Patent Description:
Accumulators located near a blow-out preventer (BOP) and other subsea equipment may be configured to provide pressure for operating hydraulic systems, such as the blow-out preventer (BOP). Subsea accumulators may store a combination of an inert gas and fluid. Initially, the subsea accumulator is charged with an initial pressure of gas, such as nitrogen. Fluid may then be pumped into the subsea accumulators to a final pressure, which may be equal to the BOP control system pressure. Compression of the gas within the subsea accumulator stores energy. The stored energy in the accumulator may be used to operate subsea equipment, such as when an emergency situation occurs resulting in a disconnect of energy from the surface. When the pressure of hydraulic fluid in the subsea system drops through use of the emergency system, the compressed gas expands, forcing the hydraulic fluid out of the accumulator and into the subsea system hydraulic lines.

When energy is supplied from the accumulators, in the absence of external energy such as from the surface, the pressure in the accumulators decreases over time as stored fluid energy is used for functions within the system. That is, as liquid is used from the accumulators, the pressure of the trapped gas decreases as a result of increasing volume for the gas, and the pressure within the subsea system hydraulic lines decreases. The decreased pressure in the fixed volume subsea system may result in limitations of components within the subsea system or through pressure limitations in the components or equipment used to convey the hydraulic fluid from the surface to the BOP. For example, a shear ram of a BOP may require a certain pressure level to shear a certain drillpipe in the event of an emergency. When that pressure level is not available from the accumulators, the BOP may fail to shear the drillpipe.

Additionally, when energy is supplied from the surface, the pressure within the subsea system may nevertheless be below an operating pressure for the subsea system. The drop in pressure from the surface to the subsea system may be due to leaks and other inefficiencies in the hydraulic fluid transfer system. Also, the drop in pressure may be from pressure limitations in the lines that convey the fluid from surface.

One conventional solution may be to increase the number of accumulators. Each additional accumulator provides an increase in the available volume of hydraulic fluid for operating the subsea systems. However, the additional accumulators may lead to an increased blowout preventer (BOP) stack weight and size, which is prohibitive to construction, installation, operation, and maintenance of the BOP or prohibitive to retrofitting additional accumulators onto a BOP stack. Thus, there is a need for providing increased pressure in a subsea system.

<CIT> discloses a system for controlling a hydraulic actuator.

<CIT> discloses a hydraulic system for supplying hydraulic fluid to a hydraulically operated device alternately at pressures of different values.

<CIT> discloses a hydraulic intensifier comprising a piston and cylinder assembly having a first piston in a chamber of low pressure cylinder and a second piston in a chamber of a high pressure cylinder.

<CIT> discloses a method of injecting high pressure fluid from a nozzle.

Pressure in subsea systems, and accumulators of the subsea systems, are increased through the use of a supercharge cylinder to generate higher pressures from an initial pressure provided from a surface vessel. The supercharge cylinder may include a piston that can be stroked to increase pressure stored in accumulators located near subsea systems, such as a blowout preventer (BOP). The increased pressure provided by the supercharge cylinder may allow the same number of accumulators to be used in the subsea system but allow additional effective hydraulic fluid to be stored in the accumulators.

According to one aspect of the present invention, there is provided a subsea system according to Claim <NUM>.

The system includes a control module to perform the steps of charging an accumulator to a base control system pressure; stroking a supercharge cylinder to increase accumulator pressure above the base control system pressure to an increased system pressure; and may also perform the step of repeatedly stroking the supercharge cylinder to increase accumulator pressure to a desired pressure above the base control system pressure. The apparatus also includes a pressure regulator coupled to the accumulator and configured to limit an output of the accumulator and may also include a shear ram coupled to the accumulator and configured to operate from pressure supplied by the accumulator, in which the accumulator may be attached to a blowout preventer (BOP).

According to a second aspect of the invention, there is provided a method according to Claim <NUM>.

The method includes stroking the supercharge cylinder. The method may include stroking the supercharge cylinder in to fill a supercharge chamber of the supercharge cylinder with new fluid from a reservoir at a surface. The method may include repeatedly stroking the supercharge cylinder to increase accumulator pressure to a desired pressure above the base control system pressure. The method includes limiting an output pressure of the accumulator to a regulated pressure. The method may include performing a function with the increased system pressure, such as performing an emergency action on a blowout preventer (BOP) including an shearing a drillpipe.

The apparatus may include a supercharge cylinder including a piston with fluid stored on a first side of the piston and a second side of the piston; a first input for receiving fluid on a first side of the piston at a base control system pressure; a second input for receiving fluid on a second side of the piston at the base control system pressure; and an output at the first side of the piston for outputting an increased pressure above a base control system pressure. The apparatus includes a supercharge control valve coupled to the supercharge cylinder, which may be configured to provide fluid to the first side of the piston and to the second side of the piston.

The apparatus also includes a hydraulic line coupled to the output of the supercharge cylinder; and an accumulator coupled to the hydraulic line. The apparatus may also include a first one-way valve configured to provide the base control system pressure to the accumulators; a second one-way valve configured to block fluid from exiting the supercharge cylinder through the second input; and/or a second one-way valve configured to block fluid from exiting the supercharge cylinder through the output when the supercharge cylinder is charging.

The foregoing has outlined rather broadly the features and technical advantages of the claimed invention in order that the detailed description that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the presently claimed invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the scope of the appended claims. The novel features which are believed to be characteristic of the claimed invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the claimed invention.

For a more complete understanding of the disclosed system and methods, reference is now made, by way of example only, to the following descriptions taken in conjunction with the accompanying drawings.

<FIG> illustrates a system for supercharging pressure in a subsea system according to one embodiment of the claimed invention. A system <NUM> may include valves <NUM> and <NUM> connecting a subsea system to an energy source, such as a pressurized hydraulic system at the surface or a pressurized hydraulic source supplied by a remote operated vehicle (ROV) coupled to the subsea system <NUM>. Accumulators <NUM> are coupled near subsea equipment and store energy to operate hydraulic systems of the subsea system <NUM>.

A supercharge control valve <NUM> redirects pressure to a supercharge cylinder <NUM> having a piston <NUM>. The piston <NUM> may have a diameter of, for example, between approximately <NUM> and <NUM> (<NUM> inches and <NUM> inches) with a rod diameter of, for example, between <NUM> and <NUM> (<NUM> inch and <NUM> inches), and a stroke length of, for example, between approximately <NUM> and <NUM> (<NUM> inches and <NUM> feet). In one embodiment, the piston <NUM> has a piston diameter of <NUM> (<NUM> inches) with a rod diameter of <NUM> (<NUM> inches) and a stroke length of <NUM> (<NUM> inches).

One way valves <NUM>, <NUM>, and <NUM> may be opened or closed to operate the subsea system <NUM> along with the supercharge control valve <NUM>. When a supercharge control valve <NUM> is activated, pressure is directed into the supercharge cylinder <NUM> to move the piston <NUM> upward in the cylinder <NUM>.

According to the invention, a pressure regulator <NUM> is be coupled to an output of the accumulators <NUM> to limit the pressure provided to subsea systems, such as emergency systems on a blowout preventer (BOP), to prevent damage to these components that may not be designed to handle higher pressures. A maximum pressure may also be regulated by selecting a desired ratio for surface area on a first side of the piston <NUM> and an opposing second side of the piston <NUM>. The fixed surface area ratio of the piston <NUM> may act as a self-limiting regulator on the supercharged pressure when the pressure at the source at the surface is fixed.

<FIG> illustrates a system configured to charge accumulators according to one embodiment of the claimed invention. The accumulators <NUM> may be charged from an external source, such as at the surface, to a base control system pressure. The valve <NUM> may open to allow pressure <NUM> to propagate to the supercharge control valve <NUM>. Because the supercharge control valve <NUM> is closed, the pressure <NUM> does not charge the supercharge cylinder <NUM>. The valve <NUM> may be open allowing the pressure <NUM> to propagate to pressure <NUM> and into the accumulators <NUM>. The valve <NUM> may be closed such that the pressure <NUM> does not reach the supercharge cylinder <NUM>.

<FIG> is a system configured to stroke the supercharge cylinder <NUM> according to one embodiment of the claimed invention. The supercharge control valve <NUM> may open to allow the pressure <NUM> to propagate to pressure <NUM> to the supercharge cylinder <NUM> and advance the piston <NUM> in the cylinder <NUM>. The valve <NUM> may be open such that as the piston <NUM> advances upward, pressure is increased in the fluid above a bottom surface of the piston <NUM>. The increased pressure in the cylinder <NUM> may result in increased pressure <NUM> in the hydraulic lines of the subsea system. The valve <NUM> may be closed to prevent exit of pressure from the input of the supercharge cylinder <NUM> forcing the increased pressure to the accumulators <NUM>. The accumulators <NUM> and other subsea equipment may operate at a pressure above base control system pressure. In one embodiment, multiple superchargers <NUM> or accumulators <NUM> may be configured to achieve fixed steps in the increased base control system pressure, such as <NUM>, <NUM> and <NUM> MPa (<NUM>, <NUM>, and <NUM> psi). In another embodiment, a single accumulator may be charged and regulated to provide the fixed steps in the increased base control system pressure.

<FIG> is a system configured to stroke the supercharge cylinder to fill with new fluid according to one embodiment of the claimed invention. The valves <NUM> and <NUM> may open to allow the pressure <NUM> to propagate to the supercharge cylinder <NUM>. The valve <NUM> may close, and the pressure <NUM> propagates to pressure <NUM> to return the piston <NUM> to a bottom position of the cylinder <NUM>. The pressure <NUM> may continue to propagate to the pressure <NUM> to operate subsea equipment and maintain the accumulators <NUM> at base control system pressure. The supercharge cylinder <NUM> allows increased pressure above base control system pressure at the accumulators <NUM> and other subsea equipment attached to hydraulic lines of the subsea system. Operation of the supercharge cylinder as shown in <FIG> assumes previous operation of the supercharge cylinder as shown in <FIG> and <FIG> such that pressure <NUM> and pressure at the accumulators <NUM> are above the pressure <NUM>. Thus, the valves <NUM> and <NUM> may remain closed as the pressure <NUM> is higher than the pressure <NUM>.

<FIG> is a flow chart illustrating one method of supercharging a hydraulic system according to one example not falling within the scope of the claimed method. Increased pressure in a hydraulic system may be achieved through the method <NUM>, which begins at block <NUM> with charging accumulators to a base control system pressure. At block <NUM>, a supercharge cylinder is stroked to increase accumulator pressure above a base control system pressure. At block <NUM>, the supercharge cylinder is stroked in to fill a supercharge chamber of the supercharge cylinder with new fluid. Operation of a system with a supercharger cylinder as described in blocks <NUM>, <NUM>, and <NUM> are generally described with respect to a particular system shown in <FIG>, <FIG>, and <FIG>.

The increased pressure in the hydraulic system may be monitored and the monitored pressure provided as feedback to a pressure control module to obtain a desired pressure within the hydraulic system. <FIG> is a schematic illustrating a system configured to provide feedback regarding a supercharged pressure according to one embodiment of the claimed invention. A control module <NUM> may receive information from a pressure sensor <NUM> coupled to a line coupled to the accumulator <NUM> and/or coupled to a high pressure side of the supercharge cylinder <NUM>. In one embodiment, a deintensifier <NUM> may couple the pressure sensor <NUM> to the line coupled to the accumulator <NUM>. The deintensifier <NUM> may provide an output pressure to the sensor <NUM> at a fixed ratio or fixed offset from the pressure in the line coupled to the accumulator <NUM>, which allows the pressure sensor <NUM> to be a low pressure sensor <NUM>. A pressure readout <NUM> and an isolation valve <NUM> may also be coupled to the pressure sensor <NUM> to allow a manual readout of the pressure. In one embodiment, the pressure sensor <NUM> and related components <NUM> may be located in a first module, such as a module on a the surface at a ship or drilling rig. The supercharge cylinder <NUM> and related components <NUM> may be located subsea, such as near a blowout preventer (BOP). In another embodiment, the components <NUM> may be located subsea, such as near the blowout preventer (BOP).

A control module <NUM> may be coupled to the pressure sensor <NUM> and to the supercharge cylinder control valve <NUM>. The control module <NUM> may execute algorithms for controlling the supercharge cylinder control valve <NUM> based on, for example, input from the pressure sensor <NUM> to obtain a desired pressure in the accumulators <NUM>. <FIG> is a flow chart illustrating one method of supercharging a hydraulic system to a desired pressure using feedback from the supercharger according to one example not falling within the scope of the claimed method. A method <NUM> begins at block <NUM> with charging accumulators from the surface. At block <NUM>, it is determined whether the system pressure is approximately equal to a reference pressure. In one example, a reference pressure may be <NUM> or <NUM> MPa (<NUM> or <NUM> psi). If not, the method <NUM> returns to block <NUM> to continue charging the accumulators from the surface. If the system pressure is approximately equal to the reference pressure, then the method <NUM> proceeds to block <NUM>.

At block <NUM>, the supercharger is activated for one stroke of the supercharger cylinder to increase the system pressure. At block <NUM>, optionally, a delay time may be implemented. At block <NUM>, the supercharger may be activated for one stroke to refill the supercharge cylinder. Then, at block <NUM>, it is determined whether the system pressure is approximately equal to a desired pressure. For example, a desired pressure may be <NUM>, <NUM> or <NUM> MPa (<NUM>, <NUM>, or <NUM> psi). If the desired pressure is not yet reached, then the method <NUM> may return to block <NUM> to activate the supercharger for another stroke of the supercharge cylinder to further increase the system pressure. When the desired pressure is obtained at block <NUM>, then the method <NUM> may proceed to performing a function with the hydraulic pressure at the desired pressure. Block <NUM> may not be performed immediately when the desired pressure is obtained. That is, the desired pressure may be stored in the accumulators until an emergency occurs that requires actuation of components using the stored pressure.

In one embodiment, the actuation of components at block <NUM> may be the actuation of a ram to shear a drillpipe. Higher pressures within the accumulators allow for larger and/or thicker drillpipe to be cut with the same shears. <FIG> is a graph illustrating increased pressure obtained at an end of a ram with one supercharged pressure according to one embodiment of the claimed invention. The graph of <FIG> shows lines <NUM> and <NUM> demonstrating a pressure drop as the volume of fluid in the accumulators drops due to consumption in operation of the ram. Marks <NUM>, <NUM>, <NUM>, and <NUM> are the pressures required at the end of the ram to shear certain drillpipes. For example, the mark <NUM> may mark a pressure required to shear a larger drill pipe than the drill pipe corresponding to mark <NUM>.

When an initial pressure for the accumulators is <NUM> MPa (<NUM> psi), the line <NUM> illustrates that the pressure decreases as fluid is consumed such that the pipe <NUM> may be sheared but the pipes <NUM>, <NUM>, and <NUM> are not sheared. That is, the accumulator with <NUM> MPa (<NUM> psi) contains insufficient pressure to operate the ram to cut drillpipes requiring pressure of marks <NUM>, <NUM>, and <NUM>. Likewise for an initial pressure for the accumulators of <NUM> MPa (<NUM> psi), the line <NUM> illustrates that the pressure decreases as fluid is consumed such that pipes requiring pressures <NUM> and <NUM> are not sheared.

Conventionally, higher pressures are initially charged in the accumulators to allow shearing of larger drillpipes. For example, the increase of initial pressure from <NUM> MPa (<NUM> psi) of line <NUM> to <NUM> MPa (<NUM> psi) of line <NUM> may allow shearing of larger drillpipes. However, charging the accumulators to higher initial pressures from the surface becomes difficult. Use of a supercharge cylinder may allow an increased pressure to be obtained at the accumulators. For example, lines <NUM> and <NUM> illustrate an initial pressure obtained of <NUM> MPa (<NUM> psi) that allows shearing of drill pipe corresponding to the pressure <NUM>. The line <NUM> shows the higher initial pressure obtained in the accumulators. A pressure regulator may be set to limit the output of the accumulators to a regulated pressure <NUM>. Thus, an output of the fluid for use by subsea systems may have a fixed pressure as fluid volume initially drops. The line <NUM> illustrates that the increased pressure through the use of the supercharge cylinder allows the drill pipe corresponding to pressure <NUM> to be sheared.

Higher pressures may be generated by the supercharge cylinder to allow larger drillpipes to be sheared. <FIG> is a graph illustrating increased pressure obtained at an end of a ram with another supercharged pressure according to one embodiment of the claimed invention. Lines <NUM> and <NUM> illustrate an initial pressure obtained of <NUM> MPa (<NUM> psi) that may allow shearing of drill pipe corresponding to the pressure <NUM>.

The higher pressures achieved with the supercharge cylinder may improve the response of hydraulic systems in a blowout preventer (BOP), such as emergency response systems to cut and/or seal a drillpipe. For example, the higher pressures may increase the diameter or thickness of pipe that may be cut and/or sealed by the BOP. The increased pressure achieved with the supercharge cylinder may provide additional hydraulic fluid for operating these hydraulic systems without increasing a number of accumulators already present at the BOP. Further, a supercharge cylinder may be added onto existing BOP infrastructure to increase the capability of the existing BOP infrastructure.

If implemented in firmware and/or software, the functions described above, such as described with reference to <FIG> and <FIG>, may be stored as one or more instructions or code on a computer-readable medium. Examples include non-transitory computer-readable media encoded with a data structure and computer-readable media encoded with a computer program. Computer-readable media includes physical computer storage media. A storage medium may be any available medium that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc includes compact discs (CD), laser discs, optical discs, digital versatile discs (DVD), floppy disks and blu-ray discs. Generally, disks reproduce data magnetically, and discs reproduce data optically.

In addition to storage on computer readable medium, instructions and/or data may be provided as signals on transmission media included in a communication apparatus. For example, a communication apparatus may include a transceiver having signals indicative of instructions and data. The instructions and data are configured to cause one or more processors to implement the functions outlined in the claims.

Claim 1:
A subsea system (<NUM>) for providing pressure for operating a hydraulic system of a subsea equipment comprising:
an accumulator (<NUM>) configured to store hydraulic fluid and gas;
a supercharge cylinder (<NUM>);
a hydraulic line coupling the accumulator to the supercharge cylinder (<NUM>);
a supercharge cylinder control valve (<NUM>) coupled to the supercharge cylinder;
a control module configured to perform the steps of:
charging the accumulator (<NUM>) to a base control system pressure; and
stroking the subsea supercharge cylinder (<NUM>) with the supercharge cylinder control valve (<NUM>) to increase accumulator pressure above the base control system pressure to an increased system pressure;
characterized in that the subsea system (<NUM>) further comprises a pressure regulator (<NUM>) coupled to the accumulator (<NUM>) and configured to limit an output of the accumulator (<NUM>) to a regulated pressure lower than the increased system pressure to prevent damage to the subsea equipment.