Abstract:
Embodiments of the present invention generally relate to a method of drying a tubular string to prevent bedwrap corrosion. In one embodiment, a method of drying a tubular string includes deploying a first bypass pig in the tubular string. The method further includes injecting propellant behind the first bypass pig, thereby driving the first bypass pig through the tubular string. A portion of the propellant bypasses the first bypass pig, thereby drying an inner surface of the tubular string.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/388,138 (Atty. Dock. No. TUBE/0002), filed Feb. 18, 2009, and U.S. patent application Ser. No. 12/388,166 (Atty. Dock. No. TUBE/0003), filed Feb. 18, 2009, both of which are herein incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention generally relate to a method of drying a tubular string to prevent bedwrap corrosion. 
         [0004]    2. Description of the Related Art 
         [0005]    Coiled tubing (CT) strings are utilized to perform a variety of functions inside oil, gas and water wells, such as pumping fluid through the CT string from the ground surface at the wellhead to the bottom of the well. Once the desired work on the well is completed, the CT string is removed from the well and recoiled onto a spool. Due to the nature of the CT string often being many thousands of feet in length and a small interior diameter, residual fluid &amp; contaminants remain in the CT string in very small quantities. 
         [0006]    Conventional methods of drying CT strings include blowing large volumes of high pressure nitrogen through the CT string in an attempt to force any remaining corrosive liquids out of the coil of tubing. Even when these methods are used in combination with conventional pipeline pigs, small amounts of corrosive fluids &amp; residue remain in the coil and continue to corrode or rot the tubing at the 6 o&#39;clock position while the coil is in storage or waiting for the next use. There is currently no known method by which all corrosive fluids &amp; residue can be removed from such CT strings. 
       SUMMARY OF THE INVENTION 
       [0007]    Embodiments of the present invention generally relate to a method of drying a tubular string to prevent bedwrap corrosion. In one embodiment, a method of drying a tubular string includes deploying a first bypass pig in the tubular string. The method further includes injecting propellant behind the first bypass pig, thereby driving the first bypass pig through the tubular string. A portion of the propellant bypasses the first bypass pig, thereby drying an inner surface of the tubular string. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0009]      FIG. 1  illustrates pigtrain deployed in a coiled tubing string, according to one embodiment of the present invention.  FIG. 1A  is an enlargement of a portion of  FIG. 1 . 
           [0010]      FIG. 2A  is a longitudinal cross-section of a trail bypass pig of the pigtrain.  FIG. 2B  is a radial cross-section of the trail bypass pig. 
           [0011]      FIG. 3A  is a longitudinal cross-section of a lead bypass pig of the pigtrain.  FIG. 3B  is an end view of the lead bypass pig. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  illustrates a pigtrain  1  deployed in a coiled tubing (CT) string  50 , according to one embodiment of the present invention.  FIG. 1A  is an enlargement of a portion of  FIG. 1 . Alternatively, the pigtrain  1  may be deployed in other tubular strings, such as a pipeline or reeled pipe. The pigtrain  1  may include one or more lead pigs  300  and a trail pig  200 . The lead and trail designations and inlet and outlet designations may be arbitrary as the pigtrain  1  may be bidirectional and/or the inlet  55   i  and outlet  55   o  may be reversed. As discussed below, the pigtrain  1  may be deployed to dry the CT string  50 . As discussed above, the CT string  50  may have residual liquid from being deployed into a wellbore. Alternatively, it may be desirable to dry the CT string  50  after manufacture on the manufacturer&#39;s production reel or after use in a pipeline. 
         [0013]    In preparing the CT string  50  for deployment of the pigtrain  1 , an inlet  55   i  and outlet  55   o  of the CT string  50  may be located at or near ground level to allow for easier access. A clamp (not shown) may be secured to each of the inlet  55   i  and outlet  55   o . Each clamp may have a flange or threaded coupling to receive corresponding flanges or threaded couplings of a pig launcher (not shown) and a pig receiver (not shown). The launcher and receiver designations may be arbitrary as the pigtrain  1  may be bidirectional. Each of the launcher and receiver may include a pipe and a bumper. The pipe may include a propellant port and a door at an end thereof for insertion or removal of the pig. The pipe may have an increased diameter relative to the CT string  50  and each of the launcher and receiver may further include a reducer connecting the pipe to the CT string  50  to facilitate ease of insertion or removal of the pigtrain  1 . 
         [0014]    The lead  300  and trail  200  pigs may be loaded into the launcher followed by the bumper. The door of the launcher may be closed and a propellant supply hose may be connected to the propellant port. The receiver bumper may also be loaded into the receiver pipe, the door closed, and a vent hose connected to the propellant supply. 
         [0015]    Propellant P may be injected into the launcher to drive the pigtrain  1  through the CT string  50 . The propellant P may be a fluid, such as compressed gas, such as dry air or nitrogen. When the pigtrain  1  reaches the receiver connected to the outlet  55   o,  the lead pig  300  may be stopped by the receiver bumper. At this point, the propellant P may be sampled and the moisture content measured and compared to a predetermined level to determine if the CT string  50  is dry after one pass or if the pigtrain  1  needs be driven back through the CT string  50  until the pigtrain  1  reaches the launcher bumper. This back and forth movement of the pigtrain  1  may be repeated until an inner surface of the coiled tubing  50  is sufficiently clean and/or dry. Alternatively, the pigtrain  1  may be transported back to the launcher and redeployed using the launcher. Alternatively, the pigtrain may be inverted and deployed using the receiver. 
         [0016]    Alternatively, the bumpers may be omitted. Alternatively, the pig launcher and receiver as illustrated in FIGS.  1  and  9 - 11  of U.S. Pat. No. 5,230,842, which is herein incorporated by reference in its entirety, may be used to launch and receive the pigtrain  1 . Alternatively, the pigtrain  1  may be deployed into the CT string  50  without using a launcher and receiver. Additionally, a second pigtrain (not shown) may be deployed in series with the pigtrain  1 . The second pigtrain may include a lead bypass pig and a trail bypass pig. The second pigtrain may be deployed adjacent to the pigtrain  1  such that the second pigtrain utilizes the lead or trail pig of the pigtrain  1  as one of its members. Alternatively, the second pigtrain may be deployed a distance from the pigtrain  1  such that a cushion of propellant exists between the pigtrains. In this alternative, the second pigtrain may have its own lead pig and trail pig. 
         [0017]    Alternatively, the pigtrain  1  may be used as part of a multi-cycle regimen for treating, such as cleaning and/or coating, the CT string  50 . One regimen may include a first cycle including deploying a pigtrain discussed and illustrated in the &#39;166 application (incorporated above), back and forth through the CT string  50  one or more times with a first working fluid, such as detergent, and a second cycle with a different second working fluid, such as water or neutralizer. 
         [0018]    The &#39;166 pigtrain may include a lead pig, a bypass pig, and a trail pig. The bypass pig may be either of the pigs  200 ,  300  and the lead and trail pigs may be similar to either of the pigs  200 ,  300  except for omission of the bypass. When the &#39;166 pigtrain is initially deployed in the CT string  50  from the launcher, the bypass pig may be in a first position closer to the lead pig than the trail pig, such as proximate to or abutting the lead pig. As the &#39;166 pigtrain proceeds through the CT string  50 , a portion of the working fluid may flow through the bypasses, thereby forcing the bypass pig to gradually move from the first position to a second position closer to the trail pig than the lead pig, such as proximate to or abutting the trail pig, relative to the movement of the &#39;166 pigtrain. The relative movement of the bypass pig may agitate the working fluid and/or liquid residue as the &#39;166 pigtrain proceeds through the CT string  50 , thereby facilitating the removal of debris from the inner surface of the CT string. 
         [0019]    The regimen may be a multi-cycle cleaning regimen for cleaning and then sealing the CT string  50  with a pressurized gage pressure or zero gage pressure atmosphere, such as dry air or nitrogen, inside the coiled tubing  50  to prevent corrosion thereof during storage. The &#39;166 pigtrain may be deployed with the detergent, such as a surfactant or basic solution, for a degreasing cycle. The cycle may be repeated until a white-metal or near white-metal finish, such as NACE number one or two, is achieved. The &#39;166 pigtrain may then be deployed with water for a rinse cycle. The &#39;166 pigtrain may then be deployed with the corrosion inhibitor. The pigtrain  1  may then be deployed with dry air or nitrogen propellant for a drying cycle. A squeegee pig, such as a foam pig, may be deployed with nitrogen or dry air propellant for a blanket cycle. The ends  55   i, o  may be sealed with the blanket inside the coiled tubing  50  at positive or zero gage pressure and the CT string  50  placed in storage. 
         [0020]    Alternatively, the regimen may be a multi-cycle interior coating regimen for the CT string  50 . The regimen may include deployment of the &#39;166 pigtrain with the detergent, such as a surfactant or basic solution, for a degreasing cycle. The &#39;166pigtrain may then be deployed with water for a rinse cycle. The &#39;166 pigtrain may then be deployed with another detergent, such as an acidic solution, for descaling. The cycle may be performed until a white-metal or near white-metal finish, such as NACE number one or two, is achieved. The &#39;166 pigtrain may then be deployed with the neutralizer. The pigtrain  1  may then be deployed with dry air or nitrogen propellant for a drying cycle. The &#39;166 pigtrain may then be deployed with the corrosion inhibitor. The coating (not shown) may be applied by injecting liquid coating material, such as a polymer (i.e., epoxy, polyurethane, or polytetrafluoroethylene) between two extruder pigs (not shown) of a pigtrain and propelling the pigtrain using dry air or nitrogen through the CT string  50 . 
         [0021]    Suitable pipeline extruder pigs are illustrated in  FIGS. 3-6  of the &#39;842 patent. The pipeline extruder pigs may be modified for use in coiled tubing or reeled pipe by omitting the intermediate disc members and shortening the base portion of the leading pig and omitting the intermediate disc members and shortening the base portion of the trailing pig. As the extruder pigs progress through the CT string  50 , they may apply a uniform thickness coating of the material onto the interior surface of the CT string  50 . After a layer of coating material has been applied, the CT string  50  may be subjected to a drying or curing process to insure the coating bonds to the tubing  50 . For instance, dry air may be passed through the tubing to dry the coating or the tubing may be subjected to heat to cure the lining material thereby creating a mechanical bond between the coating and the tubing  50 . Additional layers may be applied. Each layer may have a thickness of less than 0.0015 inch and, if multi-layer, the aggregate thickness of the coating may be less than 0.004 inch. 
         [0022]      FIG. 2A  is a longitudinal cross-section of a trail bypass pig  200  of the pigtrain  1 .  FIG. 2B  is a radial cross-section of the trail bypass pig  200 . The pig  200  may include a body  205 , a tail plate  207 , one or more brushes  210 , and a bypass  215 . A longitudinal axis L is shown for reference. The body  205  may be made from a flexible material, such as a polymer. The polymer may be foamed polymer, such as polyurethane, or a non-foamed polymer. The body  205  may be bullet-shaped and include a nose portion  205   n,  a tail portion  205   t  and a cylindrical portion  205   c.  The tail portion  205   t  may be concave or flat. The nose portion  205   n  may be conical, hemispherical or hemi-ellipsoidal. Alternatively, the nose portion  205   n  may instead be a second tail portion so that the pig  200  is bidirectional. The tail plate  207  may be bonded to the tail portion  205   n  during molding of the body  205 . The shape of the tail plate  207  may correspond to the tail portion  205   t.  The tail plate  207  may be made from a (non-foamed) polymer, such as polyurethane. 
         [0023]    The brushes  210  may each extend along an outer surface of the body  205 . Each brush  210  may include a base  211  and bristles  212  embedded therein along a length and a width thereof. The bristles  212  may be made from a metal or alloy, such as steel, or a polymer. Alternatively, grains of abrasive material, such as sand, glass, diamond dust, or carbide (i.e., silicon or tungsten) may be embedded in the base  211  instead of the bristles  212 . Each base  211  may be a strip made from a (non-foamed) polymer, such as polyurethane, ploychloroprene, or polyisoprene. Each base  211  may be a cylindrical segment to conform to the outer surface of the cylindrical portion  205   c . Each base  211  may be longitudinally straight. Alternatively, each base  211  may extend longitudinally and tangentially along the body  205  in a helical orientation or a single base  211  may be helically wound along the body  205 , thereby rotating the pig as the pig travels longitudinally through a tubular string. This spiral motion may serve to more evenly distribute wear to the brushes  210 . Alternatively, scrapers may be used instead of brushes. Alternatively, the brushes may be omitted. 
         [0024]    Each brush  210  may extend from the tail plate  207  or portion  205   t,  along the cylindrical portion  205   c,  and over a portion of the nose  205   n.  Each brush  210  may be bonded to the body by an adhesive  208 , such as a (non-foamed) polymer, such as polyurethane, ploychloroprene, or polyisoprene. The adhesive  208  may be applied around the cylindrical portion  205   c,  over the nose  205   n,  and an outer surface of the tail plate  205   t  so that the adhesive serves as an overcoat  208  for the body  205  as well as an adhesive for the brushes  210 . A tail coat  209  may be applied to the rear surface of the tail plate  207  and the bases  211 . The tail coat  209  may be a (non-foamed) polymer, such as polyurethane, ploychloroprene, or polyisoprene. The brushes  210  may be tangentially spaced around the body  205 , thereby defining a bypass  215  between each brush  210 . The bypasses  215  may each be channels extending along a length of the brushes  210 . Relative to the bypasses  215 , the brushes  210  may substantially occupy the outer surface of the cylindrical portion  205   c,  such as more than half, at least two-thirds, at least three-quarters, or at least nine-tenths of the outer surface. 
         [0025]    An outer diameter of the cylindrical portion  205   c  may be equal to, slightly greater than, or slightly less than an inner diameter of the CT string  50 . Having interference between the pig  200  and the CT string  50  may ensure tight engagement of the bristles  212  with the inner surface of the CT string  50 . 
         [0026]      FIG. 3A  is a longitudinal cross-section of a bypass pig  300 , according to another embodiment of the present invention.  FIG. 3B  is an end view of the bypass pig  300 . The pig  300  may include a mandrel  305 , a front seal  320   f,  a rear seal  320   r,  a brush  310 , and a bypass  315 . The mandrel  305  may be a rod having a threaded outer surface and made from a flexible material, such as a polymer. Alternatively, the mandrel  305  may be a threaded tubular capped at each longitudinal end thereof. 
         [0027]    The brush  310  may extend along an outer surface of the mandrel  305 . The brush  310  may include a base  311  and bristles  312  bonded thereto along a length and width thereof. The base  311  may be a helically wound strip or channel made from a metal or alloy, such as steel. The bristles  312  may be made from a metal or alloy, such as steel, or a polymer. Alternatively, a scraper may be used instead of a brush. Alternatively, the brush may be omitted. 
         [0028]    The seals  320   f,r  may each include a hub portion  321 , a disc portion  322 , and one or more bypasses  315 . The front and rear designations may be arbitrary as the pig  300  may be bidirectional. The seals  320   f,r  may each be made from a polymer, such as polyurethane, ploychloroprene, or polyisoprene. An inner surface of the hub portion  321  may be threaded corresponding to the threaded outer surface of the mandrel  305 . An inner end of each hub portion  321  may abut a respective end of the base  311 , thereby retaining the brush  310  on the mandrel  305 . The bypasses  315  may each be a channel formed in an outer surface of each of the disc portions  322  and extending longitudinally therethrough. Alternatively, the bypasses may each be a hole formed longitudinally through each of the disc portions  322 . The bypasses  315  may be tangentially spaced around each of the disc portions  322 . Alternatively, each hub  321  may be a separate member made from a polymer, such as nylon, and bonded to the disc  322 . Alternatively, nuts made from a polymer, such as nylon, may be used to straddle the disc portion  322  and the base  311  instead of the hub  321 . Alternatively, cups may be used instead of the discs  322 . Alternatively, the bypasses  315  of the front seal  320   f  may be misaligned with the bypasses  315  of the rear seal  320   r.  Additionally, the hubs or nuts may be bonded to the mandrel after threaded connection. 
         [0029]    An outer diameter of each disc portion  322  may be equal to or slightly greater than an inner diameter of the CT string  50  to ensure tight sealing engagement of the discs  322  with the CT string  50 . The bristles  312  may radially extend from the base  311  to, or slightly outward past the outer diameter of the disc portions  322  to ensure tight engagement of the bristles  312  with the CT string  50 . 
         [0030]    Returning to  FIGS. 1 and 1A , as the pigtrain  1  travels through the CT string  50 , bristles  212 ,  312  of each pig  200 ,  300  may drag along an inner surface of the CT string  50 . A portion of the propellant P may bypass the pigtrain  1  via the bypasses  215 ,  315 . As the bypassed portion of the propellant P exits the bypasses  215 ,  315 , a fluid (liquid and/or gas) jet T may be created proximately in front of the lead pig  300 , thereby facilitating removal of fluid, such as residual liquid, from the inner surface of the CT string  50 . A velocity of the fluid jet T may be sufficient to disrupt the boundary layer, thereby churning the fluid. Locating the bypass along an outer portion of the pig  1  advantageously maintains increased (i.e., maximum) local velocity of the jet T at an inner surface of the CT string  50  where the drying is occurring. The bristles  212 ,  312  may also serve to disrupt and disengage moisture droplets clinging to the CT string inner surface, thereby allowing the jet T to continuously move the moisture ahead of the pigtrain  1  and out of the CT string  50 . 
         [0031]    A number and length of the pigs  200 ,  300  may determine the amount of “drag” created by the brushes against the interior wall of the string. The amount of propellant force required to push the pigtrain  1  through the CT string  50  may also determine how much of the propellant P bypasses the pigtrain  1  at the inner surface of the tubing  50  and brush interface, thereby facilitating the removal of fluids ahead of the pigtrain  1  as the pigtrain moves through the CT string  50 . Conventional pigs inserted into a CT string and driven with propellant serve to redistribute any residual liquid in the string over a length of the string. Once the propellant is stopped after running conventional pigs, the residual, redistributed fluid simply returns to the 6 o&#39;clock position in the coil bed wraps and forms a corrosive point in the string bed wraps. Due to the nature of the pigs  200 ,  300  creating a predetermined drag force on the pigtrain  1 , at least a portion, such as a substantial portion, of the propellant P bypasses the pigtrain and creates the jet T of propellant P sufficient to move any liquid remaining in the CT string  50  ahead of the pigtrain  1 . Once the pigtrain  1  reaches the end of the CT string  50 , at least a portion, such as a substantial portion or all, of the remaining liquid has been forced out of the CT string  50  ahead of the pigtrain  1  leaving behind only the dry propellant P used to force the pigtrain  1  through the CT string  50 . 
         [0032]    Alternatively, only one of the bypass pigs  200 ,  300  may be deployed to dry the CT string  50  instead of the pigtrain  1 . Alternatively, bypass pig  200  may be the lead pig and bypass pig  300  may be the trail pig. Alternatively, the pigtrain  1  may include a plurality of lead pigs  300  and one trail pig  200 . Alternatively, the pigtrain  1  may include one lead pig  300  and a plurality of trail pigs  200 . Alternatively, the pigtrain  1  may include a plurality of lead pigs  300  and a plurality of trail pigs  200 . Alternatively, the pigtrain  1  may include only a plurality of the pigs  300 . Alternatively, the pigtrain  1  may include a plurality of the pigs  200 . 
         [0033]    Alternatively, the bypass  215  may be centrally formed through the body  205  and/or the bypass  315  may be centrally formed through the mandrel  305 . 
         [0034]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.