Patent Publication Number: US-2018038515-A1

Title: Method and apparatus for flooding a subsea pipeline

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Disclosure 
     This disclosure relates generally to the field of subsea pipelines for oil or gas, and in particular to the initial pre-commissioning of such subsea pipelines prior to their use to convey oil or gas. 
     2. Description of the Related Art 
     Offshore efforts to produce oil and gas typically require subsea pipelines for transport of oil and gas from wellheads to gathering structures, hub facilities and to onshore processing refineries. Newly constructed subsea pipelines must undergo a series of pre-commissioning steps which generally may include flooding, cleaning and gauging, hydrotesting, dewatering and drying before any oil or gas product can be introduced into the pipeline. The initial flooding operations typically include pushing, or pumping, a preinstalled pig, or pigs, through the pipeline with seawater, which may be chemically treated and filtered. The pipeline may be flooded between a pair of valved closures such as pipeline end terminations. The pig, or pigs, passing through the pipeline in conjunction with flooding may clean the pipeline of millscale and other debris, as well as assess dents, buckles and other out of round defects in the pipeline. Typically, an electric or hydraulic pump associated with or on a subsea vehicle, or Remote Operated Vehicle (“ROV”), is used to push, or pump, the pig in the initial flooding operations. 
     BRIEF SUMMARY 
     The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the subject matter disclosed herein. This summary is not an exhaustive overview of the technology disclosed herein. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
     In one illustrative embodiment, a system for flooding a subsea pipeline with seawater may include: a high pressure/low flow pump; a jet pump having a jet pump housing, a nozzle within the jet pump housing having a nozzle inlet in fluid communication with the high pressure/low flow pump and a nozzle outlet, a fluid inlet in the jet pump housing in fluid communication with the nozzle outlet, a diffuser in the jet pump housing in fluid communication with the nozzle outlet and the fluid inlet and a diffuser outlet adapted to be in fluid communication with the subsea pipeline. 
     In another illustrative embodiment, a method for flooding a subsea pipeline with seawater may include: disposing a high pressure/low flow pump in fluid communication with a nozzle inlet of a nozzle disposed within a jet pump housing of a jet pump; pumping sea water with the high pressure/low flow pump into the nozzle inlet of the jet pump and out of a nozzle outlet into the jet pump housing sucking in seawater into the jet pump housing through a fluid inlet in the jet pump housing; pumping the seawater from the nozzle outlet and the seawater from the fluid inlet through into a diffuser in the jet pump housing; and pumping seawater from the diffuser into the subsea pipeline. 
     In another illustrative embodiment, a subsea pipeline may include: at least one subsea pipe section disposed between first and second pipeline end terminations; a high pressure/low flow pump; a jet pump having a jet pump housing, a nozzle within the jet pump housing having a nozzle inlet in fluid communication with the high pressure/low flow pump and a nozzle outlet, a fluid inlet in the jet pump housing in fluid communication with the nozzle outlet, a diffuser in the jet pump housing in fluid communication with the nozzle outlet and the fluid inlet, and a diffuser outlet adapted to be in fluid communication with the first pipeline end termination of the at least one subsea pipe section; and at least one pig disposed in the at least one subsea pipe section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present system and method may be understood by reference to the following description taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a side view of a subsea pipeline section and a vessel in accordance with an illustrative embodiment; 
         FIG. 2  is a side view of the pipeline section of  FIG. 1  in more detail; and 
         FIG. 3  is an enlarged partial cross-sectional view of the pipeline section of  FIG. 2  denoted by dotted-line circle  3  of  FIG. 2 . 
     
    
    
     While certain embodiments of the present system and method will be described in connection with the present illustrative embodiments shown herein, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. In the drawing figures, which are not to scale, the same reference numerals are used throughout the description and in the drawing figures for components and elements having the same structure, and primed reference numerals may be used for components and elements having a similar function and construction to those components and elements having the same unprimed reference numerals. 
     DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     It should be understood that, although an illustrative implementation of one or more embodiments are provided below, the various specific embodiments may be implemented using any number of techniques known by persons of ordinary skill in the art. The disclosure should in no way be limited to the illustrative embodiments, drawings, and/or techniques illustrated below, including the exemplary designs and implementations illustrated and described herein. Furthermore, the disclosure may be modified within the scope of the appended claims along with their full scope of equivalents. 
     With reference to  FIGS. 1 and 2 , a subsea pipeline  40  on sea, or ocean, floor  21  has at least one pipe section  44  disposed between two pipeline end terminations  42 ,  46 . The pipeline end termination  42 ,  46  can include any type of suitable valve closure  43  for a subsea pipeline and can include hot stab connections  47  or laydown heads for abandonment, recovery, or initiation. The pipeline end terminations  42 ,  46  can also include subsea collection hubs having several pipeline terminations and valved closures. Such hubs can be dimensioned to connect a number of flowlines carrying oil and gas from various subsea fields to production lines that may run to onshore facilitates. A support vessel, or ship,  10 , or any other suitable platform for supporting operations for the subsea pipeline  40 , is located above the pipeline  40 . 
     To initially flood the pipeline  40 , at least one pig  41  may be loaded into the pipeline  40  using any suitable technique. For example, the pig  41  may be launched from the support vessel  10  using available techniques and systems connecting to the pipeline  40 . Alternatively, as shown in  FIGS. 1 and 2 , a pig launcher  50  may be associated with the pipeline end termination  42  for launching the at least one pig  40 . A pig receiver manifold  48 , may be associated with the other pipeline end termination  46  to receive the pig  41 , after it has been pushed, or pumped through pipeline  40 . 
     As seen in  FIG. 1 , support vessel, or ship,  10  on the ocean surface  25 , is generally located above the pipeline  20 . Ship  10  has at least one high pressure/low flow pump, or pumps,  60  associated with ship  10  in any suitable manner. High pressure/low flow pump  60  may be mounted upon the upper deck of ship  10  as shown in  FIG. 1 , or optionally, disposed below deck within ship  10 . The high pressure/low flow pump  60  may be of any conventional design, having the requisite pressure and flow characteristics to operate in the manner to be hereinafter described. 
     Pump, or pumps,  60  may be a test pump  61  which are sometimes found on support ships or vessels,  10  in connection with offshore operations. Pump  60  is preferably capable of pumping a fluid, such as seawater, at a pressure range of from 50 to 690 bar, at a flow rate in the range of 6 to 120 M 3 /hr for each pump. Seawater to be pumped by pump  60  may be obtained from the sea  23  in any conventional manner, such as by use of a suction line (not shown) placed within the ocean  23  and in fluid communication between the ocean  23  and the inlet, or suction side, of pump  60 . A downline  65  extends downwardly from pump  60  to a jet pump  80 , as will hereinafter be described in greater detail. A downline is a conduit between a vessel, or ship, on the ocean surface and a subsea pipeline connection. Downline  65  may be coiled tubing or a hose,  66  of any suitable construction having the requisite strength characteristics to be used in an offshore environment to pump a fluid, such as seawater, at a high pressure and low flow rate from pump  60  to jet pump  80 . Jet pump may be associated with, and rest upon, a subsea skid frame (not shown) which rests upon the ocean floor  21 . 
     With reference to  FIGS. 2 and 3 , jet pump  80  will be described in greater detail. Jet pump  80  is sometimes also referred to as an ejector and eductor. Jet pump  80  preferably includes a jet pump housing  81 , which houses the various components of jet pump  80 . Jet pump housing  81  may be made of any suitable metal or plastic material capable of subsea use in seawater upon ocean floor  21 . It must also have the requisite strength characteristics to withstand the forces exerted upon it by the seawater being pumped through it from the high pressure/low flow pump  60  and from the pressure forces exerted upon it by sea  23 . Within housing  81  is disposed a nozzle  90  having a nozzle inlet  91  and a nozzle outlet  92 . Nozzle  90  is in fluid communication with the high pressure/low flow pump  60  from its connection to the downline  65 . Housing  81  may include an annular flange  82  against which a mating flange  67  associated with the bottom end of downline  65  may be secured. Any other suitable connection between the downline  65  and pump housing  81  may be utilized such as a hose attached to downline  65 , which hose may then be stabbed into pump housing  81 . 
     Housing  81  also includes a fluid inlet  85  which may be an annular pipe section  86 , which includes an annular flange  87  at its upper end  88 . The jet pump housing  81  includes a diffuser  95  which has a diffuser inlet  96  and a diffused outlet  97  as shown in  FIG. 3 . Jet pump housing  81 , nozzle  90 , and diffuser  95  each have a longitudinal axis, and preferably, each longitudinal axis of jet pump housing  81 , nozzle  90 , and diffuser  95  coincide with each other, as shown at  83  in  FIG. 3 . Preferably, the fluid inlet  85 , or annular pipe section  86  has a longitudinal axis  88  which is preferably disposed substantially perpendicular to the longitudinal axis  83  of the jet pump housing  81 , nozzle  90 , and diffuser  95 . 
     The nozzle inlet  91  of nozzle  90  is in fluid communication with the high pressure/low flow pump  60  via downline  65  and the fluid, or seawater, being pumped by the pump  60  enters the nozzle inlet  91  and exits nozzle outlet  92 . The fluid being pumped through downline  65  would have a flow rate and pressure commensurate with the water depth, pipeline diameter, and the desired speed for the pig  41  in pipeline  40 . As an example, the flow rate may be approximately 45 M 3 /hr and at a pressure of approximately 400 bar. Nozzle  90  is a tapering tube  93  having a circular cross-sectional configuration, whereby the diameter of tube  93  at the nozzle inlet  91  decreases as tube  93  tapers to nozzle outlet  92 . As the fluid, or seawater, being pumped by pump  60  enters nozzle inlet  91 , the high pressure seawater which initially enters nozzle outlet  91  at a low flow rate is compressed as it passes through nozzle  90  toward nozzle outlet  92 . The seawater exiting the nozzle outlet  92  is then moving at a much higher velocity, or speed, but is at a much lower pressure. The increase in the velocity of the seawater fluid exiting nozzle  90  and the lowering of the pressure of the seawater exiting fluid outlet  92  results from the Bernoulli&#39;s Principle. 
     As seen in  FIG. 3 , fluid inlet  85  in the jet pump housing  81  is in fluid communication with the nozzle outlet  92 . The seawater exiting nozzle outlet  92  is at a lower pressure and creates a suction force which sucks seawater into the fluid inlet  85  from the ocean  23 . As an example, the seawater being sucked into the fluid inlet  85  may be at a pressure of approximately 200 bar at a flow rate of approximately 156 M 3 /hr. The seawater from the nozzle outlet  92  and the seawater being sucked into the jet pump housing  81  through the fluid inlet  85 , then passes through, or is pumped through, jet pump housing  81  into the diffuser  95 . The diffuser  95  in jet pump housing  81  has a diffuser inlet  96  and a diffuser outlet  97 . The diffuser  95  has a generally tapering tubular shape with a circular cross-sectional configuration and the diameter of the diffuser  95  increases from the diffuser inlet  96  to a larger diameter at the diffuser outlet  97 . The seawater as it flows, or is pumped, through the diffuser  95  from the diffuser inlet  96  to the diffuser outlet  97  flows at a slower velocity at a high flow rate, while at the same time, its pressure is increased as it exits from the diffuser outlet  97  and into pipeline  40 . The pressure of the seawater exiting the diffuser outlet  97  is at an intermediate pressure level, which is less than the high pressure of the seawater initially entering nozzle  90  and higher than the pressure of the seawater entering pump  80  through fluid inlet  85 . 
     The seawater exiting the diffuser outlet may have a flow rate in the range of from 100 M 3 /hr to 1000 M 3 /hr and a pressure in the range of from 1 bar to 40 bar above the subsea pressure where pipeline  40  is located. As an example, the flow rate may be approximately 200 M 3 /hr at a pressure of approximately 214 bar. 
     Preferably, and optionally, the fluid inlet  85  may be provided with a filter  100  which has an annular flange fitting  101  which permits filter  100  to be connected to the annular flange  87  of fluid inlet  85 . Thus, as seawater is sucked into fluid inlet  85 , it first passes through filter  100  which filters, or screens, undesired materials, such as seaweed, and other similar undesired materials, from entering jet pump  80 . 
     With reference to  FIGS. 2 and 3 , jet pump housing  81  may have an annular flange member  82 ′ adjacent the diffuser outlet  97 , and annular flange member  82 ′ of jet pump housing  81  may be secured to a mating annular flange member  67 ′ associated with a pump discharge conduit  110  which is in fluid communication with pump  80  and the pipe end termination  42  via the pig launcher  50 . Seawater exiting diffuser outlet  97  of the jet pump  80  may then pass into the pipe end termination  42  via the pig launcher  50  and into pipe section  44  of pipeline  40  to pump, or push, pig  41  within pipe section  44  from the first pipeline end termination  42  toward the second pipeline end termination  46 , as shown in  FIG. 2 . The diffuser outlet  97  of jet pump  80  could be connected to the pig launcher  50  by use of a pump discharge hose  111 , or other tubular structure (not shown), in fluid communication with pig launcher  50  and pump  80 . The pump discharge hose  111  may be connected to the diffuser outlet by any suitable connection, such as the flanged connection shown in  FIG. 3  or by a stab connection (not shown). Similarly the pump discharge hose  111  may be connected to the pig launcher by any suitable connection such as a flange connection or a stab connection. Alternatively, and optionally, the diffuser outlet  97  of jet pump  80  could be connected directly to the first pipeline end termination by a pump discharge hose (not shown) in fluid communication with the first pipeline end termination  42  and the pump  80 . 
     Although pump  80  resting upon a subsea skid frame on the ocean floor  21  adjacent subsea pipeline  40  is described in connection with  FIG. 1 , pump  80 , optionally and alternatively, could be disposed on a subsea skid frame (not shown) hanging from the downline  65  above the ocean floor  21 . The pump discharge hose  111  attached to pump  80  would then be connected to the first pipeline end termination  42  via pig launcher  50 , or a pump discharge hose (not shown) like pump discharge hose  111  could be connected directly to the first pipeline end termination  42 . Alternatively and optionally, the downline  65  could be connected to a flow line (not shown) associated with, or attached to the subsea skid frame, and the pump discharge hose  111  could be attached to the flow line of the subsea skid frame at one end of the pump discharge hose  111  and the other end of the pump discharge hose  111  could then be attached to the pig launcher  50 . 
     If desired, the seawater being pumped by the high pressure/low flow pump  60  of vessel  10  could be chemically treated before it is pumped to jet pump  80  via downline  65  to add at least one chemical to the seawater pumped from pump  60  and ultimately into the pipe section  44  of subsea pipeline  40 . If desired, seawater exiting diffuser  95  may pass through a flowmeter and/or by a pressure transducer to provide the operator of the jet pump  80  with information as to the operation of the jet pump  80 . 
     At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. When numerical ranges or limitations are expressly stated, such express ranges or limitations may be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). The use of the term “about” means ±10% of the subsequent number, unless otherwise stated. 
     Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having may be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present disclosure. 
     While several embodiments have been provided in the present disclosure, it may be understood that the disclosed embodiments might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure and the appended claims. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. 
     In addition, the various embodiments described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and may be made without departing from the spirit and scope disclosed herein.