GB2312047A - Detecting leaks in pipework of a well - Google Patents

Abstract

In lengths of pipework where the risk of abrasion is high, and/or where the result of leakage would be unacceptable, and thus particularly in the few feet/metres either side of and around a corner or elbow 11, there be employed double-walled piping with the space 17 between the walls 14,15 sealed gas tight and provided with pressure sensors 18 to detect and signal when the inner wall 15 has been breached, so that the identified section of pipe can be replaced before the outer wall 14 is similarly breached and thus before any damage is done by the well product leaking into the ambient environment.

Description

Improved PiDework This invention relates to pipework, and concerns in particular improved pipework for use in transporting the output of a well - typically an oil or gas well - on the surface downstream of the actual wellbore.

Once a well - in the present context "well" means chiefly an oil or gas well, although the term could extend to a water well - has been bored the well product (oil or gas) is allowed to exit under the well-internal pressure through a valve at the wellhead and along pipes to its intended destination. At various times in a well's life the flow of product is likely to include considerable amounts of solid matter of a highly abrasive nature. Thus, for example, in the well's early moments the product flow can include remnants of the "mud" (various clays and other particulate solid materials) used when the well was being bored, together with minerals, such as sand, which come out of the geological formations through which the bore was drilled, and rock chips and cuttings, that accumulated down the wellbore as it was being bored. Later in the well's life, and especially - for an oil or gas well with the encroachment of water, the formations though which the product flows into the well bore can start to "break down", resulting in increasing sand production.

Moreover, some of the processes commonly employed during a well's life to enhance production, such as "fracturing" (when the formation from which the product is flowing is deliberately broken up to increase the throughput), can lead to the flow back of formation solids, while solids deliberately entrained in the well fluids for the purpose of chemical treatment can and do cause severe erosion problems.

The several sorts of solids likely to be contained within the well's output flow can be extremely abrasive, and can do considerable damage to the mainly mild steel pipework employed to make up the pipes leading away from the wellhead. Indeed, so severe is the abrasive effect of the likely solids that a pipe with walls as much as 1 inch (2.5cm) thick can be "washed out" - eroded through - not in weeks or days but in hours or even minutes, particular at sections where there is a bend in the pipe (as is the case with "elbow" portions).

An obvious solution to this abrasion problem, which has not only economic but also ecological dimensions (to have oil or gas escaping into the environment is highly undesirable), is to use pipework of a thicker wall section, but for the most part all this does is put off the incipient disaster by a few hours or days - which, considering it may take a well weeks, or even months, to settle down (and stop producing abrasive solids as part of its output) is not really a satisfactory answer.

Another solution might be to use pipework made of a more abrasion-resistant material, but not only are harder substances - various stainless and tool steels, for instance - abraded through with relative ease but their use is of doubtful cost-effectiveness, even when taking the local ecology into account. The invention proposes a quite different sort of answer, which is not so much to prevent or slow down abrasion as to detect it when it occurs - when it has reached some significant but as yet harmless level - allowing the relevant section of pipe to be replaced before any further damage is done. More specifically, the invention suggests that, in lengths of pipework where the risk of abrasion is high, and/or where the result of leakage would be unacceptable, there be employed double-walled piping with the space between the walls sealed gas tight and provided with pressure sensors to detect and signal when the inner wall has been breached, so that the identified section of pipe can be replaced before the outer wall is similarly breached and thus before any damage is done by the well product leaking into the ambient environment. Although the double-walled section of pipe could be an entire length of the piping used to make up the pipework, most likely it will be a shorter part thereof - the few feet/metres either side of and around a corner or elbow - the rest of that length of piping being conventional single-walled pipe.

In one aspect, therefore, this invention provides, primarily for use in pipework employed to carry the products of a well such as an oil or gas well away from the wellhead, a double-walled pipe, with inner and outer walls, with the annular space between the walls sealed gas tight, the pipe being operatively associated with a pressure sensor able to detect and signal when a change of pressure in the annular inter-wall space indicates that the inner wall has been breached.

The double-walled, pressure-sensor incorporating pipe of the invention is mainly, though not exclusively, for use in pipework employed to carry the products of a well such as an oil or gas well away from the wellhead.

This pipework may otherwise be quite conventional - for example, it may be made of mild steel (though for certain purposes some rather special materials, such as Duplex, may be utilised), and may be from 2 to 6 inch (5 to 15cm) internal diameter, with (normal) walls from 1/4 to 1 inch (0.8 to 2.5cm) thick.

The double-walled pipe may constitute an entire length of the piping used to make up the pipework, or it may only be a small part of such an entire length - that is, either an individual short length of pipe to be joined at either end to a conventional length, or (and preferably) an entire length which has according to the invention been made double-walled over a small part of its length. Moreover, the invention's double-walled length of pipe may be any shape or dimension of pipe where such a shape/dimension is thought to be at risk from abrasion/erosion; while this can apply to straight sections of pipe, it is most likely to be relevant to tight bends such as the so-called "elbow" portions.

The double-walled pipe of the invention has inner and outer walls, with the annular space between the walls sealed gas tight. It is much preferred that the inner wall be the "normal" wall of the pipe and the outer wall be an additional wall formed around the outer surface of the normal wall - thus, for the invention's pipe to be like a length of ordinary pipe fitted with an external jacket - though it would of course be notionally possible either to make the outer wall from the normal wall and then to add an inner wall within the pipe bore or to make both inner and outer wall different from (and non-aligned with) the normal pipe wall. The two walls may be sealed gas tight in any appropriate way - advantageously simply by being welded together at either end, though brazing or even glueing is a possibility, depending upon the ambient conditions and the material being transported. For convenience the "added" wall - most preferably the outer wall - is made of the same material as the normal (the inner) wall.

The inner and outer walls may be of any thickness thought appropriate to the conditions under which the pipe is to be used, and in general the two walls will conveniently be of the same thickness. However, provided it can be guaranteed that the pipe length will be replaced very shortly (in terms of the suspected abrasion rate in use) after an inner wall breach is detected it might be advantageous to make the outer wall of some thinner material, and thus save on weight and cost.

The double-walled pipe defines an annular space between its two walls. This space can be of any suitable width (from one wall to the other), though a low width - no more than 0.1 inch (2.5mm), and most preferably about 0.05 inch (in) - is most desirable so as to avoid both internal stresses and, in the case of an externally-walled one, making the pipe too large.

Moreover, though conceivably this space could be empty a vacuum - or filled with a (non-corrosive, inert) gas such as nitrogen, most preferably it is simply filled with a flowable grease. This reduces the chance of corrosion from within while at the same time permitting any pressure change resulting from a breach of the inner wall to be communicated to the pressure sensor.

The invention's pipe is operatively associated with a pressure sensor able to detect and signal when a change in the pressure in the annular inter-wall space indicates that the inner wall has been breached. By "operatively associated" is meant that the sensor is suitably mounted on or in connection with the pipe so as to be able to sense the pressure - or, at least, a change in the pressure - within the annular space between the two walls. Thus, the sensor could actually be located within the annular space, with any power and signal conduits passing out through the outer wall, or, and as is in fact preferred, it could be mounted within one of the walls - most desirably the outer wall itself, in the manner of a plug within a hole, its active, pressure-sensing part facing into and communicating with the inter-wall space and its power (if required) and signal leads/conduits projecting out from the back into the pipe's surroundings.

The pressure sensor itself may be of any suitable variety, powered and equipped with signal output means, in any suitable way. For example, the sensor might be a simple, basic Bourdon gauge device mounted into the outer wall of the pipe, the "output" of which device merely controlled a dial, sounded an audible alarm, or triggered some visible signal (such as raising an attention flag or setting off a flashing light) in the immediate vicinity, all to be acted upon by a passing Operative, who then manually initiates some suitable pipe closure or well shut-down procedure.

Alternatively, the sensor might be some variety of electronic device, perhaps of the strain gauge type, mounted on or in the pipe and associated with, or attached to - powered from and signalling to - something much more complex and at a distance, such as an Emergency ShutDown (ESD) control panel that can automatically shut down, or isolate, the relevant pipework once a breach is detected. A typical Bourdon gauge sensor device generally appropriate for use in the invention, and capable of reliably detecting and reporting the pressures likely to be involved - which could range from 5,000 to 20,000psi (about 35 to 140Mpa) - is one of those available from DeWit. A typical electronic device of the strain-gauge type is that available from Sensotec for use with a STAN controller system (such as that model identified as the TJE AP 122). This type of sensor employs a metal diaphragm with a Wheatstone bridge sputtered on it; as the diaphragm flexes under the applied pressure so there is caused a corresponding imbalance in the bridge, and the resulting bridge output is then converted to an output signalled and transmitted to whatever control device - the STAN system, say - is connected to the sensor. Another type of sensor appropriate for use in the invention is that known as a nHi-Lo Pilot", for example the Brisco Flowline Pilot Type 2000. This sort of sensor is an on/off device triggered - in its "Hi" mode - into action when the sensed pressure exceeds some pre-set value, and employs a sliding valve working against a spring of an appropriate stiffness and operating to open a valve port in some associated pneumatic or hydraulic circuit (this then transmitting the "signal" to the main pipeline control systems).

There may, of course, be more than one pressure sensor in any one length of pipe according to the invention. This may be desirable to guard against a sensor failing, so that a potentially disastrous pipe breach is not left unnoticed simply because one sensor did not work.

An embodiment of the invention is now described, though by way of illustration only, with reference to the accompanying Drawings in which: Figure 1 shows a sectional view of a pipework elbow section constructed in accordance with the invention; and Figure 2 shows a simple schematic diagram of a control system associated with sensor equipped double-walled pipework (the elbow section of Figure 1) of the invention.

The pipe length of the invention shown in Figure 1 is an elbow section (generally 11). Basically, it is a conventional elbow section - a 90" bend about 4ft (100cm) long, 6 inch (15cm) internal diameter, 3/4 inch (1.5cm) wall thickness - with end flanges (12,13) for attachment to other pipe lengths, but around its centre section it has an outside jacket (14) to form a portion that is double walled, the "original" wall (15) of the elbow forming the inner wall. The two walls are sealing joined at either end with weld fillets (as 16), and together define an annular space (17) which in use is filled with grease (not shown here).

On the inside of the bend are two threaded apertures in one of which is located a correspondinglythreaded plug-like pressure sensor (18) and in the other of which is a blanking plug (18a). The inner, active face of the sensor is open to the space 17 between the two walls, and to and from the outer face are supplied power and signal leads (not shown here).

It will be apparent that, if the elbow section is full of a fast-moving fluid carrying with it an abrasive material, the area (marked by the wiggly line 19) on the outside of the bend is likely to be impacted by, and thus eroded by, that material. If this happens, and the inner wall pipe material is worn away, the pipe-internal pressure (of several thousand pounds per square inch) will be communicated to the inter-wall space 17, and the sensor 18 will then detect this, and send an appropriate signal to whatever equipment (not shown) is monitoring the situation.

Figure 2 shows how, using an electronic sensor device, the device is connected to a suitable power and control system.

The elbow section 11 is connected in between two pipe lengths (as 22), and has a single electronic sensor device 18) operatively mounted therein. The sensor device is supplied with power down a line (P) from a main control system (STAN), and returns its output signal along a line (S) to the STAN controller. There are, in the same pipeline arrangement, a number of other pipe sections with sensor devices in them, and these are supplied with power, and feed signals, along a set of power P and signal S lines (23). The STAN control system is in turn suitably connected to a computer (24), which under appropriate program control provides information - and alarm signals (and ESD shut down signals) - along its output line (Q).

Claims (10)

1. For use in pipework employed to carry the products of a well such as an oil or gas well away from the wellhead, a double-walled pipe, with inner and outer walls, with the annular space between the walls sealed gas tight, the pipe being operatively associated with a pressure sensor able to detect and signal when a change of pressure in the annular inter-wall space indicates that the inner wall has been breached.

2. A double-walled pipe as claimed in Claim 1 which is constituted by an entire length of pipe which has been made double-walled over a small part of its length.

3. A double-walled pipe as claimed in either of the preceding Claims, wherein the double-walled length of pipe is a so-called "elbow" portion.

4. A double-walled pipe as claimed in any of the preceding Claims, wherein the inner wall is the "normal" wall of the pipe and the outer wall is an additional wall formed around the outer surface of the normal wall.

5. A double-walled pipe as claimed in any of the preceding Claims, wherein the two walls are sealed gas tight by being welded together at either end.

6. A double-walled pipe as claimed in any of the preceding Claims, wherein the outer wall is made of a material thinner than that of which the inner wall is made.

7. A double-walled pipe as claimed in any of the preceding Claims, wherein the annular space between its two walls is about 0.05 inch (lmm) wide.

8. A double-walled pipe as claimed in any of the preceding Claims, wherein the annular space between its two walls is filled with a flowable grease.

9. A double-walled pipe as claimed in any of the preceding Claims, wherein the pressure sensor able to detect and signal a change in the pressure in the annular inter-wall space is mounted within the outer wall, in the manner of a plug within a hole, its active, pressure-sensing part facing into and communicating with the inter-wall space and its power (if required) and signal leads/conduits projecting out from the back into the pipe's surroundings.

10. A double-walled pipe as claimed in any of the preceding Claims and substantially as described hereinbefore.