Abstract:
A method for plugging a downhole wellbore including, running an anchor and swellable seal disposed at a mandrel within the downhole wellbore, setting the anchor within the downhole wellbore, releasing the anchor and the swellable seal, and swelling the swellable seal into contact with another downhole structure.

Description:
BACKGROUND 
     Well operators in the hydrocarbon recovery industry often seal tubulars to downhole wellbores such as casings and liners. Several systems exist for sealing the tubulars to the downhole wellbores and many function adequately. Most of these systems, however, include complex actuation devices. For example, many systems axially compress an elastomeric sleeve causing it to expand radially into sealing engagement with the downhole wellbore. This axial compression includes valves, pistons and actuators each having multiple moving parts and sliding seals that have potential failure modes associated therewith. Such systems are complex, costly and difficult to effectively deploy. Accordingly, the industry is receptive to simple, cost effective systems for plugging a downhole wellbore. 
     BRIEF DESCRIPTION 
     Disclosed herein is a method for plugging a downhole wellbore. The method includes, running an anchor and swellable seal disposed at a mandrel within the downhole wellbore, setting the anchor within the downhole wellbore, releasing the anchor and the swellable seal, and swelling the swellable seal into contact with another downhole structure. 
     Further disclosed herein is a downhole wellbore plugging system. The system includes, a mandrel that is runnable within a downhole wellbore and releasable therewithin, an anchor disposed at the mandrel being anchorable to the downhole wellbore, and a swellable seal disposed at the mandrel being sealable with the downhole wellbore and the mandrel. 
     Further disclosed herein is a method for plugging a downhole wellbore. The method includes, running a tool having an anchor and a swellable seal into the downhole wellbore with a wireline, anchoring the tool within the downhole wellbore, retrieving the wireline, and swelling the swellable seal into contact with another downhole structure subsequent to retrieval of the wireline. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  depicts a schematic view of a wellbore plugging system according to an embodiment disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the FIGURE. 
     Referring to  FIG. 1 , an embodiment of a wellbore plugging system disclosed herein is illustrated generally at  10 . The system  10 , among other things includes a downhole tool  12  having, a mandrel  14  with a swellable seal  18  and an anchor  22  mounted thereat. The tool  12  is positionable downhole within a wellbore  26  by a wireline  28  that is disconnectable from the mandrel  14  by a disconnectable connector  30 . The swellable seal  18  can be made of a variety of materials that swell when exposed to certain well fluids, such as hydrocarbons and water, for example. Additionally, the swellable seal  18  can swell in response to exposure to certain conditions that are commonly encountered in downhole environments, such as, high temperatures and high pressures as well as exposure to certain chemicals. The swellable seal  18 , can forcibly contact structures it comes in contact with in response to the increase in volume that occurs during swelling. Such contactable structures include walls  32  of the wellbore  26 , which may be a casing, liner or other tubular member, or open hole, or an outer surface  34  of the mandrel  14 , for example. These contact forces are sufficient to create a seal between the swellable seal  18  and the outer surface  34  as well as between the swellable seal  18  and the walls  32 . The swellable seal  18  can also be sealed to the mandrel  14  based on the original construction such that swelling of the swellable seal  18  is not needed to form the seal with the outer surface  34 . A duration of time needed from initiation of swelling to formation of a seal is dependent upon various factors, some of which will be reviewed below. 
     The swell rate, or the rate of increase in volume, of the swellable seal  18 , can vary depending upon a variety of parameters. For example, the chemical make up of both the swellable seal  18  itself and the well fluid into which the swellable seal  18  is submerged, can greatly affect the swell rate. Additionally, clearance dimensions between the swellable seal  18  and the surfaces  32 ,  34  as well as the dimensions of the swellable seal  18  itself will also affect the time required to form a seal. Typically, the greater the clearance the longer the duration before a seal is formed. A designer can, therefore, use these parameters to set a desired time duration from initiation of swelling to initiation of sealing. Delay in swelling to the point of sealing may be desirable to allow time for an operator to run the tool  12  into the desired position downhole prior to forming a seal with the walls  32 , for example. Such delays may be set from just a few hours to several days or more. 
     In embodiments of the invention, an operator will set the anchor  22  prior to forming the seal. The anchor  22  has slips  44  that are deployable and engagable with the walls  32  of the wellbore  26  to fixedly attach the system  10  to the wellbore  26 . Although the system disclosed herein has the anchor  22  positioned above the swellable seal  18 , along the mandrel  14 , alternate embodiments could just as well have the anchor  22  positioned below the swellable seal  18 . Regardless of the relative positions of the anchor  22  with the swellable seal  18 , initiation to actuate the setting of the anchor  22  can be carried out in various ways. 
     For example, setting of the anchor  22  can be initiated, and optionally actuated, from surface via the wireline  28 . The wireline  28  can be used to initiate a trigger  36  that actuates an actuator  40 , or the wireline  28  can be used to actuate the actuator  40  directly. For example, in embodiments wherein the wireline  28  is an electric wireline  28  an electrical signal could be transmitted along the wireline  28  and used to open a valve (the trigger  36 ) that permits downhole fluid under hydrostatic pressure access to a chamber containing a piston and a compressible gas at atmospheric pressure, to thereby move the piston (the actuator  40 ) to set the anchor  22 . In an alternate embodiment, the electrical transmission can be used to energize a motor (the trigger  36 ) that drives a pump (the actuator  40 ) to hydraulically set the anchor  22 . Still other embodiments, of the system  10 , could employ timing devices (the trigger  36 ), or other means, that initiate actuation in response to exposure to a specific downhole parameter, such as, elevated pressure, elevated temperature and chemical exposure, for example. 
     Regardless of the trigger  36  and the actuator  40  employed to set the anchor  22 , the anchor  22  should be set prior to setting of the swellable seal  18 . In embodiments wherein the swellable seal  18  begins swelling as soon as it is exposed to certain downhole conditions, the duration to set the swellable seal  18  needs to be longer than the time it will take to run the tool  12  to the desired depth. This will prevent rubbing damage due to excess friction between the swellable seal  18  and the walls  32  while the tool  12  is being run. Once the tool  12  is in position the swelling of the swellable seal  18  can continue until a seal is formed. 
     Optionally, an operator is free to disconnect the wireline  28  from the tool  12 , at the disconnectable connector  30 , once the anchor  22  is set, even if the swellable seal  18  has not yet sealingly engaged the walls  32 . As such, a swellable seal  18  that takes several days to fully swell and seal with the walls  32  may be a desirable condition to assure that the operator has adequate time to fully run the tool  12  to the desired depth. It may be advantageous to position the disconnectable connector  30  between the actuator  40  and the anchor  22  to thereby allow an operator to remove the trigger  36  and the actuator  40  with the wireline  28  thereby minimizing a portion of the tool  12  that remains downhole. 
     The foregoing embodiments allow a well operator to quickly and inexpensively run the tool  12  with the wireline  28  to a position within the wellbore  26 , set the anchor  22  and then retrieve the wireline  28  and then wait for the swellable seal  18  to permanently plug off the wellbore  26 . Since it is not uncommon for wells to water out from the bottom up, several of the tools  12  could be used in a single well to sequentially plug off zones from the bottom up as they begin producing water. 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.