1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to subsea oil and gas drilling equipment. More particularly, the present technology relates to accumulator valves for use in subsea oil and gas drilling hydraulic circuits.
2. Discussion of the Background
Blowout preventers (BOPS) are important safety components in subsea well drilling operations. Typically, a BOP is attached to a wellhead at the sea floor, and provides a bore through which the drill string can pass from the top of the BOP down through the bottom and into the well. The BOP is equipped with BOP rams, which are located on opposing sides of the bore and are designed to close across the bore if needed. Some rams are sealing rams, which seal around the drill pipe to close in the annulus of the well. Other rams are shearing rams, and are designed to shear the drill pipe and anything else in the bore, to completely close in the bore. The BOP and its rams provide an effective barrier against dangerous pressure surges that may develop in a well.
In order to operate the BOP rams, hydraulics are typically used to drive the rams from an open to a closed position. Hydraulic fluid is applied to the rams via a fluid conduit that connects the rams to a fluid reservoir or accumulator. A valve or series of valves in the fluid conduit controls the fluid flow through the conduit, which in turn determines the hydraulic pressure applied to the rams. The forces needed to drive the BOP rams can be large, as the equipment is heavy, and much force may be required to shear the steel drill string and other components in the bore. Accordingly, if it becomes necessary for an operator to fire the rams and close the BOP, a significant amount of hydraulic pressure is applied to close the rams.
Because the hydraulic pressure needed to close the rams is high, the corresponding rate of hydraulic fluid flow through the conduit is also high. Accordingly, when the supply valve opens to allow fluid flow to drive the rams, the change in velocity of fluid at the rams can be large and sudden. Similarly, when the supply valve closes at the end of the function, the fluid flow is suddenly stopped. These sudden changes in velocity lead to pressure spikes in the fluid at the opening and closing of the supply valve, which pressure spikes are typically referred to in the industry as hydraulic shock, or water hammer. Water hammer can cause significant damage to components on the BOP.
In addition, after maintenance or during initial start-up of BOP equipment, hydraulic lines can require air to be purged from the system. This is typically done by cycling the equipment to fill the lines. During air purging, water hammer can be induced by the rapid hydraulic velocities involved with such a fill and purge.
One embodiment of the present technology provides a subsea blowout preventer (BOP) hydraulic control system to reduce water hammer. The system includes a first hydraulic fluid source, a first fluid supply conduit in fluid communication with the first hydraulic fluid source at an upstream end, and with a BOP function at a downstream end, and a first supply valve in the first fluid supply conduit that controls the amount of fluid flow through the first fluid supply conduit to the BOP function, the first supply valve having an open state and a closed state. The first supply valve includes a first choke that controls movement of the first supply valve between the open state and the closed state and vice versa so that such movement is retarded when the first supply valve state approaches the fully open or the fully closed state to reduce pressure spikes in the fluid of the first fluid supply conduit.
Another embodiment of the present technology provides a subsea BOP hydraulic control system to reduce water hammer. The system includes an accumulator, a fluid supply conduit in fluid communication with the accumulator at an upstream end, and with a BOP function at a downstream end, and a supply valve in the fluid supply conduit that controls the amount of fluid flow through the fluid supply conduit to the BOP function, the supply valve having an open state and a closed state. The supply valve is shaped to reduce the fluid flow rate in the fluid supply conduit downstream of the supply valve relative to the fluid flow rate in the fluid supply conduit upstream of the supply valve in order to reduce hydraulic shock.
In yet another embodiment of the present technology, there is provided a method of firing a BOP function. The method includes the steps of driving the BOP function using hydraulic fluid from a hydraulic fluid source, the hydraulic fluid delivered to the function via a fluid supply conduit between the hydraulic fluid source and the BOP function, and regulating the flow rate of the hydraulic fluid in the fluid supply conduit with a supply valve positioned in the fluid supply conduit between the hydraulic fluid source and the BOP function, the supply valve having a closed position, where fluid flow through the supply valve is restricted, and an open position, where some fluid passes through the supply valve. The method also includes the steps of, to initiate the BOP function, gradually opening the supply valve to gradually increase the rate of fluid flow through the supply valve up to a predetermined amount, and, before termination of the BOP function, gradually closing the supply valve to gradually decrease the rate of fluid flow through the supply valve until the BOP function is complete.
The present technology can be better understood on reading the following detailed description of nonlimiting embodiments thereof, and on examining the accompanying drawings, in which:
The foregoing aspects, features, and advantages of the present technology can be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. The following is directed to various exemplary embodiments of the disclosure. The embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, those having ordinary skill in the art can appreciate that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.
Typically, the rams 14, 16, 18, 20 are hydraulically controlled. Hydraulic pressure can be supplied via the control pods 24, 26, which can be positioned in the LMRP 12. The provision of two control pods 24, 26, often referred to in the industry as a blue pod 24 and a yellow pod 26, allows for redundancy in the control system, and also increased control capacity. In addition to the control pods 24, 26, there can be provided accumulator tanks 28. The accumulator tanks 28 can be filled with gas at high pressure relative to the ambient pressure of the sea water, and when discharged can exert a strong hydraulic force on the rams 14, 16, 18, 20, causing them to close. The accumulator tanks 28 ore often provided as a backup option to the control pods 24, 26, as they must be recharged after each use, and so are not as convenient as the pods 24, 26 for purposes of closing the rams 14, 16, 18, 20.
Additional features of the BOP assembly of
Referring now to
With respect to the portion of the hydraulic circuit corresponding to the blue pod 24, when the blue pod isolation valve 54 is in the open state, the blue pod supply 50 is in fluid communication with a first supply valve 60. In some embodiments, such as that shown in
Once fluid passes through the blue rigid conduit 68 it can optionally pass through the blue rigid conduit isolation valve 66 downstream through the first supply valve 60 through the rigid conduit filters 64, check valve 62, and to the pod isolation valve 54. Thereafter, the fluid can pass through the blue pod supply 50. Alternately, the fluid can pass through the blue rigid conduit dump valve 69, through to the blue manual rigid conduit dump valve 80, and on to the environment. Blue pod isolation valve 54 communicates with downstream functions, such as, for example, the BOP rams 14, 16, 18, 20. Adjustment of hydraulic pressure in the blue supply line 68 can open or close the rams 14, 16, 18, 20, collectively or individually as desired by a drilling operator. Also shown in the embodiment of
Similarly with respect to the portion of the hydraulic circuit corresponding to the yellow pod 26, when the yellow pod isolation valve 56 is in the open state, the yellow pod supply 52 is in fluid communication with a second supply valve 70. In some embodiments, such as that shown in
Once fluid passes through the yellow rigid conduit 78 it can optionally pass through the yellow rigid conduit isolation valve 76 downstream through the first supply valve 70 through the rigid conduit filters 74, check valve 72, and to the pod isolation valve 56. Thereafter, the fluid can pass through the yellow pod supply 52. Alternately, the fluid can pass through to the yellow manual rigid conduit dump valve 80, and on to the environment. Yellow pod isolation valve 56 communicates with downstream functions, such as, for example, the BOP rams 14, 16, 18, 20. Adjustment of hydraulic pressure in the yellow supply line 78 can open or close the rams 14, 16, 18, 20, collectively or individually as desired by a drilling operator. Also shown in the embodiment of
One problem with some known BOP systems is hydraulic shock, or water hammer. Water hammer occurs when a fluid is forced to suddenly change velocity or direction. For example, in the BOP system of
For example, according to the embodiment of the technology shown in
In practice, the specific timing of the opening and closing of the supply valves 60, 70, including the transition periods between open and close at either end of a stroke, can be adjusted according to the specific function. In some embodiments, sensors 57 can be positioned on the equipment associated with a function to determine where the function is during the course of its stroke. If the function is the closing of BOP rams, for example, a sensor 57 may be installed on the ram piston to determine the position of the ram piston throughout the stroke. The sensor 57 can communicate with a controller 59 on a drilling vessel, or on the BOP stack assembly to indicate when the function is starting and when the piston is nearing the end of its stroke. Using this information, the controller 59 can instruct the supply valve 60, 70 (via the choke) to begin opening or closing, to move between open and closed positions at varying speeds, etc. to achieve a desired flow rate throughout the length of the stroke of the piston. The ideal flow curve for each function can be automatically determine using software in a processor attached to the controller, or can be determined by a drilling operator in real time or otherwise.
In
With reference to
Also located upstream of the BOP functions are the accumulators 28, as well as an accumulator dump valve 92 and an ROV accumulator dump valve 94. These dump valves 92, 94 are provided to vent pressure from the conduits leading from the accumulators 28 to the supply valve 96 in the event that the pressure in these conduits is too high. The dump valves 92, 94 can either bleed hydraulic fluid into the environment, or into a hydraulic fluid reservoir provided for such a purpose. Also located upstream of the BOP functions are the supply valve 96 and isolation valve 98. The supply valve 96 is described in greater detail below. The isolation valve 98 is capable of isolating all of the downstream BOP functions and components. In
Also shown in
In the embodiment of the technology shown in
While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, can appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.
This application claims priority to U.S. Provisional Patent Appln. No. 62/110,242, which was filed on Jan. 30, 2015, the full disclosure of which is hereby incorporated herein by reference in its entirety.
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