Patent Publication Number: US-6220349-B1

Title: Low pressure, high temperature composite bridge plug

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to downhole tools for use in high temperature wells, and more particularly, to a high temperature bridge plug made primarily of non-metallic composite materials. 
     2. Description of the Prior Art 
     In the drilling or reworking of oil wells, a great variety of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well, such as when it is desired to pump cement or other slurry down tubing and force the slurry out into a formation. It then becomes necessary to seal the tubing with respect 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 such downhole tools from a wellbore, it is frequently simpler and less expensive to mill or drill them out rather than to implement a complex retrieving operation. In milling, a milling cutter is used to grind the packer or plug, for example, or at least the outer components thereof, out of the wellbore. 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 disclosed in U.S. Pat. No. 4,151,875 to Sullaway, assigned to the assignee of the present invention and sold under the trademark EZ DISPOSAL packer. Other downhole tools in addition to packers and bridge plugs may also be drilled out. 
     In drilling, a drill bit is used to cut and grind up the components of the downhole tool to remove it from the wellbore. This is a much faster operation than milling, but requires the tool to be made of materials which can be accommodated by the drill bit. Soft and medium hardness cast iron have been used on the pressure-bearing components, along with some brass and aluminum items. Packers of this type include the Halliburton EZ DRILL® and EZ DRILL SV® squeeze packers. 
     The EZ DRILL® packer and bridge plug and the EZ DRILL SV® packer are designed for fast removal from the wellbore by either rotary or 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 can be broken up in small pieces. Typically, standard “tri-cone” rotary drill bits are used. 
     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 downhole tool. 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 result is that drilling times are greatly increased because the bit merely wears into the surface of the downhole tool 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 many wells experience pressures less than 10,000 psi and temperatures less than 425° F. Thus, the heavy-duty metal construction of some previous downhole tools, such as packers and bridge plugs described above, is not necessary for many applications. 
     For such well conditions, tools have been designed wherein at least some of the components, including slips and pressure-bearing components, are made at least partially of non-metallic materials, such as engineering-grade plastics. Such tools are shown in U.S. Pat. Nos. 5,271,468, 5,224,540, and 5,390,737, assigned to the assignee of the present invention. These tools are sold under the trademark FAS DRILL®. The plastic components in these tools 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. 
     These prior tools using non-metallic components utilize two sets of slips, one on each side of the packing elements to lock the tool in the wellbore and prevent it from unsetting. This is particularly helpful in high-pressure situations to keep the tool from being undesirably moved in the wellbore. However, not all well conditions have these pressure levels, and the present invention is designed to address such less severe well conditions. The present invention utilizes a single set of slips to hold the tool in the wellbore while a plurality of ratchets keep the tool from unsetting. This results in a cost reduction compared to current plugs and packers. 
     SUMMARY OF THE INVENTION 
     The present invention may be described as a packing apparatus for use in a wellbore and comprising a mandrel, a packing element disposed on the mandrel for sealing engagement with the wellbore when in a sealing position, a wedge disposed on the mandrel and having a wedge tapered surface thereon, a slip disposed on the mandrel for locking engagement with the wellbore when the packing element is in the sealing position and having a slip tapered surface engaging the wedge tapered surface, a ratchet body disposed on the mandrel and defining a ratchet cavity therein, and a ratchet disposed in the ratchet cavity and having teeth thereon adapted for locking engagement with the mandrel. Preferably, the ratchet body, slips, wedge and mandrel are made of substantially non-metallic materials. The ratchet itself is preferably made of a metallic material. 
     In a preferred embodiment, the mandrel has a shoulder thereon adjacent to one side of the packing element, and the wedge is disposed on an opposite side of the packing element from the shoulder. The mandrel is relatively movable with respect to the wedge for longitudinally compressing the packing element and expanding it radially outwardly to the sealing position. The wedge tapered surface is on an opposite side of the wedge from the packing element. 
     The ratchet body is in constant contact with an end of the slip. This end of the slip is on an opposite side of the slip from the slip tapered surface. There is substantially no relative movement between the ratchet body and the slip in a longitudinal direction with respect to the mandrel. 
     The invention may also be described as a packing apparatus for use in a wellbore and comprising a mandrel, a packing element disposed on the mandrel for sealing engagement with the wellbore when in a sealing position, a wedge disposed on the mandrel and having a substantially planar wedge tapered surface thereon, and a slip disposed on the mandrel and having a substantially planar slip tapered surface thereon engaging the wedge tapered surface. Prior slips and wedges use curvilinear surfaces which, for non-metallic materials, have been found to sometimes bind and not work smoothly. The planar surface contact between the wedge and slip of the present invention avoids this binding problem. 
     Stated in another way, the present invention is a packing apparatus for use in a wellbore and comprising a mandrel, a packing element disposed on the mandrel for sealing engagement with the wellbore when in a sealing position, a wedge disposed on the mandrel and having a substantially planar wedge tapered surface thereon, a slip disposed on the mandrel and having a substantially planar slip tapered surface thereon engaging the wedge tapered surface, a ratchet body disposed on the mandrel and defining a ratchet cavity therein, and a ratchet disposed in the ratchet cavity and having teeth thereon adapted for locking engagement with the mandrel for holding the mandrel in a set position with respect to the packing element. The slip and wedge are made of non-metallic materials, and preferably, the ratchet body and mandrel are also made of non-metallic materials. The ratchet is metallic. 
     Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiment is read in conjunction with the drawings which illustrate such embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B show a longitudinal cross section of the low pressure, high temperature composite bridge plug of the present invention as it is run into a wellbore. 
     FIG. 2 is a top end view of the bridge plug. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and more particularly to FIGS. 1A and 1B, the low pressure, high temperature composite bridge plug of the present invention is shown and generally designated by the numeral  10 . Apparatus  10  is designed to operate in a wellbore  12  having a casing  14  therein. Casing  14  has an inner surface  16 . 
     Apparatus  10  is run into wellbore  12  on a setting tool  18  of a kind generally known in the art. Setting tool  18  may be an electric wireline tool, a slick line tool, a coiled tubing tool or a mechanical setting tool. 
     Apparatus  10  comprises a central mandrel  20  having a central opening  22  therein. 
     At the upper end of central opening  22  in mandrel  20  is an enlarged bore  24  intersected by four radially oriented holes  26 . 
     Setting tool  18  has a rod portion  28  which is retained in bore  24  of mandrel  20  by four shear pins  30  which are disposed through holes  26 . 
     In the illustrated embodiment, apparatus  10  is a bridge plug and has a mandrel plug  32  disposed in an upper portion of central opening  22 . Mandrel plug  32  is held in place by pins  34 . A sealing means, such as an O-ring  36 , provides sealing engagement between mandrel plug  32  and mandrel  20 . If the application requires fluid flow through apparatus  10 , mandrel plug  32  and pins  34  are simply omitted so that fluid may flow through central opening  22  of mandrel  20 . 
     A ratchet body  38  is disposed around the upper end of mandrel  20  and connected thereto by a pin  40 . Setting tool  18  also has a setting sleeve  39  which engages ratchet body  38  at an upper end  41  thereof. 
     Ratchet body  38  defines a tapered or conical bore  42  therein. A plurality of ratchets  44  are disposed in conical bore  42  in ratchet body  38 . Thus, conical bore  42  may also be described as a ratchet cavity  42 . Ratchets  44  are loosely held together as a unit by a retainer ring  46 . Each ratchet  44  has a plurality of radially inwardly oriented ratchet teeth  48  thereon. Ratchet teeth  48  are adapted for gripping and locking engagement with outer surface  50  of mandrel  20  when apparatus  10  is in a set position, as further described herein. 
     Ratchet body  38  has a lower surface  51  which extends radially and tapers slightly upwardly with respect to mandrel  20 . Below ratchet body  38  are a plurality of slips  52  which are held together as a unit around mandrel  20  by an upper retainer ring  54  and a lower retainer ring  56 . Each slip  52  has a plurality of hard buttons or inserts  58  molded therein which are adapted for gripping engagement with inner surface  16  of casing  14  when apparatus  10  is in a set position, as further described herein. 
     Upper ends  60  of slips  52  are tapered slightly to conform with lower end  51  of ratchet body  38 . Upper end  60  of slips  52  are in constant contact with lower end  51  of ratchet body  38 . 
     A wedge  62  is shearably attached to mandrel  20  by a shear pin  64 . Wedge  62  has a plurality of tapered flat or planar surfaces  66 , each planar surface corresponding to a slip  52 . Tapered planar surfaces  66  on wedge  62  extend upwardly into slips  52  and engage a corresponding tapered flat or planar surface  68  on the lower inside of each slip  52 . As will be further described herein, the planar contact between surfaces  68  on slips  52  with surfaces  66  on wedge  62  prevents binding which can be a problem on prior art curvilinear slip and wedge surfaces, at least when the components are made of non-metallic materials. 
     Below lower end  70  of wedge  62  is an elastomeric packer element or seal  72 . 
     Referring now also to FIG. 1B, packer element  72  is supported on its lower end by an upwardly facing shoulder  74  on mandrel  20 . Mandrel  20  has a slanted lower end  76  which helps guide apparatus  10  past small obstructions in wellbore  14  as apparatus  10  is run into the well on setting tool  18 . 
     Apparatus  10  is designed to be a low pressure, high temperature composite bridge plug, and mandrel  20 , mandrel plug  32 , ratchet body  38 , slips  52  (except for inserts  58 ), and wedge  62  are preferably made of composite materials such as engineered plastics. Such materials allow for apparatus  10  to be easily drilled out of wellbore  12  when no longer required, as does the soft elastomeric material of packer element  72 . Ratchets  44  are preferably metallic, but are small enough that they do not present drilling problems. 
     In the preferred embodiment, the materials have an operating temperature of up to 350° F. The bridge plug design will hold pressure up to 2,000 to 3,000 psi from below the plug. This allows for cement to be placed on top of the plug. 
     OPERATION OF THE INVENTION 
     In operation, apparatus  10  is connected to setting tool  18 , as previously described, and run into casing  14  in wellbore  12  to the desired location. Setting tool  18  is actuated to cause rod  28  to pull upwardly on mandrel  20  while setting sleeve  39  holds ratchet body  38  and ratchet  44  in place and prevents the ratchet body and ratchets from moving. This upward pull on mandrel  20  forces wedge  62  upwardly inside slips  52 . The tapered, planar contact between surfaces  66  on wedge  62  and surfaces  66  on slips  52  cause the slips to be moved smoothly radially outwardly, breaking or disengaging upper retainer ring  54  and lower retainer ring  56 . Eventually, slips  52  are forced outwardly far enough that inserts  58  grippingly engage inner surface  16  of casing  14  adjacent thereto which acts to hold apparatus  10  in place in the wellbore. 
     As slips  52  are thus moved radially outwardly, it will be seen that upper ends  60  of the slips slide along lower end  51  of ratchet body  38 . Although these surfaces are slightly tapered as previously described, there is substantially no relative longitudinal movement between the slips and ratchet body. 
     Once slips  52  are set, wedge  62  can no longer move upwardly with respect to the slips, and further upward pull on mandrel  20  results in shearing of shear pin  64  so that the mandrel is pulled upwardly with respect to wedge  62 . It will be seen by those skilled in the art that shoulder  74  on mandrel  20  is thus moved upwardly toward lower end  70  of wedge  62  which compresses packer element  72 , expanding it radially outwardly into sealing engagement with inner surface  16  of casing  14 . 
     Once apparatus  10  has thus been set into gripping and sealing engagement with casing  14  in wellbore  12 , actuation of setting tool  18  is stopped. The elastomeric material of packer element  72  will bias mandrel  20  downwardly unless the mandrel is otherwise held in place. This is accomplished by gripping engagement of teeth  48  in ratchets  44  which hold mandrel  20  to keep it from sliding back down. Because of the wedging action of ratchets  44  in conical bore  42  and ratchet body  38 , the greater the downward force applied to mandrel  20 , the greater the gripping engagement of teeth  48  on outer surface  50  of the mandrel. 
     Once packer element  72  is sufficiently compressed to expand outwardly into sealing engagement with inner surface  16  of casing  14 , further loading on mandrel  22  by rod  28  of setting tool  18  will shear shear pins  30  which releases the setting tool from apparatus  10  so that the setting tool may be removed from wellbore  12 , leaving apparatus  10  therein. 
     As previously discussed, the composite materials of most of the components of apparatus  10  allow it to be quickly and easily drilled out of wellbore  14  when it is no longer of use. 
     It will be seen, therefore, that the low pressure, high temperature composite bridge plug of the present invention is well adapted to carry out the ends and advantages mentioned as well as those inherent therein. While the presently preferred embodiment of the apparatus has been shown for the purposes of this disclosure, numerous changes in the arrangement and construction of parts may be made by those skilled in the art. All such changes are encompassed within the scope and spirit of the appended claims.