GB2243631A

GB2243631A - Deployment and recovery of pre-packed screens

Info

Publication number: GB2243631A
Application number: GB9010088A
Authority: GB
Inventors: Nigel Snow
Original assignee: PUMPTECH NV
Current assignee: PUMPTECH NV
Priority date: 1990-05-04
Filing date: 1990-05-04
Publication date: 1991-11-06
Anticipated expiration: 2010-05-04
Also published as: NO303743B1; GB9010088D0; GB2243631B; CA2041788A1; NO911750D0; NO911750L

Abstract

A bottom hole assembly (BHA) comprises pro-packed screen 1, washpipe 2 and stinger section 3. The screen has an outer fluid permeable wall 4, an inner permeable wall 5 and an annular layer of pre-packed particulate material 6 therebetween. Fluid can flow radially inwardly through the screen into the annual space 7 between the screen inner wall and the washpipe outer wall. Washpipe sections are coupled by a subsection of pipe 8. The ends of the coupling are joined to respective ends of sections of washpipe by conventional means. Screen sections are joined together by a stinger 3. Conventional joining means may be used. The stinger has a portion of its length necked down, and this portion has a polished sealing surface 9 which can provide a contact seal to a pair of appropriately sized pipe rams (not shown). Internally of the stinger, at the same level as the external sealing surface, there is an internal polished sealing surface. An annular seal 10 carried on a sub-unit 8 forms a contact seal on this internal sealing surface. Thus, fluid from the annular space 7 cannot pass by the seal 10. A method for deployment of a BHA as described above is disclosed. The BHA may be deployed in an oil/gas well under pressure. <IMAGE>

Description

Deployment and Recovery of Pre-Packed Screens The present invention relates to a method for deployment (and recovery) of pre-packed screens in oil/gas wells. Pre-packed screens as such are known in the art, and are employed during production from the well to prevent flowback of excessive quantities of particulate material (e.g. fracture propant, sand and the like). In effect, pre-packed screens are down-hole filters to remove particulate matter from the flow.

A pre-packed screen is in tubular form (of a suitable diameter to be able to run in the wellbore) and has outer and inner fluid permeable screen walls. Fluid flows radially inwardly and passes through packed particulate material in an annular layer between the screen walls. Filtered fluid passes through to the central space inside the screen and thence flows back up the wellbore.

It is desirable to remove particulate matter from the flow because of the abrasive effects of particles which are detrimental to surface production facilities such as pumps, valves etc.

When'it is known, prior to completion of the well, that a well is likely to produce sand is it possible to pack the entire perforation interval with "gravel pack material" to act as a filter. Additionally or instead, a pre-packed screen can be fitted at the down hole end of the wellbore in the region of the perforation interval. One example of sand control using a cambination of gravel pack material and a pre-packed screen is disclosed in USP-4,856,590.

The bottom hole assembly (BHA) described in the prior patent is to be deployed and recovered on coiled tubing (known in the art). The assembly has an advantage that it includes internally a washpipe which opens at the tip of the assembly and allows liquid to be flushed through the tip of the assembly. Liquid may be supplied to the washpipe under pressure for flushing using coil tubing connected at the up hole end of the assembly. Flushing via the washpipe is particularly useful when the assembly is to be recovered because it loosens the assembly in the surrounding material and so eases withdrawal.

However, a severe disadvantage of the prior method and apparatus is that it can only be employed when the well is shut down and depressurised. It is both expensive and time consuming to "kill" the well once it is in production, and further cost and delay is incurred on bringing it back to production. Furthermore, if long lengths of screening are required to cover a long perforation interval, it would, using conventional technniques, be necessary to mobilise a rig to work over the well. A rig is required to handle lengthy rigid bottom hole assemblies. This adds both to cost and delay.

The present invention seeks to provide a method capable of deploying and retrieving lengthy pre-packed screens (e.g. 10 to 100 metres or morse). These screens will comprise an internal washpipe. The screens and washpipe can be deployed and retrieved under pressure on pre-existing live wells which only have limited or no wellhead riser capability (e.g. 3 to 20 metres riser accommodation space). The invention allows pre-packed screens with washpipe to be run into pre-existing live wells without the need to kill the well with completion fluid, brine or mad. The method can be used to run screens on braided line using a conventional wireline unit, or the screens can be run on coil tubing.Coil tubing has a particular advantage that it can accourriate highly deviated, even horizontal, wells by virtue of the ability to use the tubing to "push" the screen in the well bore. Coil tubing is used to supply fluid to the washpipe under pressure. The invention can provide a method whereby remote or elevated mounting of heavy machinery (e.g. a coiled tubing injector, with its attendant complexity and safety problems) is avoided.

The present invention also allows pre-packed screens with washpipe to be run without the use of a conventional rig. The problems associated with already-completed wells unexpectedly producing particulate material can be overcome with the present invention, even though those wells were not originally designed to take gravel packing and pre-packed screens.

Despite the constraints of a) the availability of riser accommodation on the pre-existing well head installation and b) the limitation on size of object which can be run in a pre-existing well bore, the present invention provides a simple and effective answer to the problem of retro-fitting a fluid filter in the perforation interval of a live well. It overcomes the inherent problems associated with attempting to insert into a well under pressure an assembly which is intended to allow fluid flow, without escape of well fluid during insertion.

The invention also provides an assembly incorporating a pre-packed screen, suitable for use with the method of the invention.

In the following description, the term bottom hole assembly (BHA) will be used to refer to the assembly of pre-packed screen(s), washpipe and other associated equipment which is intended to be deployed in the well bore in the perforation interval. The perforation interval is sometimes referred to in the art as the "production zone".

Hereafter the invention will be described with reference to deployment/recovery using coiled tubing, but it is to be understood that the use of wire line techniques might be applicable in certain well situations and could be used within the invention. Clearly, only by using coiled tubing can the wash-through capability of the washpipe be utilised.

The use of coiled tubing for various well treatment processes such as fracturing, acidising and gravel packing is well known. The advantages in the use of coild tubing include relatively easy and quick entry into the well without the necessity of employing complex and costly apparatus such as a work over rig. The use of coiled tubing is preferable to the insertion into the well of a tubing string which is made up of a plurality of short lengths of tubing which must be individually joined together.

Typically, up to several thousands of metres of tubing is coiled onto a large reel which is mounted on a truck or skid.

A coiled tubing injector head, typically employing chain-track drive, is mounted axially above the well head and the coiled tubing is fed to the injector for insertion into the well.

The coiled tubing is plastically deformed as it is paid out from the reel and over a gooseneck guide which positions the coiled tubing along the axis of the well bore and the injector drive mechanism.

Tools used with coiled tubing generally ccmprise a long rigid element having a central bore which, when attached to the coiled tubing, allows fluid commanication between the bore of the coiled tubing through the tool and outwardly through various valves and ports in the tool to the well bore itself.

The tools also typically include one or more packer elements which act to isolate certain portions of the well bore from each other. Such tools may be of any length but, for instance, for treatment of a particular interval in the well bore, the tool must incorporate packer elements which, when positioned in the well bore, effectively straddle and isolate that portion of the well bore from the remaining portions, both above and below the zone of interest. If the interval to be treated is particularly long, the treatment tool must be similarly of great length.Thus, tools of 25 metres in length or longer are not uncointrn. If the particular interval for treatment is at the end of the well bore the treatment tool may be locked into the well bore end and extend from the well bore end: in such a case a packer element is only required above the tool.

The injection of such a long-length tool which cannot be plastically deformed in the manner of coiled tubing and which is typically of a larger diameter than the coiled tubing itself such that it will not pass through the injector drive mechanism presents some difficulty. In order to overcome this difficulty, it has been prior practice to mount the tool in a conduit which is effectively an extension of the well casing above the well head and to position the injector drive mechanism on top of this conduit. The conduit and injector forms a pressurised cylindrical enclosure for the tool.

Obviously, this places the bulky and heavy injector drive mechanism at an extreme height above the well head when long tools are to be used. Such weight cannot be supported solely by the cylindrical conduit, and therefore, must be at least partially supported by a heavy duty crane or derrick in position over the well head. Despite employing guy-wires to steady the positioning of the top heavy elevated drive mechanism, the uneven and irregular lateral foces applied to the assembly by unreeling and bending of the coiled tubing makes such positioning difficult at best and an extreme safety hazzard at worst.

In accordance with one aspect of the present invention, a BHA of any length is mounted within a closed-end cylindrical lubricator which is then mounted on the well head. Upon establishment of fluid oammunication between the lubricator and the well head by opening of at least one well head valve, the BHA is lowered from the lubricator into the well bore with a portion of the BHA remaining within the well head at the location of the blow out prevention (BOP) stack, adjacent pipe seal rams located in the well head which are then closed to engage and seal around the BHk. The lubricator is then removed and the injector head is positioned above the well head and the coiled tubing is extended to engage the captured BHA and fluid cammunication is established between the coiled tubing and BHA.The injector drive mechanism is then connected to the well head and the pipe seal rams capturing the BHA are released and fluid communication is established between the well bore and the tubing injector drive head.

The retrieval and removal of the coild tubing and BHA is effected by performing the above steps in reverse order.

In another aspect of the invention a B of any length is mounted within a riser extending upwardly from the well head.

The riser will have at its upper end rams for capturing and sealing the BHa, and a blind ram for cottpletely sealing the bore. An injector drive head for coiled tubing can be mounted over the rams above the riser. In other respects deployment of the BH using a riser is the same as deployment using a lubricator. In certain circumstances where an exceptionally long BHk is to be deployed, a lubricator may be mounted above a riser/ram assembly, with the injector on top.

Once particular advantage of the process in accordance with the present invention in that pressure testing is possible and desirable throughout the procedure which greatly enhances the safety of the operation. Thus, the sealing of the lubricator or riser attachment to the well head can be pressure tested prior to the opening of the blind rams. Similarly, the sealing of the pipe rams against the BHA can be tested prior to removal of the lubricator or riser from the well head.

Additionally, the pressure integrity of any connection between the B and coiled tubing (if used) can be tested as well as the pressure testing of the coiled tubing in the injector drive mechanism and its seal both against the well head and against the coiled tubing can be tested prior to opening of the pipe rams. It can also be clearly seen that pressure testing of the reverse order of the retrieval operation can be effected in like manner.

Where the B is required to be of such length (e.g. 100 metres) that it cannot be accommodated at the well head in a single length in a riser or lubricator, it is a particularly advantageous feature of the invention that parts of the Dt can be assembled into a string. As each section of the BHA is completed it can be lowered into the bore hole and another section connected on top. The already-assembled part of the B is suspended from the well head by a slip ram which supports its weight. The Dt is sealed by pipe rams in order that the well bore is maintained under pressure. Once the string has been completed the entire EHA can then be deployed.

According to the invention the BHA comprises a pre-packed screen unit with an internal washpipe. The BHA has means for locating and locking the assembly in the well bore at a predetermined position.

At least a part of the outer surface of the BHA provides a sealing surface onto which an appropriately sized pair of pipe rams can form a contact seal. The sealing surface is located at a portion of the BHA which is radially impermeable to well fluid. In some cases, the sealing surface (e.g. a polished outer cylindrical surface) may be formed as an integral part of the cylindrical body of the pre-packed screen.

Alternatively, it is preferred that the sealing surface may be provided on a section of pipe in the form of a bar or a "stinger" which is detachably connected in axial alignment with the screen. Where a string BHA is to be deployed sections of screen may be interposed by stinger sections. The string may be gripped at various positions by suitable slip rams and sealed by suitable pipe rams bearing on the sealing surfaces. With stingers spaced at intervals along the length of the string, there is the possibility of gripping and sealing at chosen locations along the string. For example a string could be built sequentially by adding a pre-packed screen and a stinger section, lowering the combined sections into the well bore, sealing the bore against the pipe rams and adding another screen and stinger combination above the previous sections.

When a pre-packed screen is to be deployed (or recovered) in a live well uner pressure it is essential to prevent escape of well fluid up the internal bore of the screen. Otherwise, when the RHA is held in the pipe ram of the BOP stack well fluid under pressure will by-pass the seal on the outer surface of the stinger by passage radially through the screen walls and up the bore. The e washpipe which is carried inside the internal bore of the screen can be sealed internally at the top end with a suitable valve. Also (or instead) the top end of the washpipe can be connected to the coiled tubing under pressure to prevent fluid back-flow therethrough.

Furthermore, the washpipe bottom end may be provided with one or more non return valves such as flap valves, ball valves or rupture disc valves. According to the present invention there is additionally provided in the BHA at least one sealing means to prevent well fluid flow in the annular space defined between the external surface of the washpipe and the internal surface of the bore inside the screen/stinger. The sealing means is located at a portion of the wall of the screen/stinger which is radially impermeable to well fluid; it is particularly preferred to make the seal at the same level as the external seal which is made by the pipe ram. Most preferably, the sealing means is a subsection of pipe forming a coupling pipe connectable between washpipe sections and capable of making a contact seal between its external surface and the surrounding internal surface of a stinger section.

The seal may be made using, for example, one or more O-rings, or alternatively using for example chevron seals. The seal itself is generally carried on one of the parts in order to ensure its correct location and it makes contact with a sealing surface on the other part: it is presently preferred to carry the seal on the washpipe (or on a sub-unit attached thereto) and to have a sealing surface (e.g. a polished surface) on the inside surface of the wall of the stinger.

The preferred combination is a BHA using pre-packed screen sections coupled together by interposed stinger sections and including washpipe sections coupled together by sealing subsections. Forming both the screen and washpipe in sections advantageously facilitates the assembly of a BHA in the form of a string. An embodiment showing this arrangement will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic section of part of a BHk in string form; and Figure 2 is a schematic section of the bottom end of the B of figure 1.

As shown in figure 1 the DI comprises pre-packed screen 1, washpipe 2 and stinger section 3.

The screen has an outer fluid permeable wall 4, an inner permeable wall 5 and an annular layer of pre-packed particulate material 6 therebetween. Fluid can flow radially inwardly through the screen into the annual space 7 between the screen inner wall and the washpipe outer wall.

The washpipe has an external diameter smaller than the minimum internal diameter of the annular space. Two washpipe sections are shown coupled by a subsection of pipe 8. The ends of the coupling are joined to respective ends of sections of washpipe by conventional means.

Two screen sections are shown joined together by a stinger.

Conventional joining means may be used. The stinger has a portion of its length necked down, and this portion has a polished sealing surface 9 which can provide a contact seal to a pair of appropriately sized pipe rams (not shown).

Internally of the stinger, at the same level as the external sealing surface, there is an internal polished sealing surface. An annular seal 10 carried on a su & nit 8 forms a contact seal on this internal sealing surface. Thus, fluid from the annular space 7 cannot pass by the seal 10. Provided the pipe rams seal the outer surface of the stinger and provided the internal bore 11 of the washpipe is closed (e.g.

by a valve1 not shown) the B provides a complete seal for the well bore and prevents escape of well fluids under pressure.

In the embodiment of figure 1 an extra section is illustrated.

For practical purposes, especially when deploying a B in a severly deviated well, it is advantageous to guide the passage of the assembly in the well bore. In this embodiment a sub-unit is coupled into the string and carries a bow spring centraliser 12 which is collapsible to conform to the internal diameter of the well bore and which tends to hold the assembly centrally in the bore as it is deployed. However, use of a guide is not essential to the present invention.

As shown in figure 2, the bottom end to the B may carry a washpipe end assemly 21. The assembly is mounted on the end of the washpipe by means of a slip joint 22 which allows some relative movement between the assembly 21 and the remainder of the BH - this has the function of preventing end-load stresses being transmitted up the washpipe during deployment.

The assembly 21 carries a shear pin 23 or collet type arrangement which holds the washpipe tip during deployment but which can release the washpipe when it is to be recovered from the B once the BHA is in place.

The tip of the assembly 21 can be closed by means of a bottom flapper type assembly 24; this can be opened in situ by pumping fluid down the washpipe.

As shown, the internal bore 11 of the washpipe is closeable against flow up the bore by means of a non-return spring-and-ball check valve 25. Alternative types of check valves are for example flapper type valves and rupture disc valves (known in the art but not shown). Ideally, at least two sets of valves should be present to assure the safety of the washpipe against blow out.

A complete BHA according to this invention would have at its uppermost end a locking device for locking the Dt into the wellbore at the preselected point in the bore. Also, the Dt would have means at its uppermost end for engaging a recovery tool for recovering the EHk and/or recovering the washpipe.

It is hereagain stressed that the actual deployment and recovery of the Dt may equally well be made using wire line techniques or coiled tubing depending on the circumstances.

The presence of the washpipe is only of significant value during deployment and/or retrieval and recovery of the washpipe (leaving the pre-packed screen assembly in place) is contemplated. Clearly, if wire line techniques are used for the whole deployment and recovery operation the wash-through potential provided by the washpipe cannot be utilised.

Nonetheless the use of a wire line technique is not outside the scope of this invention.

Claims

1. A bottom hole assembly (BHA) which canEDrises: a) a pre-packed screen having an internal bore, b) an internal washpipe in the bore sealable against axial fluid flow, and c) means for locating and locking the assembly in a wellbore at a predetermined position, characterised in that: at least a part of the outer surface of the BHA provides a sealing surface onto which an appropriately sized pair of pipe seal rams can form a contact seal, the sealing surface being located at a portion of the B which is radially impermeable to well fluid, and further characterised in that there is a sealing means located at a portion of the B which is radially impermeable to well fluid, which sealing means is located in the annular space defined between the external surface of the washpipe and the internal surface of the pre-packed screen bore and which prevents axial fluid flow.

2. A B according to claim 1, wherein the external sealing surface is provided on a section of pipe in the form of a bar or "stinger" which is detachably connected in axial alignment with the pre-packed screen.

3. A DI according to claim 2, wherein the stinger has a portion of its length necked down and this portion has a polished outer sealing surface.

4. A I)tTA according to any one of claims 1 to 3, wherein the sealing means is at the same level as the external sealing surface.

5. A BHA according to any one of claims 1 to 4, wherein the sealing means is a sub-section of pipe forming a coupling pipe connectable between washpipe sections and which is capable of making a contact seal between its external surface and the surrounding internal surface of the pre-packed screen bore.

6. A BH according to any one of claims 1 to 5, wherein a seal is carried on the washpipe or coupling pipe sub-section and forms a contact seal against a polished internal surface of the pre-packed screen bore.

7. A BH as defined in any preceding claim, comprising a plurality of sections in an axially aligned string.

8. A B as defined in claim 7, comprising a plurality of pre-packed screen sections joined by interposed stinger sections.

9. A BHA as defined in claim 7 or 8, comprising a plurality of washpipe sections interposed by coupling pipe sub-sections providing sealing means.

10. A BHA substantially as hereinbefore described with reference to figure 1 or figure 2.

11. A method for deployment of a BHk as defined in any one of claims 1 to 10 in an oil/gas well under pressure which method is characterised by the steps of: a) mounting the BH in a closed-end cylindrical lubricator, b) making a sealed connection between the lubricator and well head, c) establishing fluid connection between the lubricator and well head by opening at least one well head valve thereby pressurising the internal space of the lubricator, d) lowering the B from the lubricator into the wellbore with a portion of the BHA reining within the well head at the location of the blow out prevention (BOP) stack adjacent pipe seal rams located in the well head which are then closed to engage and seal around the BHA, e) removing the lubricator and positioning a coiled tube injector or wire line unit above the well head, f) sealing the connection between the injector/wire line unit and the well head, g) releasing the seal rams capturing the B and, h) deploying the BH in the wellbore.

12. A method for deployment of a BHA as defined in any one of claims 1 to 10 in an oil/gas well under pressure which method is characterised by the steps of: a) mounting the Dt in a riser, b) mounting a blow out prevention (BOP) stack at the upper end of the riser to seal the riser and making a sealed connection between the riser and the well head, c) establishing fluid connection between the riser and the well head by opening at least one well head valve thereby pressurising the internal space of the riser, d) lowering the BEk from the riser into the wellbore with a portion of the Dt remaining within the well head at the location of the well head blow out prevention (BOP) stack adjacent pipe seal rams located in the well head which are then closed to engage and seal around the BHA, e) mounting an injector drive head for coiled tubing or a wire line unit over the BOP at the upper end of the riser, f) sealing the connection between the injector/wire line unit and the riser, g) releasing the seal rams capturing the BHk, and h) deploying the BHA in the wellbore.

13. A method according to either of claims 11 or 12, modified in that the steps are carried out in reverse order in order to retrieve the B from a welIbore.

14. A method substantially as hereinbefore described with reference to the deployment (or recovery) of a BHA as hereinbefore defined in an oil/gas well under pressure.