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CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 60/955,085, entitled “Control System for Blowout Preventer Stack”, filed on Aug. 10, 2007, and U.S. Provisional Patent Application No. 60/954,919, entitled “Control Module for Subsea Equipment”, filed on Aug. 9, 2007, each of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to subsea well drilling and in particular to a control system for controlling a blowout preventer stack connected between the subsea wellhead assembly and a riser. 
     BACKGROUND OF THE INVENTION 
     Subsea Control Modules (SCMs) are commonly used to provide well control functions during the production phase of subsea oil and gas production. Typical well control functions and monitoring provided by the SCM can include: 1) actuation of fail-safe return production tree actuators and downhole safety valves; 2) actuation of flow control choke valves, shut-off valves, etc.; 3) actuation of manifold diverter valves, shut-off valves, etc.; 4) actuation of chemical injection valves; 5) actuation and monitoring of Surface Controlled Reservoir Analysis and Monitoring Systems (SCRAMS) sliding sleeve, choke valves; 6) monitoring of downhole pressure, temperature and flow rates; and 7) monitoring of sand probes, production tree and manifold pressures, temperatures, and choke positions. 
     The close proximity of the typical SCM to the subsea production tree, coupled with its electro-hydraulic design allows for quick response times of tree valve actuations. The typical SCM receives electrical power, communication signals and hydraulic power supplies from surface control equipment. The subsea control module and production tree are generally located in a remote location relative to the surface control equipment. Redundant supplies of communication signals, electrical, and hydraulic power are transmitted through umbilical hoses and cables of various length, linking surface equipment to subsea equipment. Electronics equipment located inside the SCM conditions electrical power, processes communications signals, transmits status and distributes power to devices such as solenoid piloting valves, pressure transducers and temperature transducers. 
     Low flow rate solenoid piloting valves are typically used to pilot high flow rate control valves. These control valves transmit hydraulic power to end devices such as subsea production tree valve actuators, choke valves and downhole safety valves. The status condition of control valves and their end devices are read by pressure transducers located on the output circuit of the control valves. Auxiliary equipment inside the typical SCM consists of hydraulic accumulators for hydraulic power storage, hydraulic filters for the reduction of fluid particulates, electronics vessels, and a pressure/temperature compensation system. 
     Recognized by the inventors is that the application of production control system technology incorporated into a modular approach to drilling control systems can allow for additional redundancy, can enhance survivability during deployment, operation, and retrieval, and can reduce maintenance repair times and costs, along with many other benefits. 
     SUMMARY OF THE INVENTION 
     For drilling applications a subsea blowout preventer assembly is provided. The assembly includes a lower marine riser package (LMRP) and a blowout preventer stack (BPS). The LMRP includes a first junction plate and said BPS includes a second junction plate. The junction plates connect at least one of hydraulic, electrical or communications signal from the LMRP to the BPS. The assembly includes at least one LMRP module baseplate positioned on the LMRP and at least one LMRP control module configured to control electrical or hydraulic functionality associated with the LMRP. The LMRP control module is releasably connected to the LMRP module baseplate. The assembly also includes at least one BPS module baseplate positioned on the BPS and at least one BPS control module configured to control electrical and/or hydraulic functionality associated with said BPS. The BPS module is releasably connected to the BPS module baseplate. The LMRP and BPS modules are configured to be installed and retrieved by a remotely operated vehicle. 
     In certain embodiments, the overall assembly control systems are redundant, wherein two or more of the LMRP control modules are present on the LMRP and two or more of the BPS control modules are present on the BPS, thereby forming redundant assembly control modules. In certain embodiments, the redundant LMRP modules do not function cooperatively and the redundant BPS modules do not function cooperatively. 
     In certain embodiments, the LMRP module baseplate can also include at least one auxiliary LMRP module selected from the group consisting of a subsea regulator module, subsea valve module, subsea filter module, subsea accessory module, c subsea shuttle valve module, subsea acoustic system module, subsea pressure transducer module and subsea temperature transducer module. In certain embodiments, the BPS module baseplate also includes at least one auxiliary BPS module selected from the group consisting of a subsea regulator module, subsea valve module, subsea filter module, subsea accessory module, subsea shuttle valve module, subsea acoustic system module, subsea pressure transducer module and subsea temperature transducer module. 
     In certain embodiments, the assembly also includes a parking base plate positioned on the LMRP or the BPS, said parking base plate comprising at least two parking receptacles adapted to receive any of said modules. 
     In another aspect, a subsea blowout preventer assembly is provided that includes a lower marine riser package (LMRP) and a blowout preventer stack (BPS), wherein the LMRP includes a first junction plate and the BPS includes a second junction plate. The junction plates connect at least one of the hydraulic, electrical or communications signals from the LMRP to the BPS. Additionally, the assembly includes at least one LMRP module baseplate positioned on the LMRP and at least one releasably connected LMRP control module configured to control electrical or hydraulic functionality associated with the LMRP. Additionally, the assembly includes at least one auxiliary LMRP module selected from the group consisting of a subsea regulator module, subsea valve module, subsea filter module, subsea accessory module, subsea shuttle valve module, subsea acoustic system module, subsea pressure transducer module and subsea temperature transducer module. The assembly also includes at least one BPS module baseplate positioned on said BPS and at least one releasably connected BPS control module configured to control electrical or hydraulic functionality associated with the BPS. In addition, the assembly includes at least one auxiliary BPS module selected from the group consisting of a subsea regulator module, subsea valve module, subsea filter module, subsea accessory module, subsea shuttle valve module, subsea acoustic system module, subsea pressure transducer module and subsea temperature transducer module. The modules are configured to be installed and retrieved by a remotely operated vehicle. 
     In another aspect, a method for controlling a subsea blowout preventer assembly is provided, wherein the assembly includes a lower marine riser package (LMRP) and a blowout preventer stack (BPS). The LMRP includes a first junction plate and said BPS includes a second junction plate. The LMRP and BPS are coupled at said first and second junction plates, and the junction plates connect at least one of hydraulic, electrical or communication signal from the surface to the assembly. The method includes the steps of providing at least one LMRP module baseplate positioned on the LMRP and providing at least one LMRP control module releasably connected to the LMRP module baseplate configured to control electrical or hydraulic functionality associated with the LMRP. The method also includes the steps of providing at least one auxiliary LMRP module selected from the group consisting of a subsea regulator module, subsea valve module, subsea filter module, subsea accessory module, subsea shuttle valve module, subsea acoustic system module, subsea pressure transducer module and subsea temperature transducer module, said auxiliary LMRP module being releasably connected to the LMRP module baseplate. At least one BPS module baseplate positioned on said BPS is provided; and at least one BPS control module releasably connected to the BPS module baseplate and configured to control electrical or hydraulic functionality associated with said BPS is provided. Additionally, the method includes providing at least one auxiliary BPS module selected from the group consisting of a subsea regulator module, subsea valve module, subsea filter module, subsea accessory module, subsea shuttle valve module, subsea acoustic system module, subsea pressure transducer module and subsea temperature transducer module, said auxiliary BPS module being releasably connected to the BPS module baseplate. Finally, the method includes the steps of installing or removing at least one module selected from the group consisting of the LMRP control module, the LMRP auxiliary module, the BPS control module, and the BPS auxiliary module with a remotely operated vehicle (ROV). 
     In another aspect, a method for replacing a module on a subsea blowout preventer assembly, the assembly including a lower marine riser package (LMRP) and a blowout preventer stack (BPS), wherein the LMRP includes at least one LMRP module baseplate and the BPS includes at least one BPS module baseplate. The LMRP module baseplate is configured to receive at least one LMRP module and the BPS module baseplate is configured to receive at least one BPS module. The LMRP and said BPS each include at least one parking receptacle. The method for replacing includes the steps of: utilizing a remotely operated vehicle (ROV) to transport at least one replacement module from the surface to a module baseplate, positioning said replacement module in a first parking receptacle adapted to receive a module, and utilizing the ROV to remove at least one module from either the LMRP module baseplate or said BPS module baseplate, thereby creating an empty position in the module baseplate. The method further includes utilizing the ROV to position the removed module in a second parking receptacle adapted to receive a module and utilizing the ROV to retrieve the replacement module from the first parking receptacle and position said replacement module into the empty position in the module baseplate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating a lower marine riser package connected to a blowout preventer stack in accordance with this invention. 
         FIGS. 2A and 2B  are a schematic of a subsea control system for the lower marine riser package and the blowout preventer of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a subsea well is shown in the process of being drilled. The subsea well includes a subsea wellhead assembly located at the sea floor. A blowout preventer (BOP) stack  13  secures to the subsea wellhead assembly by means of a hydraulically actuated connector  11 . BOP stack  13  is a complex device for controlling pressure in the well. BOP stack  13  will have a number of rams  15 , some of which can close on or around drill pipe or casing. Other rams  15  can shear pipe to form a complete closure in the event of an emergency. 
     BOP stack  13  is connected to a lower marine riser package (LMRP)  19 . LMRP  19  includes a connector  20  that is hydraulically actuated for connecting to BOP stack  13 . As shown in  FIG. 1 , an annular blowout preventer (BOP)  17  can be a part of LMRP  19  and mounts on top of connector  20  for closing around pipe. Alternately, annular BOP  17  can be part of BOP stack  13  and not part of LMRP  19 ; or both BOP stack  13  and LMRP  19  can include an annular BOP  17 . LMRP  19  is connected to the lower end of a drilling riser  21 . Drilling riser  21  includes a large diameter central pipe through which drilling tools can be lowered. A number of auxiliary or rigid conduits  23  can be spaced around the central pipe for delivering hydraulic fluid and for other functions. Additionally, an electrical cable that can include a bundle of wires, and optionally includes fiber optic lines for providing communications and electrical power, extends alongside riser  21  from a drilling vessel at the surface. LMRP  19  and BOP stack  13  includes one or more modules  25  that are adaptable to perform many functions, including the control of the LMRP or BOP stack. 
     All modules  25  of both the LMRP and the BOP stack are installable and are retrievable by remotely operated vehicle (ROV). LMRP  19  can include a number of retrievable modules  25  that are releasably mounted to it. Similarly, BOP stack  13  can include a number of retrieval modules  25  that are releasably mounted to it. Each module  25  is sufficiently small and lightweight that it can be installed and retrieved using a ROV. Modules  25  on LMRP  19  can control various functions on LMRP  19  and modules  25  on BOP stack  13  can control various functions on BOP stack  13 . Modules  25  can be placed near the functionality that they control and/or with which they are associated, in contrast to prior art control devices associated with the control of a BOP stack, which are generally large and are located relatively distant from the functionality with which they are associated, and normally on the LMRP. 
     In being remotely retrievable, the replacement of one or more modules can be accomplished with a remotely operable vehicle, which can thereby eliminate the need to pull the entire apparatus, including the LMRP. Use of the ROV during maintenance operations results in reduced downtime and increased savings. 
     LMRP  19  includes at least one junction plate  29 , and in certain embodiments, two junction plates, that stab into mating engagement with mating junction plates  31  on BOP stack  13  when LMRP  19  is connected to BOP stack  13 . Junction plates  29 ,  31  connect hydraulic, electrical, and/or fiber optic lines for supplying hydraulic fluid pressure, electrical power and communications to and from the LMRP  19  to BOP stack  13 . 
     Exemplary modules can include: subsea control modules, subsea regulator modules, subsea valve modules, subsea filter modules, subsea shuttle (valve) modules, and subsea accessory modules, in addition to modules that control or are associated with subsea chemical injection, subsea choke inserts, subsea acoustic systems, subsea pressure and/or temperature transducers. 
     An example of several of the exemplary modules  25  and the functions they control are illustrated in  FIGS. 2A and 2B . The overall control system is redundant, with the modules  25  shown in  FIG. 2A , arbitrarily marked as “Yellow System”, being duplicated by the modules  25  shown in  FIG. 2B  and arbitrarily marked as “Blue System”. For convenience, the same references numerals are used for each system in most instances. The Yellow System can perform all functions of LMRP  19  and BOP stack  13  without requiring the input from the Blue System, and similarly the Blue System can perform all functions of LMRP  19  and BOP stack  13  without requiring the input from the Yellow System. In certain embodiments, the Yellow and Blue Systems are not operated at the same time. A control module  25  of the Yellow System is not typically operated with the Blue System and vice versa. An exception to this can be found in embodiments wherein the conduit valve package  36  may be operated by either Yellow or Blue Systems. Similarly, in certain embodiments, the control modules  25  mounted to LMRP  19  only control functions of LMRP  19 , and do not control the functions of BOP stack  13  and vice versa. 
     LMRP  19  may include singular or redundant hydraulic fluid supply equipment for both the modules  25  of LMRP  19  and for the modules  25  of BOP stack  13 . The hydraulic fluid supply equipment includes a base plate  33  on the Yellow System ( FIG. 2A ) and a base plate on the Blue System ( FIG. 2B ), wherein the base plates  33  can include receptacles and couplings for supporting at least one filter module  35 . Filter module  35 , like all of the other modules  25 , can be sufficiently small and lightweight so as to be installed and retrieved by an ROV. Each filter module  35  can include high flow rate filters designed to provide for local filtration of hydraulic fluid which can be supplied down one or more of the rigid conduits  23  extending alongside the riser. Additionally, a flow meter can be located within filter module  35  or base plate  33  for measuring hydraulic fluid flow through the system. A hydraulic regulator may be located within filter module  35  for stepping down supply pressure. In certain embodiments, filtered hydraulic fluid can flow from filter module  35  through module base plate  33  as a supply to all of the other hydraulically actuated equipment on both LMRP  19  and on BOP stack  13 . One or more output lines  37 , connected to an accumulator bank  38 , leads to LMRP junction plate  29  for supplying hydraulic fluid pressure to the accumulators  95  of BOP stack  13 . In certain embodiments, additional output lines  41  can be connected to the LMRP base receptacles  47  and to junction plates  29 ,  31  and further connect to the BOP base plates  69 , supplying fluid to various modules  25 . 
     Rigid conduit package  36  can be made up of subsea valve module  39 , base plate  33  and filter module  35 . In certain embodiments, a subsea valve module  39  can mount to module base plate  33  on both the Yellow System and the Blue System. Subsea valve module  39  can include a number of directional control valves, which are opened and closed by hydraulic pressure supplied by pilot valves that may be located in a control module  51 . These directional control valves can be used for various functions, such as for example, isolation and flushing of the rigid conduits  23 , filter selection, as well as valves for selection, isolation of pilot, and testing of hydraulic circuits. Module base plate  33  is connected by hydraulic fluid lines  37  and  41  to one of the junction plates  29 . Subsea valve modules  39  are installable and retrievable by an ROV. 
     In certain embodiments, both the Yellow and Blue Systems are connected to shuttle valve module base plate  43  mounted to LMRP  19 . One or more shuttle valve modules  45  can be retrievably mounted to each module base plate  43 . The shuttle valves in shuttle valve modules  45  can be connected to valve actuators and other equipment, such as for example, annular BOP  17  or LMRP connector  19 . Those functions can include connecting and disconnecting the connection between LMRP  19  and BOP stack  13 , closing annular BOP  17  and operating other LMRP hydraulically controlled functions. The hydraulic lines leading to shuttle valve base plate  43  are not shown. Each shuttle valve base plate  43  can be connected to both the hydraulic fluid lines leading from control valves of the Yellow System and from control valves of the Blue System. Depending on whether the pressure is being delivered by the Yellow System or the Blue System, each shuttle valve can automatically shift to direct the hydraulic fluid pressure to the valve actuator, connector or other equipment. Each shuttle valve module  45  can receive fluid from either the Blue or the Yellow System and can direct the fluid to the designated component of LMRP  19 . In certain embodiments, module base plates  43  and one or more shuttle valve modules  45  can include a shuttle valve package  40 . 
     The Yellow and Blue Control Systems each have a control module base plate  47  mounted to LMRP  19 . Each control module base plate  47  includes receptacles for one or more control modules. In certain embodiments, a regulator module  49  can be retrievably mounted to base plate  47 . Regulator module  49  can include a number of hydraulic regulators that provide the means for regulating the system output pressure for the different hydraulic circuits for functions on LMRP  19 . Preferably, in certain embodiments, each regulator is independently adjustable. In certain other embodiments, the solenoid pilot regulator can be a manual regulator that is preset at the surface, while the other regulators can be adjusted remotely subsea. Other configurations are also possible. Hydraulic fluid lines  57  supply hydraulic fluid pressure from rigid conduit base plate  33  to module  49 . 
     One or more subsea control modules (SCM)  51  can be retrievably mounted to each control module base plate  47  of LMRP  19 . The SCM can include a subsea electronic module (SEM) that can receive and decode multiplexed signals from the surface control unit. SCM  51  can include electronics as well as solenoid pilot valves and directional control valves. The electronics portion of each SCM  51  can be configured to receive communication signals from a surface control unit. The electronics portion can then decode the signals and convert them to hydraulic signals via electrically operated solenoid valves, which act as pilot valves for other elements such as hydraulically operated directional control valves. In certain embodiments, each SCM  51  is capable of controlling a number of hydraulic functions, either directly or as pilots to larger, high flow rate directional control valves. Some of those functions include housekeeping functions and others are control functions. Some of those functions can include, but are not limited to: operating the locking and unlocking of the connector of LMRP  19  to BOP stack  13 ; controlling the hydraulic regulators; and controlling various test valves and isolation valves on LMRP  19 . Hydraulic pilot pressure from one of the SCMs  51  will also control directional control valves in subsea valve module  39  located in rigid conduit valve package  36 . 
     In certain embodiments, a subsea valve module  55  also retrievably mounts to each module base plate  47 . In certain embodiments, subsea valve module  55  can include high flow rate directional control valves for controlling some of the large functions on LMRP  19 , such as the annular BOP  17  ( FIG. 1 ), which is part of LMRP  19  in the figure. The directional control valves are operated via hydraulic pilot signals received from one of the SCM&#39;s  51 . The fluid flow from subsea valve module  55  leads to shuttle valve module base plate  45 , which direct the fluid to the particular function. In certain embodiments, LMRP control package  32  can include base plates  47  and modules  49 ,  51  and  55 . 
     In certain embodiments, there can be two electrical cables  58 ,  60  extending from the drilling vessel. Each electrical cable  58 ,  60  independently supports power and communications to both the Yellow and Blue Systems. An electrical termination and connection assembly  59  (TCA) is located at the lower end of each electrical cable  58 ,  60 . Each TCA  59  includes connections for power and communication, which can optionally include fiber optic lines. Each TCA  59  includes electrical lines  61 ,  63  leading from it for supplying power to the Yellow and Blue Systems, respectively. Line  61  of each TCA  59  leads to Yellow System control module base plate  47  for supplying power and communications to Yellow System SCMs  51 . Line  63  of each TCA  59  leads to Blue System control module base plate  47  ( FIG. 2B ) for supplying power and communications to Blue System SCMs  51 . In certain embodiments, each TCA  59  can provide one line  61  (Yellow) and one line  63  (Blue). Thus, in embodiments with two TCAs (one for control cable  58  and one for control cable  60 ), there are two independent and redundant power and communication connections feeding the Yellow System and likewise two independent and redundant power and communication connections feeding the Blue System. Other configurations are possible, and are within the scope of this invention. 
     The Yellow System can include an electrical line  65  that connects power and communications line  61  at control module base plate  47  and leads to junction plate  29  for delivering power and signals to the various Yellow System elements on BOP stack  13 . The Blue System can include a similar electrical line  67  that connects power and communications of line  63  at control module base plate  47  and leads to junction plate  29  for delivering power and signals to the various Blue System elements on BOP stack  13 . In certain embodiments, a mirror image of this configuration can connect to the redundant second set of power and communications signals from the other TCA  59  via base plates  47  to the other junction plate  29  to feed redundant power and communications signals to both the Yellow and Blue systems. 
     BOP stack  13  can include a Yellow System and a Blue System control module base plate  69 . In certain embodiments, each base plate  69  can include multiple receptacles that receive, for example, a subsea valve module  71 , one or more subsea control modules  73  and a regulator module  77 . Subsea valve module  71  can include high flow rate directional control valves similar to subsea valve module  55 . Subsea valve module  71  supplies hydraulic fluid pressure for BOP stack  13  functions such as opening and closing rams  15 . SCMs  73  can include electronics along with pilot valves and directional control valves for controlling the various functions on BOP  13 . These functions can include, for example, the various valves of BOP stack  13 , connector to subsea wellhead, choke and kill valves, as well as housekeeping functions, such as for example, increasing and decreasing hydraulic fluid pressure controlled by regulators in the regulator module  77 . 
     Regulator module  77 , similar to LMRP regulator module  49 , regulates the hydraulic fluid pressure for the hydraulic functions on BOP stack  13 , rather than the hydraulic functions on LMRP  19 . SCMs  73  control regulator module  77  to change the hydraulic fluid pressure for the various rams  15  as well as the connector to subsea wellhead  11  ( FIG. 1 ). Various hydraulic lines  79  lead from junction plate  31  to module base plate  69  for receiving hydraulic fluid pressure from rigid conduit base plate  33 . In certain embodiments, BOP control package  34  can include base plates  69  and modules  71 ,  73  and  77 . 
     Electrical line  65  of junction plate  29  can supply electrical power and communication signals from electrical cable  58  to Yellow System SCMs  73  via electrical line  81 , which extends from BOP stack junction plate  31 . Electrical line  67 , also of junction plate  29 , supplies electrical power and communication signals from electrical cable  58  to Blue System SCM&#39;s  73  via electrical lines  83 , which extends from BOP stack junction plate  31 . A mirror image of this electrical connection arrangement provides redundant power and communications signals via the opposite junction plate set  29  and  31 , to the BOP stack SCMs  73  on both the Yellow and Blue Systems. In the event of failure of one electrical cable  58  or  60 , the other electrical cable  58  or  60  will supply all electrical power and communication signals to either the Yellow or Blue System, as needed. 
     BOP stack  13  includes a subsea module base plate  85  having receptacles adapted to receive shuttle valve modules  87 , which in turn are connected to various hydraulically actuated equipment, such as for example, pipe rams  15  ( FIG. 1 ). In certain embodiments, the shuttle valve modules  87  can be part of the shuttle valve package  40 . 
     A parking base plate  91  may optionally be mounted to BOP stack  13  or LMRP  19 . Parking base plate  91  preferably can include parking receptacles  93  adapted to receive any one of the modules  25 . In certain embodiments, an ROV would be able bring down a replacement module  25  and temporarily park it in one receptacle  93  in order to disconnect one of the other modules  25 . The ROV could then place the recently removed module  25  in the other parking receptacle  93 , pick up the replacement module and install it in one of the base plates. The ROV would then pick up the removed module from the receptacle  93  and retrieve it to the surface. BOP stack  13  also has a set of accumulators  95  that are supplied with hydraulic fluid through hydraulic line  97  leading from junction plate  31 . 
     During certain operations, the various modules  25  ( FIG. 1 ) on LMRP  19  perform functions associated with LMRP  19  and also provide filtration for all of the hydraulic systems, including those of BOP stack  13 . The various modules  25  of BOP stack  13  can be directed to the functions of BOP stack  13 . In certain embodiments, to connect BOP stack  13  to subsea wellhead  11  using the Yellow System, communication signals will be sent down one of the electrical lines  58  through lines  61 ,  65  and  81  to one of the BOP stack subsea control modules  73 . That control signal will cause a pilot valve or a directional control valve to send hydraulic fluid pressure to subsea valve module  71 , which in turn supplies hydraulic fluid pressure to the connector via one of the shuttle valves in one of the shuttle valve modules  87 . If a function is required of LMRP  19  and the Yellow system is in use, the signal can be sent via electrical line  58  or  60  to one of the SCMs  51  of the Yellow System, which in turn can cause the hydraulic function to be performed through its pilot valves and/or directional control valves or through subsea valve module  55 , via one of the shuttle valves in one of the shuttle valve modules  45 . 
     In certain embodiments, when because of a storm or some other emergency, the vessel must be quickly moved, the operator may close rams  15  and disconnect LMRP  19  from BOP stack  13 . The operator would then be able to leave the location with riser  21  and LMRP  19  trailing behind. The various rams  15  would remain closed as no hydraulic pressure would exist to cause them to open. When returning, if due to damage, LMRP  19  cannot connect back to BOP stack  13 , the operator may be able to perform certain functions with BOP stack  13  without LMRP  19 . The operator would be able to do this by connecting electrical power and hydraulic power via an umbilical and flying lead to the receptacles in BOP stack junction plate  31 . That umbilical would supply hydraulic fluid pressure and signals directly from the vessel to either the Yellow or Blue System control modules  73  and to modules  71 ,  77  and accumulators  95 . The operator could then open and close rams  15  and perform other functions interfacing with SCMs  73  or other modules. 
     In certain embodiments, the modules can be employed in retrofit applications. For example, in certain embodiments, the modules described herein can be employed on existing LMRP or BOP stack apparatuses to replace all or a portion of the control devices associated with said LMRP or BOP stack. 
     Although the following detailed description contains many specific details for purposes of illustration, one of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the exemplary embodiments of the invention described below are set forth without any loss of generality to, and without imposing limitations thereon, the claimed invention. 
     The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise. 
     Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur. 
     Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. 
     This application is related to U.S. Provisional Patent Application No. 60/955,085, entitled “Control System for Blowout Preventer Stack”, filed on Aug. 10, 2007, and U.S. Provisional Patent Application No. 60/954,919, entitled “Control Module for Subsea Equipment”, filed on Aug. 9, 2007, each of which are incorporated herein by reference in their entirety. 
     Throughout this application, where patents or publications are referenced, the disclosures of these references in their entireties are intended to be incorporated by reference into this application, in order to more fully describe the state of the art to which the invention pertains, except when these reference contradict the statements made herein.

Summary:
A modular control system consisting of multiple, remotely retrievable functional modules for controlling a blowout preventer stack. The various functional modules can be located on the lower marine riser package and blowout preventer stack positioned near the equipment with which they are associated, wherein this distribution of modules nearly eliminates the complex interface connection between the lower marine riser package and blowout preventer stack. Each of the functional modules is capable of being installed, retrieved or replaced with a single remotely operated vehicle (ROV) deployment from a vessel. The functional modules can be used to operate as a complete control system for a blowout preventer stack or can be used selectively individually or in various combinations to accommodate multiple control applications or upgrades of other control systems.