Abstract:
An inline well fluid separator is movable for pigging operations. The separator assembly has a housing with an inlet port and an outlet port. A separation unit is carried within the housing. The separation unit has an operational position in alignment with the ports to cause well fluid to flow through the separation unit. The separation unit will move to a storage position within the housing outside of the flow path to enable a pipeline pig to pass.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates in general to oil and gas processing systems, and in particular to an inline coalescing separator that allows pigs to pass through for cleaning.  
       BACKGROUND OF THE INVENTION  
       [0002]     Hydrocarbon wells typically produce a percentage of water along with the hydrocarbon fluids, which may be oil or gas. A variety of separators exist for separating the water from the hydrocarbon, operating on principles such as gravity separation, centrifugal separation, and vortex separation.  
         [0003]     A more recent type of separation unit, called a coalescing filter, comprises a plurality of tubes mounted in a cylinder parallel to the flow. The tubes are electrically conductive and insulated from the plate. The operator supplies a voltage to the tubes. Dipolar water droplets contained in the oil phase are oriented by an electrostatic field from the voltage in the tubes in a way that makes them collide or coalesce with each other. This effect causes water within the well fluid to form into larger water droplets. Larger water droplets generally move and separate faster than smaller droplets, reducing the retention time to remove water from oil in gravity separation. The well fluid normally flows from the coalescence unit to a second stage for more separation.  
         [0004]     A second stage could be another coalescence unit or it could be a unit of a different type, such as a gravity unit, a centrifugal unit, a vortex unit, or a dielectrophoresis unit. A dielectrophoresis unit also uses a high voltage electrostatic field, however the field is configured to force the water droplets into designated sections of the unit and thereby form streams of water. Electrodes in the form of undulating sheets are used. The electrode sheets are closely spaced and arranged side-by-side to define constrictive passage portions and widened passage portions. The passages formed by the sheets force the water droplets to move towards the stronger section of the electrostatic field, which is at the narrower portions. The forces imposed by the electrostatic field guide the water droplets into these predetermined passage portions, where they form high water content sections of liquid that will easily separate immediately downstream of the unit.  
         [0005]     Regardless of the type, typically, the separators are part of a processing system located near the well site. In the case of subsea wells, the operator normally places the processing equipment on a platform, which may be either fixed leg or floating. In a few instances, separators have been placed in a subsea location, which may reduce the distance that the well fluid has to be pumped, and the distance that the separated water has to be pumped before being injected into a water injection well. Coalescing filters can be sized small enough to be placed within subsea flow lines to enhance subsea well fluid processing.  
         [0006]     One problem that may arise, however, with a subsea processing system deals with cleaning the flow lines. Well fluids often contain substances, such as paraffin, that coat the interior of the flow lines. A variety of processes exist for removing the coating, including the use of chemicals and mechanical cleaning. In mechanical cleaning, the operator may utilize a pipeline pig, which is a cylindrical member that fits sealingly within the flow line. The body of the pig has scraper elements to scrape and remove the coating. The operator applies fluid pressure to the opposite end of the pig to cause it to flow through the flow line to perform the cleaning operation.  
         [0007]     A separation unit typically would not be configured to accept a pig, particularly a coalescence unit because it comprises a large number of small diameter tubes mounted parallel to the flow. For a subsea separation unit of this type, a bypass line with control valves would need to be provided. Constructing a bypass line would add to the expense and maintenance of a subsea processing installation.  
       SUMMARY OF THE INVENTION  
       [0008]     In this invention, a separation unit is mounted within a housing. The housing has inlet and outlet ports that couple the housing inline with a flow line. The separation unit is movable between an operational position in the flow path between the inlet and outlet ports to a storage position outside of the flow path to enable a pipeline pig to be pumped through the ports and the housing.  
         [0009]     In one embodiment, the separation unit pivots about a pivot point when moving from the operational phase to the storage position. An actuator causes the movement from the storage position to the operational position. The actuator may comprise a spring that continuously urges the separation unit to the storage position. The pipeline pig will contact the separation unit as it is being pumped through the flow line, compressing the spring and swinging the separation unit out of the flow path. In another embodiment, the actuator is a powered energizer that strokes the separation unit between the operational and storage positions.  
         [0010]     In still a further embodiment, the actuator moves the separation unit along a path that is perpendicular to the well fluid flow path extending through the housing. In this embodiment, the separation unit is preferably mounted in a gate that has an aperture that aligns with the inlet and outlet ports while the separation unit is in a storage position.  
         [0011]     A sleeve may be mounted between the ports to form a tubular bridge for the pipeline pig. The sleeve moves axially to disengage one end from one of the ports and provide room for the separation unit to move to the operational position. While the separation unit is in the storage position, the sleeve engages both of the ports to provide a tubular bridge for the pig to pass through.  
         [0012]     The separation unit could be of different types, but preferably comprises a coalescing filter. The filter has a plurality of electrically conductive tubes that are mounted to a carrier plate. An electrical source provides voltage to the tubes to perform the coalescing step as the well fluid flows through the tube.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic sectional view of an inline coalescing unit.  
         [0014]      FIG. 2  is a schematic side view of the coalescing unit of  FIG. 1 , showing the coalescer removed from its housing.  
         [0015]      FIG. 3  is a schematic sectional view of the coalescing unit of  FIG. 1 , with the coalescer shown being lifted from its housing  
         [0016]      FIG. 4  is a front view of the flapper of the coalescing unit of  FIG. 1 , showing the coalescer tubes.  
         [0017]      FIG. 5  is a schematic sectional view of an alternate embodiment of an inline coalescing unit, with a bridge sleeve shown in an engaged position.  
         [0018]      FIG. 6  is a sectional view of the coalescing unit of  FIG. 5 , showing the bridge sleeve in a storage position.  
         [0019]      FIG. 7  is a schematic sectional view of another alternate embodiment of an inline coalescing unit.  
         [0020]      FIG. 8  is an enlarged schematic view of the coalescing unit of  FIG. 7 , taken along the line  8 - 8  and showing the coalescer removed from its housing.  
         [0021]      FIG. 9  is a sectional view of the coalescing unit of  FIG. 7 , shown in the engaged position.  
         [0022]      FIG. 10  is a sectional view of the coalescing unit of  FIG. 7 , with the coalescer shown being lifted from its housing.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Referring to  FIG. 1 , inline coalescing unit  11  is an oil/water separator adapted to be connected into a flow line leading to additional separation equipment. Inline coalescing unit  11  has a housing or body  13  with a central cavity  15 . An upstream flow line connector or inlet port  17  joins cavity  15  perpendicular to an axis of cavity  15 . A downstream flow line connector or outlet port  9  also joins cavity  15  coaxial with upstream flow line connector  17 . Each flow line connector  17 ,  19  has a flange  21  for coupling to a flow line (not shown). As will be appreciated by those skilled in the art, flange  21  can be replaced with any other device for coupling a flow line. A passage  22  extends in a straight line from flow line connector  17 , through cavity  15  and out flow line connector  19 . Preferably, the inner diameters of the flow line connectors  17 ,  19  are the same. A cylindrical projection equal to the inner diameters of flow line connectos  17 ,  19  extends through cavity  15 .  
         [0024]     A seat ring  23  is shown mounted on the downstream side of cavity  15  surrounding the junction of cavity  15  with passage  22 . Seat ring  23  has a hole that has the same diameter as passage  22 . Seat ring  23  is coaxial with passage  22  about a longitudinal axis. Seat ring  23  has an inclined upstream face  23   a  in this embodiment. The lower side of seat ring  23  is thicker than the upper side in this embodiment, however, the upstream face  23   a  could be perpendicular to the axis of passage  22 , rather than inclined.  
         [0025]     A flapper  25  moves from a storage position, shown in  FIG. 1  by the solid lines, to an engaged position shown by the dotted lines. In the storage position, flapper  25  is located outside of the cylindrical projection passing between flow line connectors  17 ,  19  through cavity  15 . Preferably, flapper  25  is a circular disc, and in the engaged or operational position, flapper  25  abuts face  23   a , but sealing is not required. As desired, flapper  25  can be in different shapes like rectangular or square, depending on the cross-section of passage  22 . An actuator  27  moves flapper  25  to the engaged position. Actuator  27  may comprise a spring that continuously biases flapper  25  to the engaged position. Alternately, actuator  27  may comprises a powered unit that moves flapper  25  between the engaged and storage positions. Actuator  27 , which could be mechanical or hydraulic, strokes a link member  29  upward and downward. This movement causes flapper  25  to pivot about arms  31  that connect it to a portion of actuator  27 .  
         [0026]     Referring to  FIGS. 2 and 4 , flapper  25  is part of a separator that assists in separating water from oil. In the preferred embodiment, the separator comprises a coalescing unit  33 , although other types are feasible. Coalescer  33  is mounted within flapper  25  and includes an insulation plate  35  that provides electrical insulation. A plurality of electrically conductive tubes  37  are mounted to insulation plate  35 , each extending parallel to the longitudinal axis of flow line  22 . Wires  39  ( FIG. 2 ) connect each tube  37  to an electrical power supply for providing voltage. Wires  39  pass through arm  31  to the exterior.  
         [0027]     The voltage causes an electrostatic field to be applied to the oil and water mixture at tubes  37 . By exposing the mixture of water and oil to an electrostatic field, dipolar water droplets contained in the oil phase will be oriented in a way that makes them collide or coalesce with each other. This causes the water droplets to grow to bigger droplets. Generally, bigger droplets move and separate faster than smaller droplets. Consequently, coalescer  33  serves as a preliminary stage in the separation of water from oil. Alternatively it may be an independent process.  
         [0028]     Actuator  27  is secured by clamps  41  to the upper end of body  13 . Clamps  41  may be actuated remotely in the event of a subsea environment by a remote operated vehicle. Releasing clamps  41  allows actuator  27  and flapper  25  to be pulled from housing  13  for maintenance as illustrated in  FIG. 3 .  
         [0029]     In the engaged or operational position, flapper  25  will be in engagement with seat ring face  23   a . However, it need not seal because the fluid flowing through passage  22  will flow through tubes  37  mounted in flapper  25 . The electrostatic field applied to tubes  37  causes the water droplets to grow in size for further separation downstream.  
         [0030]     For pigging operations through passage  22 , the pig (not shown) is typically pumped in the direction indicated by the arrow in  FIG. 1  to clean the flow lines. If actuator  27  comprises a spring, rather than being powered, the pig would bump into flapper  25  and push it to the storage position shown in  FIG. 1  as it proceeds past. An optional latch (not shown) could lock flapper  25  in the storage position as the pig passes, then release flapper  25  once the pig has passed. If actuator  27  is externally powered, the operator supplies power, such as hydraulic pressure, to cause actuator  27  to lift link  29 , which rotates flapper  25  to the storage position. In the storage position, flapper  25  is located within cavity  15  above passage  22  and in a generally horizontal position. This storage position allows the pig to pass freely through flow line connectors  17 ,  19 .  
         [0031]     Numeral  43  in  FIG. 1  indicates a distance from the downstream side of body  13  to the upstream side at a point where flapper  25  is located. Distance  43  must be bridged by the pig as it is being pumped through flow line passages  22 . A pump-through pig relies on annular seals that sealingly engage the walls of passages  22 . The seal or seals cannot seal while traversing the bridging distance  43 . The seals of a typical pig may not be spaced apart sufficiently to allow the pig to traverse bridging distance  43 . For example, if there is only a single pig seal with a width less than bridging distance  43 , the pig would become unsealed while located in bridging distance  43 , ceasing movement.  
         [0032]     In order to overcome this particular limitation on bridging distance  43 ,  FIGS. 5 and 6  illustrate an alternate embodiment. In this embodiment, actuator  27 ′ and flapper  25 ′ are constructed as in the first embodiment. Both are located within cavity  15 ′ of body  13 ′. The downstream flow line connector  19 ′ may be the same as in the first embodiment. Upstream flow line connector  17 ′, however, is configured to receive a reciprocating bridge sleeve  45 .  
         [0033]     Bridge sleeve  45  has a piston  47  that is carried in an enlarged bore portion  49  of flow line connector  17 ′. Hydraulic fluid is supplied to selectively stroke bridge sleeve  45  from the engaged position shown in  FIG. 5  to the storage position shown in  FIG. 6 . Piston  47  is an annular member integrally formed on the outer diameter of bridge sleeve  45 . Bridge sleeve  45  has an enlarged outer diameter downstream end portion  51  that extends from piston  47  to a downstream end  53 . Downstream end  53  is inclined to mate flush with the upstream face of seat ring  23 ′. A reduced outer diameter end portion  55  extends in an upstream direction from piston  47  within an upstream bore portion  56 . Bore portion  56  is smaller in diameter than enlarged bore portion  49  but slightly larger in diameter than the flow lines (not shown) that connect to inline coalescer  11 ′. A bore  57  of uniform diameter that is the same diameter as the flow line extends completely through bridge sleeve  45 .  
         [0034]     While bridge sleeve  45  is in the engaged position of  FIG. 5 , a pig can readily pass through bores  56  and  57  while maintaining its seal. Flapper  25 ′ will be in an upper storage position located above bridge sleeve  45 . While bridge sleeve  45  is in the storage position, flapper  25 ′ is back in engagement with seat ring  23 ′ and bridge sleeve  45  is stroked to the left.  
         [0035]     The embodiments of  FIGS. 1-6  resemble a check valve. The embodiment of  FIGS. 7-10  resembles a gate valve. Inline coalescing unit  59  has a body  61  that is tubular with flow line connectors  63  extending in opposite directions, parallel and coaxial with each other. Each flow line connector  63  connects to a flow line  65  for receiving and discharging the oil and water mixture.  
         [0036]     In this embodiment, a pair of seat rings  67 ,  69  are utilized, each on an opposite side of the central cavity in body  61  at the junction with the bores of flow line connectors  63 . A gate  71  moves vertically and slidingly between seat rings  67 ,  69 . Gate  71  preferably has a passage  73  that is of the same diameter as the passages of flow line connectors  63 .  FIG. 7  shows the position that would be utilized for a pigging operation.  
         [0037]     A coalescer  75  is mounted in gate  71 , also. In this embodiment, coalescer  75  is below passage  73 , however it could alternately be above. Coalescer  75  may be the same as coalescer  33  of  FIG. 2 . An actuating stem  77  will selectively move gate  71  between the position shown in  FIG. 7  and that shown in  FIG. 9 . In  FIG. 9 , coalescer  75  is located inline for processing the oil and water flowing through flow line  65 . Actuating stem  77  is connected to an actuator  79 , such as a linear motor or a piston  81 , shown in  FIG. 8 . Piston  81  is stroked within a cylinder  83 . Wires  85  for supplying power to coalescer  75  extend through actuator stem  77 .  
         [0038]      FIG. 10  illustrates actuator  79  and gate  71  being retrieved. Opening clamps  87  allows retrieval of the components, leaving the seat rings  67 ,  69  in place.  
         [0039]     The invention has significant advantages. The separation unit may be placed inline with flow lines. The operator can perform pigging operations without a bypass loop. The system operates remotely, thus is particularly applicable to subsea environments. In some embodiments, the separation unit may be retrieved readily for repair or replacement.  
         [0040]     While the invention has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited but susceptible to various changes without departing from the scope of the invention.