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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       REFERENCE TO A MICROFICHE APPENDIX 
       [0003]    None. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The present invention relates to hydraulic control systems for actuation of subsea equipment, particularly to a hydraulic control system and method for use in deep water with a subsea Blowout Preventer (BOP) stack, more particularly for a hydraulic control system and method utilizing a retrievable control pod for the actuation of subsea Blowout Preventer (BOP) stacks. 
         [0006]    2. Description of the Related Art 
         [0007]    Offshore drilling for oil and natural gas from floating vessels is conventionally done through a drilling riser between the floating drilling vessel and a BOP stack located at the seabed. 
         [0008]    The hydraulic functions of the BOP stack may be controlled by a hydraulic control system or an electro-hydraulic control system. 
         [0009]    The first shallow-water subsea BOP control systems were discrete direct hydraulic control systems, in which hydraulic pressure is conveyed from the surface directly to a particular hydraulic actuator on the subsea BOP stack by way of a discrete hydraulic conduit. 
         [0010]    Later subsea control systems were “piloted” discrete hydraulic control systems, in which hydraulic pilot signals are conveyed down a dedicated hydraulic conduit to a pilot valve, which directs hydraulic pressure from a subsea hydraulic manifold to a particular hydraulic actuator on the subsea BOP stack. 
         [0011]    Other subsea control systems of this era included multifunction hydraulic systems which used various techniques to deliver more than one signal per hydraulic conduit; for example, coded hydraulic pulses, or a matrix of hydraulic signals, or sequenced signals at increasing pressures. 
         [0012]    Still later control systems were “discrete” electro-hydraulic systems, with one electrical conductor per hydraulic function, or “multiplexed” (or “MUX”) systems, in which coded signals are transmitted via a small number of conductors. 
         [0013]    Modern subsea control systems are almost exclusively MUX systems, which offer the advantages of ease of automation, rapid signal times between the surface and the seabed, and relatively easy retrievability of the control “pod”. 
         [0014]    However, there are still scores of older hydraulic systems extant, particularly piloted hydraulic control systems which were originally designed to be used in conjunction with guideline-deployed subsea BOP stacks. 
         [0015]    Referring now to  FIG. 1 , which is a perspective view of a typical subsea BOP stack, Lower Marine Riser Package (LMRP) and associated hydraulic control system of the prior art. For clarity, the LMRP is shown unlatched from the BOP stack, as if it were, for example, being tripped back to the surface. 
         [0016]    The Subsea BOP stack  100  has stack framework  101  which supports the subsea BOP stack and also serves to guide the stack from the surface to the seabed along guidelines  102 . Subsea BOP stack  100  also has lower female hydraulic receptacles  103 A and  103 B with fluid passages  104  which are hydraulically connected to BOP control lines  105 . 
         [0017]    Lower Marine Riser Package (LMRP)  106  forms an upper, separable part of the Subsea BOP stack, and generally comprises at least one annular BOP  106 A, drilling riser  106 B with attached choke &amp; kill lines  106 C, a flexible riser joint  106 D, an LMRP latch  107  between the LMRP  106  and the subsea BOP stack  100 , control pods  108 A and  108 B and a plurality of guideline funnels  109  guiding the LMRP along guidelines  102 . LMRP  106  also comprises upper female hydraulic receptacles  110 A and  110 B. 
         [0018]    Generally, guideline funnels  109  are diametrically opposed on opposite sides of the LMRP. (Note that the opposing guideline funnel is not shown in  FIG. 1 .) Control pods  108 A and  108 B may also fitted with their own, similar guideline funnels so that they may be retrieved separately from the LMRP. 
         [0019]    Conventionally, control pods  108 A and  108 B are painted yellow and blue respectively, as those colors can be easily distinguished subsea by a closed-circuit television camera on a subsea remotely-operated vehicle (ROV). 
         [0020]    Control pods  108 A and  108 B have control pod deployment cables  111 A and  111 B, and control pod umbilical  112 A and  112 B. Conventionally, control pod umbilicals  112 A and  112 B are clamped (not shown) to control pod deployment cables  111 A and  111 B with, for example, clamps of the types taught in U.S. Pat. Nos. 4,445,255 to Olejak, and 4,437,791 to Reynolds. 
         [0021]    Control pods  108 A and  108 B also have latching mechanism  113 A and  113 B (latching mechanism  113 B is not visible) on male members  114 A and  114 B male member  114 B is not visible) which latch the control pods into upper female control receptacles  110 A and  110 B. Control pods  108 A and  108 B also have male hydraulic connectors  115 A and  115 B (not visible) which mate with upper female control receptacles  110 A and  110 B. 
         [0022]    Referring now to  FIG. 2 , which is a perspective view of a control pod and its associated female hydraulic receptacles. Control pod  200  has control pod deployment cable  201 , control pod umbilical  202 , male member  203  with latching mechanism  204 , and male hydraulic connector  205  with frustoconical surface  205 A and a plurality of hydraulic ports  206 . 
         [0023]    Control pod  200  also has junction plate  202 A (commonly called a “kidney plate”) deposed between control umbilical  202  and control pod  200  which provides hydraulic connections between the umbilical and the hydraulic piping and vavling within the pod. 
         [0024]    LMRP  207  has upper female hydraulic receptacle  210 , which has a plurality of inner hydraulic ports  209 , inner frustoconical surface  209 A, a plurality of outer hydraulic ports  210 , and outer frustoconical surface  210 A. 
         [0025]    Subsea stack  211  has lower female hydraulic receptacle  212  with a plurality of inner hydraulic ports  214 , inner frustoconical surface  214 A, and spring mounts  213 .\ 
         [0026]    When control pod  200  is latched into LMRP  207  by latching mechanism  204 , frustoconical surface  205 A on male hydraulic connector  205  mates with frustoconical surface  209 A on upper female hydraulic receptacle  208 . 
         [0027]    When LMRP is latched to subsea stack  211  by LMRP latch  107  (in  FIG. 1 ), frustoconical surface  210 A on upper female hydraulic receptacle  208  mates with frustoconical surface  214 A on lower female hydraulic receptacle  212 . 
         [0028]    For LMRP hydraulic control functions such as annular BOP  106 A or LMRP latch  107  (both in  FIG. 1 ), hydraulic pressure is supplied by control pod  200  to a hydraulic port  206  on the male hydraulic connector  205 , which is hydraulically mated to an inner hydraulic port  209  on the upper female hydraulic receptacle  208 , and routed to a control hose (not shown) leading to the particular LMRP control function. 
         [0029]    For hydraulic functions in the BOP stack  211 , such as opening or closing of a ram-type BOP, hydraulic pressure is supplied by control pod  200  to a hydraulic port  206  on male hydraulic connector  205 , which is hydraulically mated to an inner hydraulic port  209  on the upper female hydraulic receptacle  208 , which in turn is hydraulically connected to an outer hydraulic port  210  which mates hydraulically with inner hydraulic port  214  on lower female hydraulic receptacle  212 . Inner hydraulic port  214  is in turn connected hydraulically to a BOP control hose  105  (shown in  FIG. 1 ) leading to a particular BOP stack control function. 
         [0030]    Subsea control well systems for hydraulically controlling subsea well equipment are generally shown in U.S. Pat. Nos. 3,460,614 and 3,701,549, which are incorporated by reference in their entirety. 
         [0031]    As drilling water depths got much deeper throughout the 1990&#39;s, offshore drillers initially abandoned the use of guidelines to deploy and retrieve BOP stacks, and instead tripped the BOP stack “guidelineless,” often with the aid of ROVs. They also discovered that the currents in deep water could cause severe and deleterious “vortex-induced vibration” (“VIV”) in the control pod deployment cable  201  and the control pod umbilical  202  clamped to it, often severely damaging the expensive umbilical. Consequently, most drillers have abandoned the control pod deployment cable  201  on subsea BOP stacks run in deep water, and today run the control pod umbilical  202  attached the drilling riser  106 B (in  FIG. 1 ), usually clamped to the choke &amp; kill lines  106 C. 
         [0032]    However, with the control pod umbilical attached to the riser, a control pod may be retrieved for inspection and repair only by tripping the entire LMRP with both pods attached, which is extremely expensive and time consuming. It would be advantageous to be able to retrieve one control pod at a time, without tripping the entire riser and LMRP, but to continue to run the umbilical attached to the riser to avoid deleterious VIV. 
         [0033]    Some prior art systems sought to address this issue. One prior art system, for example, taught in U.S. Pat. No. 4,328,826 to Baugh, et al, features flat, vertically stacked flat connector plates which allow the control pod to connect to the control umbilical through a connector plate, which in turn allows the control pod to be fully retrievable. However, this and other prior art systems all require that the existing control pods with frustoconical hydraulic receptacles be replaced, at very high cost. It would therefore be advantageous to be able to inexpensively modify an existing hydraulic control system comprising a riser-mounted umbilical such that the existing hydraulic control pod is retrievable independent of the LMRP, the riser, and the other control pod. 
         [0034]    Further, it would be advantageous if such a modification for an existing hydraulic control system could be easily retrofitted to the LMRP structure, and if it were sufficiently compact to fit within the confines of the existing equipment in the LMRP, which may, in some cases, require the modification to “wrap around” the other equipment. 
         [0035]    Still further, the junction plate  202 A is a complicated, heavy, and expensive machined part in which multiple hydraulic seals reside; although these seals are usually robust, the junction plate arrangement has the potential for multiple leak-paths between the umbilical and the control pod. It would therefore be advantageous to eliminate the junction plate  202 A as an interface between the pod and the umbilical. 
       BRIEF SUMMARY OF THE INVENTION 
       [0036]    The present invention is directed to hydraulic subsea control system for a subsea BOP stack comprising a retrievable hydraulic control pod with hydraulic receptacles, and an umbilical attached to the drilling riser. The hydraulic control system of the present invention comprising a subsea hydraulic umbilical line, a lower marine riser package having a hydraulic receptacle, a hydraulic control pod having a hydraulic connector for hydraulically mating with the hydraulic receptacle, at least one pod umbilical hydraulic connector hydraulically connected through umbilical connector piping to said hydraulic control pod, and at least one lower marine riser package umbilical hydraulic connector for hydraulically mating with said pod umbilical hydraulic connector and said subsea hydraulic umbilical line. When the system of the present invention is operated, a hydraulic flow path exists allowing hydraulic fluid to flow from the subsea hydraulic umbilical line through the lower marine riser package umbilical hydraulic connector through the pod umbilical hydraulic connector and into the hydraulic control pod which is hydraulically connected to the lower marine riser package hydraulic receptacle. 
         [0037]    In one aspect, the invention relates to a hydraulic control pod with a male frustoconical hydraulic connector, adapted to be retrieved from a subsea BOP stack while the umbilical control hose remains attached to the drilling riser. 
         [0038]    In another aspect, the invention relates to a method for converting a hydraulic control system to allow the subsea control pod to be retrieved while the umbilical control hose remains attached to the drilling riser. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0039]    A better understanding of the present invention can be obtained when the following detailed description of the disclosed embodiments is considered in conjunction with the following drawings, in which: 
           [0040]      FIG. 1  is a perspective view of a subsea stack and Lower Marine Riser Package (LMRP) of the prior art. 
           [0041]      FIG. 2  is a perspective view of an hydraulic control pod and associated female hydraulic receptacles on the LMRP and the subsea BOP stack, all of the prior art. 
           [0042]      FIG. 3  is a section view of a preferred embodiment of the hydraulic control system of the present invention. 
           [0043]      FIG. 3A  is a section view of the preferred hydraulic control system shown in  FIG. 3 , at “A-A” in  FIG. 3 . 
           [0044]      FIG. 3B  is a section view of the preferred hydraulic control system shown in  FIG. 3 , in the landed and latched position. 
           [0045]      FIG. 4A  is a chart of hydraulic flows in a hydraulic control system of the prior art. 
           [0046]      FIG. 4B  is a chart of hydraulic flows of the preferred embodiment of the hydraulic control system of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    Refer now to  FIG. 3 , which shows a preferred embodiment of the present invention. Control pod  300  has umbilical junction plate  300 A, male member  301  with latching mechanism  302 , male hydraulic connector  303  with frustoconical surface  303 A, and control pod deployment cable attachment point  304 . 
         [0048]    Control pod  300  also has radial connector brackets  305 A and  305 B, with attached pod umbilical connectors  306 A and  306 B, which have hydraulic ports  306 C. 
         [0049]    Pod umbilical connectors  306 A and  306 B are hydraulically connected to the valving inside the control pod  300  by umbilical connector piping  306 D. As shown, umbilical connector piping  306 D by-passes umbilical junction plate  300 A; in this embodiment, umbilical junction plate  300 A may be eliminated in order to save weight in control pod  300 . 
         [0050]    Alternately, umbilical junction plate  300 A may be retained, and umbilical connector piping  306 D may be run from pod umbilical connectors  306 A and  306 B to the hydraulic connectors on the top of umbilical junction plate  300 A. Since the internal piping inside control pod  300 A is often complex and convoluted, this approach may save time and money during a conversion. Furthermore, there may be circumstances when it is advantageous to retain umbilical junction plate  300 A despite its added weight; for example, for a spare pod which a driller may wish to configure for either shallow water drilling (with umbical run separately from the riser) or for deepwater drilling (with the umbilical attached to the riser). 
         [0051]    LMRP  307  has LMRP umbilical connectors  308 A and  308 B, attached to LMRP  307  by compliant suspension  309  and mounting brackets  310 . The complaint suspension  309  as shown comprises coil springs and spherical bearings mounted between LMRP umbilical connectors  308 A and  308 B and corresponding mounting brackets  310 , which allows LMRP umbilical connectors  308 A and  308 B to move about slightly when they are mated with pod umbilical connectors  306 A and  306 B. However, those skilled in the art will recognize that other mechanisms, such as elastomeric springs, Belleville washers, or hydraulic spring elements may be utilized without departing from the spirit of the invention. 
         [0052]    LMRP umbilical connectors  308 A and  308 B are hydraulically connected to umbilical hoses  308 C. Ideally, the umbilical hose may be configured such that the individual hoses within the umbilical bundle may be connected directly to LMRP umbilical connectors  308 A and  308 B without intervening hydraulic connections. In some circumstances, of course, the umbilical may have to be terminated on or near the riser, and jumper hoses (for example) used to connect the umbilical to the LMRP umbilical connectors. 
         [0053]    LMRP  307  also has upper female hydraulic receptacle  311 , which has inner hydraulic ports  312  and outer hydraulic ports  313  (not visible in this sectional view), inner frustoconical surface  312 A, and outer frustoconical surface  313 A. 
         [0054]    Subsea BOP stack  314  has lower female hydraulic receptacle  315  with inner frustoconical surface  315 A, and inner hydraulic ports  316  (not visible in this section view). 
         [0055]    In the embodiment shown in  FIG. 3 , pod umbilical connectors  306 A and  306 B are male wedge-type connectors and LMRP umbilical connectors  308 A and  308 B. are mating female wedge-type connectors. In another embodiment, pod umbilical connectors  306 A and  306 B are female wedge-type connectors and LMRP umbilical connectors  308 A and  308 B are mating male wedge-type connectors. In still another embodiment, pod umbilical connectors  306 A and  306 B and LMRP umbilical connectors  308 A and  308 B are frustoconical type connectors, essentially versions of the hydraulic connectors beneath the control pod. Those skilled in the art will appreciate that the mating pod umbilical connectors and LMRP umbilical connectors may be any of many types of subsea wet-mateable hydraulic connectors known in the art. 
         [0056]    Further, in the embodiment of the instant invention shown in  FIG. 3 , the control pod  300  is generally cylindrical in shape. Those skilled in the art will recognize that the control pod may be rectangular or another shape, and still be mated to a frustoconical male hydraulic connector  303 . 
         [0057]    In one embodiment of the instant invention, there are two radial connector brackets attached to the control pod. In another embodiment, there are more than two radial connector brackets. 
         [0058]    In another embodiment of the instant invention, there are two radial connector brackets with associated pod umbilical connectors; one pod umbilical connector contains hydraulic circuits for LMRP controls and the other contains hydraulic circuits for the subsea BOP. 
         [0059]    In yet another embodiment of the instant invention, there is only one radial connector bracket with an associated pod umbilical connector. In a related embodiment, the one radial connector bracket is arranged radially away from the well center. 
         [0060]    Refer now to  FIG. 3A , which shows a horizontal section through the pod (at “A-A” in  FIG. 3 ). Control pod  300  has radial connector brackets  305 A and  305 B, with attached pod umbilical connectors  306 A and  306 B. In this embodiment, radial connector brackets  305 A and  305 B are substantially horizontally opposed on opposite sides of control pod  300  (that is, the inner included angle  319  between the brackets is 180 degrees), and a vertical plane  316  through radial connector brackets  305 A and  305 B is substantially tangential to well center axis  317  (which is coincident with the center of the riser  106 B and the annular BOP  106 A in  FIG. 1 ). 
         [0061]    In another embodiment of the instant invention, radial connector brackets  318 A and  318 B are each substantially tangential to well center axis  317 . 
         [0062]    In another embodiment which may provide the most compact installation, radial connector brackets  318 A and  318 B are each substantially tangential to well center axis  317 , and the inner included angle ( 319  in  FIG. 3A ) between the brackets is minimized. 
         [0063]    For a well center-to-pod center distance D ( 320  in  FIG. 3A ) and overall radial bracket length “L” ( 321  in  FIG. 3A ), a minimum inner included angle α is defined by the following equation: Equation 1 α=2(arc cos D/L) 
         [0064]    In another embodiment of the instant invention, the included angle between the radial connector brackets will be between about 180 degrees and minimum inner included angle α as calculated by Equation 1. 
         [0065]    Another embodiment of the instant invention consists of a method to convert an existing hydraulic control system to a system with retrievable control pods and an umbilical attached to the riser, comprising the steps of affixing one or more radial connector brackets and associated pod umbilical connector to the control pod, affixing mating LMRP umbilical connector and associated compliant suspension and mounting bracket to the LMRP, and plumbing the umbilical and control pod to the respective umbilical connectors. 
         [0066]    Another embodiment of the method to convert an existing hydraulic control system further comprises the step of hydraulically by-passing the umbilical junction plate, and connecting the LMRP umbilical connectors directly to the valving within the control pod. In a related embodiment, the hydraulically by-passed umbilical junction plate may be permanently removed from the control pod in order to lower the weight of the pod, for example, for use in deep water. 
         [0067]    In another embodiment, the method to convert an existing hydraulic control system comprises hydraulically connecting the individual hoses within the umbilical bundle directly to the LMRP umbilical connectors. 
         [0068]    Generally, the most compact embodiment of the instant invention is preferred, for ease of retrofitting, compactness of the associated plumbing, and ease of subsea installation and retrieval. One such preferred embodiment comprises two pod connector brackets which are as short as practically possible (that is, with a small bracket length “L”), arrayed at the minimum interior angle α, and no junction plate  300 A (colloquially known as the “kidney plate” after its shape) or associated hydraulic piping and connections, in order to save weight in the control pod. 
         [0069]      FIG. 3B  shows the embodiment of the instant invention shown in  FIG. 3 , with control pod  300  latched into LMRP  307 , and the LMRP  307  landed and latched to the BOP stack  314 . The umbilical hoses  308 C are hydraulically connected to LMRP connectors  308 A and  308 B. LMRP connectors  308 A and  308 B are hydraulically connected to pod connectors  306 A and  306 B respectively. Pod connectors  306 A and  306 B are hydraulically connected directly to the valving in control pod  300  with umbilical connector piping  308 C. 
         [0070]    An existing hydraulic control pod may, according to the teachings of this disclosure, be modified to allow the control pod to be retrieved from the LMRP installed on the subsea stack without tripping the drilling riser and the attached umbilical control lines. In one embodiment, the method to convert an existing control pod may comprise the steps of attaching radial connector arms with hydraulic connectors to the control pod, attaching mating hydraulic connectors to the LMRP, and plumbing the umbilical hose bundle and the subsea control pod functions to the hydraulic connectors. In another embodiment, the method to modify a hydraulic control pod may comprise attaching the radial control arms at an inner included angle of between 180 degrees and the minimum inner included angle. 
         [0071]      FIG. 4A  shows hydraulic flows in hydraulic control systems of the prior art. Fluid from the umbilical  400  flows directly to the control pod  401 . Upon a signal to actuate a function in the LMRP (such as opening or closing the annular BOP), fluid flows from the control pod  401  through the upper female connector  402  to the selected LMRP function  403 . Upon a signal to actuate a function in the subsea BOP stack (such as opening or closing a ram BOP), fluid flows from the control pod  401  through the upper female connector  402  and the lower female connector  404  to the selected BOP stack function  405 . 
         [0072]      FIG. 4B  shows the hydraulic flow paths in a hydraulic control system which is an embodiment of the instant invention. Fluid from the umbilical  400  flows to an LMRP connector  406  and a corresponding pod connector  407  to the control pod  407 . Upon a signal to actuate a function in the LMRP (such as opening or closing the annular BOP), fluid flows from the control pod  401  through the upper female connector  402  to the selected LMRP function  403 . Upon a signal to actuate a function in the subsea BOP stack (such as opening or closing a ram BOP), fluid flows from the control pod  401  through the upper female connector  402  and the lower female connector  404  to the selected BOP stack function  405 . 
         [0073]    In view of this disclosure, various other modifications may be made to the hydraulic control system of the instant invention by those of ordinary skill in the art without departing from the spirit of the invention. It should be understood, therefore, that the instant invention is not limited to the disclosed embodiments, but that the scope of the invention includes all embodiments within the following claims.

Summary:
Systems and methods for improved hydraulic control systems for actuation of subsea equipment in deep water are disclosed. The hydraulic control system relies on smaller fluid flow associated with a hydraulic pressure pulse to actuate the small volume actuation control valve. In one embodiment, the system includes small diameter control umbilical hoses and pilot-operated valves with low actuation volumes. Particularly, a hydraulic control system for reducing the signal time to a subsea blowout preventer in water depth up to and greater than about 5000 feet. Some embodiments comprise a valve arrangement which hydraulically actuate one side of a hydraulic control function, while simultaneously evacuating the opposing circuit both at the seabed and at the surface. Some embodiments comprise an umbilical hose located proximate the center of an umbilical bundle. Preferably, the umbilical hose has a plurality of layers of reinforcing fibers which increase with the diameter of the reinforcement layer.