Infrastructure-independent deepwater oil field development concept
A method for developing a sub-sea hydrocarbons field includes sub-sea wells, sub-sea oil/gas separation, storing the degassed oil in a storage tank located or the seabed, liquefying natural gas aboard a vessel using liquid nitrogen aboard the vessel to obtain liquefied natural gas, transporting the liquefied natural gas to an onshore terminal, re-gasifying the liquefied natural gas, and obtaining a new batch of liquid nitrogen using energy recovered from the re-gasifying the liquefied natural gas.
This is a continuation-in-part of application Ser. No. 09/818,117 filed on Mar. 27, 2001, and assigned to the assignee of the present invention. That application is hereby incorporated by reference in its entirety.
BACKGROUND OF INVENTION1. Field of the Invention
The invention relates generally to offshore oil and gas production and transportation.
2. Background Art
A major factor in determining whether to exploit an offshore oil and gas field is the feasibility of handling and transporting the hydrocarbons to market once they are produced. Generally, hydrocarbons produced offshore must be transported to land-based facilities for subsequent processing and distribution. Temporary storage may be provided at the offshore production site for holding limited quantities of hydrocarbons produced and awaiting transport to shore. In some cases, equipment is also provided at the offshore production site for separating and/or treating the produced hydrocarbons prior to storing and transporting them to shore.
In the case of an offshore production facility located relatively close to shore, hydrocarbons (i.e., oil and/or natural gas) produced may be feasibly transported to shore through a pipeline system extending from the offshore site (e.g., offshore platform or sub-sea wells) to the shore along the ocean floor or seabed. This type of pipeline system is typically preferred, when feasible, because it permits the constant flow of hydrocarbons to shore regardless of the weather or other adverse conditions. However, in some parts of the world, the use of a seabed pipeline system for transporting hydrocarbons to shore may not be economically feasible.
For offshore facilities located a great distance from shore, construction of a pipeline to shore is typically not practicable. In these cases, floating vessels, known as tankers, are used to transport hydrocarbons to shore. Tankers are specially designed vessels, which have liquid hydrocarbon storage (or holding) facilities, typically, in the hull of the vessel. In the case of crude oil production, natural gas, water, and other impurities are typically removed from the oil prior to offloading the oil onto tankers for transport.
Because tankers float on the water surface, their operations are largely dependent upon surface conditions, such as wind, wave, and current conditions. Thus, tankers are typically not operated during severe or unfavorable conditions. Additionally, operation of a particular tanker may be interrupted periodically for maintenance and repairs. Due to the large expense associated with maintaining tankers, tankers may also be shared among several offshore sites. As a result, long delay periods may occur between tanker availability for a particular site. Therefore, it is desirable to have storage facilities available at the offshore site to avoid the need to “shut-in” (or halt) production due to tanker unavailability. Additionally, offshore storage may be desired to allow for continuous production operations, independent of tanker hook-up and disconnect operations, as discussed below.
Examples of existing offshore production and storage systems used for deepwater applications are illustrated in
Production platforms have also been developed to integrate oil storage into the hull 44 of a platform, such as a SPAR platform 40 as shown in
Other offshore storage systems for deepwater applications may also include smaller thick-walled tanks designed to be sunk to the seabed and internally controlled from the surface. Because the interiors of these tanks are completely isolated from the surrounding seawater environment, these tanks require very thick walls to withstand the hydrostatic pressure difference between the sub-sea environment and the platform environment. As a result, these systems are expensive and limited in capacity. These systems also require additional equipment such as pumps, controls, and other instrumentation, for monitoring and controlling the internal tank environment and moving fluids in and out of the tanks. Other offshore storage systems exist for use in shallow water applications; however, for the most part, these systems are not applicable for use in deepwater applications.
Natural gas produced from offshore gas and oil fields may be handled using a variety of mechanisms. For example, the natural gas may be re-injected into a subsurface formation, flared onsite, or exported by pipeline. Such mechanisms for handling natural gas is used in the industry in such locations as offshore of Nigeria, and in the North Sea. Alternatively, the natural gas obtained from a sub-sea well may be pressurized, to obtain high-pressure gas, and then transferred to a tanker in compressed form.
An FPSO may also be used to obtain natural gas and liquefy the natural gas to produce LNG. The FPSO includes buffer storage tanks for temporary storage of continuously produced LNG during absence of an LNG tanker. Once the LNG tanker has returned, the LNG is offloaded from the FPSO to storage tanks on the LNG tanker using a mooring device and a cryogenic transfer device.
SUMMARY OF THE INVENTIONIn general, in one aspect, the invention relates to a method for developing a sub-sea hydrocarbons field. The method comprises liquefying natural gas aboard a vessel using liquid nitrogen aboard the vessel to obtain liquefied natural gas, transporting the liquefied natural gas to an onshore terminal, re-gasifying the liquefied natural gas, and obtaining a new batch of liquid nitrogen using energy recovered from re-gasifying the liquefied natural gas.
In general, in one aspect, the invention relates to a system for developing an oil and gas field. The system comprises a vessel configured to liquefy natural gas to obtain liquefied natural gas using liquid nitrogen aboard the vessel, and an onshore terminal configured to obtain a new batch of liquid nitrogen using refrigeration recovered from re-gasifying the liquefied natural gas.
In general, in one aspect, the invention relates to an apparatus for developing a sub-sea hydrocarbons field. The method includes means for liquefying natural gas aboard a vessel using liquid nitrogen aboard the vessel to obtain liquefied natural gas, means for transporting the liquefied natural gas to an onshore terminal, re-gasifying the liquefied natural gas, and means for obtaining a new batch of liquid nitrogen using energy recovered from the re-gasifying the liquefied natural gas.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to the drawings wherein like reference characters are used for like parts throughout the several views,
The tank may comprise any configuration as determined by one skilled in the art, including cylindrical-shaped, box-shaped, or the like. Those skilled in the art will appreciate that the configuration of the tank is a matter of convenience for the system designer. For example, in a particular embodiment, the tank may comprise a box-shaped configuration and a web-framed steel structure so that it may be constructed using standard ship building techniques, launched from conventional shipways, and have stable floatation for open-water tow.
The storage and offtake system further includes at least one fluid channel 127, such as a standpipe more distinctly illustrated in
Referring once again to
The storage and offtake system further includes a vessel mooring system, which has at least one hawser 110. As shown in
Referring once again to
It should be understood that the storage tank 100 may include any material suitable for use as a tank, e.g., steel, concrete, or a composite material such as glass or carbon fiber reinforced plastic. The inside and outside of the tank 100 may also be coated with cement or any other coating material known in the art for protecting structures formed from a metal such as steel against deterioration due to operation in a saltwater environment. In one or more embodiments, the storage tank 100 is a gravity based, pressure balanced structure, as will be described in more detail below.
The lower portion of the offload line 103 in the embodiment shown includes a substantially rigid member, such as a marine riser 104. As shown in
In one or more embodiments, the riser 104 also functions as part of the transport vessel mooring system (further described below). In such case, the riser 104 should be designed to withstand the additional forces expected to be imposed on it by mooring a tanker (illustrated in
As previously described and shown in
Also as shown in
The upper portion of the offload line 103 may include a flexible member, such as a hose or series of rigid segments (e.g., subpipe sections) coupled by flex joints. In the embodiment shown in
In the embodiment shown, the lower end of the hose 108 is attached to the top of the riser 104 at the subsurface buoy 106, and the upper end of the hose 108 is attached to a surface buoy 112 so that the hose 108 can be easily accessed from the water surface 116 for offloading (or offtake) operations. Those skilled in the art will appreciate that the flexible upper portion of the offload line 103 may be made of any material suitable for a particular application, such as rubber, metal, composite material, or a combination thereof.
As shown in
As previously explained with respect to
Now referring to
Examples of a pressure balanced tank during normal operations in accordance with the above description are shown in
Those skilled in the art will appreciate that the tank 100 may additionally include instrumentation to ensure that the maximum and minimum oil 121 and water 123 levels for a selected tank design are not exceeded. Those skilled in the art will also appreciate that the fluid channel 127 may be constructed in any configuration and may communicate with the seawater environment outside of the tank 100 at any location, such as through a side wall of the tank 100, as determined by the system designer without departing from the spirit of the invention. In one embodiment, the fluid channel 127 is in fluid communication with the surrounding seawater environment 125 at a location away from the seabed (114 in
As shown in
Referring to
Referring now to
Now referring again to
Embodiments of a storage and offtake system may be used in conjunction with a sub-sea processing and/or gathering system as illustrated in
A system for developing an offshore oil and gas field is shown in
Sub-sea flow lines 180 convey the natural gas output from the sub-sea separator 136 to a vessel, such as a Floating Production Storage Shuttle Vessel (FPSSV) 182 using a natural gas conveyance system, which includes a riser 184, a hose 188, a hawser 190, a subsurface buoyant device 192, a flex joint 194, a swivel joint 196, and a sub-sea flow line-to-riser adapter 197. The riser 184, the offload line 186, the hose 188, the hawser 190, the subsurface buoyant device 192, the flex joint 194, and the swivel joint 196 function similarly, and have properties similar to, the riser 104, the hose 108, the hawser 110, the subsurface buoyant device 106, the flex joint 118, and the swivel joint 120 shown in
In accordance with one embodiment of the invention, the riser 184 is a top-tensioned riser used in conjunction with a flexible hose (i.e., a “hybrid riser”). In accordance with one embodiment of the invention, the riser 184 is a steel catenary riser. In accordance with one embodiment of the invention, the riser 184 is a flexible pipe. In accordance with another embodiment of the invention, natural gas conveyed to the FPSSV 182 is not compressed, i.e., is low-pressure gas.
A power and control buoy 198 provides electric power and control functions to the sub-sea separator 136 and sub-sea oil wells 132. Examples of the power and control buoy 198, in accordance with embodiments of the invention, may include the Sea Commander Buoy developed and marketed by Resource Technology Development Ltd. Functionality of the power and control buoy 198 may be similar to the buoy used in Western Australia for the East Spar Alliance, except with greater electrical capacity.
In accordance with one embodiment of the invention, the FPSSV 182 may provide electric power and control functions to the sub-sea separator 136 and sub-sea oil wells 132. Other types of buoy backup systems may be used to provide electric power and control functions to the sub-sea separator 136 and sub-sea oil wells 132, in accordance with embodiments of the invention.
Natural gas conveyed from the sub-sea separator 136 to the FPSSV 182 is liquefied aboard the FPSSV 182 to obtain Liquefied Natural Gas (LNG). An FPSSV LNG Production Facility 200 is used to liquefy the LNG. The FPSSV 182 transports the LNG to an onshore terminal 202. In accordance with one embodiment of the invention, the onshore terminal 202 may not necessarily be on dry land, but may be in close proximity to dry land, e.g., on a platform located in the proximity of shore. The use of more than one FPSSV 182 may be facilitated by use of a second riser 204, a second hose 208, a second hawser 210, a second subsurface buoyant device 212, a second flex joint 214, a second swivel joint 216, a second sub-sea flow line-to-riser adapter 218, and a surface buoy 219. The surface buoy 219 has functionality and properties similar to the surface buoy 112 in
In accordance with one embodiment of the invention, the natural gas liquefaction plant 222 uses an open-cycle, open loop process, and takes Liquid Nitrogen (LIN) as an input from one or more FPSSV storage tanks 230 via one or more pumps 232. LIN vaporized during liquefaction is vented as nitrogen gas (N2) via a nitrogen vent 234. LNG created during the natural gas liquefaction process is stored in FPSSV storage tanks 230 aboard the FPSSV.
The LNG stored in the FPSSV storage tanks 230 is transported aboard the FPSSV to the onshore terminal. In accordance with one embodiment of the invention, the onshore terminal 202 (in
In order to recover energy from re-gasification of the HP LNG 266, all or a portion of the HP LNG input 266 is input to the integrated LNG re-gasification air separation plant 276. The integrated LNG re-gasification air separation plant 276 takes as input air 278 compressed by a compressor 280. An output of the integrated LNG re-gasification air separation plant 276 is LIN 282, which is transferred to the FPPSV 182 (in
A flowchart for developing a sub-sea oil and gas field is shown in
Once the natural gas is aboard the FPSSV, the natural gas is liquefied using LIN stored aboard the FPSSV to obtain LNG (Step 306). The LNG is stored in the FPSSV storage tanks and transported to the onshore terminal (Step 308). At the onshore terminal, the LNG is re-gasified to obtain HP gas and recovered refrigeration, which is used to produce LIN (Step 310). The LIN is then loaded into the FPSSV storage tanks and transported to the offshore oil field (Step 312). In accordance with one embodiment of the invention, one of the FPSSV storage tanks is left empty, and the LIN is transported in the remaining FPSSV storage tanks. In accordance with one embodiment of the invention, some of the FPSSV storage tanks may hold LIN that is not produced using recovered energy, but has been obtained from another source other than the LNG re-gasification LIN production facility (shown as 260 in
Once the FPSSV is at the location of the offshore oil field, more natural gas is conveyed aboard the FPSSV (Step 314), and the natural gas is liquefied aboard the FPSSV using the onboard LIN to obtain more LNG (Step 316). An initial quantity of LNG obtained using the LIN is stored in the empty FPSSV storage tank. Subsequent quantities of LNG obtained using the LIN are stored in the FPSSV storage tanks that are emptied as the LIN is used in the liquefaction process. Oil (e.g., partially stabilized oil) is offloaded from the oil tank on the seabed onto a tanker periodically (Step 318). Steps 308-316 are repeated to the gas/LNG while the sub-sea oil and gas field is in operation; as is step 318 for the oil.
Embodiments of the invention may also be used to eliminate the need for costly deepwater pipelines to shore, and in some cases may be used to avoid expensive pipeline tariffs. Embodiments of the invention may be operated independent of infrastructure, such as pipelines. Embodiments of the invention may also provide larger storage capacity for offshore production sites in deepwater that is less costly to operate and maintain than prior art storage systems primarily dependent upon shuttle tankers or submerged thick walled storage vessels. Embodiments of the invention may also be used to reduce the number of shuttle tankers required in a hydrocarbon transport fleet. Embodiments of the invention may also provide cost reductions for development of sub-sea oil and gas fields.
The above advantages are merely exemplary of advantages that may be associated with one or more embodiments of the invention. Those skilled in the art will appreciate other advantages. Further, while the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed. Accordingly, the scope of the invention should be limited only by the attached claims.
Claims
1. A method for developing a sub-sea hydrocarbons field, comprising:
- liquefying natural gas aboard a vessel using a liquid coolant aboard the vessel to obtain liquefied natural gas;
- transporting the liquefied natural gas to an onshore terminal, re-gasifying the liquefied natural gas; and
- obtaining a new batch of liquid coolant using energy recovered from the re-gasifying the liquefied natural gas.
2. The method of claim 1, wherein the liquid coolant comprises liquid nitrogen and further comprising:
- transporting the new batch of liquid nitrogen offshore aboard the vessel using a plurality of storage tanks.
3. The method of claim 1, further comprising:
- de-gasifying hydrocarbons obtained from the sub-sea hydrocarbons field to produce oil and gas; and
- conveying the produced gas to the vessel and the produced oil to the storage tank on the seabed.
4. The method of claim 3, wherein the produced gas is conveyed to the vessel via a riser.
5. The method of claim 3, further comprising.
- pre-treating the produced gas before liquefying.
6. The method of claim 3, further comprising:
- storing the oil in a storage tank attached to a seabed.
7. The method of claim 1, further comprising:
- liquefying a new batch of natural gas using the new batch of liquid nitrogen aboard the vessel.
8. The method of claim 1, wherein one of a plurality of storage tanks aboard the vessel storage tanks is empty to receive an initial portion of the liquefied natural gas.
9. The method of claim 1, wherein the re-gasifying the liquid natural gas is performed at the onshore terminal.
10. The method of claim 1, wherein re-gasifying the liquefied natural gas produces high pressure gas.
11. The method of claim 10, further comprising:
- sending the high pressure gas to a pipeline.
12. The method of claim 1, wherein transporting the liquefied natural gas to the onshore terminal is performed using the vessel.
13. A system for developing an oil and gas field, comprising:
- a vessel configured to liquefy natural gas to obtain liquefied natural gas using liquid nitrogen aboard the vessel; and
- an onshore terminal configured to obtain a new batch of liquid nitrogen using refrigeration recovered from re-gasifying the liquefied natural gas.
14. The system of claim 13, further comprising:
- a sub-sea separation system configured to de-gasify hydrocarbons to produce oil and gas; and
- a natural gas conveyance system configured to use a riser to convey the gas produced from the sub-sea separation system to the vessel; and
- convey the oil produced from the sub-sea separation system to a sub0-sea storage tank.
15. The system of claim 14, further comprising:
- a natural gas pre-treating facility configured to treat the produced gas.
16. The system of claim 14, further comprising:
- a power and control buoy configured to provide electric power and control functions for the sub-sea separation system.
17. An apparatus for developing a sub-sea hydrocarbons field, comprising:
- means for liquefying natural gas aboard a vessel using liquid nitrogen aboard the vessel to obtain liquefied natural gas;
- means for transporting the liquefied natural gas to an onshore terminal;
- means for re-gasifying the liquefied natural gas; and
- means for obtaining a new batch of liquid nitrogen using energy recovered from the re-gasifying the liquefied natural gas.
Type: Application
Filed: Oct 6, 2003
Publication Date: Jan 5, 2006
Inventor: Michael Choi (Houston, TX)
Application Number: 10/679,545
International Classification: E21B 29/12 (20060101);