Abstract:
An apparatus including: a tubular suction pile; an indenter housing that surrounds the tubular suction pile, wherein the indenter housing is configured to: (a) be sunk into a seabed in response to a negative pressure created from water being removed from the tubular suction pile, and the indenter housing is configured to create a trench in the seabed; and comprise a water jetting device, within the indenter housing, that includes a first valve, a nozzle, and a channel that connects the first valve to the nozzle; and/or (b) impart a longitudinal vibration to the indenter housing and the indenter housing is configured to be sunk into a seabed in response to longitudinal vibration, and the indenter housing is configured to create a trench in the seabed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional No. 61/869,383, filed Aug. 23, 2013, which is incorporated herein in its entirety for all purposes. 
     
    
     TECHNOLOGICAL FIELD 
       [0002]    The present disclosure describes trenching and pipe burial techniques that can be used in offshore and arctic offshore regions. 
       BACKGROUND 
       [0003]    Development of offshore and offshore arctic pipelines requires consideration of unique design challenges such as seafloor scour/erosion and gouging by ice features. There are several types of ice features that may produce scouring of the seafloor, including icebergs, first year ice ridge keels and multiyear ridge keels. Ice is continuously drifting due to the action of environmental loads (e.g. wind and ocean currents) and may produce seabed scouring whenever water depth becomes lower than ice draft.  FIG. 1  shows a schematic representation of an ice gouging process. 
       SUMMARY 
       [0004]    An apparatus including: a tubular suction pile; an indenter housing that surrounds the tubular suction pile, wherein the indenter housing is configured to be sunk into a seabed in response to a negative pressure created from water being removed from the tubular suction pile, and the indenter housing is configured to create a trench in the seabed; and a water jetting device, within the indenter housing, that includes a first valve, a nozzle, and a channel that connects the first valve to the nozzle. 
         [0005]    An apparatus including: a vibration device; and an indenter housing that surrounds the vibration device, wherein the vibration device is configured to impart a longitudinal vibration to the indenter housing and the indenter housing is configured to be sunk into a seabed in response to longitudinal vibration, and the indenter housing is configured to create a trench in the seabed. 
         [0006]    A method including: lowering or dropping an indenter into a body of water, wherein the indenter includes a tubular suction pile, a housing that surrounds the tubular suction pile, and a water jetting device, within the housing, that includes a first valve, a nozzle, and a channel that connects the first valve to the nozzle; after the indenter comes to rest at a bottom of the seabed, sinking the indenter into the seabed, the sinking including creating a negative pressure by removing water from the tubular suction pile, wherein the negative pressure causes the indenter to sink to a predetermined depth in the sea bed; causing water to exit from the indenter, the water loosening soil in the seabed; and creating a trench in the seabed by pulling or pushing the indenter after the indenter is sunk into the seabed and the soil is loosened by the water. 
         [0007]    A method including: lowering or dropping an indenter into a body of water, wherein the indenter includes a vibration device, and a housing that surrounds the vibration device; causing the vibration device to impart a longitudinal vibration to the housing, said longitudinal vibration causing the housing to sink to a predetermined depth in a seabed; and creating a trench in the seabed by pulling or pushing the indenter after the indenter is sunk into the seabed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the disclosure to the particular forms disclosed herein, but on the contrary, this disclosure is to cover all modifications and equivalents as defined by the appended claims. It should also be understood that the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating principles of exemplary embodiments of the present invention. Moreover, certain dimensions may be exaggerated to help visually convey such principles. 
           [0009]      FIG. 1  is an example of a schematic representation of an ice gouging process. 
           [0010]      FIG. 2  illustrates some limitations of high cost trenching techniques. 
           [0011]      FIG. 3  illustrates an exemplary system for pipeline installation; 
           [0012]      FIG. 4A  is a plan view of an exemplary suction pile/jetting indenter. 
           [0013]      FIG. 4B  is a side view of an exemplary suction pile/jetting indenter. 
           [0014]      FIG. 5A  is a plan view of an exemplary vibrating indenter. 
           [0015]      FIG. 5B  is a side view of an exemplary vibrating indenter. 
           [0016]      FIG. 6  is flow chart of an exemplary method for installing a pipeline. 
           [0017]      FIG. 7  is a block diagram of a computer system. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Non-limiting examples of the present technological advancement are described herein. The invention is not limited to the specific examples described below, but rather, it includes all alternatives, modifications, and equivalents falling within the true spirit and scope of the appended claims. 
         [0019]    Technology that can be used for pipe burial includes dredging, plough, suction hopper, and horizontal drilling. These pipe burial techniques may not satisfy design requirements at some locations, may incur high construction costs, and may produce an unwanted environmental impact.  FIG. 2  illustrates some limitations the use of plough, suction hopper, and dredging techniques encounter based on burial depth of the pipe and water depth for the area in which burial is to occur. 
         [0020]    Ploughs provide a cost-effective solution to subsea trenching, requiring basic instrumentation and little or no mechanical tooling. Generally, ploughs can operate in soils up to 400 kPa shear strength and create trench depths ranging from 1-3 meters below the seabed using single or multiple passes. 
         [0021]    Water jetting systems (or jetters) use pumps to direct high-pressure water streams from nozzles that disperse or fluidize seabed sediments and remove obstructions like small rocks and compact soils. Nozzle, as used herein, can refer to a device designed to control a direction and/or characteristics of a fluid flow, or can be and of a pipe or tube through which fluid exits. Jetters are usually deployed directly from a support vessel or are integrated as part of a remotely operated vehicle (ROV). Water jetting offers a solution to trenching in strong, cohesive soils in the strength range of 0-500 kPa. In general, water jetters can trench to depths ranging from 1-3 meters below the seabed, depending on soil type. Jetters can be an excavation and trenching tool for seabed profiles that feature valleys and pits, or where remedial work is required to reduce free spanning of pipelines. Jetters are generally capable of operating in shallow to very deep water. 
         [0022]    By way of example, the present technological advancement can trench and bury pipelines, flowlines, and umbilicals to protect against the effects of ice scouring as depicted in  FIG. 1 . If a deep burial is needed (because of scouring, seabed erosion, or environmental reasons), the present technological advancement can be used in any offshore region. The present technological advancement can be configured to trench to depths greater than current industry norms (i.e., burial depths greater than three meters), and install/lay pipeline in that trench. In addition, the present technological advancement can open trenching for offshore structures other than pipeline. 
         [0023]      FIG. 3  illustrates a non-limiting example of the present technological advancement. In  FIG. 3 , indenter  301  is penetrated to a desired depth in the seabed  307 . An indenter is a device that is designed to create a trench in a seabed. Pipeline lay barge  303  can pull indenter  301  in order to gouge the seabed  307  for trenching. Pipeline  305  may be laid on the seabed using conventional techniques (i.e., S-lay, J-lay, etc.). 
         [0024]    While a barge is depicted, any type of above-water or below-water vessel or below water tractor may be used to pull or push the indenter. 
         [0025]    Seabed or sea floor, as used herein, refers to any underwater bottom surface where pipe can be laid including, for example, ocean bottoms, lake bottoms, river bottoms, or canal bottoms. Pipeline  305  can included, but is not limited to, oil and gas transportation pipes, communications cabling, sewage and water pipes, and other utility transportation pipes. 
         [0026]      FIGS. 4A and 4B  illustrate further details of indenter  301 , with  FIG. 4A  illustrating a plan view and  FIG. 4B  illustrating a side view. 
         [0027]    Indenter  301  can have a housing, frame, or body constructed from high strength steel. However, other materials can be used, and a person of ordinary skill in the art could select an appropriate material in order to provide sufficient strength and durability based on sand/soil conditions in which a trench will be formed. By way of example, the indenter may weigh on the order of a couple of tons, but dimensions, size, and weight would depend upon desired trench depth and soil type. 
         [0028]    Housing or indenter housing, as used herein, is synonymous with frame and body. The housing of the indenter  301  in  FIG. 4B  has a wedge shape (broad and truncate at the summit, and tapering down to the base) with a trapezoidal cross-section, but other cross-sectional shapes are possible. The trapezoidal shape provides a bottom region  319  that is configured to penetrate into the seafloor when the indenter impacts the seafloor after being dropped/lowered into the body of water. Bottom region  319  can be configured to have an edge that facilitates an initial penetration of the lower region  319  into the seafloor. For example, the bottom region  319 , which will make contact with the seabed  307 , can have a pointed or sharpened cutting edge. 
         [0029]    The indenter  301  is shown with a symmetrical shape, but symmetry is not required. The leading edge of the indenter  301  (the edge in the pulling direction) does not need to have the same shape as the trailing edge of the indenter  301 . 
         [0030]    The housing, frame or body of indenter  301  can be welded or otherwise directly/indirectly affixed to encompass or surround at least one suction pile  313 . The at least one suction pile  313  extends into and forms at least part of the bottom region  319 . The at least one suction pile  313  can include a tubular pile configured to be driven into the seabed (or more commonly dropped a few meters into a soft seabed). Then a pump, which can be included on the barge shown in  FIG. 3 , is configured to suck water out of the at least one tubular pile via valve  315 , which causes the indenter to be sunk further down into the seabed. However, the pump need not necessarily be located on the barge, and can be located any place as long as the pump is configured to remove water out of the at least one tubular pile. A pump can be connected to the suction pile via a releasable coupling which is configured to be remotely controlled by a computer. A pump can be included within indenter  301 . 
         [0031]    Using a suction pile for a moveable structure goes against conventional wisdom. Conventional suction piles are used as a deep foundation element to support or moor offshore structures and are driven to depths of  30  meters or more. Conventional suction piles are used to prevent structures from moving, whereas the indenter disclosed herein is moveable and dragged by a barge when laying pipeline. 
         [0032]    In the example shown in  FIGS. 4A and 4B , the at least one suction pile  313  is centrally located in a body of the indenter  301 . The bottom of suction pile  313  is at least partially open so that water is contained within suction pile  313  when the indenter  301  comes to rest at the seafloor. The bottom region  319  is configured to form a water tight seal with the seabed  307  when a part of the bottom region penetrates into the seabed  307 . Water tight does not mean that absolutely no water may enter the suction pile. Rather, the seal is sufficiently water tight if water can be pumped out of suction pile  313  via a pump, which is connected to a valve on a closed upper end of the suction pile, in order to sink the indenter to a desired depth due to the creation of negative pressure. Removal of the water from the suction pile  313  creates a negative pressure zone that drives the indenter  301  further into the seabed  307  until the upper surface of the indenter is about even with the seabed. Sinking the indenter into the seabed by using the suction pile can provide the indenter with a penetration depth greater than three meters. 
         [0033]    The depth of penetration of the indenter  301  can be controlled by controlling the negative pressure. Once the indenter achieves the desired depth, which may be confirmed by cameras, divers, or sensors (i.e., an echo-sounder), the pumping may be ceased and the valve  315  closed. 
         [0034]    The at least one suction pile  313  may include several suction piles closely arranged or separated from each other by a predetermined distance. The at least one suction pile  313  does not necessarily need to be disposed at a center of the indenter  301  and a suction pile may be disposed at one or more locations so long as the one or more suction piles are disposed where they can bury the indenter into the seabed  307  as discussed above. 
         [0035]      FIG. 4A  shows that the upper surface of the indenter has a rectangular shape. However, a rectangular perimeter is not required and other perimeter shapes are possible.  FIG. 4A  shows that the at least one suction pile  313  has a square shape along a bottom surface. The square-cross section is merely an example and other cross-sectional shapes are possible (i.e., rectangular and circular cross-sections). 
         [0036]      FIG. 4B  illustrates an example that combines suction pile  313  and water jetting  311 . Water jetting can be used to loosen/reduce the strength of the soil surrounding the indenter when the indenter is sunk into the seabed. Indenter  301 , with the suction pile  313  and water jetting  311 , synergistically combine to enable a target penetration depth for pipe burial (via suction pile) to be achieved while loosening the soil with water jetting to enable easier pulling of the indenter  301 . 
         [0037]    The water jetting may be facilitated by pumps that force water through jets in the pulling direction. Such a pump may be included in or on the indenter  301 , or at a remote location, such as the barge  303 . Alternatively, a simpler arrangement may be used, where a pump is not used to generate the water jetting. The leading portion of the indenter  301  (the portion on the pulling direction) can include a channel  360  connected to a valve  317  on the upper end of indenter  301  and a one-way jet or a one-way nozzle  370  on a tapering side of the indenter  301 , with the channel extending from the top of the indenter. The valve can be opened to allow a rush of water to pass through the channel, and to exit through the one-way-jet or one-way nozzle as a stream of water that loosens the soil surrounding the leading edge of the indenter  301 . Loosening the soil around the leading edge can facilitate easier pulling of the indenter  301 . The valve can be connected to a hose  320  with an end open to the surrounding water, connected to the barge, or connected to pump. 
         [0038]    Element  350  is a cable that connects indenter  301  to a computer that is programmed to control valves, pumps, sensors, and/or other equipment that are disposed in or on the indenter  301 . The computer can control the pump in order to sink the indenter to a desired depth. The computer can terminate operation of the pump based on feedback from a user, a camera and/or sensors. 
         [0039]    Indenter  301  provides many advantages when compared to the techniques discussed with respect to  FIG. 2 . These advantages include, but are not necessarily limited thereto: deeper burial depth, longer trench opening in a shorter time, and no requirement for special plough equipment. A single-step pipeline installation after trenching process also improves the portability of the process over other composite-type liners. 
         [0040]      FIGS. 5A and 5B  illustrate another exemplary indenter  301 . Elements that are the same as those discussed with respect to  FIGS. 4A and 4B  are numbered the same and are not further discussed with respect to  FIGS. 5A and 5B . 
         [0041]    In  FIGS. 5A and 5B , the suction pile has been replaced with vibration device  501 . The vibration device  501  is configured to induce a vibration in a direction substantially perpendicular to the seabed as indicated by the double-headed arrow in  FIG. 5B . Vibratory driving is a technique that drives the indenter  301  into the ground by imparting to the indenter  301  a small longitudinal vibratory motion of a predetermined frequency and displacement amplitude from a driving unit. The vibration device or driving unit  501  can be a hydraulic system that is at least partially incorporated into the indenter. The vibration device can be of type used for concrete vibrating machines or vibratory hammers used for pile installations. 
         [0042]    The vibrations serve to reduce the ground resistance, allowing penetration under the action of a relatively small surcharge. Vibratory driving will achieve a target penetration depth in excess of three meters and will loosen the soil through vibration for easier pulling of the indenter. The vibrations can be maintained while the barge pulls the indenter. 
         [0043]    A computer can control the vibration device in order to sink the indenter to a desired depth. The computer can terminate operation of the vibration device based on feedback from a user, a camera and/or sensors. 
         [0044]    It is possible that the vibration device in  FIGS. 5A and 5B  can be combined with the indenter of  FIGS. 4A and 4B . The driving unit that imparts the longitudinal vibratory motion may be fitted into or on an outside surface of the indenter  301 . The combination of the vibratory motion and negative pressure created with the suction pile can be used to sink an indenter into the seabed. Moreover, the vibratory motion can be maintained while the indenter is pulled by the barge in order to loosen soil as the indenter is pulled through the seabed. 
         [0045]    The proposed designs in  FIGS. 4A ,  4 B,  5 A, and/or  5 B provide many advantages, which can include but are not limited thereto, deeper burial depth, creation of longer trench openings in a shorter time, and elimination of a need for specialized plough equipment. The proposed designs in  FIGS. 4A ,  4 B,  5 A, and  5 B are more economical than conventional trenching techniques. 
         [0046]      FIG. 6  illustrates an exemplary method of installing a pipeline. In step  601 , an indenter discussed above with respect to  FIGS. 4A ,  4 B,  5 A, and/or  5 B is lowered or dropped into a body of water from a barge. The indenter will come to rest at the bottom of the seabed. The tapered bottom region of the indenter will sink into the seabed based on the force of impact between the seabed and the indenter. In step  603 , the indenter will be further sunk into the seabed by the creation of negative pressure with a suction pile and/or imparting a longitudinal vibratory motion that drives the indenter into the seabed until the indenter reaches a desired depth. In step  605 , which is optional, water jetting can be used to loosen the soil in a pulling direction. In step  607 , the barge pulls the indenter in order to form a trench in the sea bed. In step  609 , pipe is laid into the trench. A single-step pipeline installation after the trenching can improve the portability of the process over other composite-type liners. 
         [0047]      FIG. 7  is a block diagram of a computer system  400  that can be used to execute an embodiment of the present techniques. A central processing unit (CPU)  402  is coupled to system bus  404 . The CPU  402  may be any general-purpose CPU, although other types of architectures of CPU  402  (or other components of exemplary system  400 ) may be used as long as CPU  402  (and other components of system  400 ) supports the operations as described herein. Those of ordinary skill in the art will appreciate that, while only a single CPU  402  is shown in  FIG. 7 , additional CPUs may be present. Moreover, the computer system  400  may comprise a networked, multi-processor computer system that may include a hybrid parallel CPU  402 /GPU  414  system, The CPU  402  may execute the various logical instructions according to various embodiments. For example, the CPU  402  may execute machine-level instructions for performing processing according to the operational flow described. 
         [0048]    The computer system  400  may also include computer components such as non-transitory, computer-readable media. Examples of computer-readable media include a random access memory (RAM)  406 , which may be SRAM, DRAM, SDRAM, or the like. The computer system  400  may also include additional non-transitory, computer-readable media such as a read-only memory (ROM)  408 , which may be PROM, EPROM, EEPROM, or the like. RAM  406  and ROM  408  hold user and system data and programs, as is known in the art. The computer system  400  may also include an input/output (I/O) adapter  410 , a communications adapter  422 , a user interface adapter  424 , a display driver  416 , and a display adapter  418 . 
         [0049]    The I/O adapter  410  may connect additional non-transitory, computer-readable media such as a storage device(s)  412 , including, for example, a hard drive, a compact disc (CD) drive, a floppy disk drive, a tape drive, and the like to computer system  400 . The storage device(s) may be used when RAM  406  is insufficient for the memory requirements associated with storing data for operations of embodiments of the present techniques. The data storage of the computer system  400  may be used for storing information and/or other data used or generated as disclosed herein. For example, storage device(s)  412  may be used to store configuration information or additional plug-ins in accordance with an embodiment of the present techniques. Further, user interface adapter  424  couples user input devices, such as a keyboard  428 , a pointing device  426  and/or output devices to the computer system  400 . The display adapter  418  is driven by the CPU  402  to control the display on a display device  420  to, for example, present information to the user regarding available plug-ins. 
         [0050]    The architecture of system  400  may be varied as desired. For example, any suitable processor-based device may be used, including without limitation personal computers, laptop computers, computer workstations, and multi-processor servers. Moreover, embodiments may be implemented on application specific integrated circuits (ASICs) or very large scale integrated (VLSI) circuits. In fact, persons of ordinary skill in the art may use any number of suitable hardware structures capable of executing logical operations according to the embodiments. The term “processing circuit” includes a hardware processor (such as those found in the hardware devices noted above), ASICs, and VLSI circuits. In an embodiment, input data to the computer system  400  may include various plug-ins and library files. Input data may additionally include configuration information. 
         [0051]    The present techniques may be susceptible to various modifications and alternative forms, and the exemplary embodiments discussed above have been shown only by way of example. However, the present techniques are not intended to be limited to the particular embodiments disclosed herein. Indeed, the present techniques include all alternatives, modifications, and equivalents falling within the spirit and scope of the appended claims.