Abstract:
A sampling assembly for taking single or multiphase production fluid samples from a subsea well. The sampling assembly includes a receiving structure that houses a saver sub and a retrievable skid. The sampling assembly allows for repeated retrieval of collected samples and replenishment of empty sample chambers using the retrievable skid. A releasable connection interface between the retrievable skid and the saver sub allows an ROV to connect the retrievable skid to the saver sub and provide electrical and hydraulic power to the sampling assembly for taking samples.

Description:
BACKGROUND 
     During the lifespan of an oil reservoir, samples from the reservoir can be collected and analyzed. To effectively sample the production fluid from a well, and more particularly a subsea well, sampling systems are often located in close proximity to the wellhead. Wellhead sampling presents a challenge due to the potential for dispersed and mist flow from the wellhead containing both liquid and gas phases (multiphase flow). To take a liquid sample, the liquid phase must be separated from the gas phase. Multiphase flows exhibiting a dispersed or mist flow regime can be difficult to separate into component liquid and gas phase flows, in turn making the collection of liquid-only samples more difficult. 
     Further, sample systems may use a flow device, such as a venturi or an orifice plate, to generate a pressure differential proportional to the production flow. If the production flow rate is too low, the pressure differential generated by the flow device may be insufficient to retain a sample that contains both liquid and gas. 
     Further, multiple samples may be taken during the life of the well. Connecting and unconnecting equipment can be time consuming and servicing connections permanently mounted on the wellhead or other subsea structure can be difficult. 
     SUMMARY 
     An oil or gas well and related sampling assembly of this disclosure can be used to sample production fluids from the oil or gas well. The assembly includes a receiving structure that houses a saver sub, a retrievable skid, and protection plates. The receiving structure can be fixably attached to a manifold, an Xmas tree, or a length of pipe from which samples will be taken. The saver sub accesses the production flow via its connection with the receiving structure and then releasably connects with the retrievable skid. The receiving structure allows production fluid samples to be taken throughout the lifecycle of the manifold and the saver sub reduces the number of makes and breaks on the couplings in the manifold—instead, the interface between the retrievable skid and the saver sub is cycled with every sample taken. Among other valves and couplings, the retrievable skid houses the sample collection chambers. 
     Once the samples have been collected, a remotely operated vehicle (ROV) removes the retrievable skid and brings it to the surface. After the sample chambers are emptied and replaced, the sampling bottles are placed back in the retrievable skid, returned subsea, and reinstalled in the sampling system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  shows a perspective view of a receiving structure in accordance with various embodiments; 
         FIG. 2  shows a cross-sectional view of the saver sub interface on the receiving structure; 
         FIGS. 3 and 4  show perspective views of protection plates in accordance with various embodiments; 
         FIGS. 5 and 6  show perspective views of a saver sub in accordance with various embodiments; 
         FIG. 7  shows a bottom view of an embodiment of the multiple quick connect components on the saver sub that interface with the receiving structure; 
         FIG. 8  shows a top view of an embodiment of the multiple quick connect components on the saver sub that interface with the retrievable skid; 
         FIG. 9  shows a perspective view of the retrievable skid in accordance with various embodiments; 
         FIG. 10  shows a top view of an embodiment of the multiple quick connect components on the chassis plate of the retrievable skid that interface with the saver sub; 
         FIG. 11  shows a perspective view of the retrievable skid; 
         FIG. 12  shows a perspective view of a pump driven sampling assembly in accordance with various embodiments; 
         FIG. 13  shows an exploded view of a pump driven sampling assembly; 
         FIG. 14  shows an alternative embodiment of a pump driven sampling assembly; and 
         FIG. 15  shows a perspective view of an embodiment of a protection plate mounted on the receiving structure. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is directed to various embodiments of the invention. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
     Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the terms “couple,” “connect,” “engage,” and “attach” are intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. The term “fluid” may refer to a liquid or gas and is not solely related to any particular type of fluid such as hydrocarbons. The term “pipe,” or the like refers to any fluid transmission means. 
       FIG. 1  shows the receiving structure  100 , comprised of a base platform  110 , a saver sub interface  130 , a plurality of posts  140 , and a sloped top structure  170 . The base platform  110  is generally rectangular but may be configured in any suitable shape. The posts  140  extend from and connect the base platform  110  to the sloped top structure  170 . The sloped top structure  170  includes sides that slope inward toward the center of the base platform  110 , creating upper perimeter  171  and lower perimeter  172 ; the upper perimeter being larger than the lower perimeter. In a preferred embodiment, the angle of the sloped top structure  170  is between thirty degrees and sixty degrees. 
     Two middle saver sub guides  155  extend from the surface of the base platform  110 . The middle saver sub guides  155  bend outward toward the lower rectangular perimeter  172  such that the upper portion of the middle saver sub guides  155  is angular and disposed on the lower rectangular perimeter  172 . Two corner saver sub guides  150  are disposed on the surface of the raised platform  120 . Two corner retrievable skid guides  160  are disposed on the surface of the base platform  110 . Each of the four corner guides (2-saver sub guides  150 , 2-retrievable skid guides  160 ) are made up of two middle saver sub guides  155  positioned orthogonally next to each other such that the lower portions of the guides contact each other, forming an “L” shape. A triangular web  158  bridges the gap between the top angular portions of the guides. The top portions of the corner guides  150 ,  160  bend outward toward the lower rectangular perimeter  172  such that the triangular web  158  and upper portion of guides  150 ,  160  are angular and disposed on the lower rectangular perimeter  172 . 
     The raised platform  120  is disposed on the surface of the base platform. The raised platform  120  may be rectangular in shape with two corners cut out on the side toward the center of the base platform  110 ; the two cut outs allowing the middle saver sub guides  155  to attach to the surface of the base platform  110 . The saver sub interface  130  is disposed on the surface of the raised platform  120  and houses various components (not shown) for interfacing with the saver sub. 
       FIG. 2  shows a cross-sectional view of the saver sub interface  130 , which includes: a top plate  135 , side walls  136   a , and the multiple quick connect (MQC) mating components. The MQC components include: bushing guides  131 , a lockdown housing  134 , and two pass through holes  133 . The MQC allows production fluid to be communicated between the manifold and saver sub (to be described in more detail below). The lockdown housing  134  is typically located in the center of the top plate  135 , is cylindrical, and protrudes below the surface of the top plate  135 . The lockdown housing  134  attaches with a locking mechanism on the saver sub (to be discussed in more detail below). On either side of the lockdown housing  134  are two pass through holes  133  that accommodate couplings (not shown). On either side of the pass through holes  133  are two bushing guides  131 . The bushing guides  131  are secured to the saver sub interface  130  by lock nuts  132 , and receive guide pins located on the saver sub (to be discussed in more detail below). 
       FIGS. 3 and 4  show protection plates  200  and  201 . The protection plates  200 ,  201 , mount side by side on the sloped top structure  170  of the receiving structure  100 . Each protection plate has a locking mechanism  220  that mates with the sloped top structure  170  of receiving structure  100 . In addition, protection plate  200  also has saver sub guides  210 , similar to the corner saver sub guides  150  located on the receiving structure  100 . 
     As shown in  FIGS. 5 and 6 , saver sub  300  includes a base structure  310 , a top plate  320 , a plurality of posts  340 , a three port bottle  370 , pipe work  380 , and retrievable skid guides  350 . The base structure  310  includes a top surface  310   a , a plurality of side surfaces  310 , and additional couplings and guidance pins to be described in more detail below. The top surface  310   a  includes notches cut out of two corners, creating indented sides  310   b ,  341 . A hole  375  is cut out of the top surface  310   a  to allow the three port bottle  370  to sit approximately half above and half below the top surface  310   a.    
       FIG. 7  shows an underside view of the lower surface  311   c . The lockdown boss  334  is disposed on the underside of lower surface  311   c  and connects to the lockdown housing  134  on the receiving structure  100  as shown in  FIG. 2 . Couplings  333  are spaced from the lockdown boss  334 . The couplings  333  interface with the pass through holes  133  on the receiving structure  100 , as shown in  FIG. 2 , and are positioned accordingly. The receiving structure guide pins  331  are disposed on the underside of the lower surface  311   c  and aid in the proper alignment of the saver sub  300  with the receiving structure  100  during installation. The receiving structure guide pins  331  fit inside the bushing guides  131  shown in  FIG. 2 . 
       FIG. 5  shows a plurality of posts  340  and  341  extending between the base structure  310  to the top plate  320 . As shown in  FIG. 8 , the top plate  320  includes a lockdown bucket  330 , a lift mandrel  365 , retrievable skid guides  350 , and the mating MQC components: two retrievable skid guide pins  360 , lockdown boss  361 , one half inch coupling  362 , and two one inch couplings  363 . 
     The lockdown bucket  330 , shown in  FIG. 5 , serves as the connection point for the ROV to lock the saver sub  300  onto to receiving structure  100  in a method as is known to those skilled in the art. The lockdown bucket  330  includes a releasable connection moveable between a locked and unlocked position and operable by the ROV. The lift mandrel  365  is disposed on the top plate  320  and protrudes above the top plate  320 . The lift mandrel  365  includes alternating cylindrical and conical sections, and is engageable by a lifting adapter (not shown) as is known by those skilled in the art. The lower portion of the two retrievable skid plate guides  350  are disposed on the top plate  320  and extend from the surface of the top plate  320  at the two posts  341 . The upper portion of the retrievable skid guides  350  is angled to aid the ROV operator to guide the retrievable skid  400  into the receiving structure  100  next to the saver sub  300 . 
     Two couplings  363  are located along top plate  320 . The couplings  363  interface with the retrievable skid MQC components (to be described below). The lockdown boss  361  is disposed in the smaller rectangular portion of the top plate  320 . The lockdown boss  361  mates with the lockdown boss of the retrievable skid (to be discussed below). The one half inch coupling  362  is disposed on the top plate  320  a distance away from the lockdown boss  361 . The coupling  362  also interfaces with the retrievable skid MQC components. The retrievable skid guide pins  360  are disposed away from coupling  362  and engage the bushing guides located on the retrievable skid (to be discussed in greater detail below). 
       FIG. 5  shows pipe work  380  disposed between the top plate  320  and the base structure  310 , which moves fluid between the manifold (not shown) and the retrievable skid  400 . The pipe work  380  connects various components; for example, pipe work  380  connects coupling  333  to the three port bottle  370  as well as the three port bottle  370  to the couplings  363 . 
       FIG. 11  shows the retrievable skid  400  with buoyancy shells  404   a  and  404   b . The buoyancy shells  404   a ,  404   b  are attached to the chassis plate  403  (shown in  FIG. 9 ) and, thus, form part of the structural frame of the retrievable skid  400 . The buoyancy shells  404   a ,  404   b  also serve to reduce the in-water weight of the retrievable skid  400 . However, it should be appreciated by one of skill in the art that the buoyancy shells  404   a ,  404   b  are not necessary for the retrievable skid  400 . 
       FIG. 9  shows the retrievable skid  400  without the buoyancy shells. The retrievable skid  401  includes a truss  402 , lockdown bucket  430 , hotstab  470 , pump  440 , sample chambers  420  (four are shown), and MQC components: bushing guides  460 , couplings  462  and  463 , and skid lockdown boss  461 . The truss  402  includes a chassis plate  403  with a plurality of cut outs to accommodate the mounting of various retrievable skid components, including the buoyancy shells  404   a ,  404   b  shown in  FIG. 11 . The chassis plate  403  provides the structural support for the retrievable skid  400  and any impact loads received by a retrievable skid component is transferred to the chassis plate  403 . A plurality of additional posts also form the truss  402 . 
     The lockdown bucket  430  is disposed on the chassis plate  403  such that the aperture of the lockdown bucket  430  is disposed on the top surface of the truss  402 . The lockdown bucket  430 , shown in  FIG. 11 , serves as the connection point for the ROV to lock the retrievable skid  300  onto to the saver sub  300  in a method as is known to those skilled in the art. The lockdown bucket  430  includes a releasable connection moveable between a locked and unlocked position and operable by the ROV. 
     The aperture of the electro-hydraulic hotstab receptacle  470  (referred to as “hotstab” hereinafter) is similarly disposed on the top surface of the truss  402 . The hotstab  470  mates with a hotstab counterpart on the ROV as known to those skilled in the art. The hotstab  470  is used for hydraulic power of the pump  440  and for power and communication for other components, supplied by the ROV (not shown). A flexible hose  475  connects the hotstab the hotstab pod  477 . The hotstab pod  477  is connected through the electrical harness  480  and the connector  490  to the sensor which is mounted to the chassis plate  403 . 
     The pump  440 , preferably a positive displacement pump, is preferably disposed in approximately the chassis plate  403  and connects to the hotstab  470 , the three port bottle  370  of the saver sub  300 , and the sample chambers  420 . The pump  440  is powered by the hotstab  470  and receives hydraulic power from an ROV (not shown). The pump  440  draws production fluid samples through the three port bottle  370 , fills the sample chambers  420 , and flushes the system. In a preferred embodiment, the pump  440  has three pumping modes: single phase, multiphase, and flushing. 
     The sample chambers  420  can be, for example, cylindrical, grouped in a 2×2 matrix formation, and disposed radially on the bottom surface of the chassis plate  403 , such that the sample chambers  420  surround the pump  440 . Although four sample chambers  420  are shown, any number of sample chambers may be used and positioned in any appropriate configuration. The preferred embodiment of a sample chamber  420  has three separate compartments—one for the fluid sample, one for MEG/water/glycol, and one for nitrogen. Filling the sample chamber  420  with fluid is facilitated by drawing water/glycol from the middle compartment, thus, drawing in the fluid sample. Once the sample chamber  420  is returned to the surface, 10% of the fluid sample is purged. Then the valve that communicates between the water and nitrogen compartments is opened, which allows a gas cap to be introduced to the sample. 
     The MQC components are shown in  FIG. 10 . The bushing guides  460  and the two one inch couplings  463  are disposed on the chassis plate  403 . All the couplings  462 ,  463  extend above and below the surface of the chassis plate  403 . The skid lockdown boss  461  also extends above and below the surface of the chassis plate  403 . The MQC components on the retrievable skid  400  interface with the upper MQC components of the saver sub  300  in like manner as the lower saver sub MQC components interface with the MQC components of the receiving structure  100 . 
       FIGS. 12 ,  13 , and  15  show an embodiment for a sampling assembly for sampling production fluids from an oil or gas well. The well includes a structure, such as a manifold, an Xmas tree, or a length of pipe (not shown, generally referred to as “manifold”) and a sampling assembly that includes a receiving structure  100 , a saver sub  300 , a retrievable skid  400 , and protection plates  200 ,  201 . The receiving structure  100  is secured to the manifold, from which production fluid samples will be taken. The receiving structure  100  is connected to the production flow in a manner known to those skilled in the art. The receiving structure  100  is considered non-releasably connected to the manifold, preferably welded into place. The connection is designed as a long term, permanent type connection rather than a quick connect/disconnect configuration. Via an ROV, as known to those skilled in the art, the saver sub  300  is guided by and installed on the raised platform  120  of the receiving structure  100 . The retrievable skid  400  is installed after the saver sub  300  and is transported and installed via ROV on the receiving structure  100  adjacent to the raised platform  120 . In a preferred embodiment, when the saver sub  300  and the retrievable skid  400  are installed in the receiving structure  100 , the receiving structure  100  transfers the load from the saver sub  300  and retrievable skid  400  to the manifold. 
       FIG. 13  depicts the components of the pump driven sampling assembly prior to integration. The saver sub  300  attaches to the receiving structure  100  at the saver sub interface  130  disposed on the raised platform  120 . Next, the retrievable skid  400  is placed, by ROV, in the receiving structure  100 ; the retrievable skid  400  partially overlaps and interfaces with the saver sub  300 . 
     The saver sub  300  accesses the production flow via its MQC connection with the receiving structure  100 . The retrievable skid  400  is then connectable to the saver sub  300  with the MQC “quick” connect/disconnect connection. Thus, the receiving structure  100  allows samples to be taken throughout the lifecycle of the manifold and the saver sub  300  reduces the number of makes and breaks on the couplings between the manifold and the receiving structure  100 —instead, the interface between the retrievable skid  400  and the saver sub  300 , and also possibly the interface between the saver sub  300  and the receiving structure  100 , is cycled with every sample taken. This saves the wear and tear on the manifold itself and allows for servicing the receiving structure  100  by replacing the saver sub  300  when needed as opposed to replacing parts on the manifold itself. 
       FIG. 15  shows the receiving structure  100  with protection plate  200  installed. Prior to the saver sub  300  installation, protection plate  200  is disposed on the receiving structure in the diametrically opposite side from the raised platform  120 . Saver sub guides  210  located on protection plate  200  serve to guide the saver sub  300 , as shown in  FIG. 10 , into the proper location over the raised platform  120  and the saver sub interface  130 . Both protection plates  200 ,  201  may be installed when the receiving structure  100  has no components installed or when only the saver sub  300  is installed. Both protection plates  200 ,  201  are removed to allow for installation of the retrievable skid  400 . 
     The retrievable skid  400  shown in  FIG. 12  extends above the top of the receiving structure  100 . In a preferred embodiment, the retrievable skid  400  can support its own weight and can withstand impacts from the ROV.  FIG. 14  shows an alternative embodiment that includes an alternative receiving structure  102 , an alternative saver sub  302 , and an alternative retrievable skid  402 . In this embodiment, the alternative saver sub  302  and alternative retrievable skid  402 , when integrated in the alternative receiving structure  102 , are fully recessed below the level of the protection plates,  200 ,  201  as shown in  FIG. 14 , which reduces potential ROV impacts. 
     Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.