Abstract:
A method and apparatus of plugging and abandoning a well includes using a plug apparatus and installing bentonite elements in an oil well production casing having a bore. The plug apparatus is lowered into the production casing bore to a selected elevation using a slick line or the like. The apparatus has a tool body and slip dies that are movably mounted upon the tool body to move between extended and retracted positions. Afer the tool body is positioned at a selected location within the casing bore, tension is applied to the slick line to move the slip dies to an extended position wherein the slip dies engage the casing and secure the tool body in a desired location. The casing bore is then displaced with water above the tool body. Bentonite elements are then dumped into the water filled wellbore. The bentonite elements are allowed to swell to form a plug. The tool body can be retrieved from the casing bore if desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Priority of U.S. Provisional Patent Application Ser. No. 60/428,428, filed Nov. 21, 2002, incorporated herein by reference, is hereby claimed. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     REFERENCE TO A “MICROFICHE APPENDIX” 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to down hole oil well tools. More particularly, the present invention relates to a well abandonment plug apparatus that can be anchored at a selected position in a well and retrieved at a later time if desired. 
     2. General Background of the Invention 
     The present invention provides a plug that can be used in the Zonite (treated bentonite) abandonment technique of stripper wells. The design of the present invention is for a non-sealing plug to act as a base for the installation of the Zonite for the wells primarily in California and for a sealing plug for utilization of the wells primarily in New Mexico and Texas. The well plugs of the present invention are retrievable. The slickline abandonment plug of the present invention can be used with conventional slickline or wire rope running tools. 
     BRIEF SUMMARY OF THE INVENTION 
     Chevron Corporation (prior to its merger with Texaco in the fall of 2001) became involved with the development of an alternative abandonment technique for “stripper” wells in California. Stripper wells reference wells that require artificial lift to produce and have producing zones in which the formation pressure has become less than the original (virgin) pressure. 
     The technique developed involved the use of bentonite in the plugging process instead of cement. An integral part of the technique involves setting of a device inside the production casing that would act as a base for the Zonite installation. 
     The conventional method of abandoning stripper wells involves the use of cement and electric line set plugs. This process is relatively slow and expensive. Additionally, the cement slurry set in the wellbore has a high specific gravity and low viscosity. When a cement plug is set across perforations, because of its weight and viscosity, cement will fall through the perforations into the formation prior to setting up. Regulations require a plug of substantial height above the perforations (the “isolation plug”). Several attempts can be required to obtain a plug that will suffice. To counter this, an electric line set plug is sometimes set above the perforations to prevent the cement from dropping into the formation, adding significantly to the cost of the abandonment. 
     Regulations require a second plug to be set in the wellbore just below ground level, namely a “surface plug”. Ensuring this plug stays in place also required an electric line plug. The abandonment is completed by digging out around the wellhead, cutting off the casing strings (e.g. with a cutting torch) and backfilling the location. All plugs set must be tested either with pressure or by setting weight on the plug. 
     The abandonment technique that is being used and marketed involves the use of Zonite (e.g., a treated bentonite) rolled into balls approximately the size of a golf ball. After establishing a base for the installation of the Zonite (the plug of the present invention was designed to function as the base) the wellbore is displaced with fresh water and the Zonite balls are dumped in to the wellbore. The Zonite settles to the base, which is provided by the plug, and begins hydrating in the fresh water, thereby swelling up to form the isolation plug required by regulations. This plug is tested by tagging it with either slickline, the sand line or jointed pipe. The surface plug is set &amp; tested in the same manner and the remainder of the plugging and abandonment (P&amp;A) is concluded as with the conventional method. 
     The slick line abandonment plug of the present invention provides a design based upon the needs of the Zonite abandonment technique. The plug of the present invention was originally required to be a “base” for the Zonite installation. Problems encountered led to the additional requirement for the plug to be retrievable. In the effort to obtain regulatory approval in states other than California, the additional requirement of having sealing capability was added to plug. The plug of the present invention and its sealing variation have been designed and tested and meet these requirements. 
     The present invention provides a method and apparatus for plugging and abandoning a well. The present invention provides a method of installing bentonite elements in an oil well production casing having a bore. As part of the method, a tool body is lowered into the production casing bore to a selected elevation using a lifting and lowering device such as a slick line or wire line. The tool body has sockets that hold slip dies that are movably mounted in the sockets between extended and retracted positions. 
     At least some of the slip dies are moved to the extended position when the tool body reaches a selected elevation within the well. In the extended position, the slip dies engage the casing wall, anchoring the tool body to the selected elevational position. 
     The casing bore is displaced with water above the tool body. Bentonite elements are dumped into the water filled well bore. The bentonite elements are allowed to swell to form a plug. As part of the method, at least some of the slip dies are maintained in a retracted position when the tool body is lowered into the well. 
     A retainer can be used to hold the slip dies in the retracted position during lowering into the well. Shear pins can be part of the tool body and retainer. By lifting up on the slick line or wire line, these shear pins can be sheared to release the slips for enabling the tool dies to engage the casing. 
     In the preferred embodiment, springs can be used to urge the slick dies to the extended position. 
     As part of the method, the bentonite elements are preferably between about one and two inches in diameter. 
     The apparatus of the present invention provides a well abandonment apparatus that includes a tool body that is configured to be lowered into a production casing bore to a selected elevation. The tool body has upper and lower end portions. 
     A plurality of slip dies are attached to the tool body at sockets provided on the tool body. The sockets can be tubular passages that preferably form an acute angle with the central longitudinal axis of the tool body. Each slip is movable between a retracted and an extended position. The slip dies move to the extended position to engage the casing and anchor the tool body at a selection elevation within the well. Bentonite elements can be provided that are placed in the well above the tool body. These bentonite elements swell when contacted with the water enabling a plug to be formed above the tool body. 
     A running tool can be provided that holds the upper slip dies in the retracted position when the tool body is lowered into the well bore. 
     A slip activating means can be provided for moving the slip dies while the tool body is in the well bore to the extended position. This slip activating means can be, for example, shear pins that are sheared when the slick line is pulled in a upward direction. In such a situation, the lower slip dies are already extended when running to the well in a downward direction. In that direction, the slip dies do not bite into the well casing wall because the direction of travel urges them to retract back into their sockets. However, when the direction of travel the tool body is attempted to reverse by pulling up on the slick line or wire line, the lower slips engage the casing wall and hold the tool body at a selected position. Continued upward tension applied to the slick line or wire line causes shear pins to shear, separating the retainer from the tool body enabling the upper slips to expand to the extended position and engage the casing wall. In this position, the tool body is anchored so that it will not travel in either direction until it is time to be retrieved. 
     The tool body of the present invention can be retrieved. In the preferred embodiment, retainers are provided that hold the slips in a maximum extended position. However, when sufficient upward tension is applied to the wire line or slick line, a lower opening or recess provided at the lower end portion of the tool body enables a slight deformation inwardly of the lower end portion of the tool body so that the slips can move downwardly and cut the retainer. The retainer can be on o-ring, for example. The lower slips (and their springs) then fall into the well bore, separating from the tool body so that it can be retrieved. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements and wherein: 
         FIG. 1  is a perspective view of the preferred embodiment of the apparatus of the present invention; 
         FIG. 2  is a top view of the preferred embodiment of the apparatus of the present invention; 
         FIG. 3  is a fragmentary view of the preferred embodiment of the apparatus of the present invention showing one of the slip portions; 
         FIG. 4  is fragmentary view of the preferred embodiment of the apparatus of the present invention showing the spring portion; 
         FIG. 5  is an exploded perspective view of the preferred embodiment of the apparatus of the present invention; 
         FIG. 6  is a sectional elevation view of the preferred embodiment of the apparatus of the present invention showing the slips in an extended, gripping position; 
         FIG. 7  is a partial perspective view of the preferred embodiment of the apparatus of the present invention showing the slip retainer; 
         FIG. 8  is a sectional elevation view of the preferred embodiment of the apparatus of the present invention showing the upper slips in a retracted, running position; 
         FIG. 9  is a sectional elevation view showing the preferred embodiment of the apparatus of the present invention positioned inside a wellbore during insertion into the well; 
         FIG. 10  is a sectional elevation view of the preferred embodiment of the apparatus of the present invention showing deployment of the apparatus at a selected position within a wellbore; 
         FIG. 11  is a partial sectional elevation view of the preferred embodiment of the apparatus of the present invention illustrating retrieval of the tool body; 
         FIG. 12  is a another sectional elevation view of the preferred embodiment of the apparatus of the present invention illustrating retrieval of the tool body; and 
         FIG. 13  is a schematic sectional elevation view showing deployment of the apparatus of the present invention in a well as part of a well abandonment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 ,  5 - 6 ,  8  and  9 - 10  show the preferred embodiment of the apparatus  10  of the present invention. Well plug apparatus  10  provides a plug body  11  having upper end portion  12  and lower end portion  13 . A neck fitting  14  is attached to upper end  12  at socket  20 . Socket  20  provides internal threads that engage the externally threaded section  21  of neck fitting  14 . 
     Neck fitting  14  has a transverse annular shoulder  15  with larger diameter cylindrical section  17  above it and smaller diameter cylindrical section  16  below it. Conical section  18  can be provided above cylindrical section  17 . Upper end portion  12  of plug body  11  has a transverse surface  19  that communicates with socket  20 . 
     Plug body  11  has a plurality of ribs  22  with a plurality of grooves  23  spaced between the ribs  22 . Each of the ribs  22  is longitudinally extending. The ribs  22  are circumferentially spaced and extend radially as shown in the top view of FIG.  2 . Every other one of the grooves  23  communicates with a slip socket  33  for receiving one of the slip dies  28  or  29 . In the preferred embodiment, there are three upper slip dies  28  and three lower slip dies  29 . Each of the slip sockets  33  forms on an angle (see  FIGS. 6 and 8 ) with the central longitudinal axis  55  of the plug body  11  and neck fitting  14 . The slips are movable between an extended position that is shown in  FIG. 6 and a  retracted position that is shown for the upper slip  28  in FIG.  8 . 
     Springs  35  are contained within each of the slip sockets  33 . The springs  35  urge each of the slips  28  or  29  to the extended position shown in FIG.  6 . When in the position of  FIG. 6 , the slips  28 ,  29  prevent movement of the plug body  11  in either direction when the apparatus  10  is contained in a well. In  FIG. 10 , the upper slips  28  and the lower slips  29  are urged by springs  35  to bite into the casing by engaging the well casing internal wall surface  40 . 
     When the slips  28  or  29  are in the extended position of  FIG. 6 , upper  25  and lower  27  O-rings act as stops to prevent the slips  28  or  29  from being pushed completely out of the slip sockets  33  by the springs  35 . The springs  35  engage a slip  28  or  29  at one end portion of the spring  35  and at the other end portion of the spring  35  engage a closed end  34  of the slip socket  33 . 
     The plug body  11  can be sized and shaped to run inside casing and tubing in sizes ranging for example from 2-⅜″ tubing to 13-⅜″ casing. The plug tool  10  can be designed as “one size fits all” for each size (OD—outside diameter) of tubing or casing. Plug body  11  can be machined from bar stock. After machining the body  11 , springs  35 , slip dies  28 ,  29 , shear pins  51  and landing pin or fishing neck  14  are assembled to the tool body  11 . 
     The tool  10  can be run into a wellbore  41  on slick line or wire rope  44 . As it is run into the well, slip dies  28 ,  29  are recessed into radial grooves  23  and slip sockets  33  in the plug body  11  (see FIGS.  8 - 9 ). The upper slips  28  are recessed into sockets  33  using retainer  43 . The lower slips  29  are simply urged into their sockets  33  because the tool body  11  is traveling in the direction of arrows  54 , wherein friction with wall surface  40  pushes lower slips  29  into their sockets  33 . Upon reaching the desired depth, the tool  10  is set by merely pulling up on the wire rope  44  and tool body  11  at neck fitting  14  thereby shearing the shear pins  51  to enable removal of retainer  43  and allowing the slip dies  28  to engage the well casing wall  40 . 
     The plug  10  can be retrieved at a later time by latching the fishing neck  14  with a commercially available retrieving tool  60  or overshot (which can be run on a slick line, wire rope  44  or jointed pipe) and pulling up on the tool  10  until the lower slips  29  cut lower o-ring  27 , releasing the lower slips  29  (see FIG.  12 ). The plug body  11  can then be pulled from the wellbore  41 . 
     The plug body  11  can be manufactured of steel, aluminum or plastic. A steel version can be machined, as with the aluminum, or forged, or a plastic version can be molded. 
     This landing pin or neck  14  has two primary functions. A first function is to retain the running tool body  11  at annular shoulder  15  parallel to the nose of the landing pin  14  during insertion (see FIGS.  9 - 10 ). The shear pins (or screws)  51  can be part of the landing pin or neck  14 . 
     A threaded portion  21  on the landing pin  14  attaches to the plug body  11  at internal threads in socket  20  to form a threaded connection. Threads at  20  on the running tool body  11  are right hand threads (which means screwing the male threads to the female threads in a clockwise manner to attach). 
     A second function of landing pin  14  is for retrieval purposes see  FIGS. 11-12 . Common wireline retrieval tools can be used to attach to landing pin  14 . Basically, landing pin  14  is a standard receptacle used in the oil industry (a standard connector). 
     The landing pin  14  is generally referred to as the “fishing neck” in generic oilfield terminology. A “landing tool” assembly is generically known as the “running tool”. A retrieval tool is called the “pulling tool”. 
     The primary purpose of the plug body  11  is to facilitate the functions of the slip dies  28 ,  29  and the springs  35 . Radial grooves or splines  23  allow fluid to bypass the outside diameter of the plug body  11 . Incorporated within three of the grooves  23  on each side are slip sockets  33  used to hold the slip dies  28 ,  29  and springs  35 . There can be a total of twelve (12) grooves  23  in the plug body  11 . Six of the grooves  23  are utilized by the slip dies  28 ,  29  and springs  35 . 
     The upper end  12  of the plug body  11  has female threads at socket  20  which the landing pin  14  attaches to at a threaded connection. Female threads in socket  20  can be concentric with the outside diameter of the body  11 . 
     A bottom opening, receptacle, or socket  36  is provided with a threaded bore section  39  that can be used to facilitate (or attach) an optional sealing device. This tapered counter bore or socket  36 , 39  located at the bottom of the plug body  11  has two primary functions. Firstly, to give flexibility characteristics when retrieving the plug body  11 . Fingers  37  and slots  38  are next to socket  36 . Fingers  37  flex inwardly toward socket  36  when the tool body  11  is to be removed (see FIG.  12 ). Secondly, it can be used for an optional unidirectional seal assembly. 
     A mating plug assembly (not shown) conforms to the tapered counter bore  36 , 39  which in turn restricts the external slip die pockets  33  to flex inward. The slip dies  28 ,  29  retain the plug body  11  from moving or disengaging the plug body  11 . 
     A perpendicular hole can be located on the outside diameter of the plug body and communicating with the outside of the plug body  11 , and intersecting the threaded bore  36 ,  39 . The purpose of this transverse or perpendicular bore is to allow differential pressure to inflate an optional seal assembly. 
     External grooves  24 ,  26  located respectively on opposite ends (upper  12  and lower  13 ) of the plug body  11  are to hold the O-rings  25 ,  27  respectively which retain the slip dies  28 ,  29  and springs  35 . 
     The slip dies  28 ,  29  are designed with a round or cylindrical primary base  30  having circular ends in order to fit within the grooves  23  of the plug body  11 . Incorporated within the round base  30  of the slip die is a rectangular boss  31  in which machined teeth  32  are located. The teeth  32  are designed to bite/grasp the internal surface  40  of the casing, which in turn, retains the plug body  11  within the casing. The greater the force that is applied to the slip dies  28 ,  29 , the tighter the grip or teeth engagement with the casing inner surface  40 . 
     The plug body  11  requires opposing slip dies  28 ,  29  positioned on each side of body  11 . When all slip dies  28 ,  29  are engaged, the plug body  11  is not allowed to move in either direction. In the retrieval process this only applies in one direction. 
     The bottom end  13  of the plug body  11  is designed to bend or collapse under the excessive force which will in turn allow the lower bottom slip dies  29  to shear the bottom O-ring  27  (see  FIG. 12 ) and become non-functional and therefore drop down into the well bore  41 . 
     The teeth  32 , which are the integral part of the slip die  13  are designed to be harder than all grades of casing. This design is to ensure positive engagement (grip) with the casing wall casing  40 . 
     The primary purpose of the springs  35  is to ensure the engagement of the slip dies  28 ,  29 . The springs  35  on the upper end portion  12  of the plug body  11  are compressed with slip retainer  43  of the running tool  60  and allow the upper slip dies  28  to retract within the plug body (see FIGS.  8  and  9 ). When the plug body  11  is located within the desired casing depth and the running tool  43  is removed (see FIG.  10 ), appendages  47 ,  48 , and  49  of slip retainer  43  move out of splines  23  and allow the top springs  35  to force the upper slip dies  28  against the casing bore. 
     The bottom springs  35  are used to maintain lower slip dies  29  engagement of the casing bore while running the plug tool assembly  10  down hole. The springs  35  provide constant pressure on the slip dies  28 ,  29  which provides the slip dies  28 ,  29  to grip or engage the casing bore when moving upward in the opposite direction. The springs  35  also assist in the retrieval process of the plug body  11  by discarding the lower slip dies  29  which allows the plug body to release. 
     The primary function of the O-rings  25 ,  27  is to retain the slip dies  28 ,  29  and springs  35 . The O-rings  25 ,  27  have sufficient shear characteristics that allow the bottom slip die  29  and spring assembly  35  to separate from (collapse) the plug body  11  upon retrieval (See FIG.  12 ). 
       FIG. 13  shows the apparatus  10  of the present invention in relation to a well bore  41  having a casing lining, providing casing surface  40  and showing the earth&#39;s surface  42  above the well bore  41 . 
     In  FIG. 13 , there are two plug bodies  11  disposed at differing elevations within the well bore  41 . A first section of bentonite  56  is shown in between two plug bodies  11  in FIG.  13 . This first, lower section  56  of bentonite is placed in the well after the first plug body  11  has been lowered and set using the procedure shown in  FIGS. 9 and 10  and described herein. After the first bentonite section  56  has been added to the well bore  41 , a second plug body  11  is placed above the first bentonite section  56  as shown in  FIG. 13. A  second bentonite section  57  is then added to the well bore  41  above the upper plug body  11  as shown in FIG.  13 . Thus, two plug bodies  11  and two bentonite sections  56 ,  57  can be used to fully and completely plug and abandon the well bore  41 . 
       FIGS. 11 and 12  show removal of a plug body  11  using wire line or slick line  44  in combination with a retrieval tool  60 . The retrieval tool  60  is lowered in the direction of arrows  61  in FIG.  11 . The retrieval tool  60  can provide a plurality of lifting members  63 , each disposed in an angle to socket  62 . Pins  65  within the sockets  62  engage slots  64  of the lifting member  63  as shown. This enables the lifting member  63  to be retracted into the sockets  62  so that they can retract when engaging the larger diameter portion  17  of neck fitting  14 . Each of the lifting members  63  provides a shoulder  66  that engages the annular shoulder  15  of neck fitting  14  as shown in FIG.  11 . For removal of the tool body  11 , the retrieval tool  60  is pulled upwardly in the direction of arrows  67  in  FIG. 12  using a lifting device (e.g., crane, boom, winch) and a slick line or wire line  44 . When this occurs, the fingers  37  that are spaced apart by slots  38  flex as schematically illustrated by arrow  68  in FIG.  12 . This flexing enables the slips  29  to shear o-ring  27 , breaking it into o-ring sections  27 A that fall into the well bore. Once the lower slips  29  have fallen from their respective sockets  33 , the tool body  11  can be retrieved as shown in FIG.  12 . 
     The present invention is not limited to any specific casing size (such as the 5.5″ and 7″). It can be manufactured for any casing size such as: 5.5″, 7″, 7 ⅝″, 9 ⅝″, 10 ¾″, 13 ⅜″ etc. Larger plug  10  sizes may require more slip sockets and grooves. 
     PARTS LIST 
     The following is a list of parts and materials suitable for use in the present invention:
       10  well plug apparatus     11  plug body     12  upper end portion     13  lower end portion     14  neck fitting     15  annular shoulder     16  cylindrical section     17  cylindrical section     18  conical section     19  transverse surface     20  socket     21  externally threaded section     22  rib     23  groove or spline     24  upper circumferential groove     25  o-ring     26  lower circumferential groove     27  o-ring     27 A cut o-ring sections     28  upper slip die     29  lower slip die     30  cylindrical base     31  rectangular boss     32  teeth     33  slip socket     34  closed end     35  spring     36  socket     37  finger     38  slot     39  internally threaded section     40  well casing internal wall surfaces     41  well bore     42  earth surface     43  slip retainer     44  wire rope     45  coupling     46  flange     47  appendage     48  appendage     49  appendage     50  socket     51  shear pin     52  externally threaded pin     53  internally threaded socket     54  arrow     55  central longitudinal axis     56  first bentonite section     57  second bentonite section     60  retrieval tool     61  arrow     62  angled socket     63  lifting member     64  slot     65  pin     66  shoulder     67  arrow     68  arrow   

     The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.