Burst plug for a downhole fluid passage

A burst plug for positioning in a downhole fluid passage has: a shear disc installable in a sealing position in the fluid passage. The shear disc is openable by applying fluid at a burst pressure against the shear disc. The burst plug has a retainer and sleeve formed to retain the shear disc in a fluid flow blocking position after the shear disc is removed from its sealing position. The sleeve has a shear disc retaining position in locking engagement with the retainer when fluid at burst pressure is in communication therewith. The sleeve thereafter assumes a shear disc removal position when fluid in communication therewith is reduced to a selected pressure lower than the burst pressure. In the shear disc removal position, the sleeve and retainer disengage from the blocking position, allowing the shear disc and retainer to be expelled from the fluid passage.

FIELD OF THE INVENTION

The present invention relates to a downhole tool mechanism and, in particular, a burst plug for a downhole tool.

BACKGROUND OF THE INVENTION

Burst plugs are used in some downhole tools to provide a removable plug in the tool. Some fluid conveyed down hole tools, for example, include fluid passage bores that must be plugged for fluid conveyance, but are intended to be opened after placement to permit fluid flow therethrough. For example, in a pump down cement float, such as for example one of those described in PCT/CA2003/001889, filed Dec. 8, 2003 or Canadian patent application 2,311,160, published Dec. 9, 2001 (both to the present assignee), the float includes a bore along its length for passage downwardly therethrough of cement fluids, a check valve in the bore and a pressure responsive plug such as an expellable plug, also called a burst plug or disc, for holding pressure during pump down but removable, as by expelling or bursting at pressures above pumping pressure, to allow fluid flow through the bore, as controlled by the valve.

In those kinds of pump down cement floats, the float is conveyed down hole with the burst plug plugging the bore, but when desired, the fluid pressure above the float is increased to remove the plug from its plugging position in the bore. When pressuring up to burst the plug and open the bore, the check valve and/or the formation can be damaged by the surge of liquid that passes the check valve when the plug is removed.

SUMMARY OF THE INVENTION

In accordance with a broad aspect of the invention, there is provided a burst plug for positioning in a downhole fluid passage, the burst plug comprising: a shear disc installable in a sealing position in the fluid passage and openable by applying fluid at a burst pressure against the shear disc, a first part formed to retain the shear disc in a fluid flow blocking position after the shear disc is removed from its sealing position and the first part being selected to assume a shear disc retaining position when fluid at burst pressure is in communication therewith and thereafter to assume a second shear disc removal position when fluid in communication therewith is reduced to a selected pressure lower than the burst pressure.

In accordance with another broad aspect of the invention, there is provided a downhole tool comprising: a body including an upper end and a lower end, a fluid passage bore extending through the body from the upper end to the lower end, an upper seal creating a seal about body and a burst plug positioned in the bore, the burst plug including a shear disc in a sealing position to substantially prevent flow through the fluid passage bore and being responsive to a burst pressure to remove the shear disc from its sealing position and configure the shear disc in a flow-blocking position in the bore and being responsive to a second pressure lower than the burst pressure to move the shear disc from its flow-blocking position to increase fluid flow through the bore.

In accordance with another broad aspect of the invention, there is provided a method for opening a fluid passage bore through a downhole tool, the method comprising: providing a downhole tool including a body having an upper end and a lower end, a fluid passage bore extending through the body from the upper end to the lower end, an upper seal creating a seal about the body and a burst plug positioned to control fluid flow through the fluid passage bore, the burst plug including a shear disc in a sealing position to substantially prevent flow through the fluid passage bore and permitting staged removal; applying fluid at a burst pressure to remove the shear disc from its sealing position and move the shear disc to a flow-blocking position; reducing the fluid pressure to a second pressure lower than burst pressure; and using the second lower pressure to move the shear disc from its flow-blocking position to allow increased fluid flow through the bore.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

FIG. 1shows a portion of a fluid pressure-conveyed downhole tool in the form of a cement float10including the cement float body12with a fluid passage bore14extending from its lower end12ato its upper end (not shown), a check valve15in the bore to seal against fluid flow through the bore from lower end to upper end, an upper seal16, in this embodiment formed as a cup, capable of creating a seal about body12to prevent fluid flowing down past the tool when it is positioned in a wellbore and a controlled release burst plug18positioned in bore14to provide a removable plug therein.

Burst plug18may be positioned in a downhole fluid passage such as bore14of a pump down cement float, or other down hole tool, to provide a plug therein to permit the tool to be pumped down by a pump-down fluid pressure acting against the plug and upper seal cup16. However, burst plug18may be opened by removal of all or a portion thereof from bore14when desired to permit flow through the bore. Burst plug18includes a shear disc20installed in a sealing position in bore14. Shear disc20is configured to be create a substantial seal against fluid passing through bore such that, for example, it may be acted upon by pump-down fluid pressure and can permit pump-down conveyance of a tool in which it is positioned. Shear disc20is further configured to permit staged removal thereof by application of fluid pressure thereto. In staged removal, a first pressure is used to burst disc20and position it in a flow blocking position and a second pressure, which is lower than the first pressure, is used to further open the bore by expelling disc20from the flow-blocking position in the bore. The flow-blocking position is selected to protect against fluid at the first pressure freely passing through the burst plug. The shear disc may take various forms and may for example include various pressure breakable mounting configurations, including any of a mounting flange, a shear pin connection, a membrane, snap rings, sleeves, etc., various sealing mechanisms including o-rings, seals incorporated into the mounting configuration (i.e. a sealing portion on the mounting flange), bodies of various thicknesses including membranes, solid plugs, etc.

In one embodiment, the shear disc can be formed to be capable of mounting in a downhole fluid passage bore in a sealing position, to block flow through the bore, and in a first stage of removal is formed to open, as by bursting or breaking away from the sealing position, when fluid pressure thereabove is raised to a burst pressure, the burst pressure being selected to be at or above the pressure rating of the shear disc. Shear disc20, in one embodiment, however, may be configured after opening to remain in a blocking position in the bore, for example, caught against a retainer22mounted in the bore. In the blocking position, the shear disc may totally prevent flow through the bore or may allow some fluid flow therepast. In one embodiment, for example, the burst plug is configured such that when the shear disc is in the blocking position, a low volume of fluid may flow past the shear disc.

In a second stage, the shear disc and/or the retainer can be expelled from bore12once the pressure above the assembly is reduced to a second pressure lower than the burst pressure. To achieve the second lower pressure, the fluid pressure that caused the shear disc to break away from its sealing position can be reduced gradually as by leaking past the shear disc in its flow-blocking position and/or by reduction at surface, as by opening a valve.

To provide a two-stage removal, a portion of the burst plug may be configured to remain in position in the tool when under burst pressure conditions, but to disengage from the tool when the pressure is reduced. Such an effect may be provided, for example, by forming a portion of the burst plug, such as retainer22, to remain mounted in the tool when under a high pressure load and to assume a second removable position when a fluid pressure load lower than the higher pressure is applied thereto. Such a pressure response may be provided, for example, by use of materials with conditions that vary under different pressure loads, such as elastically or plastically deformable materials. For example, in one embodiment, the burst plug may include an elastically deformable portion that deforms to maintain the shear disc in a flow-blocking position relative to the tool when under burst pressure loads, but assumes another position when fluid pressure less than burst pressure is applied thereto that permits removal of shear disc20from its flow-blocking position.

One embodiment of a burst plug assembly118according to the present invention is shown inFIG. 2. Burst plug assembly118includes three main parts including a shear disc120, a retainer122and an installation sleeve124.

Installation sleeve124is mountable in or at an open end of downhole fluid passage. Mounting may be by connection to or biasing against the material forming the downhole passage, but in any event creates a seal between the sleeve and the material forming the downhole passage to substantially prevent fluid leakage therebetween. With reference toFIG. 1, for example, installation sleeve124is shown mounted at the upper end of bore14. Installation sleeve124has a side wall forming an axial bore125therethrough. In operation, axial bore125is placed in communication with the downhole fluid passage. As such, in the illustrated embodiment ofFIG. 1, axial bore125of the sleeve acts as an extension of the tool's bore. In the illustrated embodiment, sleeve124is intended to be held in position relative to the bore, but is not intended to pass through the bore. In the illustrated embodiment, for example, sleeve124includes an enlarged portion121with an outer diameter greater than the inner diameter of the tool's bore. Enlarged portion121of the illustrated embodiment forms a seal121athat acts against the tool to create a seal therebetween.

Sleeve124further includes an exposed outer surface123. For operation, sleeve124is mounted relative to the downhole fluid passage such that outer surface is open to fluid pressures uphole of the tool on which the sleeve is to be mounted.

Sleeve124includes structures for engaging shear disc120in its sealing position and for releasably locking retainer122.

In the illustrated embodiment, for example, sleeve124defines a land and lock shoulder126for sealingly engaging a flange128on the shear disc. It will be appreciated that the flange128and shoulder126may be configured to operate as in other pressure-actuated shear plug systems such that the flange fails or pulls away from the shoulder when a pressure above the flange/shoulder connection's fail pressure rating is applied against disc120. As such, it will be appreciated that shoulder126is positioned on the sleeve such that disc is in communication with fluid pressures uphole of the tool on which the sleeve is mounted.

Sleeve124further includes a locking profile130for releasably engaging retainer122against axial movement through the sleeve at high uphole fluid pressures and a shoulder132for releasably engaging retainer122when it is under substantially no pressure load. It is noted that in the illustrated embodiment, locking profile130includes a plurality of grooves134formed to be capable of interengagement with corresponding grooves136located on the outer surface of retainer122. Grooves134,136, may be for example, a series of non-helical, 8 Stub Acme-type grooves. Grooves134are formed radially inwardly of exposed outer surface123. Sleeve124is at least in part formed of a resilient material that is selected to change shape in response to a high pressure load but to return to an original shape when such pressure load is removed. In particular, at least a portion of the annular wall between exposed outer surface123and grooves136is formed resiliently to deform from a normal position to a compressed position in response to a selected pressure load above a selected limit but to return to the normal position when the pressure load is reduced below the selected limit. The selected pressure may be less than the burst pressure rating of the shear disc. In the illustrated embodiment, the selected pressure may be between the pump-down pressure intended for operation of the tool in which the burst plug assembly is to be used and the burst pressure of the shear disc.

Retainer122includes an outer surface and a fluid passage bore140extending from its upper end122ato its lower end122b. As noted above, the outer surface includes grooves136, or other structures, formed to releasably interlock with locking profile130on sleeve124. Upper end122ais formed as a cup including an annular wall142defining therebetween an indentation144. Bore140opens from indentation144. Annular wall142may be formed of a resilient material and may be formed to operate as a cup seal to expand in response to a pressure differential between indentation144and the outer surface of the annular wall. In such an embodiment, annular wall142may be selected to expand in response at least to burst pressure conditions. Lower end122bincludes a releasable breakaway seal146formed and positioned to releasably engage shoulder132on sleeve124. Although breakaway seal146may take other forms, such as a shear flange, in the illustrated embodiment, seal146may be formed of resilient materials and may be formed to move in response to fluid flow therepast out of engagement with shoulder132. The resilient properties of seal146may be selected to respond to pressures lower than burst pressure.

Shear disc120includes flange128, as noted above, which separates an uphole side120afrom a downhole side120b. Downhole side120bis formed to fit into indentation144of the retainer. In one embodiment, the downhole side is formed with side walls150that closely fit against annular wall142such that a sealing configuration may be formed between the parts. The downhole side of shear disc120, as shown, or the bottom wall of indentation includes seal compromising grooves154to permit partial fluid flow between the parts to bore140.

Burst plug assembly118may be positioned in a downhole tool to control fluid flow through its bore. For operation, the sleeve is positioned in communication with the bore of the tool with exposed outer surface123exposed to uphole pressures. The retainer and the shear disc are positioned in the sleeve. In preparation for use, shear disc120is installed with its flange128engaged and sealed against land and lock shoulder126and retainer122is installed with its break away seal146supported against shoulder132. In this position, downhole side120bis spaced from, which in use will be uphole of, retainer122.

In operation, fluid pressure in communication with the tool from above (as may be adjusted from surface) acts against uphole side120aof shear disc120. When shear disc120is in its sealing position, shown inFIG. 2A, flange128seals against land126and prevents fluid from moving therepast. Shear disc120is selected to remain in this position during pump down pressures, for example, which in one embodiment may be less than 1,500 psi.

Depending on the selected pressure under which the resilient portion of the sleeve's annular wall is selected to deform, when pump-down pressures are applied, the resilient portion of the sleeve's annular wall may, as desired, either be (i) in its normal position such that grooves134and136are out of engagement with each other (as shown) or (ii) in its constricted position with grooves136driven into engagement with grooves134. Fluid pressure from above is isolated from retainer122and breakaway seal146of the retainer is engaged on shoulder122, to hold the retainer in place.

When it is desired to open the bore of the tool by removal of the shear disc120, fluid pressure above shear disc120may be increased to a pressure capable of shearing the disc. For example in one embodiment, a burst pressure equal to or greater than 1,500 psi may be useful. The burst pressure will also be in communication with and acting against outer exposed surface123of the sleeve. Burst pressure inFIG. 2Bis illustrated by arrows P. The resilient portion of sleeve124may be selected to deform at a pressure below burst pressure such that by the time the fluid pressure is elevated to burst pressure, the annular wall has constricted radially inwardly to drive grooves136of the sleeve into engagement with grooves134of the retainer.

When disc120shears, for example by failure at flange128caused by a stress concentration therealong, disc120lands against retainer122, as shown inFIG. 2B. After disc120shears out of its sealing position, fluid at burst pressures will come into contact with the retainer. By this time, however, the retainer is firmly engaged by sleeve124so that retainer is held to provide resistance to axial displacement of the retainer from the sleeve against the fluid surge at burst pressure and the force of disc120landing against the retainer. The formation of the upper end of the retainer including resilient annular wall142about the indentation causes fluid pressures to drive wall142out against sleeve124to create a seal against fluid passing between the sleeve and the retainer. In addition in the illustrated embodiment, this reaction of wall142in response to fluid pressures at burst pressure, causes an opening to be formed between the retainer and shear disc120to permit fluid to pass therebetween to grooves154and thereafter to bore140. The fluid flow path provided between the disc and the retainer and through bore140permit fluid flow past the burst plug assembly but in a controlled manner to avoid damaging a valve of the tool, for example valve15inFIG. 1, or other components of the tool or well therebelow.

The interlock between grooves134and136permits the fluid to pass through the retainer without the retainer being ejected from sleeve124and therefore from the bore. Annular wall142embodies the primary seal preventing burst pressure from invading between retainer122and the sleeve, which would drive the grooves apart. The resilient nature of sleeve124ensures that once the pressure above the burst plug is reduced to a pressure below the selected pressure for the resilient material, as by relieving the pressure at surface and, to a much lesser degree, leaking between walls142and150and through grooves154and bore140, walls142and the resilient portion of sleeve124resumes its normal shape. In particular, with reference toFIG. 2C, after the fluid pressure is reduced below burst pressure and in particular below the selected pressure at which the resilient materials respond, walls142resume their normal condition, which is in close tolerance against walls150of shear disc120and the sleeve wall between outer surface123and grooves136relaxes such that grooves136pull out of engagement with grooves134. In such a condition, the retainer may be expelled from sleeve124, and from the bore of the tool, by overcoming the engagement of breakaway seal146to shoulder132. This may occur simply by the residual weight of fluid column above the retainer, but may be selected to occur by again raising the fluid pressure to an elevated pressure but which is less than the burst pressure. The elevated pressure may be selected not to damage any components of interest below the burst plug.

To facilitate removal of the retainer from the bore of the tool, it may be desirable to form retainer such that a fluid path is set up along the outer surface, between retainer122and sleeve124, to drive grooves134,136apart and to drive breakaway seal146out of engagement with shoulder132. For example, a fluid bypass147may be formed between the retainer and the sleeve, for example on the outer surface of the retainer where a portion of grooves136have been removed. As another example, uphole side120aof the disc may be formed with downwardly ramped surfaces leading to its edges to direct fluid towards annular wall142. Since wall142, after burst pressure is dissipated, will be in close tolerance against disc120, fluid passing down over the uphole side of disc120will tend to flow between retainer122and sleeve124. Disc120and wall142may be correspondingly sized and shaped to facilitate movement of fluid over the surface of the shear disc and over the wall toward the outer surface of the retainer. For example, the height of wall142may follow or be slightly stepped back from the curvature of the shear disc at its edges.

In previous cement floats, energy stored primarily in the pressured liquid column is released suddenly when the disk bursts resulting in both a ‘rebound’ of the casing at surface and a down hole pressure surge felt by the formation directly below the casing. Using a burst plug assembly according to the present invention, pump down tool disc burst capacity can still be achieved in the existing pressure of, for example, equal to or greater than about 1500 psi, but the bore may not fully open until after the pressure has been reduced slowly. This, thereby, protects the formation and the tool below the shear disc from burst pressures.

It will be appreciated that the entire sleeve may be formed of resilient materials, if desired. It will also be appreciated that the two-stage burst plug may be provided by forming a part other than the sleeve, such as the retainer, to react to pressure changes to be engaged in the tool at burst pressures but removable at lower pressures.

FIG. 1also shows a wiper plug stand160according to another aspect of the present invention. The wiper plug stand is an insert for the uppermost cup seal16of a cement float, and includes a body161that rests against base16aof the cup seal to raise the effective height of the base of the cup seal. Body161is formed of durable materials capable of acting as a stop against which items intended to land on seal cup16may be prevented from damaging contact with the seal cup walls16b.

A packer cup in which the wiper stand might be useful is described in detail in PCT/CA2003/001890, but of course a wiper stand according to the present invention may be useful in other forms of packer cups where it is intended that items are to be landed on top of the packer cup.

Wiper stand includes a mounting arrangement to secure the stand in the packer cup. In the illustrated embodiment, the mounting arrangement includes a protrusion162that engages in a groove164in the inner wall of the packer cup. The mounting arrangement must secure the stand without compromising the sealing operation of the seal. Thus, protrusion162permits the passage therepast of fluid to act against the packer cup walls and permits sealing flex of the packer cup walls.

The wiper stand is selected to prevent a bottom plug wiper or other device landing thereon from invading into the packer cup so far as to collapse it and compromise its function as a seal and or introduce debris that may clog cement flow paths. In the illustrated embodiment, the wiper stand height was selected to land the bottom of a wiper plug with just the first ‘fin’ into the top of the cup.

In the illustrated embodiment, the wiper stand also holds burst plug18in place, but of course the disc may be held by other means if desired, even if the wiper stand is not used with it. On the other hand, the wiper stand need not be used with the controlled burst plug, if so desired. In particular, it is to be understood that the controlled release burst plug and the wiper stand can be used independently of each other if desired. Also, the burst plug and the wiper stand can be used on other downhole applications and tools, apart from a cement float, if desired.

In the illustrated embodiment, the controlled release burst plug and a wiper stand functions may, if desired, be installed in cement floats of existing designs with only a minor modifications thereto to accept installation of the wiper stand and the burst plug. For example, if it was desired to install the burst plug in an existing design of a cement float, the bore of the an existing cement float may have to be adapted to accept the retainer. If it was desired to install a wiper stand in a packer cup of an existing design downhole tool, it may be necessary to form the packer cup or the tool body to retain the stand.

All parts relevant to the assembly may be variously constructed and of various materials. In one embodiment, for example, the burst plug and the wiper plug stand may be manufactured of drillable materials, for example using polymerics such as 70 Duro hi-temp polyurethane.