EP0454466A2 - Drillable well bore packing apparatus - Google Patents

Abstract

A downhole well bore packing apparatus (eg. a packer or bridge plug) includes a component which bears compressive loading and is made of plastics material. Such components can be lock ring housings (24), slips (28,54), slip wedges (32,46) or slip supports (24,58) for example. After use of the packing apparatus downhole, it can be relatively easily drilled out.

Description

• This invention relates to packing apparatus for use in a well bore and to its subsequent removal from the well bore.
• In the drilling or reworking of oil wells, it is often desirable to seal tubing or other pipe in the casing of the well. For example, when it is desired to pump cement or other slurry down tubing and force the slurry out into a formation, it becomes necessary to seal the tubing to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well. Packers and bridge plugs designed for these general purposes are well known in the art.
• When it is desired to remove many of these packers and plugs from a well bore, it is frequently simpler and less expensive to mill or drill the packer out rather than to implement a complex retrieving operation. In milling, a milling cutter is used to grind the packer or plug, or at least the outer components thereof, out of the well bore. Milling is a relatively slow process, but it can be used on packers or bridge plugs having relatively hard components such as erosion-resistant hard steel. One such packer is described in our U.S. patent specification no. 4,151,875 (Sullaway) and sold under the trademark EZ Disposal™ packer.
• In drilling, a drill bit is used to cut and grind up the components of the packer or bridge plug to remove it from the well bore. This is a much faster operation than milling, but it requires the packer or bridge plug to be made out of materials which can be accommodated by the drill bit. Typically, soft and medium hardness cast iron are used on the pressure bearing components, along with some brass and aluminium items. Packers of this type include the Halliburton EZ Drill^R and EZ Drill SV^R squeeze packers.
• The EZ Drill SV^R squeeze packer, for example, includes a lock ring housing, upper slip wedge, lower slip wedge, and lower slip support made of soft cast iron. These components are mounted on a mandrel made of medium hardness cast iron. The EZ Drill^R squeeze packer is similarly constructed. The Halliburton EZ Drill^R bridge plug is also similar, except that it does not provide for fluid flow therethrough.
• All of the above-mentioned packers are described in Halliburton Services Sales and Service Catalog No. 43, pages 2561-2562, and the bridge plug is disclosed in the same catalog on pages 2556-2557.
• The EZ Drill^R packer and bridge plug and the EZ Drill SV^R packer are designed for fast removal from the well bore by either rotary of cable tool drilling methods. Many of the components in these drillable packing devices are locked together to prevent their spinning while being drilled, and the harder slips are grooved so that they will be broken up into small pieces. Typically, standard "tri-cone" rotary drill bits are used which are rotated at speeds of about 75 to about 120 rpm. A load of about 5,000 to about 7,000 pounds (2270 to 3180 kg) of weight is applied to the bit for initial drilling and increased as necessary to drill out the remainder of the packer or bridge plug, depending upon its size. Drill collars may be used as required for weight and bit stabilization.
• These drillable packing devices have worked well and provide improved operating performance at relatively high temperatures and pressure. The packers and plug are designed to withstand pressures of about 10,000 psi (68.9 MPa) and temperatures of about 425°F (218°C) after being set in the well bore. Such pressures and temperatures require the cast iron components previously discussed.
• However, drilling out iron components requires certain techniques. Ideally, the operator employs variations in rotary speed and bit weight to help break up the metal parts and re-establish bit penetration should bit penetration cease while drilling. A phenomenon known as "bit tracking" can occur, wherein the drill bit stays on one path and no longer cuts into the packer plug. When this happens, it is necessary to pick up the bit above the drilling surface and rapidly recontact the bit with the packer or plug and apply weight while continuing rotation. This aids in breaking up the established bit pattern and helps to re-establish bit penetration. If this procedure is used, there are rarely problems. However, operators may not apply these techniques or even recognize when bit tracking has occurred. The results is that drilling times are greatly increased because the bit merely wears against the surface of the packer or plug rather than cutting into it to break it up.
• While cast iron components may be necessary for the high pressures and temperatures for which they are designed, it has been determined that most wells cemented throughout the world experience pressures less than 10,000 psi (68.9 MPa) and temperatures less than 425°F (218°C). In fact, in the majority of wells, the pressure is less than about 5,000 psi (34.5 MPa), and the temperature is less than about 250°F (121°C). Thus, the heavy duty metal construction of the previous packers and bridge plugs described above is not necessary for many applications, and if cast iron components can be eliminated or minimized, the potential drilling problems resulting from bit tracking might be avoided as well.
• We have now sucessfully tackled this problem by providing packers and bridge plugs wherein at least some of the components, including pressure bearing components, are made of plastics material rather than of metal. Such plastics components are much more easily drilled than cast iron, and new drilling methods may be employed which use alternative drill bits such as polycrystalline diamond compact bits, or the like, rather than standard tri-cone bits.
• According to the present invention, there is provided a well bore process which comprises the steps of positioning a well packing device into sealing engagement with the well bore; and subsequently drilling said device out of said well bore, characterised in that the device includes a component subject to substantially compressive loading which is made of a plastics material.
• The invention also includes a well bore packing apparatus which comprises a centre mandrel; slip means disposed on said mandrel for grippingly engaging said well bore, said slip means comprising a slip wedge made of plastics material; and packing means disposed on said mandrel for sealingly engaging said well bore when in a set position.
• The well bore packing apparatus of the present invention utilizes the same general geometric configuration of previously know drillable packers and bridge plugs, but replaces at least some of the metal components with engineering grade plastics which can still withstand the pressures and temperatures exposed thereto in many well bore applications. The plastic components are easier to drill out and allow the use of alternative drilling techniques to those previously known.
• A preferred component in the slip means to be made of plastics may be, for example, a lock ring housing, a slip, a slip wedge or a slip support. The slips themselves may require the addition of hardened inserts for the actual engagement with the well bore. The slip means may be an upper slip means disposed above the packing means, and the apparatus may further comprise a lower slip means disposed below the packing means, the lower slip means also comprising a component made of a plastic material.
• Most of the components of the slip means are subjected to substantially compressive loading when in a sealed operating position in the well bore, although some tensile loading may also be experienced. The centre mandrel typically has tensile loading applied thereto when setting the packer and when the packer is in its operating position. In another embodiment, the mandrel may also be made of a plastics material.
• One preferred plastics material for at least some of these components is a glass reinforced phenolic resin, preferably one having a tensile strength of about 18,000 psi (124 MPa) and a compressive strength of about 40,000 psi (276 MPa), although the invention is not intended to be limited to this particular plastic or to a plastic having these specific physical properties. The plastics materials are preferably selected such that the packing apparatus can withstand well pressures less than about 10,000 psi (68.9 MPa) and temperatures less than about 425°F (218°C). In one preferred embodiment, but not by way of limitation, the plastics materials of the packing apparatus are selected such that the apparatus can withstand well pressures up to about 5,000 psi (34.5 MPa) and temperatures up to about 250°F (121°C).
• In the method of the invention, the well packing device is preferably a packer or bridge plug, and the plastic component therein is preferably selected from at least one of the lock rings housings, slip wedges and slip supports as previously mentioned. The device may also include a component subject to at least some tensile loading, which is also made of plastics material. This plastics component subject to tensile loading may for example be the centre mandrel of the packing device.
• Preferably, the step of drilling is carried out using a polycrystalline diamond compact bit. Regardless of the type of drill bit used, the process may further comprise the step of drilling using a drill bit without substantially varying the weight applied to the drill bit.
• In another aspect of the invention, the well bore process can comprise the steps of positioning and setting a packer or plug in the well bore, a portion of the packer or plug being made of engineering grade plastic; contacting the packer or plug with well fluids; and then drilling out the packer or plug using a drill bit having no moving parts, such as a polycrystalline diamond compact bit. This or a similar drill bit might have been previously used in drilling the well bore itself, so the process may be said to further comprise the step of, prior to the step of positioning and setting the packer, drilling at least a portion of the well bore using a drill bit such as a polycrystalline diamond compact bit.
• In one preferred embodiment, the step of contacting the packer is at a pressure of less than about 5,000 psi (34.5 MPa) and a temperature of less than about 250°F (121°C), although higher pressures and temperatures may also be encountered.
• In order that the invention may be more fully understood, reference is made to the accompanying drawings, wherein:
• FIG. 1 illustrates an embodiment of packing apparatus of the present invention positioned in a well bore with a drill bit disposed thereabove; and
• FIG. 2 illustrates in axial section one embodiment of drillable packer made in accordance with the invention.
• Referring now to the drawings, and more particularly to FIG. 1, the well bore packing apparatus of the present invention is shown and generally designated by the numeral 10. Apparatus 10 is shown in a sealing, operating position in a well bore 12. Apparatus 10 can be set in this position by any manner known in the art such as setting on a tubing string or wire line. Adrill bit 14 connected to the end of a tool ortubing string 16 is shown above apparatus 10 in a position to commence the drilling out of apparatus 10 from well bore 12. Methods of drilling out apparatus 10 will be further discussed herein.
• Referring now to FIG. 2, the details of a squeeze packer embodiment 20 of packing apparatus 10 will be described. The size and configuration of packer 20 is substantially the same as the previously described prior art EZ Drill SV® squeeze packer. Packer 20 defines a generallycentral opening 21 therein.
• Packer 20 comprises acenter mandrel 22 on which most of the other components are mounted. Alock ring housing 24 is disposed around an upper end ofmandrel 22 and generally encloses alock ring 26.
• Disposed belowlock ring housing 24 and pivotally-connected thereto are a plurality ofupper slips 28 initially held in place by a retainingband 30. A generally conical upper slip wedge is disposed aroundmandrel 22 adjacent to upper slips 30.Upper slip wedge 32 is held in place onmandrel 22 by awedge retaining ring 34 and a plurality ofscrews 36.
• Adjacent to the lower end ofupper slip wedge 32 is an upper expandingshoe 38 connected to the upper slip wedge by apin 39. Below upper expandingshoe 38 are a pair ofend packer elements 40 separated bycenter packer element 42. A lower expandingshoe 44 is disposed adjacent to the lowermostend packer element 40.
• A generally conicallower slip wedge 46 is positioned aroundmandrel 22 adjacent to lower expandingshoe 44, and apin 48 connects the lower expanding shoe to the lower slip wedge.
• Lower slip wedge 46 is initially attached tomandrel 22 by a plurality ofscrews 50 and awedge retaining ring 52 in a manner similar to that forupper slip wedge 32. A plurality oflower slips 54 are disposed adjacent tolower slip wedge 46 are are initially held in place by a retainingband 56. Lower slips 54 are pivotally connected to the upper end of alower slip support 58.Mandrel 22 is attached tolower slip support 58 at threaded connection 60.
• Disposed inmandrel 22 at the upper end thereof is atension sleeve 62 below which is aninternal seal 64. A slidingvalve 66 is slidably disposed incentral opening 21 at the lower end ofmandrel 22 adjacent tofluid ports 68 in the mandrel.Fluid ports 68 inmandrel 22 are in communication withfluid ports 70 inlower slip housing 58. The lower end oflower slip support 58 is closed belowports 70.
• Slidingvalve 66 defines a plurality ofvalve ports 72 which can be aligned withfluid ports 68 inmandrel 22 when slidingvalve 66 is in an open position. Thus, fluid can flow throughcentral opening 21. As illustrated in FIG. 2, slidingvalve 66 is in a closed position whereinfluid ports 68 are sealed by upper and lower valve seals 74 and 76. Opening and closing ofvalve 66 is in a manner known in the art.
• Packer 20 is positioned in well bore 12 and set into gripping and sealing engagement therewith in a manner substantially identical to similar packers and plugs of the prior art. Full details of this setting operation are disclosed in the above-referenced U. S. Patent No. 4,151,875 to Sullaway, a copy of which is included herein by reference, so only a brief description of the setting operation will be described herein.
• By pulling upwardly onmandrel 22 while holdinglock ring housing 24, the lock ring housing is moved relatively downwardly along the mandrel which forcesupper slips 28 outwardly and shears screws 36 to pushupper slip wedge 32 downwardly againstpacker elements 40 and 42.Screws 50 are also sheared andlower slip wedge 46 is pushed downwardly towardlower slip support 58 to forcelower slips 54 outwardly. Eventually,upper slips 28 andlower slips 54 are placed in gripping engagement with well bore 12 andpacker elements 40 and 42 are in sealing engagement with the well bore. The action ofupper slips 28 and 54 prevent packer 20 from being unset. As will be seen by those skilled in the art, pressure below packer 20 cannot force the packer out of well bore 12, but instead, causes it to be even more tightly engaged.
• In prior art drillable packers and bridge plugs of this type,mandrel 22 is made of a medium hardness cast iron, andlock ring housing 24,upper slip wedge 32,lower slip wedge 46 andlower slip support 58 are made of soft cast iron for drillability. Most of the other components are made of aluminum, brass or rubber which, of course, are relatively easy to drill. Prior art upper andlower slips 28 and 54 are made of hard cast iron, but are grooved so that they will easily be broken up in small pieces when contacted by the drill bit during a drilling operation.
• As previously described, the soft cast iron construction oflock ring housing 24, upper andlower slip wedges 32 and 46, andlower slip support 58 are adapted for relatively high pressure and temperature conditions, while a majority of well applications do not require a design for such conditions. Thus, the apparatus of the present invention, which is generally designed for pressures lower than 10,000 psi (68.9 MPa) and temperatures lower than 425°F (218°C), utilizes engineering frade plastics for at least some of the components. For example, one embodiment of the apparatus is designed for pressures up to about 5,000 psi (34.5 MPa) and temperatures up to about 250°F (121°C), although the invention is not intended to be limited to these particular conditions.
• In a first preferred embodiment, at least some of the previously soft cast iron components of the slip means, such as thelock ring housing 24, upper andlower slip wedges 32 and 46 andlower slip support 58 are made of engineering grade plastics. In particular, upper andlower slip wedges 32 and 46 are subjected to substantially compressive loading. Since engineering grade plastics exhibit good strength in compression, they make excellent choices for use in components subjected to compressive loading.Lower slip support 58 is also subjected to substantially compressive loading and can be made of engineering grade plastic when packer 20 is subjected to relative low pressures and temperatures.
• Lock ring housing 24 is mostly in compression, but does exhibit some tensile loading. However, in most situations, this tensile loading is minimal, andlock ring housing 24 may also be made of an engineering grade plastic of substantially the same type as upper andlower slip wedges 32 and 46 and alsolower slip housing 58.
• Upper andlower slips 28 and 54 may also be of plastic in some applications. Hardened inserts for gripping well bore 12 when packer 20 is set may be required as part of the plastic slips.
• Lock ring housing 24,upper slip wedge 32,lower slip wedge 46, andlower slip housing 58 comprise approximately 75% of the cast iron of the prior art squeeze packers. Thus, replacing these components with similar components made of engineering grade plastics will enhance the drillability of packer 20 and reduce the time and cost required therefor.
• Mandrel 22 is subjected to tensile loading during L setting and operation, and many plastics will not be acceptable materials therefor. However, some engineering plastics exhibit good tensile loading characteristics, so that construction ofmandrel 22 from such plastics is possible. Reinforcements may be provided in the plastic resin as necessary.
Example
• A packer 20 was constructed in whichupper slip wedge 32 andlower slip wedge 46 were constructed by molding the parts to size from a phenolic resin plastic with glass reinforcement. The specific material used was Fiberite 4056J manufactured by Fiberite Corporation of Winona, Minnesota. This material is classified by the manufacturer as a two stage phenolic with glass reinforcement. It has a tensile strength of 18,000 psi (124 MPa) and a compressive strength of 40,000 psi (276 MPa).
• The test packer 20 held to 8,500 psi (58.6 MPa) without failures to the wedges, more than sufficient for most well bore conditions.
Drilling Out The Packer Apparatus
• Drilling out any packer apparatus 10, such as the illustrated packer 20, may be carried out by using a standard drill bit at the end oftubing string 16. Wire line drilling may also be used. With a standard "tri-cone" drill bit, the drilling operation is similar to that of the prior art except that variations in rotary speed and bit weight are not critical because the plastic materials are considerably softer than prior art cast iron, thus making packer 20 much easier to drill out. This greatly simplifies the drilling operation and reduces the cost and time thereof.
• In addition to standard tri-cone drill bits, and particularly if packer 20 is constructed utilizing engineering grade plastics formandrel 22 as well as forlock ring housing 24,upper slip wedge 32,lower slip wedge 46 andlower slip housing 58, alternate types of drill bits may be used which were impossible for packers constructed substantially of cast iron. For example, polycrystalline diamond compact (PDC) bits may be used.Drill bit 14 in FIG. 1 is illustrated as a PDC bit. Such drill bits have the advantage of having no moving parts which can jam up. Also, if the well bore itself was drilled with a PDC bit, it is not necessary to replace it with another or different type bit in order to drill out packer 20.
• While a specific squeeze packer configuration of packing apparatus 10 has been described herein, it will be understood by those skilled in the art that other squeeze packers of this general configuration mentioned may also be constructed utilizing components selected of engineering grade plastics. Additionally, bridge plugs of this general configuration may also be manufactured with plastic components.
• It will be seen, therefore, that the well bore packing packer apparatus and methods of drilling thereof of the present invention are well adapted to carry out the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment of the apparatus and various drilling methods have been discussed for the purposes of this disclosure, numerous changes in the arrangement and construction of parts and the steps of the methods may be made by those skilled in the art.

Claims (10)

1. A well bore process which comprises the steps of positioning a well packing device (10) into sealing engagement with the well bore (12); and subsequently drilling said device out of said well bore, characterised in that the device includes a component subject to substantially compressive loading which is made of a plastics material.
2. A process according to claim 1, wherein said device is a packer or a bridge plug.
3. A process according to claim 1 or 2, wherein said component in said device is a lock ring housing (24), slip (28,54), slip wedge (32,46) or slip support (24,58).
4. A process according to claim 1,2 or 3, wherein the device includes a component which is subject to at least some tensile loading and which is made of a plastics material.
5. A process according to claim 4, wherein said component subject to tensile loading is a centre mandrel (22) of said device.
6. A process according to any of claims 1 to 5, wherein said step of drilling is carried out with a polycrystalline diamond compact bit (14).
7. A well bore packing apparatus (10) which comprises a centre mandrel (22); slip means (28,32,46,54) disposed on said mandrel for grippingly engaging said well bore, said slip means comprising a slip wedge (32,46) made of a plastics material; and packing means (42) disposed on said mandrel for sealingly engaging said well bore when in a set position.
8. Apparatus according to claim 7, wherein said slip means comprises slips (28,54) also made of plastics material.
9. Apparatus according to claim 7 or 8, wherein said mandrel is also made of a plastics material.
10. Apparatus according to claim 7,8 or 9, wherein said plastics material is a glass reinforced phenolic resin.

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