Patent Publication Number: US-4095421-A

Title: Subsea energy power supply

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a primary or secondary (backup) system for actuating a submerged hydraulic system. Specifically, the invention pertains to a primary system for actuating submerged fluid-actuable equipment. Also it pertains to a secondary power system to backup a primary one that has temporarily failed so that the fluid actuatable equipment is still operatable. 
     2. Prior Art 
     Subsea systems (powered by electric, hydraulic or pneumatic power) can be used for many purposes. They may, for example, control subsea tank valves or subsea wellheads. 
     By way of example, we will explain the use of this invention with a &#34;blowout preventer (BOP) stack&#34; used in drilling wells on the ocean floor. The BOP provides means for closing a well head either fully or around a drill pipe to contain well pressure or circulate, condition and return fluids to and from a subsea oil well so as to maintain well pressure control. On occasion its primary power system may fail to provide power to operate the BOP stack. 
     The current procedure used in case of such a failure utilizes a diver-connected power source instead of devices that are actuated by apparatus which utilize the ambient pressure in which the system is submerged. This procedure is time-consuming, and at depths over several hundred feet may be impossible to accomplish without a submarine vessel. One alternate approach, which is likewise time-consuming, is to lower an energizing hydraulic spear (attached to hydraulic lines) down into a receptacle on the BOP stack. The receptacle is hydraulically connected to actuators that operate selected functions of the BOP stack. If this is not possible, control of the subsea system may be lost or at least required to be temporarily abandoned. 
     Noteworthy is that failure of the source of power becomes less probable when the method and apparatus of this invention is used as the primary power source. The reason is that it does not rely entirely on the operation of a hydraulically or electrically powered system. Further, the negative energy supply system is a quick-response one, since it is located adjacent to the equipment it operates. Contrasted to this is a hydraulic system which has a source of fluid located at the water surface such as on a drilling platform. The response of such a system to operate deeply submerged equipment is considerably slower than the present invention because of the long distance the fluid must travel. 
     BRIEF SUMMARY OF THE INVENTION 
     The main component of the present embodiment of my invention is a pressure vessel, receiver or chamber sealed to hold atmospheric pressure. Alternatively, it may be adapted to be vented above the water surface in a manner which allows atmospheric pressure to be maintained in the submerged receiver. It can then be connected to a subsea actuator. In turn, the actuator&#39;s intake and discharge ports are connected respectively to remotely operated valves that control the flow of fluid to and from the discharge ports so as to operate equipment that is necessary to control a wellhead. More specifically, the valves expose the actuator&#39;s intake ports to the sea and vent its discharge ports to the chamber at atmospheric pressure. 
     The present invention can be utilized to appropriately open the intake port of the actuator to the sea, while simultaneously venting its discharge port to the receiver. A pressure difference (resulting from the hydrostatic pressure at the subsea location of the intake port and the substantially atmospheric pressure of the chamber at the discharge port) operates the actuator. This pressure difference within the actuator is then adaptable to close valves, start and stop pumps or other subsea equipment that needs a force to operate it. 
     In shallow waters, a pressure amplifier can be provided to increase the available water pressure to supply the pressure differential needed to operate the actuator. Further, means can be provided to purge the vented pressure vessel once it receives a charge of the fluid that operates the actuator. 
     Besides these aspects and advantages of the invention, other ones will become apparent from the drawings, description of the preferred embodiment, and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of one specific embodiment of the apparatus that can be controlled with the present invention. This figure shows a side elevation of a subsea blowout prevention equipment used to control drilling operations of a subsea well head system from a floating platform. The present invention is connectable to operate the blowout equipment. 
     FIG. 2 is a schematic illustration of one form of apparatus suitable for carrying out the present invention which includes a subsea receiver sealed at atmospheric pressure or at a vacuum. This is the arrangement the apparatus of the invention is in prior to actuation. 
     FIG. 3 is a schematic illustration of the present invention showing the actuator vented to the receiver at a predetermined pressure. This is the arrangement the invention takes when it is activated. 
     FIG. 4 is a schematic illustration of present invention having a pressure switch to control the actuator instead of the sonic receiver/transmitter of FIG. 1. 
     FIG. 5 is a schematic illustration of another embodiment of this invention. This figure illustrates a backup system for operating an electrically powered device submerged in a body of water. 
     FIG. 6 is a schematic illustration of the present invention of FIG. 2 with a pressure amplifier to amplify the operating pressure resulting from the hydrostatic pressure at the subsea location of the invention. 
     FIG. 7 is a schematic illustration of another embodiment of the present invention in which a subsea receiver is vented to the atmosphere. 
     FIG. 8 is a schematic illustration of the present invention of FIG. 7 which is arranged so the subsea receiver may be blown out by using a vent. 
     FIG. 9 is a schematic illustration of the present invention with a purging pump and an auxiliary tank to purge the sealed submerged receiver. 
     FIG. 10 is a schematic illustration of the present invention used as a primary source of power that actuates a subsea system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The subsea negative energy power supply may be a primary, auxiliary or backup system for operating a hydraulically actuable device, such as subsea actuator 106, FIGS. 2-10. A pair of actuators 106 can operate the rams of the BOP stack (FIG. 1) that are pneumatically, hydraulically or electrically actuable as explained below. This stack customarily includes a series of vertically interconnected BOP&#39;s of different types which are operated independently of each other to control well fluids in the event the well pressure exceeds the drilling fluid head. 
     In the apparatus illustrated in FIG. 1, numeral 118 represents a bag-type BOP (fits around a drill pipe including drill collars). The numerals 122, 124 and 126 designate ram-type BOP&#39;s (blocks the drilling hole or fits only around a drill pipe). Numerals 128 and 130 represent a hydraulically powered marine riser and well head connectors. Connector 128 is connected to marine riser 132 below ball joint 234 and detachably connected to the top of the BOP stack; connector 130 is detachably connected to the well casing head. 
     Also of significance is the hydraulic or pneumatic control system for such a blowout preventer stack. The hydraulic or pneumatic fluid (controlled at the surface) generally flows through hoses that are fabricated into bundle 116. This flow path is in series with accumulator 22 -- the subsea storage space for hydraulic or pneumatic fluid power generated by equipment located above the water surface. Consequently, subsea connectors 128, 130, preventers 118, 122, 124, 126, are controllable from a water surface location. Nevertheless, a person skilled in the art will appreciate that not all of these devices are needed to practice the method of the present invention in every situation. 
     As stated before, it is desirable that at least the BOP&#39;s operate independently of each other. To accomplish this in normal operation, hydraulic fluid from a pressure source at the ocean surface is stored under pressure in accumulator 22, FIG. 1. Pressurized hydraulic fluid is conducted to valve 232 through hydraulic line 180. This valve is controlled from the surface by hydraulic, pneumatic or electrical signals through control line 229. Depending upon the function to be performed by actuator 106, hydraulic fluid passes through the control valve through either line 120 or 121. Similarly, exhaust fluid will be discharged from actuator 106 through either line 121 or 120 to control valve 232 which is vented through port 233. The apparatus of the present invention, to repeat, may be used to provide a back-up system to the primary control system described above. Typical illustrations are shown in FIGS. 2-9 where the water surface is indicated by numeral 100. 
     In FIGS. 2-9, the actuator is shown in a subsea position connected to a first valve means, control valve 107 with plugged outlet 152. This valve isolates the energizing side 210 of actuator 106 from communication with the source of pressurized hydraulic fluid, (see FIGS. 2 and 3). Simultaneously, it places the energizing side of actuator 106 in communication with the water at the depth of the submerged location. A second valve means, control valve 108 with plugged outlet 150, is located at the discharging or exhaust side 201 of actuator 106. This valve isolates the discharge of actuator 106 from the BOP control system while simultaneously placing the discharging side of the actuator in communication with the receiver 105. 
     Thus, valve 108 is normally closed to the receiver or chamber 105 whose interior is at a predetermined pressure (that is a pressure less than that found exterior to receiver 105). And valve 107 is normally closed to the hydrostatic head provided by the depth of the water it is in. If power that usually operates the valves fails, valves 107 and 108 can be constructed and arranged to be actuated from a location remote therefrom. 
     For instance, an acoustic transmitter 102 located, e.g. on an offshore platform at the surface of a body of water, initiates or generates a sonic signal through the water to acoustic receiver 104 located adjacent to the subsea bottom. It converts the sonic signal to an electric pulse. This pulse closes relays 109 and 110 so as to allow storage battery 155 or other power sources such as another accumulator or another system using the present invention to actuate respectively valves 107 and 108, positioned near the submerged location. As a result, normal BOP control piping 120 and 121 -- hydraulically in series with, for example, control valves for the BOP&#39;s -- is disconnected from the energizing or opening side, 210, FIG. 3 of actuator 106 and exposed to the water or hydrostatic pressure at the depth of the location of the actuator. At the same time, the discharging side, 201, of actuator 106 is hydraulically connected to receiver 105. Consequently, the difference in hydrostatic pressure at the depth of the location and the pressure of receiver 105 is made available to actuate actuator 106 which discharges hydraulic fluid through discharge port 201 into receiver 105, FIG. 3. 
     Alternatively, this sequence can be set off by pressure switch 220, with a self-contained power source, connected to the control piping, FIG. 4. When it senses a pressure change beyond a predetermined range, valves 107 and 108 are triggered by it from their normal position to operate the actuator as above. 
     In the case of a back up system for operating an electrically powered system submerged in a body of water, FIG. 5, the actuator 106 is connected to the electrically powered system so that it is operable by the actuator. For example in FIG. 5, the system comprises valve 211, a fail open valve, which is ordinarily opened and closed by electric actuator 215. This valve controls the flow through a subsea pipeline 212. A way to make the system operable by the actuator 106 is to provide a supplementary hydraulic circuit that has actuator 106 connected to a second control valve 213 located adjacent to the valve 211. A first two-way valve 202 is connected to the energizing side 210 of actuator 106, and a second two-way valve 203 is connected between the discharging side 201 of the actuator and receiver 105. This receiver has a predetermined gaseous pressure within it. 
     Valve 202 is a means for exposing the energizing side of the actuator to the hydrostatic pressure at its submerged location. Valve 203 is a means for communicating the discharging side of the actuator with the receiver. Valves 202 and 203 are operated simultaneously by the acoustic receiver 104 through relays 109 and 110 when a signal is received from the surface acoustic transmitter 102. This arrangement allows the resulting pressure difference between the internal pressure of the receiver and the hydrostatic pressure at the depth the actuator is at to operate the actuator and equipment connected to it. This occurs as water flows from the body of water into the energizing side of the actuator and fluid is pushed out the discharge side of the actuator into the receiver. 
     Other apparatus can be added into the system so that the system is readily adaptable to its environment. For instance, a water depth amplifier or pressure amplifier 216, FIG. 6 can be connected to the closing side of actuator 106. The water depth or pressure amplifier increases the operating pressure at the water depth of the submerged location when the hydrostatic pressure is insufficient to actuate actuator device 106. In other words, an amplifier can be provided to increase the operating pressure at the water depth of actuator 106 when this depth does not provide enough of a pressure difference between the hydrostatic pressure and the internal pressure in the submerged receiver to actuate this actuator. 
     The description now turns to receiver 105, FIGS. 2-10, also referred to as a chamber, pressure vessel, tank or receptacle. It is at a predetermined pressure, as already mentioned, which may be substantially atmospheric pressure (FIGS. 2-6, 9); vented to the atmosphere, FIGS. 7, 8 and 10); or sealed at a vacuum (FIGS. 2-6 and 9). Thus, receiver 105 is a means for containing an internal pressure less than the fluid pressure exerted on the submerged equipment. 
     The location of receiver 105 is such that the accompanying pressure drop associated with piping as well as miscellaneous entrance and exit pressure losses through the valves does not reduce the hydrostatic head below the amount needed to adequately operate a given piece of subsea equipment. Two examples are given to illustrate this. 
     First take the case of subsea equipment, located at 40 feet below sea level which requires little pressure to operate, say 2 psi, while tank 105 is located 10 feet below the water surface. If the over-all pressure drop leaves sufficient pressure difference to operate the equipment, the location and the pressure within the receiver is satisfactory. On the other hand, if the equipment requires a great deal of pressure (say 1500 psi), and it is located at water bottom (say 3000 feet below sea level) while the receiver with an internal pressure at atmospheric pressure is at the water surface, the result is an insufficient pressure differential to operate the equipment. This, however, is not the case if the receiver is located near the water bottom. 
     In brief, the only condition on both location and pressure of the receiver is that they result in enough of a pressure difference between the pressure in it and the hydrostatic head to operate the subsea equipment. Of course, I imply that appropriate accounting is taken for miscellaneous losses through any pipes, valves or the like. 
     When vent stack 117 is used to influence the pressure in the receiver, FIG. 7, the stack can be connected to control valve 112, which may be located at any point along the length of the vent. The valve is interconnected with the control panel through relay 170 so that it will automatically open when power is no longer received from panel 101. Further, float valving 157, FIG. 7, may be provided to prevent liquid from leaving the stack when it is not desirable to mix the hydraulic fluid with the surrounding sea after a hydraulic discharge has been received in receiver 105 and it becomes emminent the discharge may over flow. 
     The vent stack 117 may be used to blow out receiver 105 as now described and illustrated in both FIGS. 8 and 10. First, valve 158 is remotely opened by a signal from acoustic transmitter 102 to receiver 104 which sends an electric pulse to relay 111 which operates valve 158. Then air or other gas at a pressure greater than the hydrostatic pressure at valve 158 flows into the stack after opening valve 171 from compressor 160, a source of pressure. This pressure closes check valve 157 and forces the contents or the receiver out into the subsea or into an auxiliary tank (not illustrated). 
     When no vent stack is available, a purging pump 130 may be appropriately connected to tank 105, FIG. 9. The pump removes the exhaust fluid the tank receives when the actuator is operated by the subsea negative energy system. This discharge can be pumped to relocatable auxiliary tank 221 after remotely opening valve 172 through relay 173. Subsequently it can be removed from its subsea location for cleaning without disrupting the fail-safe capability of the system after closing valves 174 and 175. 
     When this invention is used as the primary source of power, FIG. 10, such as controlling subsea pipeline 212 by valve 213 through actuator 106, several things must be kept in mind. For example, the hydraulic fluid becomes the sea water. The auxiliary tanks, such as tank 221 described above, become redundant because the sea water can obviously be mixed with itself. It also follows that modifications must be made to the valving and control system to accommodate the sea water flowing through them. For example, there is need for only one control valve 202 and relay 109, though two may be arranged as illustrated in FIG. 5. Another point is that concern must be taken regarding quantity and size of receivers such as receiver 105 and associated pumps to empty them once filled from charges of water. 
     Many other variations will be apparent to those skilled in the art. It is not desired, therefore, to be limited to the specific embodiment shown and described, but only by limitations of the appended claims.