Patent Grant
9683411
The present disclosure relates to marine riser assemblies and systems useful in offshore oil and gas production facilities, and to methods for the deployment thereof.
Subsea oil and gas production developments in recent years have been occurring in deeper water and thus entering more challenging offshore regions. Riser configuration designs are seeking to overcome numerous challenges such as highly dynamic offshore facility motions and environmental loadings, high top tension, and high hydrostatic pressure due to water depth. In practice, it has been demonstrated that in order to make deepwater large bore riser designs work, operators are frequently forced to utilize either very stable host topsides structures, e.g. spars, or more motion accommodating riser systems, e.g. freestanding hybrid riser (FSHR) systems. Both of these methods are currently used, but both of these methods have drawbacks. From a facility perspective, the use of a spar is not practical in some areas because of the lack of local export pipeline infrastructure. From a riser perspective, large bore risers encounter technical challenges as a result of the highly dynamic applications and sometimes do not meet strength and fatigue requirements. Existing deepwater riser systems such as FSHR have overcome dynamic application challenges by incorporating a flexible pipe jumper into the system design. However, this is a quite expensive solution due to system complexity and the installation requirements. In some instances, a design alternative to overcome technical and commercial challenges is to use a flexible pipe for the entire riser system. A particular challenge is the flexible pipe inner diameter limitation with increasing hydrostatic pressure resulting from increased water depth increasing the risk of collapse. In projects requiring large inner diameter risers, this may result in an increased riser count with smaller diameters if flexible pipe is being used, or it may completely eliminate flexible pipe as a riser option. Increased riser count requires multiple hang off slots on the topside structure, seabed congestion and results in capital expense increase.
There exists a need for motion accommodating riser systems useful in deepwater oil and gas developments which would avoid the above mentioned challenges with existing flexible pipe riser systems.
In one aspect, a riser assembly is provided for transporting fluids between a topside structure at a topside location and a subsea fluid handling component at a subsea location. The riser assembly includes an upper riser capable of transporting fluids having an upper end terminating at the topside structure. The riser assembly includes a flow diverting structure capable of allowing fluids to pass therethrough and having an upper interface having a single upper bore configured to connect to the upper riser and a lower interface having at least two lower bores in fluid communication with the single upper bore. The lower interface is configured to connect to at least two lower risers.
In another aspect, a system is provided for transporting fluids between a topside structure at a topside location and a subsea fluid handling component at a subsea location. The system includes the above described riser assembly, and further includes at least two lower risers capable of transporting fluids connected to and in fluid communication with the flow diverting structure, wherein each of the at least two lower risers is connected to one of the at least two bores, such that the upper riser is in fluid communication with the at least two lower risers.
In another aspect, a method of deployment of a riser system for transporting fluids between a topside structure at a topside location and a subsea fluid handling component at a subsea location is provided. The method includes connecting the riser assembly to the topside structure such that the upper riser of the riser assembly terminates at the topside structure. The method further includes connecting a first lower riser to one of the at least two lower bores of the flow diverting structure such that the upper riser, the flow diverting structure and the first lower riser are connected, and the upper riser is in fluid communication with the first lower riser. This permits the lower risers to be installed at a later time if desired.
These and other objects, features and advantages of the present invention will become better understood with reference to the following description, appended claims and accompanying drawings where:
A riser assembly and a system using the riser assembly will now be described.
A flow diverting structure 4, also referred to herein as a diverting structure 4, capable of allowing fluids to pass therethrough is configured to connect to the upper riser 2. The upper riser can be disconnectable from, or reversibly connectable to, the diverting structure 4. The flow diverting structure 4, shown schematically, has an upper interface having a single upper bore therethrough and a lower interface having at least two lower bores therethrough. The at least two lower bores are in fluid communication with the single upper bore. The at least two lower bores are configured to connect to at least two lower risers 6. The lower risers 6 can be disconnectable from, or reversibly connectable to, the diverting structure 4. In one embodiment, the riser assembly further includes the at least two lower risers 6. In one embodiment, the at least two lower risers 6 can each be a multilayered flexible pipe, a rigid pipe, a composite pipe, or a combination of thereof. In one embodiment, each of the at least two lower risers 6 has an inner diameter between about 4 inches (10 cm) and about 16 inches (41 cm). In one embodiment, each of the at least two lower risers 6 has a depth capability of up to 3000 meters. When the upper riser 2, the flow diverting structure 4 and the at least two lower risers 6 are connected, the upper riser 2 is in fluid communication with the at least two lower risers 6.
In one embodiment, the flow diverting structure 4 can be a wye connector having an upper interface having a single upper bore and a lower interface having at least two lower bores. Nonlimiting examples of such wye connectors are disclosed in U.S. Pat. No. 8,616,074 (Kearns et al.). The single upper bore of the wye connector can be directly connected to the upper riser 2, and the two lower bores of the wye connector can be directly connected to the lower risers 6. In one embodiment, the flow diverting structure 4 further has an interface for launching and receiving a subsea pig into and out of the flow diverting structure 4. A subsea pig launcher and receiver can be integrated to the flow diverting structure 4 or can be temporarily assembled to the flow diverting structure 4 as a modular sub-component.
In one embodiment, the flow diverting structure 4, also referred to as the diverting structure 4, can further include at least one isolation valve 30 there within for isolating flow between the upper riser 2 and any of the at least two lower risers 6. In one embodiment, the flow diverting structure 4, can further include at least one check valve 31 there within for preventing flow in a direction as desired between the upper riser 2 and any of the at least two lower risers 6. In one embodiment, the diverting structure 4 can further include additional instrumentation 32. Such instrumentation can include a flow meter, a pressure sensor, a temperature sensor, a subsea sampling device, or a combination thereof.
In one embodiment, the riser assembly further includes a hang-off module 8 configured to connect to the topside structure 3 and the upper end 2a of the upper riser 2. The hang-off module 8 provides fluid communication between the upper riser 2 and piping (not shown) located on the topside structure 3. The hang-off module 8 restrains the mechanical loads, tensile loads and bending loads imparted from the riser assembly. In one embodiment, the hang-off module 8 can be a piping flange.
In one embodiment, as illustrated in
In one embodiment, at least one optional buoyancy element 12 can be connected to the diverting structure 4 to position the diverting structure 4 at a desired, predetermined water depth. Likewise, in one embodiment, at least one optional buoyancy element 11 can be connected to the upper riser and/or one or more of the lower risers. In one embodiment, the flow diverting structure 4 is located at a predetermined water depth determined by calculating a depth of hydrostatic collapse and a top tension capacity of the upper riser 2. In one embodiment, the predetermined water depth is from about 500 meters to about 3000 meters.
In some embodiments, the diverting structure 4 can further include an interface for the connection of a service line 20A operable from the production unit topside structure 3 which can be a multi service vessel (MSV). The service line 20A can be provided for injecting fluids such as gas lift, nitrogen and chemicals as desired into the riser assembly 10. Such fluids can assist in increasing production of fluids as may be desirable depending upon reservoir pressure. Chemicals can assist in preventing hydrate formation. The service line 20A can also be used for flow back after well intervention or stimulation to provide an alternative path for flow back fluids rather than through the upper riser 2. In one embodiment, the flow diverting structure 4 can be used as an access point for intervention in the riser assembly, e.g., for riser inspection. In one embodiment, the diverting structure 4 can further include an interface for the connection of a service line operable from the production unit topside structure 3 for receiving fluids such as well fluids flow back from well stimulation.
In one embodiment, the diverting structure 4 can further include an interface for the connection of a control umbilical 20B. Such a control umbilical 20B can be used to remotely control the functions in the diverter structure 4, such as opening and closing of valves, controlling power and communication for sensors and monitoring devices, launching and receiving pigs, and the like. The diverting structure 4 can further include an interface for operating the control umbilical 20B. The control umbilical 20B can be operable from the topside structure 3.
In one embodiment, the upper riser 2 and the at least two lower risers 6 include at least one umbilical passing therethrough. One of the at least one umbilicals can pass through the upper riser 2 and one of the at least two lower risers 6.
In embodiments as illustrated in
In one embodiment, a method of deployment of a riser system for transporting fluids between a topside structure 3 at a topside location and a subsea fluid handling component 5 at a subsea location is provided. The method includes connecting the riser assembly to the topside structure 3 such that the upper end 2a of the upper riser 2 terminates at the hang off module 8 connected to the topside structure 3. At such point in time or at a later time, a first lower riser 6 can be connected to one of the at least two lower bores of the flow diverting structure 4 such that the upper riser 2, the flow diverting structure 4 and the first lower riser 6 are connected and the upper riser 2 is in fluid communication with the first lower riser 6. At this point the system can be operated using only the first lower riser 6 to transport fluids. At a later point in time, the capacity of the riser system can be expanded by connecting a second or additional lower riser 6 to another of the at least two lower bores of the flow diverting structure 4. In this way, the invention enables phase development of a subsea facility with the ability to install one of the lower risers 6 initially and additional lower riser(s) 6 at a later date as needed.
One embodiment of a method of deployment of a riser system is illustrated in
An alternative embodiment of a method of deployment of a riser system is illustrated in
A number of advantages can be realized using the riser assembly shown in
As compared with multiple small risers connected to the topside structure 3, fewer hang off slots on the topside structure 3 are required. Pipe design is already available for the upper riser 2 (up to 20 in inner diameter) and for the lower riser 6. The facility riser count overall can be reduced. As a result, riser pull in can be done more quickly.
As compared with FSHRs, the riser assembly of the present disclosure results in a much simpler system overall. A heavy lift vessel is not required for installation of the riser assembly, bottom riser assembly and buoyancy can. Riser installation can be accomplished much more quickly.
It should be noted that only the components relevant to the disclosure are shown in the figures, and that many other components normally part of a riser system are not shown for simplicity.
For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and connected claims are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” include plural references unless expressly and unequivocally limited to one referent.
Unless otherwise specified, the recitation of a genus of elements, materials or other components, from which an individual component or mixture of components can be selected, is intended to include all possible sub-generic combinations of the listed components and mixtures thereof. Also, “comprise,” “include” and its variants, are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that may also be useful in the materials, compositions, methods and systems of this invention.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. All citations referred herein are expressly incorporated herein by reference.
From the above description, those skilled in the art will perceive improvements, changes and modifications, which are intended to be covered by the appended claims.
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