Patent Grant
9657553
This application is the U.S. national stage application of International Application PCT/IB2012/054729, filed Sep. 12, 2012, which international application was published on Aug. 1, 2013. as International Publication WO2013/10979 in the English language. The international application is incorporated herein by reference. in entirety. The international application claims priority to Norwegian Patent Application No. 20120067, which is incorporated herein by reference.
The invention concerns a subsea system for intermediate storage of liquid to be received from or delivered to one ore more mechanical devices.
Some subsea operations require regularly liquid supply from the surface via umbilicals. At large depths long umbilicals are required, and replenishing of liquid goes slow. Liquid to be consumed is therefore usually stored on the seabed.
In various subsea operations there is a risk of improper opening or closing of valves, resulting in momentary pressure rise or pressure fall that may harm seals or other pressure sensitive components. In other situations influence of temperature on liquids inside confined spaces will make it necessary quickly to supply or remove liquid in a controlled manner in order to avoid harmful pressure variations.
Thus, there is a need for pressure stabilizing devices, preferably in the form of quick responding modulating valves that connect the area in question with a high pressure supply system or a low pressure receiving system.
In many situations it is desirable to reuse the liquid, which means that the systems must be able to return the liquid as required.
In most subsea installations electric power is available. Hence, it is appropriate to use electrically driven pumps. To reuse liquid that has been removed to prevent pressure build-up, the receiving system for that liquid must be able to receive and return it in a simple and reliable manner.
As the oil industry has been involved in larger sea depths, it has been increasingly important to find good solutions to these needs.
The present invention is based on a system for reception/storage and supply of liquid. The main element is a storage tank that in the normal situation is virtually without internal pressure, valves for regulation of liquid supply from mechanical devices to the storage tank, and one or more pumps that is adapted for pumping of the liquid from said storage tank to said mechanical devices or to intermediate accumulators.
The low, nearly non-existing, pressure in the storage tank is achieved by taking basis in a storage tank that is completely filled with liquid. The attached pump is then taking out liquid through an outlet/intake in the bottom part of the storage tank, and a very low pressure is obtained almost immediately. The amount of liquid that has been removed from the tank is representing the available storage capacity of the tank. Relevant mechanical devices include, inter alia, pressure equalization systems, actuators and power amplifiers.
The storage system is based on a simple operational principle that makes it easy to generate large forces, and move fairly large amounts of a liquid during a short time.
The invention also relates to methods of using the invention to generate power or hydraulic energy in a way that has substantial advantages compared to the use of known technology.
This system has features that provide many opportunities beyond solving the above types of problems related to pressure equalization. Some of these applications are shown in more details below.
The present invention is further described hereinafter and by the attached claims.
The present invention provides a subsea system for uptake and supply of a liquid from and to one or more mechanical devices, the system comprising a storage tank arranged for being filled with the liquid and having at least one outlet, the at least one outlet being in fluid communication with a lower internal volume of the storage tank, a valve assembly being arranged on a feed line, a pump having a high-pressure side and a low-pressure side, and a return line being connected to a high-pressure side of the pump, the valve assembly with the low-pressure side of the pump and the feed line being in fluid communication with the at least one outlet, wherein a closed, liquid-free volume is defined in an upper portion of the storage tank above the liquid volume surface of the storage tank, and the feed line is connected to the low-pressure side of the pump and to at least one of the at least one outlet such that the pump may withdraw liquid from the storage tank when the valve assembly on the feed line is closed, thereby reducing the pressure in the liquid-free volume to a level substantially below ambient liquid pressure, the opening of the valve assembly allowing liquid to flow from the mechanical device to the storage tank, wherein the mechanical device is subjected to a pressure difference between ambient water and the liquid-free volume and accordingly starts generating hydraulic power.
In a subsea system as described above, the at least one outlet can be in fluid communication with a lower internal volume of the storage tank via a tube, such as a vertical riser. If it is desired to have the at least one outlet located on the side of the storage tank, the tube can be angled to have it linked to the outlet.
In a subsea system as described above, the outlet can be arranged in a lower part of the storage tank, preferably near the bottom of the tank, thus to ensure that all liquid can be drawn out of the tank even when said liquid has virtually no pressure.
In a subsea system as described above, the pump may include an inlet on the low pressure side, and the inlet may be arranged below the outlet of the storage tank. In a subsea system as described above, the pump may be a “positive displacement” type pump, preferably comprising at least one reciprocating pump piston unit.
In a subsea system as described above, the low-pressure side of the pump can be in fluid communication with the supply line at a point between the storage tank and the valve assembly.
In a subsea system as described above, the valve assembly can be an open/shut-off valve, a back pressure regulator or any valve or combination of valves suitable for controlling fluid flow through the feed line.
In a subsea system as described above, the supply line can be in fluid communication with the hydraulic fluid in a hydraulic actuator, the barrier fluid in a subsea motor chamber, or in fluid communication with any fluid system that requires or have the benefits from the regulation of fluid pressure to said fluid system.
In a subsea system as described above, the return line can be in fluid communication with the high-pressure side of the pump.
In a subsea system as described above, the return line can be in fluid communication with the supply line at a point on the supply line, the point lies on the opposite side of the valve assembly in relation to the storage tank.
Included in the present invention is the use of a subsea system, as described above, to regulate the pressure of fluids in a subsea system, said fluids include hydraulic fluids, barrier fluids and any other oil- or water-based fluids.
In the application described above, subsea system, for example a production piping, a pump, such as a subsea “booster” pump, an actuator, a hydraulic pressure amplifier or a storage tank for fluids.
The present invention also provides a method for achieving a subsea system capable of rapid absorption of a liquid, wherein the method comprises the steps of:
The term “fluid communication” is meant to describe the type of link between two objects, i.e. that a fluid can pass unhindered between the two objects in a controlled manner, such as through a pipe.
The term “a lower internal volume of the storage tank” is intended to include the volume of the storage tank located in the lower half of the storage tank, preferably in the lower quarter or tenth.
The invention is described with reference to
A relevant solution for achieving pressure equalization might be to establish a chamber with a flexible contact surface to the surrounding water. In principle, this can often be an appropriate solution since fluid must be delivered from subsea systems that often have a higher pressure than the surrounding water. Liquid that is dumped to such a chamber can optionally be reused by having it pumped back to the system in a controlled manner. An alternative solution might be to use compressed gas to generate low pressure in an expandable storage chamber. One such concept is outlined in
PI*AI=PII*AII+PIII*AIII
We take as an example; =AII=AIII=AI/2
Two embodiments of a system for storing and supplying liquid according to the present invention are shown in
Units 7, 9, 11 are interconnected by a pipe or hose system as shown in
Storage tank 7 should contain the least possible amount of vapor and gas. The amount of vapor and gas in the tank 7 can be minimized by initially having the tank 7 oriented with an outlet 8 oriented upward (as shown in
A pumping device that shall be able to remove liquid from a virtually pressure free storage tank can not be constructed as a conventional suction pump. “Positive displacement” pumps are suitable for this. Such a pump arrangement is preferably based on one or more reciprocating piston units, wherein the displacement of each piston unit along one displacement direction is used to limit a liquid flow from the storage tank, and to push the majority of this into an expanding pump chamber. Similarly, the opposing displacement of the piston is used to squeeze the pump chamber together, and thereby squeeze fluid out of the pump arrangement.
In the embodiment shown in
In the embodiment shown in
The functional principle of a pump, suitable for use as pump 9 in a system according to the present invention, is described with reference to
The movement of the piston unit is preferably provided by having the piston rod 19 connected to a reciprocating actuator that is driven by hydraulic power from a not shown hydraulic pump in combination with a direction controlling valve. This is considered as prior art, and are not described further.
Position a) shows the piston unit 14 in the left end position when the offset to the right is starting up. In this situation, the pump chamber VI has its smallest volume. The pump arrangement is filled with fluid via a channel 21 which is connected to the storage tank outlet 8. Position b) illustrates that the piston unit has come quite far to the right, and the spring-loaded piston 22 is now limiting chamber VII. The piston units 14 movement to the right causes reduction in chamber VII volume, whilst chamber VI volume is being increased Thus the pump chamber VI becomes filled with fluid via channel 20 and the check valve 17. This liquid filling will not start until the piston unit has moved so far to the right that the chamber VII is bounded by the piston 22. Liquid volume bounded in chamber VII is greater than the volume of the pump chamber VI, which therefore will be completely filled up.
Position c) shows the piston unit 14 at the right end position. Chamber VI is filled with liquid and can not absorb all of the liquid that was captured by the chamber VII. The remaining amount of liquid in chamber VII has prevented the piston 22 from following the last part of the rightward movement of the piston unit 14. Accordingly, the spring 18 becomes slightly compressed.
Position d) shows the situation after the piston unit 14 has completed the bulk of his left-directed movement that pumps the fluid through the check valve 15 and through the outlet 16. In the illustrated position, chamber VII is again been opened up, so that more liquid flows into it. Piston unit 14 is moved further towards left end position, and the duty cycle is then repeated.
Gravity ensures that the remaining liquid always fill up the low-lying portion of the storage tank. The upper part will contain only vapor and little gas, and the pressure in the storage tank will fall to the fraction of 1 bara as soon as the pump 9 has removed some fluid. The pump arrangement described here is able to pump all the liquid from the storage chamber. The storage tank 7 can thus be emptied so that it is ready to absorb an amount of liquid on the size of the tank total interior volume.
It would be easy to ensure that the storage tank capacity is maintained. Normally there is no possibility of gas intrusion, which otherwise could reduce the storage capacity. Any intrusion of fluid can be detected by level gauges arranged in the storage tank.
The valve assembly 11 is in the simplest version a remote open/shut-off valve, but this will vary according to the actual application of the invention.
The following description will focus on four key uses of the invention:
In addition to this application, the system of the invention could be used in any context where it is required to remove and later on reuse liquid in subsea installations.
The same storage tank 7 can be utilized for securing multiple volumes, each volume then preferably being connected to a separate valve assembly 11. It is also possible to connect several pump arrangements to the same tank 7, and to pump received fluid to any desired destination.
Another important application of the invention has been to provide a system for intermediate storage and reuse of the barrier fluid in electric high-power equipment—such as subsea booster pumps, see
In the following, subsea booster pumps will be used for simple exemplification. It is today normal to dump the barrier fluid from these pumps into the well stream—preferably via the pump module. Upon stopping of the pump, the engine compartment is quickly cooled down. This means that the barrier fluid in quantities of up to 40 liters must be supplied relatively quickly to prevent a dangerous pressure drop in the motor chamber. Up to now the compensation of this fluid is preferably provided by means of accumulators, which are supplied with fluid under pressure via an umbilical from the surface. At great depths the umbilical is very long, and a replenishment of the above mentioned quantities can take up to one day. Because there is always a risk of accidental stop of the pump, the liquid accumulators must at all times contain sufficient amount of liquid to compensate for at least one stop. it may take a long time before it is relevant to restart the pump if a couple of accidental breakdown occurs within a relatively short period.
There is a continuous consumption of barrier fluid because the rotary seals have a certain leakage. This leakage is normal in size from 1 to 2 liters per day. Significant cost reductions and time savings can be achieved by focusing on reuse of barrier fluid that had to be removed, so that umbilical can be dimensioned to compensate only for consumption.
The control valve 27 compensates for an increase in the reference pressure by delivering fluid from HP liquid supply unit 25. Upon drop in the reference pressure, regulator 28 comes into operation and dumps fluid from the motor chamber to the pump inlet as required. The pressure variations are usually small and represent little loss of barrier fluid.
If the pump stops, the motor chamber must have a supply of fluid. The volume that must be supplied may typically be 25-40 liters. This is taken from the HP liquid supply unit 25, which will later on be compensated for the fluid that has been delivered via an umbilical 26.
When the pump is re-started, the liquid in the engine compartment is quickly heated and expands correspondingly. Hence, a liquid volume, corresponding to what was previously refilled, will be dumped into the pump and thus follow the well flow to the surface. For booster pumps that are operating at great depths, the supply pressure to the control valve 27 can typically be in the range 400 to 1000 bara. Due to low compressibility in highly pressurized gas, the HP liquid supply unit 25 may be of considerable size, especially if one wants to have a certain buffer with respect to volume of liquid that can be supplied.
A third important application of the invention is to provide a system for medium and large depths that is suitable to generate driving force for actuators or to provide hydraulic power.
In many contexts are hydraulic pressures being used for operation of valves, for establishing locking forces etc. In an application as in
The force that can be produced in this manner is illustrated by the following calculation example that is referring to the actuator of
We assume a piston 31 has a diameter of 15 cm, and the installation is positioned at 400 meters depth. This means that the piston area A=π*7.52=176.7 cm2. When opening the valve assembly 11, the actuator will generate a force corresponding to:
F=41 kp/cm2*176.7 cm2=7¼ tons.
This is not an unreasonable actuator size, and a force of this size is considered to be ample to operate many types of valves. An offset of for example 50 cm would require a volume of 8.8 liters being occupied by storing tank. If desired, this could be accomplished in a few seconds by appropriate choice of pipe dimensions. For the same actuator sizing, the generated power increases linearly with depth. For example, at 2000 msw, the power that can be generated by a corresponding actuator is;
F=201 kp/cm2*176.7 cm2=35.5 tons.
If there is a need for quick resetting of the actuators, one may use a setup as shown in
In certain situations, one needs to have access to hydraulic energy in order to perform necessary operations. Such hydraulic energy can be produced by utilizing the pressure difference between the ambient water pressure and a low pressure, using an actuator in which the piston rod is enlarged and adapted to establish pressure in a liquid filled volume. Such a solution is outlined in
In U.S. Pat. No. 6,202,753 B1 a similarly designed cylinder is used to generate hydraulic pressure energy by correspondingly ensuring that the chamber III is bounded in a state in which pressure is low or possibly vacuum.
The functioning of the patented embodiment and present invention differ in significant respects, which includes.
Otherwise, by employing various embodiments of the invention, one can address the same functions as shown in the above patent, with respect both to generate hydraulic energy and to establish the necessary locking force to for example a “Blow-out preventer”.
At large depths, an embodiment outlined in
At smaller depths, it may be advantageous to connect the cylinder towards a HP liquid supply unit as shown in
In this embodiment one can keep the gas accumulators in the HP liquid supply unit at a relatively low pressure level, and thus take advantage of good gas compressibility.
To further exploit the capacity of the aforementioned gas accumulators, a pressure reducer valve 36 can be arranged between the gas reservoirs and the liquid filled accumulators. The outlet pressure from this valve is preferably pre set to equal the lowest pressure level required to generate the desired force.
In order to have the HP liquid supply unit recharged and ready for re-activation, the gas must be returned to the gas accumulators. The easiest way to achieve this is to arrange a check valve on the pressure reducer valve. Upon activation of the pump, the pressure downstream of the pressure reducer valve quickly becomes greater than the pressure in gas accumulators. The check valve (not shown in the figure) will then open and allow gas to charge the accumulators.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20120067 | Jan 2012 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2012/054729 | 9/12/2012 | WO | 00 | 11/14/2014 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2013/110979 | 8/1/2013 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6192680 | Brugman | Feb 2001 | B1 |
| 6202753 | Baugh | Mar 2001 | B1 |
| 20050178557 | Johansen et al. | Aug 2005 | A1 |
| 20060254763 | Tips et al. | Nov 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 2215408 | Sep 1989 | GB |
| 331478 | Jan 2012 | NO |
| 0112305 | Feb 2001 | WO |
| 2009045110 | Apr 2009 | WO |
| WO 2009045110 | Apr 2009 | WO |
| 2009132300 | Oct 2009 | WO |
| 2010142612 | Dec 2010 | WO |
| Entry |
|---|
| International Search Report and Written Opinion for PCT/IB2012/054729 dated Nov. 23, 2013. |
| Response to Written Opinion for PCT/IB2012/054729 dated Feb. 28, 2014. |
| Written Opinion for PCT/IB2012/054729 dated Jun. 25, 2014, Oct. 31, 2016. |
| Number | Date | Country | |
|---|---|---|---|
| 20150068606 A1 | Mar 2015 | US |
