Patent Publication Number: US-8967271-B2

Title: Subsea overpressure relief device

Description:
BACKGROUND 
     1. Field 
     Embodiments described herein generally relate to systems and methods for subsea hydrocarbon production. More particularly, such embodiments relate to systems and methods for subsea pressure relief systems. 
     2. Description of the Related Art 
     Subsea production systems are widely used for producing oil and gas containing production fluids from deepwater fields. Subsea pipelines can be used to transport the production fluids from a wellhead to a receiving platform. Such fluids can include, but are not limited to, gaseous hydrocarbons, liquid hydrocarbons, additives (e.g., diluents added to heavy fluids and/or corrosion control additives), or any combination thereof. These pipelines typically rest on or near the ocean bottom and can extend for miles at depths exceeding 1,000 m of water. Periodically, such as during tropical storms, hurricanes, or other events (planned or unplanned), production can be halted with the support crew typically evacuated from the receiving platforms. Regulations may require various shut-in procedures which can involve the closing of valves, etc. Unstable conditions can occur during these shut-ins. For example, the pressure in a well can increase during a shut-in causing pressure increases within downstream equipment such as the subsea pipelines and/or risers and such pressure increase can cause the downstream equipment to rupture. 
     Subsea protection systems have been designed to address this problem. Specifically, high integrity pressure protection systems (HIPPS) have been used to protect against pressure increases. HIPPS, however, are complicated systems that include an array of piping, valves, control systems, and other equipment that can also fail during shut-ins. Additional, safety relief options include an offset riser, a relief riser, an additional HIPPS, and a pipe-in-pipe annulus relief. These options, such as an offset riser and relief riser can add considerable expense to a project. Also, an additional HIPPS can overcomplicate the subsea processing arrangement. 
     There is a need, therefore, for new systems and methods for subsea pressure relief systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a cross-sectional, elevational side view of an illustrative subsea pressure relief system for subsea environments, according to one or more embodiments described. 
         FIG. 2  depicts a cross-sectional view of an illustrative pressure relief device, according to one or more embodiments described. 
         FIG. 3  depicts a cross-sectional view of another illustrative pressure relief device, according to one or more embodiments described. 
         FIG. 4  depicts a cross-sectional, perspective side view of another illustrative subsea pressure relief system for subsea environments, according to one or more embodiments described. 
         FIGS. 5A-C  depict cross-sectional, elevational side views of an illustrative subsea pressure relief system showing different steps in a sequence of operation, according to one or more embodiments described. 
     
    
    
     DETAILED DESCRIPTION 
     Systems and methods for relieving pressure from a subsea transport line are provided. The subsea overpressure relief system can include a vessel having a bottom end that can be at least partially open and in fluid communication with a subsea environment. The vessel can include a relief line having a first end and a second end. The first end can be coupled to one or more subsea transport lines coupled to one or more subsea production units. The second end can be coupled to a top end of the vessel and the relief line can include one or more pressure relief devices at least partially disposed therein. The method can include flowing a fluid through the subsea transport line, where a relief line can be coupled to and in fluid communication with the transport line, and where the relief line can have at least one asymmetrical rupture disk at least partially disposed therein. The method can also include rupturing the asymmetrical rupture disk when the pressure of the fluid exceeds a predetermined pressure such that at least a portion of the fluid in the transport line can be diverted through the relief line and the ruptured asymmetrical rupture disk at least partially disposed therein. The method can also include flowing the portion of the fluid from the relief line into a substantially vertically oriented vessel that can be coupled to and in fluid communication with the relief line. The vessel can include a top end and one or more sidewalls having an open bottom end terminating into a subsea environment. The method can further include stopping the flow of the fluid through the relief line and removing at least a portion of the fluid in the vessel via a gas injection line coupled to the top end of the vessel. 
       FIG. 1  depicts a cross-sectional, elevational side view of an illustrative pressure relief system  100  for subsea environments  185 , according to one or more embodiments. The pressure relief system  100  can include one or more vessels  102 , one or more vent lines  104 , one or more relief lines  106 , and one or more pressure relief mechanisms or devices  118 . The vessel  102  can have an inner surface  105  that at least partially defines an interior volume  110 . The vessel  102  can have an inner cross-sectional shape that can be rectangular, multisided, elliptical, circular, oval, or any combination thereof. Depending, at least in part, on the configuration of the inner surface  105 , the inner surface  105  can at least partially form an interior volume  110  having, for example, a rectangular, cylindrical, spherical, ellipsoidal, spheroidal (e.g., prolate or oblate), frusto-conical, and/or a shape functionally similar to a frusto-conical configuration. The interior volume  110  can include a variable containment zone  170 . The variable containment zone  170  can be at least partially defined by a liquid level or liquid surface  122  or interface surface  123  depending on the composition of the pressurized product to be captured by the device. 
     The vessel  102  can be in open fluid communication with the subsea environment  185 . For example, a second or “bottom” end  112  of the vessel  102  can be in open fluid communication with the subsea environment  185 . The bottom end  112  can include a screen, grating, tray or other structure or combination of structures designed to allow fluid to flow therethrough or therepast and prevent particles or solids of a predetermined size from passing therethrough. As used herein, the terms “subsea environment,” “subsea,” and “sub-sea” are used interchangeably and refer to the environment of a volume of water below a surface of a body of water. 
     The vessel  102  can be in fluid communication with one or more transport lines or transport conduits  108 . The transport line  108  can include risers or other production fluid transport lines, umbilicals, hydraulic lines or any other line containing a fluid under pressure. The transport line  108  can be located subsea, on an offshore platform, in the ground or earth, and/or on land. For example, the transport line  108  can include one or more conduits or pipelines in fluid communication with one or more subsea production units, such as a subsea wellhead. In another example, the transport line  108  can be or include an underground casing, riser, drill string, wellbore, or the like to which a wellhead or other equipment can be connected to for the production of hydrocarbons. The relief line  106  can be coupled to the transport line  108  at any location along the transport line  108 . For example, the relief line  106  can be coupled to the transport line  108  at a location on or near a sea floor. 
     The vessel  102  can have a first or “top” end,  109 . The top end  109  of the vessel  102  can be at least partially enclosed. For example, the top end  109  can include one or more inlet ports  111  and one or more outlet ports  113 . Ports  111  and  113  can be disposed at any location along or about the top end  109 . For example, ports  111  and  113  can be disposed at or near the center of the top end  109 . The relief lines  106  and the vent lines  104  can be in fluid communication with the inlet ports  111  and the outlet ports  113 , respectively. The relief line  106  can include one or more first ends  115  and one or more second ends  116 . The first end  115  can be coupled to transport line  108  at any location along the transport line  108 . The second end  116  can be coupled to the vessel  102  at any location along the top end  109  or the sidewalls  105  of the vessel  102 . For example, the second end  116  can be coupled to the vessel  102  via the inlet port  111 . 
     In one or more embodiments, the vessel  102  can have an internal volume  110  ranging from about 1 m 3  to about 10,000 m 3 , about 10 m 3  to about 5,000 m 3 , about 30 m 3  to about 1000 m 3 , or about 50 m 3  to about 500 m 3 . The size of the vessel  102  can permit the vessel to contain at least a portion of an oil spill from leaking into the surrounding environment and/or to the surface. The size of the vessel can be determined by performance requirements and economic factors rather than technical limitations. 
     The pressure relief device  118  can be disposed at any location within the relief line  106  between the first end  115  and the second end  116 . Any number of pressure relief devices  118  can be at least partially disposed within the relief line  106 . For example, the relief line  106  can include 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more pressure relief devices  118  at least partially disposed therein. In another example, the relief line  106  can include less than 10, less than 6, less than 4, or less than 3 pressure relief devices  118  at least partially disposed therein. For example, the relief line  106  can include from 1 to 8, from 2 to 6, or from 2 to 4 pressure relief devices  118 . The pressure relief device  118  can include any type of mechanism, valve, or other structure suitable for reducing pressure within a line, Illustrative, pressure relief devices  118  can be or include, but are not limited to, rupture disks, pressure relief valves, safety valves, and the like, and any combination thereof. The pressure relief device  118  can have an actuation pressure or rupture pressure less than a failure pressure of the transport line  108  and the relief line  106 . 
     The pressure relief device  118  can be a rupture disk. The rupture disk can be formed from any desired material. For example, the rupture disk can be formed from carbon steel, stainless steel, graphite, Hastelloy®, or any combination thereof. The material(s) from which the rupture disk can be formed from can be capable of rupturing, bursting, breaching, puncturing, breaking, fracturing, or otherwise failing under pressure. The material(s) from which the rupture disk can be formed from can be capable of rupturing, bursting, breaching, puncturing, breaking, fracturing, or otherwise failing under a predetermined pressure. The rupture disk can include grooves, weakened sections, and/or other features that can promote rupture. The predetermined pressure can be any desired pressure that can be less than a rupture or fail pressure of the transport line  108  and the relief line  106 . For example, the rupture disk can withstand any pressure less than a rupture or fail pressure of the transport line  108  and the relief line  106 . In another example, the rupture disk can be configured or adapted to rupture or burst at a pressure, e.g., a predetermined pressure, ranging from about 500 kPa to about 500,000 kPa, about 1,000 kPa to about 250,000 kPa, about 2,000 kPa to about 140,000 kPa, or about 3,000 kPa to about 100,000 kPa. The rupture disk can be configured or adapted to rupture at a specific predetermined pressure, e.g., 10,000 kPa, or within a predetermined range of a specific predetermined pressure, e.g., within about 500 kPa of 10,000 kPa. 
     The rupture disk can be or include an asymmetrical rupture disk, such that the rupture disk can rupture or burst in only one direction axial to the relief line  106 . For example, an asymmetric rupture disk can rupture in a direction of fluid flowing from the transport line  108  and toward the vessel  102 . The rupture disk can be prevented from rupturing in the opposite direction or in a direction of fluid flowing from the vessel  102  and toward the transport line  108 , by a reinforcement means or backstop  120 . The backstop  120  can be a structural element such as bars, a grid, a perforated plate, or any other structure that can be sufficient to prevent the rupture disk from rupturing in the direction of the backstop  120  and that can allow fluid to pass in the event the of rupture of the asymmetric rupture disk. For example, the backstop  120  can include a network of bars as shown in  FIG. 2  and/or a one or more perforated plates as shown in  FIG. 3 . 
     The vessel  102  can an also include one or more sidewalls  107  in addition to the bottom end  112  and the top end  109 . The bottom end  112  can be a distal end of the sidewalls  107  with respect to the top end  109 . In another example, the sidewalls  107  can be disposed intermediate to the bottom end  112  and the top end  109 . The top end  109  can have a cross-sectional area less than or equal to, or greater than the bottom end  112  and the sidewalls  107 . In addition, a frusto-conical section  114  can be disposed intermediate the top end  109  and the sidewalls  107 . In an example, the bottom end  112  can have a cross-sectional area greater than the cross-sectional area of the top end  109  and the sidewalls  107  can taper from the bottom end  112  to the top end  109 , resulting in a continuously narrowing diameter from the bottom end  112  to the top end  109 . 
     As discussed above, the vessel  102  can be at least partially opened at or near the bottom end  112  of the one or more sidewalls  105 , such that the interior volume  110  of the vessel  102  can be in fluid communication with the subsea environment  185 . For example, the bottom end  112  can be in open fluid communication with the subsea environment  185  such that liquid surface  122  of seawater or other liquid can form at or above the bottom end  112 , between the one or more sidewalls  105 . A hydrostatic pressure of the subsea environment  185  can be greater or less than an internal pressure within the vessel  102 , thereby causing water from the subsea environment  185  to rise into the vessel  102  or fall, and form a liquid surface  122  within the vessel  102 . An internal pressure can be present in the interior volume  110  of the vessel  102  above the liquid surface  122 . The internal pressure can be at equilibrium with the hydrostatic pressure, providing the variable containment zone  170  with a stable bottom surface defined by the interface surface  123  which can be dependent on the liquid surface  122  and the volume and density of liquids in the vessel. When the internal pressure and the hydrostatic pressure are at equilibrium, the vessel  102  can have a static variable containment zone  170  that can be at least partially defined by the liquid surface  122 . 
     The vessel  102  can be vertically or substantially vertically oriented. As used herein, the term “substantially vertical” refers to about −30 degrees to about 30 degrees, about −25 degrees to about 25 degrees, about −20 degrees to about 20 degrees, about −15 degrees to about 15 degrees, about −10 degrees to about 10 degrees, about −5 degrees to about 5 degrees, about −3 degrees to about 3 degrees, about −2 degrees to about 2 degrees, about −1 degree to about 1 degree, about −0.1 degree to about 0.1 degree, or about −0.0001 degree to about 0.0001 degree with respect to vertical longitudinal central axes of the vessel  102 . 
     The vent line  104  can include a first end  128 , a second end  132 , and a gas injection port  130 . The first end  128  can be coupled to the vessel  102  at any location. For example, the first end  128  can be coupled to the top end  109  of the vessel  102 . In an example, the first end  128  can be coupled to the top end  109  proximate to where the pressure relief line  106  can be coupled to the top end  109 . In another example, the first end  128  can be coupled to the top end  109  at a location below or above the location at which the relief line  106  can be coupled to the top end  109 . In one or more embodiments, the first end  128  can be coupled to the outlet port  113 . The vent line  104  can include one or more first ends  128  in which each first end  128  can be coupled to a corresponding one or more outlet ports  113 . 
     The vent line  104  can include at least one vertical segment or substantially vertically oriented segment  134 . In one or more embodiments, the vertical segment  134  can include the second end  132  of the vent line  104 . For example, the vent line  104  can terminate at the vertical segment  134  into the subsea environment  185 . 
     The second end  132  of the vent line  104  can terminate within the subsea environment  185 . The second end  132  can be in open fluid communication with a subsea environment  185 . In an example, the second end  132  can include one or more screens, one or more gratings, and/or one or more other structures designed to allow fluid to flow therethrough, but preventing solids of a predetermined size or dimension from passing therethrough. In one or more embodiments, an interior volume  140  of the vent line  104  can be partially defined by a liquid surface  126 . The second end  132  can be in open fluid communication with subsea environment  185  such that a liquid surface  126  of seawater can form at or above the second end  132 , within the vent line  104 . A hydrostatic pressure of the subsea environment  185  can be greater than an internal pressure within the vent line  104 , thereby causing water from the subsea environment  185  to rise into the vent line  104  and form the liquid surface  126  within the vent line  104 . An internal pressure can be present in the interior volume  140  of the vent line  104  above the liquid surface  126 . The internal pressure can be at equilibrium with the hydrostatic pressure, providing the interior volume  140  with a stable bottom surface defined by the liquid surface  126 . When the internal pressure and the hydrostatic pressure are at equilibrium, the vent line  104  can have a static interior volume  140  that can be at least partially defined by the liquid surface  126 . 
     The second end  132  of the vent line  104  and the bottom end  112  of the vessel  102  can be vertically offset from each other. In one or more embodiments, the second end  132  can be disposed at a location above the bottom end  112 . For example, the second end  132  can be disposed at a distance D above the depth of the bottom end  112 . The distance D can range from about 10 cm to about 10,000 cm, about 50 cm to about 5,000 cm, about 75 cm to about 2,000 cm, about 100 cm to about 1,000 cm, or about 250 cm to about 750 cm. In another example, the vertical segment  134  can have a height less than a height of the vessel  102 . For example, the height of the vertical segment  134  range from about 1% to about 99%, about 5% to about 95%, about 10% to about 90%, about 20% to about 80%, about 30% to about 70%, or about 40% to about 60% less than the height of the vessel  102 . 
     The gas injection port  130  can be disposed at any location along the vent line  104 . For example, the gas injection port  130  can be coupled to the vent line  104  at a location near the outlet port  113 . In one or more embodiments, the gas injection port  130  can be formed from the vent line  104  at a junction  136 . The junction  136  can be disposed near the first end  128  of the vent line  104 . In another example, the gas injection port  130  can be coupled directly to the vessel  102  at any location rather than being coupled to the vent line  104 . For example, the gas injection port  130  can be coupled to the top end  109  of the vessel  102 . In another example, the gas injection port  130  can be coupled to the top end  109 , adjacent to where the pressure relief line  106  can be coupled to the top end  109 . In another example, the gas injection port  130  can be coupled to the top end  109  at a location below or above the location at which the relief line  106  can be coupled to the top end  109 . In a further example, the gas injection port  130  can be coupled to the outlet port  113 . 
     The vessel  102  can function in a similar manner as a diving bell or an underwater habitat equipped with a moon pool. The internal pressure within the interior volume  110  of the vessel  120  can be at or about ambient pressure and thus directly related to subsea depth. The amount of hydrostatic force present under subsea conditions can determine the size and dimensions of the variable containment zone  170  within the vessel  102 . As the hydrostatic force increases, the variable containment zone  170  compresses, and the water level within the vessel  102  rises resulting in the reduction in volume of the variable containment zone  170 . 
     Once the vessel  102  is placed at a desired depth, the amount of interior volume  110  can be adjusted by means of compressed gas(es). In one or more embodiments, the compressed gas can include any inert or non-reactive gases. For example, the compressed gas can include air, carbon dioxide, argon, nitrogen, helium, or the like. The compressed gas can be supplied to the vessel  102  via a connecting hose or pipe (not shown). The compressed gas can be supplied to the vessel  102  at or just below the surface of the water level. For example, the compressed gas via line  138  can be supplied to the vessel  102  after the vessel  102  has been secured to a subsea processing unit, a subsea production unit, the seafloor, or other location. The compressed gas via line  138  can be introduced to the vessel  102  via the connecting hose, and the connecting hose can be connected to or coupled with the gas injection port  130 . The compressed gas via line  138  can be injected into the interior volume  110  as the vessel  102  descends to a desired depth. In an example, the gas via line  138  can be injected into the interior volume  110  once the vessel  102  is in position at the seafloor or at a desired depth. In another example, gas via line  138  can be injected at or near the surface of a body of water prior to lowering the vessel to a desired depth. The relief line  106  and the vent line  104  can each include one or more valves (not shown). Any number of the valves may be in the actuated to a closed position when gas is introduced into the interior volume  110  of the vessel  102  in order to prevent the gas from escaping through the relief line  106  and the vent line  104 . 
     The pressure relief apparatus  100  can be disposed near one or more wellheads (not shown). The one or more wellheads can be disposed subsea, on or near a seafloor. In one or more embodiments, the pressure relief apparatus  100  can be disposed near a riser (not shown) and/or near one or more subsea processing units, subsea production units, or the like (not shown). The subsea processing unit can include one or more risers or other production fluid transport lines. The transport line  108  can be coupled to or in fluid communication with the subsea processing unit, the subsea production unit, or the like. The transport line  108 , fluidly coupled to the relief line  106 , can include the risers and/or other production fluid transport lines. In one or more embodiments, the relief line  106  can be coupled to the transport line  108  that can contain production fluid. The pressure relief device  118  can fluidly isolate the vessel  102  from the production fluid in the transport line  108  before the pressure relief device  118  breaches, punctures, bursts, ruptures, or otherwise forms one or more flow paths therethrough. 
     In operation, the transport line  108  can contain one or more hydrocarbonaceous fluids or hydrocarbon-containing fluids or other fluids under pressurized conditions. The pressure of the fluid within the transport line  108  can vary, sometimes approaching or even exceeding the pressure rating the of the transport line  108 , the relief line  106 , or other lines, vessels, or apparatus in fluid communication with the transport line  108 . The pressure relief device  118 , e.g., a rupture disk, disposed in the relief line  106  can fail at a rupture pressure less than a rupture or fail pressure of the transport line  108 , the relief line  106  or other lines, vessels, or apparatus in fluid communication with the transport line  108 . As pressure in the transport line  108  and the relief line  106  exceeds the rupture pressure of the pressure relief device  118 , the pressure relief device  118  can rupture, fail, or otherwise form one or more flow paths therethrough. After the pressure relief device  118  fails, the fluid contents of the transport line  108  can travel past the pressure relief device  118 , through the remainder of the relief line  106  and into the vessel  102 . The fluid contents can include solids, water, liquid hydrocarbons, and gases. The water and solid components of the fluid contents can mix with the water phase in the vessel  102  and thus enter the subsea environment  185 . The liquid hydrocarbons (organic phase) and gases can fill the interior volume  110  of the vessel  102  above the interface surface  123 . As the amount of liquid and/or gaseous hydrocarbons enter the vessel  102  increases, excess liquid hydrocarbons and/or gases can enter the vent line  104 . The outlet port  113  of the vessel  102  can be generally disposed toward the top of the vessel  102  and the vented portion of the fluid can be primarily gaseous with the liquid portions remaining within the vessel variable containment zone  170  below the liquid level  122 . The open second end  132  of the vent line  104  can terminate into the subsea environment  185  at a depth less than a depth of the open bottom end  112 . A distance D between the depth of the second end  132  and the bottom end  112  can result in a lower hydrostatic pressure at the second end  132  than the bottom end  112 . This pressure differential can result in the excess fluid exiting the vent line  104  before the pressure in the interior volume  110  can exceed the hydrostatic pressure at the bottom end  112 , thus ensuring that the liquid surface  122  will remain inside the vessel  102 . The hydrostatic forces acting against the incoming fluid can be less than the failure pressure of the transport line  108 , the relief line  106 , or other lines, vessels, or apparatus in fluid communication with the transport line  108 . Thus, the failure of the rupture disk, for example, can prevent the failure of the transport line  108 , the relief line  106 , and/or or other lines, vessels, or apparatus in fluid communication with the transport line  108 . 
     The production fluid introduced to the relief vessel  102  via the one or more relief lines  106  can be gas, liquid organic compounds, and/or particulates. As the production fluid enters the interior volume  110  of the vessel  102 , the production fluid can begin to separate into two or more separate phases. For example, the production fluid can include a liquid water phase, an organic hydrocarbon phase, a gaseous phase, and/or a particulate or solids phase. The various phases can separate by gravity based on their relative densities. Heavier particulates can settle to the bottom where a collection device (not shown) could be located while gas, or gases, can rise to the top. A liquid gas interface  122  is shown but additional interfaces between liquids, such as interface surface  123 , can exist below this interface. The separation between these liquid interfaces can be further enhanced by arranging the geometry of the relief line  106  and vessel  102  so as to impart a rotational motion to the production fluid with separation caused by a resulting radial force. 
     The gaseous phase can include hydrocarbon gases, such as methane, ethane, propane, butane, and the like. The gaseous phase can also include inert gases such as carbon dioxide, nitrogen, and the like. The organic phase can include hydrocarbons having from about 1 to about 36 carbon atoms, from about 2 to about 32 carbon atoms, from about 4 to about 28 carbon atoms, from about 8 to about 24 carbon atoms, or from about 12 to about 36 carbon atoms. The solids or particulates contained in the production fluid can include asphaltenes, sand, wax, hydrates, or any combination thereof. 
     The gaseous phase can be removed through the gaseous vent line  104  and/or through the gas injection port  130 . For example, the gaseous phase can be removed from the vessel  102  via a designated gaseous phase removal line (not shown). The organic phase can be removed through the gaseous vent line  104  and/or through the gas injection port  130 . For example, the organic phase can be removed from the vessel  102  via a dedicated organic phase removal line (not shown). The solids or particulates contained in the production fluid can include asphaltenes, sand, wax, hydrates, or any combination thereof. 
     The production fluid in relief line  106  can have a gas concentration ranging from a low of about 0 wt %, about 10 wt %, about 20 wt %, about 30 wt %, about 40 wt % to a high of about 50 wt % about, 60 wt %, about 75 wt %, about 90 wt %, or about 100 wt % based on the total weight of the production fluid in relief line  106 . For example, the production fluid in relief line  106  can have a gas concentration ranging from about 1 wt % to about 99 wt %, about 5 wt % to about 95 wt %, about 10 wt % to about 90 wt %, about 20 wt % to about 80 wt %, about 10 wt % to about 60 wt %, about 25 wt % to about 45 wt %, about 50 wt % to about 90 wt %, or about 60 wt % to about 80 wt % based on the total weight of the production fluid in relief line  106 . The production fluid in relief line  106  can have a liquid concentration ranging from a low of about 0 wt %, about 10 wt %, about 20 wt %, about 30 wt %, about 40 wt % to a high of about 50 wt % about, 60 wt %, about 75 wt %, about 90 wt %, or about 100 wt % based on the total weight of the production fluid in relief line  106 . For example, the production fluid in relief line  106  can have a liquid concentration ranging from about 1 wt % to about 99 wt %, about 5 wt % to about 95 wt %, about 10 wt % to about 90 wt %, about 20 wt % to about 80 wt %, about 10 wt % to about 60 wt %, about 25 wt % to about 45 wt %, about 50 wt % to about 90 wt %, or about 60 wt % to about 80 wt % based on the total weight of the production fluid in relief line  106 . The production in the relief line  106  can have a solids or particulates concentration ranging from a low of about 0 wt %, about 5 wt %, about 10 wt %, about 15 wt %, about 20 wt % to a high of about 25 wt % about, 30 wt %, about 40 wt %, about 45 wt %, or about 50 wt % based on the total weight of the production fluid in relief line  106 . For example, the production fluid in relief line  106  can have a solids or particulates concentration ranging from about 1 wt % to about 50 wt %, about 2 wt % to about 40 wt %, about 2 wt % to about 25 wt %, about 5 wt % to about 20 wt %, or about 10 wt % to about 15 wt % based on the total weight of the production fluid in relief line  106 . The production fluid in relief line  106  can have a water concentration ranging fro a low of about 0 wt %, about 5 wt %, about 10 wt %, about 25 wt %, about 30 wt % to a high of about 40 wt % about, 50 wt %, about 60 wt %, about 75 wt %, or about 90 wt % based on the total weight of the production fluid in relief line  106 . The production fluid via relief line  106  can enter the vessel  102  upon the failure of the pressure relief device  118 . 
     The variable containment zone  170  can include all material within the vessel  102  disposed above the interface surface  123 . For example, the variable containment zone  170  can include an inert gas. The inert gas can include air, carbon dioxide, argon, nitrogen, helium, or the like. The variable containment zone  170  can also include the organic phase and/or the gaseous phase. The organic phase can contain hydrocarbons less dense than water and can rest above the organic phase surface  123 . The gaseous phase can include any material in a gaseous phase at subsea pressures and can include any material present within the vessel  102  above the liquid surface  122 . The variable containment zone  170  can include hydrocarbonaceous gases and/or liquids as well as water and particulates. 
     Referring now to  FIG. 2 , the backstop  120  can allow fluid to pass freely therethrough. For example, the backstop  120  can include a structure that results in a minimal pressure drop across the backstop  120 . As depicted in  FIG. 2 , the backstop  120  can be a network of bars or a grid having lateral members  204  and transverse members  202  disposed immediately adjacent to or in contact with the pressure relief device  118 . The lateral members  204  and the vertical members  202  can be sufficiently spaced apart from each other such that fluid can pass freely therethrough. The lateral members  204  and the vertical members  202  can be secured to an inner wall  206  of the relief line  106 . In an example not shown, the grid can include any shape or orientation of support members. For example, support members (not shown) can be arranged diagonally resulting in a hexagonal void space between the support members. 
     As depicted in  FIG. 3 , the backstop  120  can be a perforated plate having a plurality of holes or perforations  208  disposed immediately adjacent to or in contact with the pressure relief device  118 . The holes  208  can be of sufficient size and/or quantity that that fluid can pass freely therethrough. The perforated plate backstop  120  can be secured to the inner wall  206  of the relief line  106 . 
       FIG. 4  depicts a more detailed schematic of an illustrative pressure relief system  400 , according to one or more embodiments. The relief system is shown having a vessel  402 , a gaseous vent line  404 , a relief line  406 , and multiple relief mechanisms  418   a ,  418   b . The vessel  402  can have an inner surface  405  that at least partially defines an interior volume  410 . The vessel  402  can include one or more sidewalls  407 , a bottom end  412 , and a top end  409 . For example, the sidewalls  407  can terminate in a subsea environment. As shown, the bottom end  412  can be a distal end of the sidewalls  407  from the top end  409 , resulting in the vessel  402  being in open fluid communication with a subsea environment. 
     The vessel  402  can be connected to a transport line  408 . A relief line  406  can be coupled to the transport line  108  at any location along the transport line  408 . The vessel  402  can be coupled to the transport line  408  via the relief line  406 . The relief line  406  can include a first end  415  and a second end  416 . The first end  415  can be coupled to transport line  408  and the second end  416  can be coupled to the vessel  402  at the top end  409  of the vessel  402 . At least one rupture disk (two are shown  418   a ,  418   b ) can be disposed within the relief line  406  at any location between the first end  415  and the second end  416  of the relief line  406 . 
     The relief line  406  can include a first segment  460 , a second segment  480 , and a third segment  490 . The first segment  460  can be coupled to the transport line  408 , and the third segment  490  can be coupled to the top end  409  of the vessel  402 . The first segment  460  and the third segment  490  can be joined via the second segment  480 . The first segment  460  can be coupled to the second segment  480  via flanges, collet connectors, or other connection devices  465  and  466 . The third segment  490  can be coupled to the second segment  480  via flanges, collet connectors, or other connection devices  467  and  468 . The second segment  480  can include the rupture disks or relief devices  418   a ,  418   b . The second segment  480  can also include a pressure indicator  470 . The pressure indicator  470  can be disposed between the first rupture disk  418   a  and the second rupture disk  418   b . An access line  472 , having a valve  471 , can also be disposed on the second segment  480  between the first rupture disk  418   a  and the second rupture disk  418   b . The access line  472  can allow communication with the void between the rupture disks or relief devices  418   a  and  418   b  to introduce or remove fluid and adjust the fluids pressure for testing or operational purposes. 
     The first segment  460  can include one or more valves (two are shown  462   a ,  462   b ), the second segment  480  can include one or more valves (two are shown  464 ,  469 ), and the third segment  490  can include one or more valves (one is shown  474 ). When the rupture disks  418   a ,  418   b  need maintenance or repair, the second segment  480  can be removed from the first segment  460  and the third segment  490  via flanges  465 ,  466  and  467 ,  468 . The second segment  480  can be raised to an offshore rig, platform, ship, or work boat, for example, for the maintenance and repair. During normal operation, the valves,  462   a ,  462   b ,  464 ,  469 , and  474 , are in an open position; however, to close the system for maintenance or repair, the valves  462   a ,  462   b ,  464 ,  469 , and  474  can be closed. The vessel  402  can be supported by support members (not shown) independent of the relief line  406 . 
     The vent line  404  can include a first end  428  and a second end  432 . The vent line  404  can also include a gas injection port  430 . The first end  428  can be coupled to the vessel  402  at the top end  409 . The vent line  404  can include at least one vertical segment  434 . The vertical segment  434  can be at least a portion of the vent line  404  that is at least substantially vertical. In one or more embodiments, the vertical segment  434  can include the second end  432  of the vent line  404 . For example, the vent line  404  can terminate at the vertical segment  434  into the subsea environment. 
     The second end  432  and the bottom end  412  can be vertically offset from each other. In one or more embodiments, the second end  432  can be disposed at a location above the bottom end  412 . For example, the second end  432  can be disposed at a distance D above the depth of the bottom end  412 . The distance D can range from about 10 cm to about 10,000 cm, about 50 cm to 5,000 cm, about 100 cm to about 1,000 cm, or about 250 cm to about 750 cm. 
     The gas injection port  430  can be coupled to the vent line  404  at a location above the top end  409  of the vessel  402 . The gas injection port  430  can be used to inject inert gas into the vessel  402  in order to provide a volume of gas within the vessel  402 . The gas injection port  430  can also be used to withdraw gas phase and organic phase components that empty from the transport line  408  into the vessel  402 . The gas injection port  430  can be opened and closed via a valve  436 . 
       FIGS. 5A-5C  depict an operation sequence of an illustrative subsea pressure relief system  500 . In  FIG. 5A , fluid under pressure can flow through transport line  508 . The fluid in the transport line  508  can be present in the relief line  506  past the open valve  562  and up to the rupture disk  518 . Compressed inert gas can occupy the remaining volume of the relief line  506 , the variable containment zone  570 , a portion of the interior volume  510  of the vessel  502 , and a portion of the vent line  504 . The valve  536  in vent line  504  can be closed to hold the compressed gas in the system  500 . 
     As shown in  FIG. 5B , when the pressure in the transport line  508  exceeds the rupture pressure of the rupture disk  518 , the rupture disk  518  can rupture. The fluid in the transport line  508  can then escape and flow through the ruptured rupture disk  518  and the relief line  506  and into the vessel  502 . As the fluid escapes from the transport line  508  and enters the vessel  502 , pressure within the vessel  502  builds and pushes against the subsea hydrostatic forces as indicated by arrows  580 , thus forcing the liquid level  522  downward. The fluid under pressure in the vessel  502  can escape into the gaseous vent line  504  and exit the system  500  as indicated by arrow  581 . 
     In  FIG. 5C , the valve  562  in the relief line  506  can be closed, and the valve  536  in the vent line  504  can be opened. This arrangement of the valves can allow for the fluid to be withdrawn from the system  500  (see arrow  582 ). The fluid can be withdrawn from the system  500  via a hose or pipe (not shown) that can be lowered from an offshore rig, platform, ship, or work boat, for example. The fluid can be withdrawn at least partially by aid of the hydrostatic forces pushing against the fluid in the vessel  502  (see arrows  524 ) and the vent line  504  (see arrows  528 ). 
     The valves,  562  and  536 , can be opened and closed in any manner. For example, the valves,  562  and  536 , can be linked to a control system and can be opened and closed from a remote location, such as an offshore platform or on-shore facility (not shown). In another example, the valves,  562  and  536 , can be manually opened and closed by divers, submarines, ROVs (remotely operated vehicles) or other submersible vehicle. 
     The pressure relief device  118  can be manually and/or remotely activated to permit and/or prevent fluid flow therethrough. For example, the pressure relief device  118  can be manually opened and closed by divers, submarines, ROVs (remotely operated vehicles) or other submersible vehicle. In another example, the pressure relief device  118  can be linked to a control system and can be opened and closed from a remote location, such as an offshore platform or on-shore facility (not shown). 
     Embodiments of the present disclosure further relate to any one or more of the following paragraphs: 
     1. A subsea relief system, comprising: a vessel having a bottom end that is at least partially open and in fluid communication with a subsea environment; and a relief line having a first end and a second end, wherein the first end is coupled to one or more subsea transport lines coupled to one or more subsea production units, wherein the second end is coupled to a top end of the vessel, and wherein the relief line comprises one or more pressure relief devices at least partially disposed therein. 
     2. The system of paragraph 1, wherein the one or more pressure relief devices comprises one or more rupture disks, one or more pressure relief valves, or combinations thereof. 
     3. The system of paragraphs 1 or 2, wherein the vessel further comprises one or more sidewalls, and at least a portion of an inner surface of the one or more sidewalls has a frusto-conical shape. 
     4. The system according to any one of paragraphs 1 to 3, wherein the one or more pressure relief devices comprises an asymmetrical rupture disk. 
     5. The system according to any one of paragraphs 1 to 3, wherein the asymmetrical rupture disk comprises a backstop disposed within the relief line between a rupture disk and the first end. 
     6. The system of paragraph 5, wherein the backstop causes the rupture disk to rupture in a direction away from the backstop. 
     7. The system according to any one of paragraphs 1 to 6, wherein the vessel is substantially vertically oriented. 
     8. The system according to any one of paragraphs 1 to 7, wherein the vessel comprises one or more sidewalls, and wherein the one or more sidewalls are at least substantially vertically oriented and terminate into the subsea environment forming the at least partially open bottom end. 
     9. The system according to any one of paragraphs 1 to 8, further comprising a vent line having a first end and a second end, wherein the first end of the vent line is coupled to the top end of the vessel, and wherein the second end of the vent line terminates within the subsea environment at a height above the bottom end of the vessel and below the first end of the vent line. 
     10. The system of paragraph 9, wherein the vent line comprises a substantially vertically oriented segment that comprises the second end. 
     11. The system according to any one of paragraphs 1 to 10, further comprising a gas injection line in fluid communication with the internal volume of the vessel. 
     12. The system of paragraph 9, wherein the gas injection line is coupled to the vent line at a location proximate the top end of the vessel, and wherein the gas injection line is adapted to fluidly connect with a conduit for introducing compressed gas to the vessel and removing hydrocarbons from the vessel. 
     13. A subsea relief system, comprising: a transport line having a hydrocarbon containing fluid flowing therethrough; a relief line having a first end coupled to the transport line and one or more asymmetrical rupture disks at least partially disposed therein; a substantially vertically oriented vessel comprising a top end, one or more sidewalls, and a bottom end terminating into a subsea environment, wherein a second end of the relief line is in fluid communication with the vessel; and a vent line having a first end in fluid communication with the vessel and a second end terminating into the subsea environment at a height above the bottom end of the vessel and below the first end of the vent line. 
     14. The system of paragraph 13, wherein the vent line comprises a substantially vertically oriented segment that comprises the second end. 
     15. The system of paragraphs 13 or 14, the height has a distance ranging from about 10 cm to about 10,000 cm. 
     16. The system according to any one of paragraphs 13 to 15, wherein the substantially vertically oriented vessel has an internal volume comprising a variable containment zone disposed above a liquid surface of a liquid phase disposed within the internal volume. 
     17. The system of paragraph 16, wherein the variable containment zone contains hydrocarbonaceous material and the liquid phase comprises water. 
     18. A method for relieving pressure in a subsea transport line, comprising: flowing a fluid through the transport line, wherein a relief line is coupled to and in fluid communication with the transport line, and wherein the relief line comprises at least one asymmetrical rupture disk at least partially disposed therein; rupturing the asymmetrical rupture disk when a pressure of the fluid exceeds a predetermined pressure such that at least a portion of the fluid in the transport line is diverted through the relief line and the ruptured asymmetrical rupture disk at least partially disposed therein; flowing the portion of the fluid from the relief line into a substantially vertically oriented vessel that is coupled to and in fluid communication with the relief line, and wherein the vessel comprises a top end and one or more sidewalls having an open bottom end terminating into a subsea environment; stopping the flow of the fluid through the relief line; and removing at least a portion of the fluid in the vessel via a gas injection line coupled to the top end of the vessel. 
     19. The method of paragraph 18, wherein the fluid comprises crude oil, water, hydrocarbonaceous gases, and carbonaceous solids and the fluid in the vessel separates into at least three distinct phases comprising a liquid phase, an organic phase, and a gaseous phase. 
     20. The method of paragraphs 18 or 19, further comprising injecting a gas into the vessel via the gas injection line prior to rupturing the asymmetrical rupture disk with the fluid. 
     Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits, and ranges appear in one or more claims below. All numerical values are “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art. 
     Various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Furthermore, all patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted. 
     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.