Abstract:
Methods and apparatus for allowing the injection of hydrate inhibitors into a valve cavity without washing out the valve seals, generally comprising a valve having a sealing member, such as a gate or a ball, that provides for fluid communication between the valve cavity and the valve flowbore. One embodiment of a valve constructed in accordance with the present invention is an expanded gate valve comprising a valve body having a flowbore intersecting a valve cavity and a gate assembly disposed within said cavity. The gate assembly is a parallel expanding gate assembly having ported, juxtaposed members that are moveable into a sealing arrangement with upstream and downstream valve seats disposed about the flowbore. The gate assembly further comprises a flow path that enables direct fluid communication between the aligned ports and the valve cavity. This flow path enables hydrate inhibitors injected into the valve cavity to flow freely into the port and the flowbore without crossing the sealing faces of the gate assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         FIELD OF THE INVENTION  
         [0003]    This invention relates to valves used in environments susceptible to the formation of hydrates. More particularly, this invention relates to methods and apparatus for preventing the formation of hydrates in valves, namely gate valves and ball valves.  
         BACKGROUND OF THE INVENTION  
         [0004]    Clathrate hydrates are crystalline compounds that occur when water forms a cage-like structure around guest molecules, particularly gaseous molecules. Clathrate hydrates, especially in the petroleum industry, are referred to as gas hydrates, gas hydrate crystals, or simply hydrates. Typical hydrates formed in petroleum (hydrocarbon) environments are composed of water and one or more guest molecules such as methane, ethane, propane, isobutane, normal butane, nitrogen, carbon dioxide, and hydrogen sulfate. In general, hydrates will form when a mixture of water and hydrocarbon gases are mixed at high pressures and low temperatures.  
           [0005]    The formation of hydrates is of particular concern in subsea hydrocarbon exploration and production where water and gaseous hydrocarbons are often in close proximity at high pressures and low temperatures. If hydrates form within subsea components they are capable of preventing actuation of critical components and of blocking the flow of fluids through the system. It is therefore desirable to take provisions to prevent the formation of hydrates in these systems.  
           [0006]    To overcome these problems, several thermodynamic measures are possible in principal: removal of free water, maintaining an elevated temperature and/or reduced pressure, or the addition of freezing point depressants (antifreeze). As a practical matter, the last mentioned measure, i.e., adding freezing point depressants, has been most frequently applied. Thus, lower alcohols and glycols, e.g., methanol, have been added to act as antifreezes. It has been known that in lieu of antifreezes, one can employ a crystal growth inhibitor that inhibits the formation of the hydrate crystals and/or the agglomeration of the hydrate crystallites to large crystalline masses sufficient to cause plugging. Thus, surface active agents such as phosphonates, phosphate esters, phosphonic acids, salts and esters of phosphonic acids, inorganic polyphosphates, salts and esters of inorganic polyphosphates, polyacrylamids, and polyacrylates have been used.  
           [0007]    One application that is particularly susceptible to the formation of hydrates is the secondary recovery system known as Water Alternating Gas (WAG). In a WAG system, alternating volumes of water and hydrocarbon gases are injected through an injection well into a hydrocarbon bearing formation in order to force the stored hydrocarbons into production wells drilled in the same formation. This technique is used to increase the volume of production through the adjacent production wells. When used in cold environments, including subsea, the water and the gas are often mixed at high pressures and low temperatures which are often close to the conditions at which hydrates will form.  
           [0008]    Hydrates that form in the WAG flowline are a concern but are easily prevented by directly injecting chemicals into the flowline. More difficult is the prevention of hydrate formation within the cavity of valves used to control the flow of water and gas. If hydrates form within the valve cavities, the valves can no longer be opened or closed and the system must be shut down. Simply injecting an inhibiting chemical into the valve cavity has the potential problem of forcing material across the valve seal faces and possibly washing out the seals.  
           [0009]    Therefore, there remains in the art a need for methods and apparatus to prevent the creation of hydrates within valve manifolds and in particular within the valve cavities. Therefore, the present invention is directed to methods and apparatus for allowing the injection of chemicals into a valve cavity without risking washout of the valve seals.  
         SUMMARY OF THE PREFERRED EMBODIMENTS  
         [0010]    Accordingly, there is provided herein methods and apparatus for allowing the injection of hydrate inhibitors into a valve cavity without washing out the valve seals. The present invention generally comprises a valve having a sealing member, such as a gate or a ball, that provides for fluid communication between the valve cavity and the valve flowbore. Fluid communication between the valve cavity and the valve flowbore provides a direct fluid path and prevents a buildup of pressure within the cavity, thus preventing washout of the valve seals.  
           [0011]    One embodiment of a valve constructed in accordance with the present invention is an expanded gate valve comprising a valve body having a flowbore intersecting a valve cavity and a gate assembly disposed within said cavity. The gate assembly is a parallel expanding gate assembly having ported, juxtaposed members that are moveable into a sealing arrangement with upstream and downstream valve seats disposed about the flowbore. The gate assembly further comprises a flow path that enables direct fluid communication between the aligned ports and the valve cavity. This flow path enables hydrate inhibitors injected into the valve cavity to flow freely into the port and the flowbore without crossing the sealing faces of the gate assembly.  
           [0012]    One embodiment of a valve manifold employing aspects of the present invention comprises a first valve that controls flow from a water inlet and a second valve that controls flow from a gas inlet. Both valves are connected to a common outlet. Each valve comprises a valve body having a flowbore intersecting a valve cavity in which is disposed a sealing member. Each valve is also adapted to receive hydrate inhibitors, such as methanol, injected directly into the valve cavity. Each sealing member has features that, in an open position, allow direct fluid communication between the valve cavity and the flowbore without effecting the performance of the valve through washout or erosion of any sealing surfaces.  
           [0013]    Thus, the present invention comprises a combination of features that allow fluid to be injected directly into a valve cavity, through a sealing member, and into a flowbore without degrading the sealing performance of the valve. For example, certain embodiments of the present invention allow for injection of hydrate inhibiting chemicals into a valve cavity and flowbore without washing out the sealing surfaces of the valve. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    For a more detailed understanding of the preferred embodiments, reference is made to the accompanying Figures, wherein:  
         [0015]    [0015]FIG. 1 is a schematic section view of an expandable gate valve in a closed position;  
         [0016]    [0016]FIG. 2 is a schematic section view of an expandable gage valve in an open position;  
         [0017]    [0017]FIG. 3 is one embodiment of an expandable gate assembly;  
         [0018]    [0018]FIG. 4 is second embodiment of an expandable gate assembly;  
         [0019]    [0019]FIG. 5 is a third embodiment of an expandable gate assembly;  
         [0020]    [0020]FIG. 6 is one embodiment of an slab-type gate;  
         [0021]    [0021]FIG. 7 is a schematic section view of typical dual-cavity block valve such as is used in a WAG manifold;  
         [0022]    [0022]FIG. 8 is a schematic section view of typical dual-cavity block valve such as is used in a WAG manifold;  
         [0023]    [0023]FIG. 9 is a schematic section view of typical dual-cavity block valve such as is used in a WAG manifold; and  
         [0024]    [0024]FIG. 10 is a partial section view of a ball valve. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness.  
         [0026]    The present invention relates to methods and apparatus for injecting a material through a valve cavity and into a flowbore without degrading the sealing performance of the valve. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. In particular, while repeated reference is made to the injection of chemicals used to inhibit the formation of hydrates, it is to be understood that the embodiments of the present invention find utility in the injection of any substance into a flowbore through a valve. Furthermore, while the embodiments described herein are gate valves and ball valves, the concepts and principals of the present invention can be applied to other valves and similar sealing equipment. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results.  
         [0027]    Referring now to FIG. 1, a schematic representation of one embodiment of a gate valve assembly  10  is shown. Assembly  10  generally comprises a valve body  12 , gate  18 , and sealing rings, or seats  24 . Body  12  has a valve cavity  14  arranged perpendicular to a flowbore having an upstream portion  15  and a downstream portion  16 . Injection port  26  provides hydraulic access to cavity  14 . Seats  23 ,  24  are mounted where flowbore  15 ,  16  intersects with cavity  14 . Gate  18  is preferably a split, or double gate assembly comprising a first portion  20  and second portion  22  that in a closed position, as shown in FIG. 1, that uses a biasing member (not shown), such as a spring, to push the portions outward toward seats  23 ,  24 .  
         [0028]    In one method of operation, the pressure in upstream flowbore  15  is higher than the pressure in downstream flowbore  16 . Fluid pressure from upstream portion  15  will second portion  22  against the first portion  20  and create a seal on a seal face of first portion  20  between the downstream flowbore  16  and seat  24 . The higher pressure fluid from upstream flowbore  15  will get into cavity  14  and mix with any fluid injected through port  26  to prevent the formation of hydrates. Another option is to maintain the pressure in cavity  14  higher than both upstream flowbore  15  and downstream flowbore  16 . Gate  18  expands when the pressure within cavity  14  is higher than the pressure upstream  15  or downstream  16  of valve  10 , thus creating two seal barriers in one valve cavity by sealing against both seats  23 ,  24 . In this closed position, fluid injected through injection port  26  flows freely throughout cavity  14  but is isolated from both valve flowbores  15 ,  16 .  
         [0029]    Gap  28  preferably provides a flow path between the portions to allow injected fluid to fill cavity  14 . Gate  18  may also comprise port  30  that provides hydraulic communication direct to the gate flowbore  32 .  
         [0030]    [0030]FIG. 2 depicts the valve of FIG. 1 in an open position. Gate  18  has been moved within cavity  14  so that gate flowbore  32  aligns with valve flowbore  16 . In an open position, gate portions  20 ,  22  do not fully energize seats  23 ,  24 , but may form a low pressure seal between gate  18  and seats  23 ,  24 . Gap  28  and port  30  preferably provide a free flowing fluid path for material injected into cavity  14  through injection port  26  to reach all of cavity  14  as well as gate flowbore  32  and valve flowbore  16 . Because fluid is allowed to pass through gap  28  and port  30 , it will not flow across the sealing surfaces of gate  18  or seats  24 , thereby decreasing the chances of washing out the seal surfaces.  
         [0031]    Gap  28  and port  30  are preferably sized to allow the volume of material injected through injection port  26  to flow freely without restriction. Injection port  26  is sized to supply a sufficient amount of fluid to cavity  14  and gap  28  and port  30  are sized so that fluid will distribute throughout the cavity without significant increases in velocity. Injection port  26  preferably ranges from between ½″ and 1″ in diameter. Gap  28  and port  30  preferably have a combined cross-section area comparable to the area of port  26 . Therefore, the above described embodiment of the present invention allows material to be injected into valve cavity  14 , with gate  18  in either an open or closed position, without washing out the seal surfaces of gate  18  or seats  24 .  
         [0032]    One feature of the embodiment described above is the ability for unobstructed fluid communication throughout the valve cavity and into the flowbore while the valve gate is in an open position. This unobstructed fluid communication is achieved by providing fluid paths through the gate valve and into the flowbore. These fluid paths may be of any configuration as is practical to the chosen application. In FIG. 1, these flow paths comprise expanded gap  28  and port  30 . FIG. 3 depicts a split gate assembly  34 , comprising a first portion  36  and second portion  38  with a common flowbore  44 . Gap  40  preferably provides a flow path through gate  34 . Gate assembly  34  may also comprise port  42  that is formed between valve portions  36 ,  38  that provides a flow path into flowbore  44 .  
         [0033]    [0033]FIG. 4 depicts a split gate assembly  46 , comprising a first portion  48  and second portion  50  with a common flowbore  56 . Gap  52  preferably provides a flow path between gate portions  48  and  50 . Each gate portion  48 ,  50  also comprises a port  54  that that provides a flow path into flowbore  56 .  
         [0034]    [0034]FIG. 5 depicts a split gate valve assembly  58 , comprising a first portion  60  and second portion  62  with a common flowbore  66 . Gap  64  preferably provides a flow path sized to provide a sufficient flow area so that no additional port is required.  
         [0035]    [0035]FIG. 6 depicts a slab-type gate  68 , which comprises a single piece gate with a flowbore  70 . Slab-type gate valves are sealed by using upstream fluid pressure to seal against the downstream seat and do not rely on the expansion of the valve gate. Port  72 , through gate  68  and into flowbore  70  provides fluid communication from the valve cavity into the flowbore with the gate in an open position.  
         [0036]    FIGS.  7  to  9  depict a dual-block valve  74  used in a WAG manifold where water and gas are injected into the formation to aid in secondary recovery of hydrocarbon resources. Valve  74  comprises a body  94  having a gas inlet  80 , water inlet  92 , and an outlet  86 . Valve  74  also comprises gates  76 ,  78  that control the flow of water and gas into the valve. Gates  76 ,  78  are shown as split gates, such as are shown in FIGS. 1 and 2, and are disposed within cavities  82 ,  90 . FIG. 7 depicts both gates  76 ,  78  in closed positions where the gates have expanded to seal against valve seats both upstream and downstream of the gate. In the position shown in FIG. 7, a hydrate inhibiting material, such as methanol, can be injected through injection ports  84 ,  88  into cavities  82 ,  90 . The inhibiting material is preferably injected at a pressure higher than the pressure in either inlet  80 ,  92  or outlet  86 . As previously described, split gates  76 ,  78  will expand to seal both upstream and downstream of the gate, thus isolating the cavities  82 ,  90  from the water and gas. The inhibiting material will mix with any fluid in cavity  82 ,  90  and prevent the formation of hydrates which could impede the actuation of gates  76 ,  78 .  
         [0037]    [0037]FIG. 8 shows valve  74  configured to inject gas into a well. Gate  78 , which controls the flow from gas inlet  80 , is opened while gate  76 , which controls flow from water inlet  92 , remains closed. Hydrate inhibiting chemicals injected through injection port  84  into cavity  82  can flow freely into the gas flow, thus preventing the formation of hydrates in cavity  82  and outlet  86 . FIG. 9, shows valve  74  configured to inject water into a well. Position of gates  76 ,  78  has been reversed so that gate  76  is open and gate  78  is closed. Hydrate inhibiting chemicals injected through injection port  88  into cavity  90  can flow freely into the water flow, thus preventing the formation of hydrates in the cavity  90  and outlet  86 . Therefore, valve  74 , by way of gates  76 ,  78 , which provide hydraulic flow paths between their respective cavities and the flowbore when in an open position, allows the injection of hydrate inhibiting material, or any other material, into both valve cavities and the flowbore of both the water and gas inlets. Thus, the formation of hydrates can be prevented throughout the entire dual-block valve.  
         [0038]    [0038]FIG. 10 shows a partial section view of a ball valve  94 . Ball valve  94  comprises a body  96  having a flowbore  102  therethrough. Body  96  also comprises a cavity  110  adapted to receive a ball  98  and sealing elements  100  that seal between ball  98  and body  96  around flowbore  92 . In an open position, as shown in FIG. 10, ball flowbore  104  is aligned with valve flowbore  102 . Injection port  106  through body  96  allows injection of fluid, such as a hydrate inhibitor, into cavity  110 . When in the open position, flow port  108  through ball  98  allows the injected material to flow into ball flowbore  104  and valve flowbore  102 . Injected material will be fully distributed around both the interior and exterior of ball  98 . Therefore, in a hydrate forming environment, the injection of a hydrate inhibiting material will prevent the formation of hydrates both in cavity  110  and flowbore  102 ,  104 , which prevents hydrates from interfering with the operation of valve  94 .  
         [0039]    In ball valves, slab gate valves, and other applications where, in the closed position, the cavity is equalized with the higher pressure flowbore, care must be taken when injecting fluid into the valve cavity not to washout the non-sealing seat by continuing to flow fluid into the cavity. In these application it may be desired to stop the injection of fluid or use specially designed seals to prevent washout.  
         [0040]    Therefore, the above described embodiments provide for valves that allow for the injection of hydrate inhibitors into a valve cavity, through a sealing member, such as a gate or ball, and into the flowbore of the valve. This prevents the formation of hydrates both in the flowbore and in the valve cavity, ensuring that the valve can actuate when needed. The sealing member is specially adapted with flow ports, or other flow paths, that enable the free flow of fluid from the cavity and into the flowbore without flowing over seal areas that are susceptible to washout. The embodiments of the present invention find particular utility in applications that involve the use of water and hydrocarbon gases at conditions of high pressure and low temperature.  
         [0041]    The embodiments set forth herein are merely illustrative and do not limit the scope of the invention or the details therein. It will be appreciated that many other modifications and improvements to the disclosure herein may be made without departing from the scope of the invention or the inventive concepts herein disclosed. Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.