This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Advances in the petroleum industry have allowed access to oil and gas drilling locations and reservoirs that were previously inaccessible due to technological limitations. For example, technological advances have allowed drilling of offshore wells at increasing water depths and in increasingly harsh environments, permitting oil and gas resource owners to successfully drill for otherwise inaccessible energy resources. To drill for oil and gas offshore, it is desirable to have stable offshore platforms and/or floating vessels from which to drill and recover the energy resources. Techniques to stabilize the offshore platforms and floating vessels include, for example, the use of mooring systems and/or dynamic positioning systems. However, these systems may not always adequately stabilize components descending from the offshore platforms and floating vessels to the seafloor wellhead.
For example, a riser string or riser (e.g., a pipe or series of pipes, such as riser joints, that connects the offshore platforms or floating vessels to the floor of the sea) may be used to transport drill pipe, casing, drilling mud, production materials or hydrocarbons between the offshore platform or floating vessel and a wellhead. The riser is suspended between the offshore platform or floating vessel and the wellhead, and may experience forces, such as underwater currents, that cause deflection (e.g., bending or movement) or vortex induced vibrations (VIV) in the riser. Acceptable deflection can be measured by the deflection along the riser, and also at, for example, select points along the riser. These points may be located, for example, at the offshore platform or floating vessel and at the wellhead. If the deflection resulting from underwater current is too great, drilling must cease and the drilling location or reservoir may not be accessible due to such technological constraints. If the vibrations due to the currents are too great, the riser and/or the wellhead may experience accelerated fatigue damage.
One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
Systems and techniques for stabilizing a riser (e.g., a riser string made up of a series of riser joints coupled to one another) extending from offshore platform, such as a drillship, a semi-submersible platform, a floating production system, or the like, are set forth below. During offshore drilling operations, high current or high loop current is sometimes occurred, and it may cause large drag force and/or deflection on the riser (e.g., especially for buoyancy joints of the riser, which may have diameters up to 55″ or more) and vortex induced vibrations (VIV), which can cause riser failure and, thus, require cessation of drilling and/or production operations. In some embodiments, fairings and/or helical strakes may be used along the riser. However, these helical strakes tend to aid in VIV suppression but not necessarily in reducing the drag force. Additionally, installation and removal of fairings and/or /helical strakes may be time consuming, thus slowing operations of the offshore platform.
Accordingly, additional embodiments herein may include specialty riser joints with weathervaning buoyancy (e.g., drilling and/or production specialty riser joints that may form a portion or all of the riser) that are designed to operate to greatly reduce the drag coefficient and drag force on the riser. By altering the shape of the specialty riser joints' buoyancy from a cylindrical or circular shape to that of an elongated shape (e.g., an elliptical or airfoil shape), the drag coefficient and drag force of the specialty riser joints can be greatly reduced. Also, the VIV may be greatly reduced and/or eliminated.
In some embodiments, the specialty riser joints may be fixed with respect to an axial, radial, and circumferential directions. In other embodiments, the elongated shape of the specialty riser joints may allow for the specialty riser joints to be fixed with respect to an axial and a radial direction, while capable of rotation in a circumferential direction. This circumferential motion may be in response to, for example, forces imparted to the specialty riser joints by currents. Through rotation of the specialty riser joints, the drag coefficient and drag force of specialty riser joints resulting from the shape thereof may be preserved even as currents change in the field.
With the foregoing in mind,
As illustrated in
As illustrated in
This angle 24 may be modified through the dynamic positioning of the offshore vessel 10. That is, through the movement of the offshore vessel 10 in response to the currents 20, the static angle 24 of the bottom flex joint 30 may be reduced and/or eliminated to meet any operational requirements associated with, for example, the blow out preventer 16, the wellhead 18, and/or the riser 12. However, adjustment of the position of the offshore vessel 10 to reduce and/or eliminate the static angle 24 of the bottom flex joint 30 may also increase the the angle 32 of top flex joint 34 beneath drill floor 36 with respect to the vertical axis 26. This may cause the portion of the riser 12 beneath the drill floor as it passes through the moonpool 38 to interfere with the hull 39 of the offshore vessel 10. This interference between the riser 12 and the hull 39 is to be avoided.
Thus, force applied to the riser 12 from the currents 20 (or other environmental forces) may cause the riser 12 to stress the BOP 16 or cause key seating, as the angle 24 that the riser 12 contacts the BOP 16 may be affected via the deflection of the riser 12. Likewise, the currents 20 and/or efforts to mitigate the force of the currents 20 (e.g., dynamic positioning of the offshore vessel) may cause the riser 12 to contact the edge of the moonpool 38 of the offshore vessel 10. To reduce the deflection of the riser 12, and to reduce the chances of occurrence of the aforementioned problems caused by riser 12 deflection, additional systems and techniques may be employed.
The elongated riser joints 40 may have an elongated shape such as an elliptical shape (which, may in some embodiments, include an offset of its center along a rotational axis, for example, axial direction 42), an airfoil shape (e.g., a fin, a blade, or a vane), a shape with a leading edge that tapers to a trailing edge (e.g., a teardrop), or the like. The elongated riser joints 40 have also have a non-circular shape as well as a non-cylindrical shape as the elongated shape. For example, the elongated riser joints may have one or more streamline bodies as the elongated non-circular and non-cylindrical shape. Indeed, while circular shaped riser joints may have a drag coefficient to approximately 1.2 for laminar flow, the elongated riser joints 40 may have a reduced drag coefficient of approximately 0.25˜0.6 along with reduced and/or eliminated VIV with respect to circular riser joints. An elongated riser joint 40 may be, for example, a buoyancy joint and the elongated riser joint 40 may have an elliptical cross section may include a length to width ratio of approximately 2:1, which can reduce drag and drag coefficient to approximately 0.435 while also greatly reducing and/or eliminating VIV. As previously noted, the elliptical cross section of the elongated riser joints 40 may include a offset of their center to the rotation axis for example, axial direction 42, so as to create weathervane movement, rotation, or the like. In some embodiments, the amount of offset from the center of the elongated riser joints 40 may be chosen dependent on, for example, desired amount of rotation, the environment in which the elongated riser joints 40 will be utilized, or the like. As illustrated in
The buoyancy foam 54, in some embodiments, is rotatable around the main tube 58, through which, for example, drill pipes 19 may pass. As illustrated, the main tube 58 may be circular in shape and terminate in a flange 60 or a connector (e.g., a slick joint designed to prevent damage to the riser 12 and restrict lateral movement of one or more lines passing along the riser 12) with, for example, one or more apertures 62 through which choke and kill lines may pass, one or more apertures 64 through which a hydraulic line may pass, and one or more apertures 66 through which a booster line may pass. The flange 60 may allow for connection of the elongated riser joint 40 with another elongated riser joint 40 and/or a standard riser joint. The elongated riser joint 40 may also include fixed buoyancy foam 68 that, for example, directly surrounds the main tube 58 and one or more of the choke and kill lines, the hydraulic line, and the booster line. The material used for the buoyancy foam 54 and the fixed buoyancy foam 68 may be identical or, for example, the material used for the buoyancy foam 54 may be a non-absorbent (e.g., fluidly sealed) material while the material used for the fixed buoyancy foam 68 may not necessarily be a non-absorbent (e.g., fluidly sealed) material.
Furthermore, as illustrated in
The buoyancy assembly 74 may also include a bearing 76 that may be formed between the one or more fasteners 56 and may interconnect with (e.g., be rotatably coupled to) the clamp 72 to allow for rotation of the buoyancy assembly 74 and, thus, the buoyancy foam 54, in a circumferential direction 46 about the main tube 58 (e.g., the buoyancy assembly 74 may thus be rotatably coupled to the main tube 58) to provide rotation of the buoyancy assembly 74 with respect to the flange 60. The bearing 76 may interface with (e.g., be coupled to while still allowing for rotation about) a support 77 that surrounds the main tube 58 and the support 77 may itself be statically coupled to the main tube 58. Thus, the bearing 76 (and, accordingly, the buoyancy assembly 74) is rotatably coupled to (e.g., coupled to while still allowing for rotation about) the support 77 and may allow for rotation in a circumferential direction 46 about the support 77 (and, thus, the main tube 58). As illustrated, the support 77 may include one or more apertures to allow for passage of a choke line, a kill line, a hydraulic line, a booster line, or the like through the support along the main tube 58.
In some embodiments, the bearing 76 may be a plain bearing such as a bushing or a journal (e.g., radial or rotary) bearing. Likewise, the bearing 76 may be a rolling-element bearing (e.g., a rolling bearing) that carries the load of the buoyancy assembly 74 and/or the buoyancy foam 54 via rolling elements (e.g., balls or rollers), while allowing for rotational motion (e.g., rotation of the buoyancy assembly 74 and, thus, the buoyancy foam 54 coupled thereto in a circumferential direction 46 about the main tube 58). As illustrated, the buoyancy assembly 74 may additionally include support 78 in the region between the band 70 and the bearing 76. The material used for the support 78 may be identical to or different from the material of one or more of the buoyancy foam 54 and the fixed buoyancy foam 68 or, in some embodiments, the support 78 may be metal, such as a steel or other metallic plate, that may be utilized to hold one or more the buoyancy foam 54 and the fixed buoyancy foam 68 in place. Additionally, it should be noted that
While
Additionally, the buoyancy foam 54 may rotate through rotation of the enclosures in a circumferential direction 46 in response to external forces, for example, currents 20 around the main tube 58, whereby the main tube 58 is circular in shape and terminates in a flange 60 with apertures 62, 64, and 66. The elongated riser joint 40 with an airfoil shape 82 may also include fixed buoyancy foam 68 that, for example, directly surrounds the main tube 58 and one or more of the choke and kill lines, the hydraulic line, and the booster line. Furthermore, the elongated riser joint 40 with an airfoil shape 82 may include the clamp 72 and the buoyancy assembly 74 discussed above with respect to
As previously discussed, elongated riser joints 40 (whether shaped as illustrated in
Table 1 describes the speed of currents 20 at particular depths over periods of time, for example, one year and ten years. Using this information, a determination of the location (e.g., depth) of an elongated riser joint 40, two or more consecutively disposed elongated riser joints 40 (e.g., two or more elongated riser joints 40 directly coupled to one another), and/or two or more non-consecutively disposed elongated riser joints 40 (e.g., two or more elongated riser joints 40 disposed along the riser 12 but not directly coupled with one another) can be made. Once this determination is made, disposing the elongated riser joint(s) 40 may occur. However, it may be appreciated that other information separate from or in addition to the information of Table 1 may be used in determining location(s) and/or numbers of elongated riser joints 40 disposed along the riser 12.
In some embodiments, the buoyancy foam 54 may be coupled to the main tube 58 prior the elongated riser joint 40 being lowered into the sea (e.g., on the drillship 10 while the riser string 12 is being made up). Alternatively, the buoyancy foam 54 may be coupled to the main tube 58 once disposed in the sea (e.g., once the elongated riser joint 40 is deployed). For example, a Remotely Operated Vehicles (ROV) may be utilized to affix the buoyancy foam 54 to the riser 12 or pup joint in step 66. An ROV may be a remotely controllable robot/submersible vessel with that may be controlled from the drillship 10. The ROV may move to a selected point in the riser string (e.g., to the deployed elongated riser joint 40) and couple buoyancy foam 54 may be coupled to the main tube 58 at the predetermined position (depth) determined for the elongated riser joint 40.
This written description uses examples to disclose the above description, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may 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. Accordingly, while the above disclosed embodiments may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the embodiments are not intended to be limited to the particular forms disclosed. Rather, the disclosed embodiment are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the embodiments as defined by the following appended claims.
The present application is a continuation of U.S. application Ser. No. 15/716,070, entitled “Weathervaning Riser Joint,” and filed Sep. 26, 2017, now U.S. Pat. No. 10,107,048 which issued on Oct. 23, 2018, which is a Non-Provisional Application claiming priority to U.S. Provisional Patent Application No. 62/401,639, entitled “Weathervaning Riser Joint”, filed Sep. 29, 2016, which is herein incorporated by reference.
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Number | Date | Country | |
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Number | Date | Country | |
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Parent | 15716070 | Sep 2017 | US |
Child | 16166411 | US |