Abstract:
Embodiments of the present invention generally relate to a bypass pig. In one embodiment, a pig for cleaning a tubular string includes a cylindrical body and two or more scrapers disposed along an outer surface of the body. The scrapers are operable to engage and clean an inner surface of the tubular string. The pig further includes a bypass formed between the scrapers. The bypass is operable to: intake a portion of propellant from a tail of the body, conduct the portion of propellant along an outer surface of the body, and discharge the portion of propellant in front of the body.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention generally relate to a bypass pig. 
         [0003]    2. Description of the Related Art 
         [0004]    Pipeline pigs are propelled by fluid pressure through the interior of pipelines to clean wax, sludge, scale, debris, and other materials from the inner surfaces of the pipeline. Pipeline pigs may also be used to fill a pipeline with water for hydrotesting and remove the water once testing is finished. Pipeline pigs may also be used to verify tolerances of the pipeline and inspect for corrosion. Pipeline pigs may also be used to remove accumulated liquids or solids in pipelines. Pipeline pigs may also be used to separate different types of fluids which may be traveling through the same pipeline. 
         [0005]    Two common types of pipeline pigs are foam pigs and mandrel pigs. Conventional foam type pipeline pigs usually have a generally cylindrical body formed of polyurethane foam. The foam type pipeline pigs are much lighter in weight and are more flexible than mandrel pigs. However, foam type pigs are usually disposable since they cannot be redressed. Conventional mandrel pigs usually have two or more resilient cups mounted on an elongate rigid central shaft or on a hollow, generally cylindrical rigid body. The cups have a peripheral lip which extends radially to engage the interior of the pipeline and transmits a radial component of the propelling fluid pressure to the inner walls of pipeline to affect a tighter fit. Some mandrel pigs may also be provided with wire brush members on their periphery for scraping the inner wall of the pipeline. 
       SUMMARY OF THE INVENTION 
       [0006]    Embodiments of the present invention generally relate to a bypass pig. In one embodiment, a pig for cleaning a tubular string includes a cylindrical body and two or more scrapers disposed along an outer surface of the body. The scrapers are operable to engage and clean an inner surface of the tubular string. The pig further includes a bypass formed between the scrapers. The bypass is operable to: intake a portion of propellant from a tail of the body, conduct the portion of propellant along an outer surface of the body, and discharge the portion of propellant in front of the body. 
         [0007]    In another embodiment, a pig for cleaning a tubular string includes a cylindrical body and a scraper wound around and along an outer surface of the body. The scraper is operable to engage and clean an inner surface of the tubular string. The pig further includes a bypass formed between windings of the scraper. The bypass is operable to intake a portion of propellant from a tail of the body, conduct the portion of propellant along and around an outer surface of the body, and discharge the portion of propellant in front of the body. 
         [0008]    In another embodiment, a method of cleaning a tubular string includes injecting propellant behind a pig, thereby propelling the pig through the tubular string; and bypassing a portion of the propellant along an outer portion to a front of the pig, thereby creating a jet in front of the pig. 
         [0009]    In another embodiment, a pig for cleaning a tubular string includes a mandrel and a seal. The seal is coupled to the mandrel, operable to engage an inner surface of the tubular string, and has a bypass formed longitudinally therethrough. The pig further includes a scraper disposed along the mandrel. The scraper is operable to engage and clean an inner surface of the tubular string. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    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. 
           [0011]      FIG. 1A  is a longitudinal cross-section of a bypass pig, according to one embodiment of the present invention.  FIG. 1B  is a radial cross-section of the bypass pig. 
           [0012]      FIG. 2  illustrates a use of the bypass pig, according to another embodiment of the present invention. 
           [0013]      FIG. 3A  is a longitudinal cross-section of a bypass pig, according to another embodiment of the present invention.  FIG. 3B  is an end view of the bypass pig. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1A  is a longitudinal cross-section of a bypass pig  1 , according to one embodiment of the present invention.  FIG. 1B  is a radial cross-section of the bypass pig. The pig  1  may include a body  5 , a tail plate  7 , one or more scrapers  10 , and a bypass  15 . A longitudinal axis L is shown for reference. The body  5  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  5  may be bullet-shaped and include a nose portion  5   n,  a tail portion  5   t  and a cylindrical portion  5   c.  The tail portion  5   t  may be concave or flat. The nose portion  5   n  may be conical, hemispherical or hemi-ellipsoidal. Alternatively, the nose portion  5   n  may instead be a second tail portion so that the pig is bidirectional. The tail plate  7  may be bonded to the tail portion  5   n  during molding of the body  5 . The shape of the tail plate  7  may correspond to the tail portion  5   t.  The tail plate  7  may be made from a (non-foamed) polymer, such as polyurethane. 
         [0015]    The scrapers may be brushes  10  and may each extend along an outer surface of the body  5 . Each brush  10  may include a base  11  and bristles  12  embedded therein along a length and a width thereof. The bristles  12  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  11  instead of the bristles  12 . Each base  11  may be a strip made from a (non-foamed) polymer, such as polyurethane, ploychloroprene, or polyisoprene. Each base  11  may be a cylindrical segment to conform to the outer surface of the cylindrical portion  5   c.  Each base  11  may be longitudinally straight. Alternatively, each base  11  may extend longitudinally and tangentially along the body  5  in a helical orientation or a single base  11  may be helically wound along the body  5 , 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  10 . 
         [0016]    Each brush  10  may extend from the tail plate  7  or portion  5   t,  along the cylindrical portion  5   c,  and over a portion of the nose  5   n.  Each brush  10  may be bonded to the body by an adhesive  8 , such as a (non-foamed) polymer, such as polyurethane, ploychloroprene, or polyisoprene. The adhesive  8  may be applied around the cylindrical portion  5   c,  over the nose  5   n,  and an outer surface of the tail plate  5   t  so that the adhesive serves as an overcoat  8  for the body  5  as well as an adhesive for the brushes  10 . A tail coat  9  may be applied to the rear surface of the tail plate  7  and the bases  11 . The tail coat  9  may be a (non-foamed) polymer, such as polyurethane, ploychloroprene, or polyisoprene. The brushes  10  may be tangentially spaced around the body  5 , thereby defining a bypass  15  between each brush  10 . The bypasses  15  may each be channels extending along a length of the brushes  10 . Relative to the bypasses  15 , the brushes  10  may substantially occupy the outer surface of the cylindrical portion  5   c,  such as more than half, at least two-thirds, at least three-quarters, or at least nine-tenths of the outer surface. 
         [0017]      FIG. 2  illustrates a use of the bypass pig  1 , according to another embodiment of the present invention. The pig  1  may be deployed in a tubular string, such as coiled tubing  200 , reeled pipe, or a pipeline. In preparing the coiled tubing  200  for deployment of the pig  1 , an inlet  205   a  and outlet  205   b  of the tubing  200  may be located at or near ground level to allow for easier access. The inlet  205   a  and outlet  205   b  are arbitrary and may be reversed. 
         [0018]    A clamp (not shown) may be secured to each of the inlet  205   a  and outlet  205   b.  Each clamp may have a flange to receive corresponding flanges of a pig launcher (not shown) and a pig receiver (not shown). A suitable pig launcher and receiver are illustrated in FIG. 1 of U.S. Pat. No. 5,230,842, which is herein incorporated by reference in its entirety. Each of the launcher and receiver may include a header pipe and a chamber pipe. The header pipe may include ports for venting, draining, measuring pressure, and/or injecting cleaning fluid. The chamber may include a propellant port, one or more pressure gage ports, and a door at an end thereof for insertion or removal of the pig. The chamber pipe may have an increased diameter relative to the header pipe and each of the launcher and receiver may further include a reducer connecting the two pipes. The inner diameter of the header pipe may correspond to the inner diameter of the coiled tubing and the inner diameter of the chamber pipe may be greater than the outer diameter of the bristles  12  to facilitate ease of insertion or removal of the pig  1 . 
         [0019]    The outer diameter of the cylindrical portion  5   c  may be equal to, slightly greater than, or slightly less than the inner diameter of the coiled tubing  200 . Having interference between the pig  1  and the coiled tubing  200  may ensure tight engagement of the bristles  12  with the inner surface of the coiled tubing  200 . Alternatively, the pig may be deployed into the coiled tubing  200  without using a launcher. 
         [0020]    Once the launcher and receiver have been connected to the respective inlet  205   a  and outlet  205   b,  the pig  1  may be inserted into the launcher and a propellant P, may be injected into the launcher chamber behind the pig  1 . The propellant P may be a fluid, such as a liquid or compressed gas, such as ambient air, dry air, or nitrogen. The pig  1  may be launched into the coiled tubing  200 . As the pig  1  travels through the coiled tubing  200 , the bristles  12  may drag along an inner surface of the coiled tubing  200 , thereby dislodging debris from the inner surface. A portion of the propellant P may bypass the pig  1  via the bypasses  15 . As the bypassed portion of the propellant P exits the bypasses  15 , a fluid jet T may be created proximately in front of the pig  1 , thereby facilitating removal of debris from the inner surface of the coiled tubing  200 . A velocity of the fluid jet T may be sufficient to disrupt the boundary layer, thereby churning the debris and the fluid jet T. The fluid jet T may also clean debris from the bristles  12 . 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 coiled tubing  200  where the cleaning is occurring. 
         [0021]    The pig  1  may continue through the coiled tubing  200  until the pig  1  is caught by the receiver connected to the outlet  205   b.  The pig  1  may then be removed and re-inserted into the launcher and the trip repeated. Alternatively, if the pig is bi-directional, the pig may be sent back-through the coiled tubing  200  to the inlet  205   a.  The cycle may be repeated until a white-metal or near white-metal finish, such as NACE number one or two, is achieved. 
         [0022]    The coiled tubing  200  may be new or used. If new, the pig may be used to clean manufacturing debris. Coiled tubing  200  is typically made from plate rolled and longitudinally welded together. Manufacturing debris, such as weld flash or flux may be left inside the coiled tubing  200 . If the coiled tubing has returned from a wellbore, a film of drilling fluid, such as mud, and associated debris, such as sand or clay, may be left inside the coiled tubing  200 . 
         [0023]    If the pig  1  should encounter a major obstruction, the propellant pressure may be increased to either force the pig  1  past the obstruction or burst the pig, thereby loosening the obstruction. 
         [0024]    Once the coiled tubing  200  has been sufficiently cleaned, an inner surface thereof may be coated. 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 coiled tubing  200 . 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  120  and  122  and shortening the base portion of  118  of the leading pig  112  and omitting the intermediate disc members  120   a  and  122   a  and shortening the base portion of  118   a  of the trailing pig  114 . As the extruder pigs progress through the tubing  50 , they may apply a uniform thickness coating of the material onto the interior surface of the tubing  50 . After a layer of coating material has been applied, the coiled tubing  200  may be subjected to a drying or curing process to insure the coating bonds to the tubing  200 . 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. 
         [0025]      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 scraper  310 , and a bypass  315 . The mandrel  305  may be a rod having a threaded outer surface and made from a metal or alloy, such as steel. Alternatively, the mandrel  305  may be a threaded tubular capped at each longitudinal end thereof. 
         [0026]    The scraper  310  may be a brush extending 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. An inner surface of the base  311  may be threaded corresponding to the threaded outer surface of the mandrel  305 . The bristles  12  may be made from a metal or alloy, such as steel, or a polymer. 
         [0027]    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 metal or alloy, such as steel, and bonded to the disc  322 . Alternatively, nuts 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.    
         [0028]    An outer diameter of each disc portion  322  may be equal to or slightly greater than an inner diameter of the coiled tubing  200  to ensure tight sealing engagement of the discs  322  with the coiled tubing  200 . 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 coiled tubing  200 . 
         [0029]    In operation, the pig  300  may be deployed in the coiled tubing  200  using the launcher and receiver, discussed above. The pig  300  may be deployed instead of the pig  1  or as a subsequent cleaning step to deployment of the pig  1 . As the pig  300  travels through the coiled tubing  200 , the bristles  312  may drag along an inner surface of the coiled tubing  200 , thereby dislodging debris from the inner surface. A portion of the propellant P may bypass the pig  300  via the bypasses  315  (and leak through the brushes). As the bypassed portion of the propellant P exits the bypasses  15 , the fluid jet T may be created proximately in front of the pig  1 , thereby facilitating removal of debris from the inner surface of the coiled tubing  200 . 
         [0030]    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.