US-12624794-B2 - Subsea storage of a water miscible storage fluid

US12624794B2US 12624794 B2US12624794 B2US 12624794B2US-12624794-B2

Abstract

The present invention relates to a subsea storage system for storing a water miscible storage fluid and methods related thereto.

Inventors

Marius Bjørn
Kristian MIKALSEN
Tom Grimseth
Geir Vingelven

Assignees

GRANT PRIDECO, INC.

Dates

Publication Date: 20260512
Application Date: 20220217
Priority Date: 20210226

Claims (20)

1 . A subsea storage system comprising a subsea storage unit storing a water miscible storage fluid, wherein the subsea storage unit comprises a wall defining an inner storage volume for storing fluids, wherein the inner storage volume comprises a top side facing the sea surface, a vertical side and a bottom side facing the seafloor, wherein the inner storage volume comprises: a barrier fluid as a layer between the storage fluid and seawater extending across an entire horizontal cross section of the inner storage volume for separating the storage fluid from the seawater, the barrier fluid being immiscible with both the storage fluid and seawater; an upper section that extends down from the top side to the barrier fluid within the inner storage volume; and a lower section that extends up from the bottom side to the barrier fluid within the inner storage volume, wherein the upper section comprises at least one upper section opening for fluid connection from the inner storage volume for loading and unloading the subsea storage unit with fluid, wherein the lower section comprises at least one lower section opening configured to provide a fluid connection from the inner storage volume to the ambient sea, wherein the stored storage fluid is positioned above the barrier fluid within the inner storage volume, wherein seawater within the inner storage volume is positioned below the barrier fluid, wherein the inner storage volume is pressure equalized by the fluid connection to the ambient sea, wherein the subsea storage system further comprises a monitoring system configured to monitor at least one fluid layer or fluid interphase within the subsea storage unit, and wherein the monitoring system comprises: a data processor configured to analyze data; a plurality of sensors displaced vertically adjacent to a vertical surface of the inner storage volume and configured to detect characteristics of the at least one fluid layer or fluid interphase within the subsea storage unit; and at least one transmitter configured to transmit data from the plurality of sensors to the data processor.
2 . The subsea storage system according to claim 1 , wherein the barrier fluid has a thickness of at least 1%, or a thickness between 2-30%, 5-25%, 7-20%, 10-17% or 12-15% of a maximum vertical extent of the inner storage volume.
3 . The subsea storage system according to claim 1 , wherein the storage fluid is liquid ammonia.
4 . The subsea storage system according to claim 3 , wherein the plurality of sensors includes a pH-sensor configured to detect the pH of at least one of the fluids within the subsea storage unit.
5 . The subsea storage system according to claim 1 , wherein the plurality of sensors are configured to detect characteristics of one or more fluid layers or fluid interphases at different vertical levels within the subsea storage unit independently.
6 . The subsea storage system according to claim 1 , wherein the subsea storage unit comprises: an outer wall disposed adjacent to the wall so as to provide a two-walled subsea storage unit; and an annulus between the outer wall and the wall, wherein the annulus comprises an annulus fluid, and wherein the plurality of sensors of the monitoring system comprises a detector configured to detect characteristics of the annulus fluid.
7 . The subsea storage system according to claim 1 , wherein the subsea storage unit comprises one or more fluid deflectors or fluid distributors located in a proximity of the upper section opening or the bottom section opening for preventing disruption of the barrier fluid by flow of liquid to or from the at least one lower section opening or the at least one upper section opening.
8 . The subsea storage system according to claim 1 , wherein the wall comprises an anti-stick surface facing the inner storage volume, wherein the anti-stick surface has a low wettability for at least one or more of the fluids within the inner storage volume.
9 . The subsea storage system according to claim 1 , further comprising a fluid conduit fluidly connected to the at least one upper section opening or the at least one lower section opening, wherein the fluid conduit is fluidly connectable to a surface installation for evacuating or adding fluids.
10 . A subsea storage system according to claim 9 , wherein the fluid conduit comprises: a flow meter configured to measure and collect data of fluid flowrate; a transmitter configured to transmit data from the flow meter to the monitoring system; and a remote controlled valve comprising a receiver connected to the monitoring system, the remote controlled valve being configured to receive a signal from the monitoring system and to adaptively control the flowrate of the storage fluid into the inner storage volume.
11 . The subsea storage system according to claim 1 , wherein the subsea storage unit comprises at least one maintenance opening for fluid connection from the inner storage volume to an outside of the subsea storage unit, wherein the at least one maintenance opening is located at a distance that is 10-90% of a vertical extent of the inner storage volume below the top side, and wherein the at least one maintenance opening is suitable for evacuating or adding fluids.
12 . The subsea storage system according to claim 11 , wherein the subsea storage unit comprises at least one maintenance fluid conduit configured to provide a fluid connection from the inner storage volume to the outside of the subsea storage unit, wherein the at least one maintenance fluid conduit extends within the inner storage volume from the inner storage volume top side to a maintenance fluid conduit end distal from the wall, and wherein the maintenance fluid conduit end of the at least one maintenance fluid conduit respectively comprises the at least one maintenance opening.
13 . The subsea storage system according to claim 1 , wherein the plurality of sensors includes at least two sensors respectively located adjacent to opposite vertical sides of the inner storage volume, the at least two sensors being configured to detect characteristics of fluid layers or fluid interphases within the inner storage volume.
14 . The subsea storage system according to claim 1 , wherein the plurality of sensors of the monitoring system comprises: an acoustic reflector located within the inner storage volume and being configured to reflect an acoustic signal; and an acoustic transceiver adjacent to a vertical surface of the inner storage volume and being configured to transmit and receive the acoustic signal, wherein the subsea storage system further comprises at least one transmitter configured to transmit data from the acoustic transceiver to the monitoring system, and to measure time of flight for the acoustic signal through a fluid within the inner storage volume, and wherein the acoustic signal is reflected from the acoustic reflector for detecting characteristics of the at least one fluid layer or fluid interphase within the subsea storage unit.
15 . The subsea storage system according to claim 1 , wherein the plurality of sensors of the monitoring system comprises: a cesium source configured to emit gamma rays horizontally through a layer of fluid within the inner storage volume; and a gamma ray receiver configured to detect gamma rays located adjacent to the vertical side or within the inner storage volume, wherein the subsea storage system further comprises a transmitter configured to transmit data from the gamma ray receiver to the monitoring system for detecting characteristics of the at least one fluid layer or fluid interphase within the subsea storage unit.
16 . The subsea storage system according to claim 1 , wherein the plurality of sensors of the monitoring system comprises an inductive sensor located adjacent to the vertical side or within the inner storage volume, and the subsea storage system further comprises a transmitter configured to transmit data from the inductive sensor to the monitoring system, for detecting characteristics of one or more fluid layers or fluid interphases within the subsea storage unit.
17 . The subsea storage system according to claim 1 , wherein the plurality of sensors of the monitoring system comprises a capacitive sensor located adjacent to the vertical side, and wherein the subsea storage system further comprises a transmitter configured to transmit data from the capacitive sensor to the monitoring system, for detecting characteristics of one or more fluid layers or fluid interphases within the subsea storage unit.
18 . The subsea storage system according to claim 1 , further comprising a fluid conduit fluidly connected to at least one maintenance opening, wherein the fluid conduit is fluidly connected to a surface installation, and wherein the fluid conduit comprises: at least one flow meter configured to measure and collect data of fluid flowrate; at least one transmitter configured to transmit data from the at least one flow meter to the monitoring system; and a remote controlled valve comprising a receiver connected to the monitoring system, the remote controlled valve being configured to receive a signal from the monitoring system and to adaptively control the flowrate of fluid into or out of the inner storage volume.
19 . The subsea storage system according to claim 1 , wherein the monitoring system is configured to monitor different fluid layers or different fluid interfaces within the inner storage volume within the subsea storage unit, and wherein the plurality of sensors are configured to detect characteristics of the different fluid layers or different fluid interfaces within the inner storage volume.
20 . The subsea storage system according to claim 1 , wherein the monitoring system is configured to monitor an emulsified barrier fluid phase within the subsea storage unit, and wherein the plurality of sensors are configured to detect the emulsified barrier fluid phase within the subsea storage unit.

Description

TECHNICAL FIELD The present invention relates to a subsea storage system for storing a water miscible storage fluid and methods related thereto. BACKGROUND AND PRIOR ART There is extensive concurrence on the future of ammonia as a prime hydrogen carrier for ship propulsion, platform power and even small island power supply. The current infrastructure capacity is about 180 mil tons ammonia per year. It is expected that demand and supply will outgrow this capacity, and that extensive infrastructure with regards to fabrication facilities, transportation systems and power generation systems will be added to the current infrastructure. Along with growth in the above-mentioned infrastructure, the demand for storage of ammonia is expected to grow. Thus, it is expected that there will be a need for practical and safe storage systems for large quantities of ammonia in many locations around the world. Easy maintenance of such storage system is also desirable. Ammonia is a gas at room temperature and 1 bara pressure. Storing a substance in the gas phase is sub optimal due to the large volume tanks required. Gases are thus typically stored in liquid form. Ammonia is in the liquid form at minus 37 degrees C. and 1 bara, or at a pressure of about 8.5 bara and room temperature, or at several compromises between these values according to the physical state of liquid ammonia at a given temperature and pressure. Subsea storage offers the benefit of an environment where ammonia may be kept in liquid form by the natural pressure and temperature of the ambient sea without requiring artificial pressure or additional cooling. Subsea storage of liquified gases such as ammonia is known from WO2009/133663, which discloses that a gas such as ammonia can be stored in an impermeable flexible undersea storage vessel that utilizes the undersea conditions for maintaining the gas in a liquid form. The storage vessel could be made of polymeric fabrics such as Kevlar. U.S. Pat. No. 9,540,169 discloses a subsea storage tank for storage of bulk fluids which comprises an upper shell and a lower shell bolted together. The interior comprises a bladder that acts as a barrier between the bulk fluid in one half of the tank and seawater that is allowed to enter free on the opposite side of the barrier to compensate for the varying pressure resulting from varying amounts of bulk fluid in the tank. This tank adds the security of a shell and a test system that signals need for maintenance but requires subsea maintenance or that the entire tank is serviced at the surface. US2008041068 describes a gas storage facility on the bottom of the ocean in deep water. The gas storage facility comprises a pressure equalized tank-system wherein the tank comprises an inflexible thin walled vessel for storing compressed gas under water. The storage vessel has a gas intake port near the top region and is pressure equalized by the surrounding water in that a water intake port is located at the bottom region of the gas storage facility. It is stated that the gases for storage may be natural gases such as liquid natural gas (LNG) or compressed natural gas (CNG). Depending on the gas that is to be stored it may be necessary to provide a barrier between the gas and water for example for avoiding diffusion of gas into the water and/or formation of hydrates. Examples of barriers may be floating membranes, inflatable/compressible bags for gas containment of gas or a layer of fluid which provides an immiscible boundary, such as an oil-water emulsion layer at the layer interface. The gas storage facility comprises a control system for monitoring the gas level but does not provide information about the level of all phases or on the state of the barrier. The formation of an oil-water emulsion would not be compatible with storage of water miscible liquids because an oil-water emulsified barrier would not be effective. It is thus an object of the present invention to provide a subsea storage system for water miscible fluids that at least mitigates the above-mentioned drawbacks of the prior art. More particular it is an object of the present invention to provide a subsea storage system for water miscible fluids that offers possibility of in situ control and/or maintenance of the subsea storage unit without the need for costly subsea disassembly or retrieving the subsea storage system to the surface. Also, it is an object of the present invention to provide a method for maintenance of a subsea storage system according to the present invention. SUMMARY OF THE INVENTION The present invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the invention. In a first aspect the invention concerns a subsea storage system comprising a subsea storage unit for storing a water miscible storage fluid. The subsea storage unit comprises a wall defining an inner storage volume for storing fluids, wherein the inner storage volume compri