of testing, still contain the high pressure reference gas which has been used in creating the required differentials. It Is extremely desirable for this gas in some way to be vented before the string reaches the well head, so that thGre are no potentially dangerous pressures trapped within the tools when the test string is received at the surface.

Additionally, it Is an advantage if there be incorporated within the test string some means of isolating the upper-portion of the tubing thereof, and of subsequently providing a route for communication between this tubing and the annulus, so that tubing-contained well liquid above the test string can then be circulated out of the tubing before it is raised to the surface. The isolation is conveniently accomplished using a ball valve suitably placed near the top of the test string, and such a ball valve particularly suitable for effecting this isolation is described in our co-pending British Patent Application No. 89/09,903.0 (Publication No:; FN P1062). However, reliance upon a single valve Is not advisable, and consequently there is a strong case in favour of the utilisation of a second valve in the test apparatus. This latter valve can then be used either in addition to the main valve or, in the event of the latter not operating correctly, as an alternative thereto.

The present invention seeks to facilitate the procedure for discontinuation of an oil well testing programme by providing apparatus for the venting and Isolation procedures Just described. Moreover, the apparatus permits those operations to be carried out as an automatic sequence, following the application of a single actuating pressure pulse to the annulus. For the venting of the reference gas, the Invention suggests pressure release apparatus having two spaced pistons located at opposite ends of a chamber filled with that gas and blocking both a gas vent to annulus and a hydraulic liquid passageway (to further up the test 4 _string), the pistons being held together by a shear pin until the application of a predetermined pressure (higher than the gas reference pressure) at the outside ends of those pistons causes the pin to shear, allowing sequential movement of the two pistons towards each other, with the effect of firstly opening the gas vent to annulus, and secondly opening the passageway to a chamber of hydraulic liquid.

The hydraulic liquid pressure within this passageway then causes actuation of ball valve apparatus for isolating the upper section of tubing. This apparatus is in the form of a ball-valve-driving piston blocking another passageway for hydraulic liquid, which piston is forced to move under the influence of the pressure, breaking a nestraining shear pin as it does so, and closing the ball valve while opening this other hydraulic liquid passageway, permitting transfer of hydraulic pressure to apparatus for venting the contents of the tubing to annulus. Finally, this venting apparatus contains a longitudinally-movable sleeve member the position of which determines whether or not flow is permitted, via a vent port, from the test string tubing to the annulus.

In one aspect, therefore, this invention provides pressure release apparatus useable in a well test pipe string which comprises, positioned and/or mounted within the string tubing: a gas chamber for holding reference pressure gas; two spaced slidable pistons, positioned one at each end of the gas chamber, and each adapted to have tube-external pressure acting on the outer end thereof, which pistons are capable of relative movement along the gas chamber but which are (normally) secured together by one or more shear pin; a vent port permitting escape of the reference gas out of the pipe string, but (normally) blocked by one or other piston; and a liquid chamber for holding hydraulic liquid, and connectable to a passageway, the connection being (normally) blocked by one or other piston; whereby application of a sufficient pre-determined externally- derived pressure to both pistons causes pin-shearing relative movement of the pistons thus permitting subsequent piston movement to open both the reference gas vent port and the passageway to the hydraulic liquid chamber.

In a second aspect, the invention provides valve operating apparatus for operating a ball valve useable in a well test pipe string, which apparatus comprises, positioned and/or mounted within the string tubing: a slidable piston, operatively connected to the valve ball, but which is (normally) held stationary by one or more shear pin; and a passageway for holding a hydraulic liquid and (normally) blocked by the piston; wherein application of a sufficient predetermined pressure differential across the piston causes pin-shearing movement thereof, both actuating the valve and opening the passageway.

In a third aspect, the invention provides venting apparatus useable in a well test pipe string containing ventable liquid, which apparatus comprises, positioned and/or mounted within the string tubing., a slidable piston, (normally) held stationary by one or more shear pin; and a vent port for permitting escape of the pipe 6 strinE-' s contents out of the Pipe String, but (normally) blocked by the piston; wherein application of a sufficient predetermined pressure differential across the piston causes pin-shearing movement of the piston, thus permitting subsequent piston movement to open the vent port.

The invention in its various aspects is for the most part intended for use in connection with the testing of wells, specifically oil wells, and is therefore described in connection therewith hereinafter. Indeed, the operation of the invention is described as though the pipe string were located within the bore of the well, the space therearound being the annulus to which tube-external pr essure Cannulus pressure") is applied to operate the various parts of the apparatus.

The pressure release apparatus of the invention's first aspect includes a gas chamber which in use contains reference pressure gas. Most conveniently, this chamber is generally annular and lies within the tubing walls of the test string. The gas (which may be any of those commonly employed to provide reference pressure - nitrogen, for example) may be supplied to the chamber in any suitable way; for instance, via a narrow tubing-wall-contained passageway connected to the test string's main reference pressure gas reservoir (as described and claimed In our aforementioned Application No: 89107,098.1.

The reference gas chamber has a piston at each end - upper and lower, when in use - thereof. Preferably both are elongate floating annular pistons, of dimensions (naturally) which are suited to the size of the gas chamber. In a particularly preferred embodiment of the invention, each piston has a greater external i 7 diameter at the point thereof which in use lies adjacent the extreme end of the gas chamber, and is at that point sealed (conveniently by a suitable elastomer seal) to the gas chamber walls, thus ensuring complete closure of the gas chamber. The remainder of each piston lies at least partly within the gas chamber itself, and advantageously one of them is provided with a latch profile into which a latch key located on the other may lock when the apparatus Is operated in order to hold the two pistons together, and so prevent them moving to reblock the gas vent port or the hydraulic liquid passageway. This latch key and profile may take any convenient form.

Each piston has tube external - annulus - pressure acting towards its outer end. This pressure may, in each case, be applied either directly or indirectly. in the preferred embodiment of the invention, however, it is applied to the lower piston directly, via a simple port to annulus, and to the upper piston indirectly, via a chamber containing a hydraulic liquid (this liquid, also referred to hereinafter, may be of any convenient kind, and serves to prevent the influx of well liquid principally drilling mud into Inner parts of the test string, where it could cause blockages).

The pistons are capable of relative sliding movement along the gas chamber - that is to say, they are engineered such that they may travel longitudinally so as to lie one ensleeved within the other - but in their initial positions, one at each end of the reference gas chamber, their movement in this manner is prevented by one or more sheer pin which holds them in place. This pin ensures that the pressure release apparatus is not unintentionally actuated following those pulses of increased annulus pressure applied - 8 during the well testing procedure to operate the testing tools. Accordingly, its pressure rating (or, in the case of more than one pin, the total rating) must be greater than the highest pressure differential required for actuation of any of those tools. The apparatus has been operated successfully using an applied annulus pressure differential of 2, 500 PSI and five shear pins each rated at 500 PSI.

The vent port to annulus through which the reference pressure gas is released is a simple port through the outer tubing walls, the exit of which Is blocked by the body of either of the gas-chamber-contained pistons. In the preferred embodiment of the invention, this is that piston which in use lies at the lower end (in use> of the chamber.

It is in general preferred if that piston blocking the gas vent port (conveniently the lower piston) move first, to unblock the vent, followed by the other piston (the upper one, opening the hydraulic liquid passageway). This may be achieved by so shaping each piston that the effective area acted on by the increased tubing external pressure is greater in the case of the gas-vent-blocking (lower) piston.

There is also provided within the pressure release apparatus a chamber which in use holds a hydraulic liquid, and has a passageway associated therewith. This liquid chamber is, like the gas chamber, preferably annular in form. Its volume is determined by the volume of hydraulic liquid required to actuate the other tools contained within the test string. In the preferred embodiment of the Invention, as will be described further hereinafter with reference to the accompanying Drawings, It is this chamber of hydraulic liquid which also provides the indirect annulus pressure to the upper 9 - gas-chamber-contained piston as previously described. The annulus pressure is communicated to the liquid via a floating piston adjacent a port to annulus at the passageway-distant end of the liquid chamber.

Extending from the hydraulic liquid chamber is a passageway the entrance to which is initially blocked by the body of (preferably) the upper of the two gas chamber pistons. This passageway is advantageously of relatively narrow bore, and thus may be located within the outer tubing walls. In the preferred embodiment of the invention it leads to the valve- operating apparatus of the second aspect of the invention, which is described in more detail hereinafter. When the well testing procedure has been completed, application of the predetermined pressure to the annulus actuates the pressure release apparatus, causing the lower piston to move upwards, shearing the pin as It does so, thus enabling the upper piston to move downwards and thereby opening both the reference gas vent port and the passageway (so allowing hydraulic liquid from the chamber to flow into the passageway). The hydraulic liquid at this (relatively high) pressure is thus transmitted to the ball valve, permitting the closure thereof which constitutes the second stage of the shut down procedure.

The ball valve-operating apparatus of the invention's second aspect utilises a slidable piston. This is conveniently another elongate annular piston, about 25-30 cm (8-12 in) in length. It is 'Islidable" in a longitudinal direction, and for a limited distance, preferably within an annular chamber net in the tubing walls and held initially at atmospheric pressure. The volume of this chamber is such that the pressure therein does hot exceed about 100 PSI when compression occurs due to the movement of the piston. Most preferably there is on the body of the piston a latch key which, at the end of the piston's travel, may co-act with a corresponding latch profile on the inner tubing wall and thus prevent any piston return movement.

The piston is operatively connected to the valve ball. Both the piston itself and the mechanism by which it is operated by the piston may be broadly conventional. Thus, the ball is conveniently a sphere of approximately 10 cm (4 in) diameter with a passageway therethrough about 5 cm (2 in) in diameter, and having flattened opposing sides constituting bearing surfaces which locate the ball within the width of the passageway. The ball is housed within a seating adjacent the internal walls of the tubing within which it operates. The purpose of the seating of this, as any other, ball valve, is to ensure a sealing yet slidable fit with the ball. Conveniently it takes the form of two generally annular pieces set into the internal walls of the tubing. In the preferred embodiment of the invention the piston is directly connected to the ball via a pin projecting therefrom. which co-acts with an off-axis slot in the ball's flattened side so that lateral movement of the piston causes the ball to rotate.

The piston is, prior to actuation, held stationary by one or more shear pin set between the piston and part of the inner tubing walls. This pin merely ensures that the piston Is kept In place whilst the apparatus is being assembled and the test string run in to the well, and therefore need only be of a very modest rating 600 PSI, for example.

z Operation of the ball valve is initiated by the application of a predetermined pressure differential across the piston, thus providing at the.. lower.. end thereof a pressure greater than the annular chambercontained atmospheric pressure acting on the other end. This pressure must additionally be of sufficient magnitude to cause the pin to shear. It is conveniently supplied using a hydraulic liquid, and It is particularly advantageous if this hydraulic liquid pressure originate from the passageway previously opened by the operation of the pressure release apparatus of the invention discussed hereinbefore. In the same way, the passageway for hydraulic liquid opened by the ball-valve- actuating travel of the piston - which passageway is again na.rrow, and best located within the tubing walls - propitiously leads towards the venting apparatus of the invention's third aspect which is about to be described.

In its third aspect the invention provides venting apparatus including a slidable piston by means of which liquid within the test string may be circulated out before the string Is brought to the surface. In the preferred embodiment this piston is an elongate sleeve, the body of which constitutes part of the internal wall of the test string tubing (the internal diameter of the sleeve is consequently in this case comparable to the tubing diameter).

The piston is longitudinally slidable within the test string, in an upwards (In use) direction, from an original position where it is preferably sealed into place against another specially adapted part of the tubing walls known as the upper mandrel sub. The maximum distance through which the piston may slide once free of restraint is advantageously defined by an annular sleeve mandrel. In use this mandrel lies above the piston, partially ensleeving the upper end thereof. At its upper end Is an inwardly-projecting shoulder against which the piston body will eventually come to rest.

Between the lower end of the sleeve mandrel and a shoulder located on the tubing-distant (outer) side of the sleeve piston, there is preferably defined an annular chamber at atmospheric pressure. This facilitates rapid movement of the piston following application of the actuating pressure differential (as will be described in greater detail hereinafter).

The piston body closes at least one vent port that is- to say, it lies between the test string tubing and a vent leading therefrom to the annulus through the tuning wall. In the preferred embodiment of the invention there are as many vent ports as practical having regard to the tubing retaining the necessary physical strength, in order to achieve as high a flow rate between tubing and annulus as possible concomitant with structural stability. Four pairs of vent ports, equi-angularly spaced, are satisfactory.

The sleeve piston is initially fixed to the sleeve mandrel by a shear pin which prevents it from moving until intentionally actuated. A shear pin with a rating of 600 PSI has been found to be most satisfactory for this purpose.

The venting appara.tus of the invention Is driven by the creation of a pressure differential across the ends of the piston. This differential is preferably applied, as in the case of the apparatus described previously, via a hydraulic liquid, which transmits to the lower face of the piston shoulder a pressure increase applied 13 initialls? to the annulus from the well surface. In the preferred embodiment, this hydraulic liquid pressure is that which has been transported along the passageway opened by the ball-valve-actuating piston in the previously-discussed apparatus of the invention's second aspect. The lower face of the piston shoulder experiences, as mentioned earlier, only atmospheric pressure within the annular chamber. Thus, the piston is forced upwards, shearing the shear pin, and continues its travel until Its upper face reaches the shoulder of the mandrel. During this movement direct communication is opened between the tubing and the vent ports.

Following its upwards travel, the sleeve piston, as with the other pistons, is prevented from returning by the action of a sleeve latch key on the sleeve mandrel and a corresponding latch profile on the piston itself.

As described above, the preferred embodiment of the invention Incorporates all three pieces of inventive apparatus described herein - and, moreover, deploys them in a manner which permits their sequential and interdependent actuation. However, other embodiments of the invention are envisaged in which, for example, the ball valve apparatus need not be included but the tubing is instead closed off by the operation of the test string's usual sub-surface control valve (the provision of a second valve in the form of the.. safety circulating valve.. does, however, provide a valuable back up should the first valve fail). Another possible embodiment utilises two different circulating sleeve sections at different positions in the test string, and each of which - by changing the number of shear pins in the.. control section.. - will be operated by the application of a different annulus pressure.

The materials of manufacture of the apparatus of the invention may be any of those commonly used within the art for similar construction. Thus, the apparatus and tools within the test string may be of mild steel, and the seals of any suitable elastomeric substance.

1.

- 15 An example of the invention will now be described, though by way of illustration only, with reference to the accompanying Drawings, in which:

Figure 1 is a simplified cross-sectional view of an offshore oil well with a test string including apparatus of the invention; and shows in "half" cross section a test string incorporating an apparatus of the invention (Figures 2A to 2H show adjacent sections of the apparatus; the right.hand side of each individual Figure runs on to the left hand side of the subsequent one; the left sides are the low sides, while the right sides are the high ones).

Figure 1 depicts a floating drilling rig (101, not shown in detail) from which has been drilled an oil well (generally 102) having a well bore (103) reaching down to a rock stratum constituting the formation (109) of Interest. Located at the top of the well bore 103 is a blow-out preventer mechanism (BOP; 104, not shown In detail) which is connected to the rig 101 by a marine riser (105). Cemented into the well bore 103 are a shallow casing (106) and a deep casing (107); the lower end of the latter has a multitude of perforations (as 108) permitting communication between the well bore 103 and the oil formation 109.

Situated within the well bore 103 is a test string (110) comprising tubing (113> ending in a set of test tools (see below). The string 110 is set at its lower end into a packer (111), and a seal sleeve (112) seals the packer 111 to the test string 110, thus Isolating the tubing 113 thereof from the annulus (114).

Above the seal sleeve 112 is a gauge carrier (115) which contains electronic or mechanical gauges (not shown) which collect downhole pressure and temperature data during the test sequence. Above the gauge carrier 115 are a constant pressure reference tool (1M and the subsurface control valve (118>. A circulating sleeve (119) permits removal of any formation fluid remaining within the test string 110 prior to its withdrawal from the well bore 103. At the top of the test string is a subsea test tree (120) which serves both as a primary saferty valve and as a support for the rest of the test string 110.

As is shown in Figure 2, the components of the tool are located within a housing (8) within the walls of the test string tubing. At the lower end (Figures 2A, B and C) of the tool, situated between the internal tubing wall and a fixed inner mandrel (20), are two elongate pistons: a lower piston (7) and an upper piston (11). Prior to activation of the tool these pistons are held in position relative to each other by shear pins (13) in the piston bodies. The free lower end of the lower piston 7 initially lies adjacent a lower end sub (1); the upper end of the upper piston is similarly restrained by the body of the inner mandrel 20.

On the body of the lower piston 7 Is a latch profile (9), which corresponds to a latch key (12) located on the upper piston 11. Well liquid from the annulus enters the tool by way of a port (5) adjacent the lower face of piston 7. Elastomer seals (6) prevent 17 - communication between the gas filled chambers (10 and 14) and the well liquid entering port 5.

Well liquid also enters the tool through another port (M which opens to annular chamber (18) surrounding the centre section of upper piston 11.

Above the upper piston 11 is another annular chamber (24) which contains hydraulic oil, Initially at atmospheric pressure. This chamber, which may be charged prior to use of the tool via a subsequently sealed port (23), is bounded at its lower end by upper piston 11 and at its upper end by a floating piston (25). A further port to annulus (26> is located adjacent the upper face of the piston 25.

Further up the te.st string tubing (Figures 2D and E) lies the tool's ball valve. The ball (37) is housed within lower and upper ball seats (35 and 38 respectively), which are in turn set between a lower bore mandrel (28) and an upper ball mandrel (42). An elongate ball valve piston (39) Is situated between the mandrels (28, 42) and the housing 8. The piston is connected to ball 37 via a ball pin (36), but its movement is initially restricted by a shear pin (44). A latch key (45) on the piston 39 corresponds to a mandrel latch profile (46) on upper ball mandrel 42. An annular chamber (47) adjacent the upper end of piston 39 contains gas at atmospheric pressure. Projecting into this chamber from the upper ball mandrel 42 is a mandrel stop (48). A passageway (22) transmits, once the tool has been actuated, pressurised hydraulic liquid to the lower face of ball piston 39.

The uppermost part (Figures 2F, G and H> of the tool is the circulating sleeve section. An elongate sleeve piston (34) having a shoulder (52> thereon extends upwards from an upper mandrel sub (51). The piston 54 is fixed at its upper end to a sleeve mandrel (61) by a shear pin (63). The piston body in its initial position serves to prevent communication between the tubing bore (4) and two vent ports (55 and 56) to annulus. A sleeve latch profile (59) on sleeve piston 54 in use permits the piston to be retained in position by sleeve latch key (62) on sleeve mandrel 61.

Between the body of the sleeve piston 54 and the tubing walls is an annular chamber (60), held initially at atmospheric pressure. Seals (64) ensure that there is no communication between this chamber and the tubing bore 4.

A passageway 40 allows the flow of hydraulic liquid within the tool to thi lower face of sleeve piston shoulder 52. Seals (57> prevent communication of the liquid from this passageway to ports 55 and 56, whilst further seals (58) prevent that liquid from entering annular chamber 60.

Prior to commencement of the testing programme, the test string containing the tool is lowered into the well bore. As this lowering progresses the reference pressure of the nitrogen within passageway 3 and chambers 10 and 14 increases so as always to equal the instantaneous hydrostatic pressure. Well liquid, also at hydrostatic pressure, enters the tool through ports 5, 17 and 26. Floating piston 25 consequently experiences a pressure'differential, with well liquid at hydrostatic pressure acting on its upper face, and hydraulic liquid at atmospheric pressure acting on Its lower. The piston 25 Is thus induced to move downwards until the hydraulic liquid within the chamber 24 attains hydrostatic pressure.

When the required test depth is reached, the test string is stabbed into the packer (as shown In Figure 1). The reference pressure within the test string's reference gas reservoir (not shown In Figure 2) is then "trapped" at the hydrostatic pressure. This may.be carried out by the application to the annulus from the top of the well of a pressure a predetermined amount greater than the hydrostatic pressure acting on the tool at the test depth. This application creates a pressure differential across lower piston 7, with the new increased annulus pressure acting, via port 5, on its lower face and only hydrostatic - reference - pressure acting on its upper face from chamber 14. However, the piston does not move in these circumstances because this pressure differential is insufficient to cause shear pin 13 to break, Once the trapping of the reference pressure has been effected, the application of the higher pressure to the annulus is discontinued, and the components of the test string which communicate with the annulus once more experience hydrostatic pressure only. During the well testing programme various Increased pressures are similarly periodically applied to the annulus in order to actuate the test tools within the string. However, in all these cases the pressure differential created across lower piston 7 is still too small to cause shear pin 13 to break, and thus the tool of the invention is not actuated.

Upon completion of the testing procedure, there Is applied to the annulus a larger pressure than any of those previously employed, which again produces a - 20 pressure differential across lower piston 7, but this time one which is sufficient to break shear pin 13. Thus the piston 7 moves upwards, until it is halted by a projecting stop on inner mandrel 20. At the same time, the pressure differential created across upper piston 11 (with the reference pressure of chambers 10 and 14 acting on its lower face and the increased annulus pressure acting on its upper face via port 17 and chamber 18) causes that piston, now no longer restrained by shear pin 13, to move downwards. This travel continues until the piston 11 reaches the upper face of piston 7, and latch key 12 locks into latch profile 9 (thus preventing return movement of upper piston 11). Once this travel is complete, passageway 22 is open to the hydraulic liquid at the increased annulus pressure) within chamber 24. This pressure is thus now communicated upwards through the tool in passageway 22. A further consequence of the movement of upper piston 11 is that the positions of seals thereon (15 and 19) are now such that there is direct communication between reference-gas-containinS annular chamber 10 and port 17 to annulus. This allows the gradual venting to annulus of the now redundant reference pressure as the test string is lifted out of the well, ensuring that no high gas pressures are trapped within the test string when It is removed from the well.

The applied-increased annulus pressure is transmitted along passageway 22 to the lower face of ball valve piston 39. The upper face of this piston, however, only experienees the atmospheric pressure of annular chamber 47. The piston 39 Is thus suddenly forced upwards, breaking shear pin 44, until its upper face reaches mandrel stop 48. This causes the valve ball 37 to be rotated by ball pin 36 into Its closed porgition, preventing further flow of well fluid (oil) up 1 the tubing bore 4. A sealing fit is ensured by metal-to-metal seals between the ball 37 and the ball seats 35 and 38. The ball valve piston 39 is locked Into Its new position by latch key 45 and latch profile 46. This position of the piston 39 allows direct communication between passageways 22 and 40, the latter of which now also fills with hydraulic liquid at the increased annulus pressure. If, exceptionally, incomplete movement of valve piston 39 prevents this communication, hydraulic oil will in any event eventually pass from passageway 22 to passageway 40 by way of a narrow bore passageway (32).

Passageway 40 permits hydraulic liquid at increased annulus pressure to reach the lower face of sleeve piston shoulder 52. A pressure differential is thus created thereacross, since the upper face is experiencing only the atmospheric pressure of chamber 60. This pressure differential causes upward movement of sleeve piston 54, shearing the pin 63, until the piston eventually reaches sleeve mandrel 61. This travel opens the tubing bore 4 to vent ports 55 and 56 (these are two of four like pairs disposed around the tubing). Latch key 62 co-acts with latch profile 59 to hold the sleeve piston 54 In position. The contents of the test string above the valve can then be circulated out of the test string prior to its release from the packer and elevation to the surface.

Claims

1. Pressure release apparatus useable in a well test pipe string which comprises, positioned and/or mounted within the string tubing: a gas chamber for holding referenc e pressure gas; two spaced slidable pistons, positioned one at each end of the gas chamber, and each adapted to have tube-external pressure acting on the outer end thereof, which pistons are capable of relative movement along the gas chamber but which are (normally) secured together by one or more shear pin; a vent port permitting escape of the reference gas out of the pipe string, but (normally) blocked by one or other piston; and a liquid chamber for holding hydraulic liquid, and connectable to a passageway, the connection being (normally) blocked by one or other piston; whereby application of a sufficient pre-determined externally-derived pressure to both pistons causes pin-shearing relative movement of the pistons thus permitting subsequent piston movement to open both the reference gas vent port and the passageway to the hydraulic liquid chamber.

2. Pressure release apparatus as claimed In Claim 1, wherein the gas chamber generally annular, and lies within the tubing walls of the test string.

31 Pressure release apparatus as claimed in either of the preceding Claims, wherein the gas is supplied to the chamber via a narrow tubingwall-contained passageway connected to the string's main reference pressure gas reservoir.

4. Pressure release apparatus as claimed in any of the preceding Claims, wherein the piston at each end of the reference gas chamber is an elongate floating annular piston.

51 Pressure release apparatus as claimed in Claim 5, wherein each piston has a greater external diameter at the point thereof which In use lies adjacent the extreme end-of the gas chamber, and is at that point sealed to the gas chamber walls, thus ensuring complete closure of the gas chamber.

6. Pressure release apparatus as claimed in Claim 5, wherein the remainder of each piston lies at least partly within the gas chamber itself, and one of them is provided with a latch profile into which a latch key located on the other day lock when the apparatus is operated in order to hold the two pistons together, and so prevent them moving to re- block the gas vent port or the hydraulic liquid passageway.

7. Pressure release apparatus as claimed in any of the preceding Claims, wherein the tube-external pressure acting towards each piston's outer end is applied to the lower piston directly, via a simple port to annulus, and to the upper piston indirectly, via a chamber containing a hydraulic liquid.

8. Pressure release apparatus as claimed in any of the preceding Claims, wherein the vent port to annulus through which the reference pressure gas Is released is a simple port through the outer tubing walls, the exit of which is blocked by.the body of that gas-chamber-contained piston which in use lies at the lower end (in use) of the chamber.

9. Pressure release apparatus as claimed In any of the preceding Claims, wherein in operation that piston 24 - blocking the gas vent port move first, to unblock the vent, followed by the other piston opening the hydraulic liquid passageway, and this Is achieved by so shaping each piston that the effective area acted on by the increased tubing external pressure is greater in the case of the gas- vent-blocking piston.

10. Pressure release apparatus as claimed in any of the preceding Claims, wherein the chamber which in use holds a hydraulic liquid, and has a passageway associated therewith, is, like the gas chamber, annular in form.

11. Pressure release apparatus as claimed in any of the pr'eceding Claims, wherein it is the chamber of hydraulic liquid which also provides the indirect annulus pressure to the upper gas-chamber-contained piston, which annulus pressure is communicated to the liquid via a floating piston adjacent a port to annulus at the passagewaydistant end of the liquid chamber.

12. Pressure release apparatus as claimed in any of the preceding Claims, wherein the passageway extending from the hydraulic liquid chamber and the entrance to which is initially blocked by the body of the upper of the two gas chamber pistons is of relatively narrow bore, and thus is located within the outer tubing walls.

13. Pressure release apparatus as claimed in any of the preceding Claims and substantially as described hereinbefore.

14. Valve-operating apparatus for operating a ball valve useable in a well test pipe string, which apparatus comprises, positioned andlor mounted within the string tubing.. a slidable piston, operatively connected to the valve ball, but which Is (normally> held stationary by 7 - 25 one or more shear pin; and a passageway for holding a hydraulic liquid and (normally) blocked by the piston; wherein application of a sufficient predetermined pressure differential across the piston causes pin-shearing movement thereof, both actuating the valve and opening the passageway.

15. Valve-operating apparatus as claimed in Claim 14, which is in association with pressure release apparatus as claimed in any of the preceding Claims.

16. Valve-operating apparatus as claimed in either of Claims 14 and 15, wherein the slidable piston Is an elongate annular piston 'Islidable" in a longitudinal direction, and for a limited distance, within an annular chamber set In the tu6ing walls and held initially at atmospheric pressure.

17. Valveoperating apparatus as claimed in any of Claims 14 to 16, wherein there is on the body of the slidable piston a latch key which, at the end of the piston's travel, co-acts with a corresponding latch profile on the Inner tubing wall, and thus prevents any piston return movement.

18. Valve-operating apparatus as claimed in any of Claims 14 to 17, which is operatively connected to Its valve ball via a pin projecting therefrom which co-acts with an off-axis slot in the ball's (flattened) side so that movement of the piston causes the ball to rotate.

19. Valve-operating apparatus as claimed in any of Claims 14 to 18, wherein operation of the ball valve is initiated by the application of a predetermined pressure differential across the piston, which pressure is supplied using a hydraulic liquid, and wherein this hydraulic liquid pressure originates from the passageway previously opened by the operation of a pressure release apparatus of the invention as claimed in any of Claims 1 to 13.

20. Valve-operatinS apparatus as claimed in any of Claims 14 to 19, wherein the passageway for hydraulic liquid opened by the ball-valveectuating travel of the piston is narrow, and located within the tubing walls.

21. Valve-operating apparatus as claimed in any of Claims 14 to 20 and substantially as described hereinbefore.

22. Venting apparatus useable in a well test pipe string containing ventable liquid, which apparatus comprises, positioned and/or mounted within the string tubing: a slidable piston, (normally) held stationary by one or more shear pin; and a vent port for permitting escape of the pipe string's contents out of the pipe string, but (normally) blocked by the piston; wherein application of a sufficient predetermined pressure differential across the piston causes pin-shearing movement of the piston, thus permitting subsequent piston movement to open the vent port.

23. Venting apparatus as claimed in Claim 22 which is in association with a valve-operating apparatus as claimed In any of Claims 14 to 21.

24. Venting apparatus as claimed In either of Claims 22 and 23, wherein the slidable piston is an elongate sleeve the body of which constitutes part of the Internal wall of the test string tubing.

25. Venting apparatus as claimed In any of Claims 22 to 24, wherein the alidable piston is so slidable in an upwards (in use) direction, from an original position where it is sealed into place against the upper mandrel sub, the maximum distance through which the piston may slide once free of restraint being defined by an annular sleeve mandrel which in use lies above the piston, partially ensleeving the upper end thereof, and which has at its upper end an inwardly-projecting shoulder against which the piston body will eventually come to rest.

26. Venting apparatus as claimed in any of Claims 22 to 25, wherein, between the lower end of the sleeve mandrel and a shoulder located on the tubing-distant (outer) side of the sleeve piston, there is defined an annular chamber at atmospheric pressure, this chamber facilitating rapid movement of the piston following application of the actuating pressure differential.

27. Venting apparatus as claimed in any of Claims 22 to 26, wherein the piston body closes eight pairsof vent ports.

28. Venting apparatus as claimed In any of Claims 22 to 27 which Is driven by the creation of a pressure differential (across the ends of the piston) applied via a hydraulic liquid, this hydraulic liquid pressure being that which has been transported along the passageway opened by the ball-valve-actuating piston in the valveoperating apparatus as claimed in any of Claims 14 to 21.

29. Venting apparatus as claimed In Claims 24 and 25, and in any of Claims 26 to 28, wherein following its upwards travel the sleeve piston is prevented from returning by the action of a sleeve latch key on the sleeve mandrel and a corresponding latch profile on the piston itself.

- 28 30. Venting apparatus as claimed in any of Claims 22 to 29 and substantially as described hereinbefore.

31. A well test pipe string whenever employing pressure release apparatus, valve-operating apparatus and/or venting apparatus as claimed in any of the preceding Claims.

Published 1990atThePatent Office. State House, 6671 High Holborn, LondonWC1R4TP. Further copies maybe obtainedfrom. The Patent Office. Sales Branch. St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex tecbmques ltd. St MarY Cray, Kent, Con. 1187