Flexible And Extensible Riser

Abstract

An improved riser structure for use in transporting drilling mud to a floating drilling vessel from a submarine wellhead. The riser structure is defined principally of essentially rigid riser ducting within the length of which, and preferably closer to the vessel than to the wellhead, is disposed a laterally and longitudinally flexible sleeve coupled to the ducting to form a part of a mud flow path from the wellhead to the vessel.

Parent Case Text

REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 725,784 filed May 1, 1968, now abandoned.

Description

FIELD OF THE INVENTION

This invention pertains to submarine drilling. More particularly, it pertains to an improved riser structure for conducting drilling mud from a submerged wellhead or drill hole to a floating vessel, and is especially useful where drilling operations are performed in relatively shallow water depths.

BACKGROUND OF THE INVENTION

Nature of the Problem

In the drilling of oil wells and the like at submarine and land-based locations by rotary tool techniques, drilling mud is circulated down a hollow drill pipe, through the drilling tool, and up the drilled hole to a drilling rig installation where the mud is processed for further such circulation. The drilling mud serves to clear the drilling tool of cuttings and to flush such cuttings from the drilled hole. The drilling mud also maintains pressure in the drilled hole to prevent blow outs in the event high-pressure gas or oil pockets are encountered as the hole is drilled.

Where an oil well is drilled on land or from an offshore structure supported on the ocean bottom, the distance from the drill hole to the drilling rig structure is constant; in such instances the flow path of the mud from the hole to the rig is defined by a mud riser pipe of fixed length disposed coaxially outside of the drill pipe between the hole and the drilling rig. In situations where a submarine well is drilled from a floating vessel, however, it is necessary that the riser duct be of variable effective length to follow vertical movements of the vessel relative to the drilled hole, such movements being produced by tidal and wave action on the vessel; no such requirement exists relative to the drill pipe which is connected to the vessel via a rotary table in such a manner that vertical movements of the vessel are automatically accommodated.

A floating drilling vessel also can move laterally relative to a submerged drill hole in response to forces applied to the vessel by ocean currents, tidal surges and currents, and wind and wave action. Where the water depth between the drilling vessel and the ocean floor is relatively great, say on the order of 100 feet or more, lateral movements of the vessel relative to the drill hole are accommodated by bending of the drill string and riser pipe. It is in water depths of less than 100 feet or so that vessel lateral movements are troublesome, especially in terms of the riser pipe which is more resistant to bending than the drill pipe because of its larger diameter and generally smaller wall thickness. Moreover, in shallow water, the effects of tidal surges and wave action on the vessel frequently are greater than upon vessels moored in deepwater. Therefore, especially with regard to drilling operations carried out on floating vessels moored in shallow water, it is desirable that the riser structure, through which drilling mud is returned to the vessel from the drill hole, be capable of accommodating significant vertical and lateral movements of the vessel relative to the drilled hole.

It will be appreciated that the FIGURE of 100 feet mentioned above is only approximate. The exact water depth at which the problem described above ceases to be a problem is dependent upon several variables the principal ones of which are the diameter and thickness of the riser pipe, the nature and height of a submerged wellhead structure to which the lower end of the riser is connected, and the type and geometry of the vessel mooring system.

Review of Prior Arrangements

U.S. Pat. No. 3,313,345 illustrates the commonest riser pipe construction used in connection with floating drilling vessels. In this arrangement an upper portion of the riser passage is defined by pipe of diameter greater than the pipe defining the lower and more extensive portion of the length of the riser, a simple telescoping connection being provided between the upper and lower portions of the riser structure. The telescoping connection binds readily as the vessel moves appreciably laterally relative to the drill hole.

U.S. Pat. No. 2,676,787 described a laterally flexible riser structure which does not permit appreciable vertical motion of the vessel relative to the drill hole.

The flexible riser joint described in U.S. Pat. No. 3,189,372 permits no axial extension of the riser and only slight axial shortening of the riser assembly.

The prior actual and proposed riser arrangements reviewed above, therefore, do not provide practical solutions to the problem addressed by this invention, namely, the provision of practical riser duct structure capable of effective and economic use between a submarine drill hole and a floating vessel moored in relatively shallow water.

SUMMARY OF THE INVENTION

This invention provides an effective, efficient and economic mud riser structure capable of accommodating vertical and lateral movements of a floating vessel, moored in relatively shallow water, relative to a submerged drill hole. The present structure is simple to install and is reliable in operation.

Generally speaking, the present mud riser comprises a first length of tubular and essentially rigid ducting, such as conventional riser pipe, which is open at its opposite ends. One end of the first ducting is adapted for connection to a submerged wellhead structure. A second length of tubular and essentially rigid ducting, which also may be defined by conventional riser pipe, is adapted at one end thereof for connection to a floating drilling vessel for discharging fluid flowing therethrough from such ducting. The other end of the second ducting is open. Between the adjacent ends of the first and second ductings is connected open-ended laterally and longitudinally flexible sleeve means which cooperates with the ductings to define a variable length fluid flow passage from the one end of the first ducting to the one end of the second ducting.

As used herein, the term "floating vessel" means a displacement vessel of conventional hull form, a barge, a catamaran, and less conventional semisubmersible, positively buoyant drilling platforms which are moored in a body of water rather than being negatively buoyant and seated on the ocean floor. Also, the term "wellhead structure" includes a blowout preventer stack, and similar structure, which is disposed between the lower end of the riser proper and the drill hole and to which the lower end of the riser is connected in use.

DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of the present invention are more fully set forth in the following detailed description of preferred embodiments thereof, which description is presented with reference to the accompanying drawings, wherein:

FIG. 1 is an elevation view, partly in cross section, of a riser structure according to this invention installed between a submerged wellhead structure and a floating drilling vessel;

FIG. 2 is a fragmentary elevation view, partly in cross section, of another riser structure;

FIG. 2A is a detail view of a portion of the structure shown in FIG. 2;

FIG. 3 is an elevation view, partly in cross section, of a component of yet another riser structure;

FIG. 4 is an enlarged fragmentary cross section view of a portion of the component shown in FIG. 3;

FIG. 5 is an elevation view of another riser structure; and

FIG. 6 is an elevation view of yet another riser structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a drilling vessel 10 floats on the surface of a body of water 11 over a submerged geological formation 12. The drilling vessel has a central drilling well 13 disposed centrally below a drilling rig structure installed on the deck of the vessel. The drilling rig structure includes a derrick 15 which supports a drilling platform 16 above vessel deck 14. A conventional rotary table 17 is mounted on the platform over the drilling well. A drill string 18 extends downwardly from the rotary table through a blowout preventer stack 19 which is supported on a landing base 20, the landing base in turn being supported on the floor 21 of body of water 11, which may be an ocean or the like. The drill string extends downwardly from the landing base through a well casing to a rotary drilling tool (not shown).

The upper end of the drill string 18 is connected to a kelly joint 24 which typically is an elongate tubular element having a hexagonal cross-sectional configuration. The kelly joint cooperates with a hexagonally configured opening in the rotary element of the rotary table to impart angular motion to the drill string. The configuration of the kelly and the rotary table is such that the connection between the kelly and the rotary table automatically accommodates vertical motion of vessel 10 relative to landing base 20.

A riser structure 26 is coupled between the upper end of blowout preventer stack 19, the blowout preventer and the landing base cooperating to define a wellhead structure for the installation shown in FIG. 1, and extends to adjacent the underside of drilling platform 16. The riser structure is provided to conduct drilling mud upwardly from the wellhead structure to the floating vessel during the performance of drilling operations. As indicated above, during drilling operations, drilling mud, which normally has a specific gravity considerably greater than one, is circulated downwardly through drill string 18, outwardly through the drilling tool carried by the lower end of the drill string, and upwardly through the drilled hole and the riser structure. The function of the drilling mud is to remove cuttings from the vicinity of the drilling tool, and to provide a high hydrostatic load in the drill hole to prevent blowouts should a pocket of high-pressure gas or oil be encountered by the drilling tool in geologic formation 12. The drilling mud flowing upwardly through the riser structure is passed via a suitable conduit 27 to a filtration and treatment facility (not shown) located on the vessel for reprocessing prior to reinjection of the mud into the drill hole via the drill string.

Riser structure 26 includes a lower portion defined by tubular, essentially rigid ducting 28, such ducting having opposite open ends. The lower end of ducting 18 is secured to the upper end of the blowout preventer stack at a suitable coupling 29. Ducting 28 has an open upper end 30 which preferably is disposed closer to vessel 10 than to the wellhead structure. The riser structure also includes an upper portion defined by rigid tubular ducting 31 which has an open lower end 32 disposed adjacent end 30 of ducting 28. The upper end of ducting 31 carries an outlet fitting 33 to which conduit 27 is connected to adapt such ducting for discharge of drilling mud flowing upwardly therethrough laterally from the riser structure. Upper ducting 31 is suspended from the underside of drilling platform 16 by cables 34 led from the upper end of the ducting over suitable pulleys 35 to an appropriate cable tensioning structure such as winch 36. Ducting lengths 28 and 31 are disposed concentric to and outside of drill string 18 below the drilling platform and preferably are defined by conventional riser pipe of the type widely used in the petroleum exploration industry.

An elongate, laterally and longitudinally flexible sleeve 39, having opposite open ends 40 and 41, is coupled between the lower end of ducting 31 and the upper end of ducting 28 to provide a continuous mud flow path between the submerged wellhead structure and vessel 10. Sleeve 39 preferably is defined by a tube of heavy fabric which has been impregnated with an elastomeric material, such as natural or synthetic rubber or an asphaltic compound, to render it waterproof and resistant to abrasion by cuttings present in drilling mud flowing upwardly therethrough. The opposite ends of sleeve 39 are fitted to the exterior of surfaces of the adjacent ends of ducting lengths 28 and 31, and are held to the adjacent ducting by rubber cushion rings 42 engaged around the exterior of the sleeve adjacent the open ends of the ducting and clamped to the ducting by clamp rings 43.

The combination of rigid ductings 28 and 31 and sleeve 39 provides a riser structure which is adjustable in axial extent in response to movement of the vessel 10 vertically of landing base 20 in response to wave and tidal action applied to the vessel. Also, the riser structure can accommodate substantial lateral movement of the vessel relative to the landing base, such lateral movement of the vessel being produced by wind, wave, tidal and current action on the vessel. Riser structure 26 is particularly useful where the depth of water over ocean floor 21 has a depth on the order of about 100 feet or less such that the conditions described above would be troublesome were a telescoping slip joint used in lieu of sleeve 39.

It is preferred that sleeve 39 be located closer to the upper end of ducting 31 than to the lower end of ducting 28 along the length of riser structure 26. The higher the sleeve along the length of the riser structure, the less the hydrostatic load which is imposed upon the sleeve by drilling mud present within the riser structure.

FIG. 2 illustrates another riser structure 45 which includes first and second ducting lengths 28 and 31 in accord with the foregoing description. For the purposes of simplicity of illustration, the drill string, derrick and associated structure have been eliminated from the content of FIG. 2.

A sleeve 46 has its opposite open ends 47 and 48 engaged with the lower end of ducting 31 and the upper end of ducting 28, respectively. Like sleeve 39, the major portion of sleeve 46 is defined by a fabric tube, which tube may have one or more fabric plies, impregnated with an elastomeric material such as synthetic or natural rubber or an asphaltic compound. The sleeve extends upwardly from end 47 along the exterior of the ducting and then is folded back upon itself to extend downwardly to end 48 adjacent the upper end of ducting 28. Sleeve end 48 is disposed around the outer circumference of the upper end of ducting 28 and is folded in upon itself, as shown in FIG. 2, so that sleeve ends 47 and 48 open toward rather than away from each other. Each end of sleeve 46 is held against the adjacent end of respective ductings 28 and 31 by a rubber collar or the like and a circumferential steel strap 50. An abrasion resistant protective elastomeric covering 51 is engaged over the connection of each of sleeve ends 47 and 48 to ductings 31 and 28, respectively.

FIG. 2A is an enlarged detail view of the connection of sleeve end 47 to the lower end of ducting 31, the connection of sleeve end 48 to the upper end of ducting 26 being similar, as described above.

A pair of sealed, positively buoyant, hollow rings 52 are secured to the exterior of sleeve 46 between sleeve ends 47 and 48. Rings 52 maintain the sleeve in the position shown in FIG. 2 and prevent the sleeve from bellying downwardly of the upper end of ducting 28. The use of rings 52, therefore, prevents cuttings and other items which might settle out of drilling mud flowing upwardly through the riser structure from accumulating in the sleeve, thereby assuring that minimum loads are placed upon the sleeve during use of riser structure 45.

As an alternative to the use of positively buoyant rings secured to the exterior of sleeve 46, sleeve 46 can be connected to an air compressor 54, as shown in FIG. 2. The compressor is connected to the sleeve via a hose 55 which includes a control valve 56 and a pressure regulator 57. Hose 55 is connected to the sleeve via a suitable fitting 58 which is secured to the sleeve closer to sleeve end 47 than to sleeve end 48. Sufficient air is introduced into the sleeve to maintain the sleeve substantially in the condition shown in FIG. 2. As upper ducting 31 moves toward and away from lower ducting 28, such motion is accommodated by the upper reverse fold 59 of the sleeve merely changing its position along the developed length of the sleeve. In the event that ducting 31 were moved sufficiently far away from ducting 28 to completely straighten out the sleeve, the air charged into the interior of the sleeve would pass upwardly through ducting 31 without harm to the riser structure or to the mud treatment facility to which conduit 27 leads form the upper end of ducting 31.

Preferably, the total effective length of each of sleeves 39 and 46 between the ends thereof is greater than the maximum vertical movement which it is anticipated that vessel 10 will encounter relative to the submerged wellhead structure to which the lower end of ducting 28 is connected.

FIGS. 3 and 4 show another sleeve 60 which is connected between the upper end of ducting 28' and the lower end of ducting 31' in another riser structure 61, according to this invention. Ductings 28' and 31' are similar to ductings 28 and 31 shown in FIGS. 1 and 2 except that the adjacent open ends of ductings 28' and 31' are bounded by peripheral radially extending flanges 62 and 63, respectively. Sleeve 60 is a composite member which has outwardly extending circumferential terminal flanges 64. Between its terminal flanges, the body of sleeve 60 is defined by alternate equidiameter cylindrical portions 65 and hemitoroidal convolution portions 66 which are oriented concave to the interior of the sleeve. The cylindrical portions 65 which lie nextadjacent to terminal flanges 64 are longer than the portions 65 which lie intermediate the ends of the sleeve to provide clearance for bolting rings 67 and bolts 68 which are relied upon to connect the sleeve between ducting flanges 62 and 63.

As shown in FIG. 4, sleeve 60 is defined by an elastomeric material 69, such as natural or synthetic rubber, which has plural plies 70 of reinforcing fabric disposed therein adjacent its inner and outer surfaces. Also, within each cylindrical portion 65 of sleeve 60, a plurality of steel-reinforcing rings 73 are embedded in the elastomeric material between the sets of fabric plies disposed adjacent the respective ones of sleeve surfaces 71 and 72. A greater number of rings 73 are embedded in cylindrical portions 65 which lie adjacent sleeve terminal flanges 64 than embedded within the length of the remaining cylindrical portions intermediate the ends of the sleeve.

A plurality of bolting holes 74 are formed through each terminal flange of sleeve 60 at locations corresponding to the locations of an equal number of bolting holes 75 formed through ducting flanges 62 and 63. A pair of correspondingly apertured bolting rings 67 are also provided for sleeve 60. In use, the sleeve is bolted between ducting flanges 62 and 63 as shown in FIG. 3.

Sleeve 60 functions in a manner similar to the functioning of an accordion bellows in response to vertical and lateral motion of a floating drilling vessel relative to a submerged wellhead structure between which riser structure 61 is installed. As the vessel rises or falls relative to the submerged wellhead loads, sleeve 60 is extended or shortened by opening or closing of hemitoroidal convolution portions 66. During lateral motion of the floating vessel relative to the submerged wellhead structure, the sleeve deforms to accommodate such motion in a manner readily apparent from the structure of sleeve 60 in the light of the foregoing comments concerning accordion bellows.

Sleeve 60 is so constructed that it has essentially the cross-sectional configuration illustrated in FIG. 4 when free of axial tension or compression loads. For any given application, sleeve 60 should be constructed so that the maximum difference in vertical distance anticipated between the floating vessel and the submerged wellhead structure is less than 1) the number of convolutions 66 provided in the sleeve times 2) the difference between the maximum and minimum axial distance permitted between adjacent sleeve cylindrical portions 65 by a single convolution portion 66.

It is preferred that sleeve 60 be constructed with a large number of relatively small convolution portions 66 rather than a large number of relatively large convolution portions, thereby to provide a sleeve which presents minimum fluid flow resistance to drilling mud flowing upwardly through the sleeve during use of riser structure 61.

In the drilling of subsea oil wells and the like from floating vessels, it is common practice to guide a blowout preventer stack 19 into proper engagement with a landing base 20 be means of guide cables 80 (see FIG. 5) extending between the landing base and the floating drilling vessel. Where guide cables are used, usually at least three such cables are run between the landing base and a suitable cable tensioning mechanism, such as a constant tension winch 81, mounted on the drilling vessel. The guide cables are secured to the upper ends of upright pylons 82 mounted to the landing base, the blowout preventer and other devices lowered to the landing base being guided along the cables by suitable guide cylinders 83 supported on the blowout preventer and the like by support arms 84. Guide cables 80 may be relied upon to provide lateral stability to another sleeve 85 which forms a part of another rise structure 86 according to this invention.

Sleeve 85 preferably is used in conjunction with rigid upper and lower ducting lengths 28' and 31' of the type described above relative to the structure shown in FIG. 3, although it is within the scope of this invention that sleeve 85 may be used with ducting lengths 28 and 31, if desired. Sleeve 85 comprises a tube of water proof and abrasion resistant elastomeric material reinforced with one or more plies of fabric embedded therein. Tube 87 has a maximum length which is somewhat greater than the maximum anticipated vertical travel of floating vessel 10 relative to the submerged wellhead structure. At appropriate stations 88 spaced along the length of the tube, a plurality of rings or the like are secured to the exterior surface of the tube. There are the same number of rings fitted to the tube at each station 88 as there are guide cables relied upon to stabilize sleeve 85; the rings are arranged around the circumference of the tube at each station in a pattern corresponding to the pattern according to which guide cables 80 are arranged about drill string 18 when one looks downwardly upon landing base 20. A support cable 90, each of which may include a turnbuckle 91, is extended from each ring 89 ta slip ring 92 which is engaged loosely about the guide cable adjacent which the appropriate ring is disposed. The lengths of cables 90 are adjusted so that the tube is maintained substantially concentric to the drill string which extend through it between the opposite ends of the tube. The tube may be secured to the adjacent open ends of ducting 28' and 31' by means of bolting flanges 93 formed integral therewith, or such connection may be made in the manner illustrated in FIG. 1, if desired, in which case no terminal bolting flanges are provided at the opposite ends of tube 87.

FIG. 6 illustrates another riser structure 95 which includes a sleeve 96 for use in conjunction with a lower riser ducting length 28' and upper riser ducting length 97 which is similar to ducting 31' except that it carries a lower terminal-bolting flange 98 which has an outer diameter greater than the diameter of bolting flange 63 associated with ducting 31'.

Sleeve 96 is comprised of a tube 99 of elastomeric material, preferably reinforced with desired layers of fabric, arranged in a plurality of hemitoroidal convolutions 101, each of which is connected integrally to the adjacent convolutions and each of which is disposed concave to the interior of the sleeve. (As used with respect to convolutions 101, as well as with respect to convolutions 66 of sleeve 60, the term "hermtiroidal" means that configuration which results when a torus is cut by a cylindrical parting plane disposed concentric to the axis of symmetry of the torus, the parting cylinder having a diameter equal to one-half the sum of the major and minor diameters of the torus radially of its axis of symmetry.) At each of its opposite ends, tube 99 defines a bolting flange 100, each of which is clamped against an adjacent ducting flange 62 and 98 by a bolting ring 67 and bolts 68.

Below ducting flange 62, an annular bracket assembly 103 is clamped to ducting 28'. The bracket assembly extends radially outwardly of ducting 28' beyond the outer diameter of flange 98 at the lower end of ducting 97.

A plurality of guide rods 104 have their lower ends secured to the bracket assembly at equally spaced locations circumferentially of ducting 28'; preferably three guide rods 101 are provided at locations spaced 120.degree. apart about the circumference of the lower ducting. Each guide rod 104 extends parallel to the axis of drill string 18 which is passed axially through the riser structure. At its upper end, each guide rod carries a lug 105 which extends radially inwardly from the guide rod toward, but not to, the outer circumference of upper ducting 97. Adjacent its inner end, and within the periphery of flange 98, each lug defines a vertical hole 106 therethrough. The length of each guide rod 104 is sufficient to extend from bracket assembly 103 to above flange 98 when sleeve 96 is fully extended.

A secondary guide rod 107 is passed through each lug hole 106 and is connected at its lower end to the upper surface of upper ducting terminal flange 98, as shown in FIG. 6. Each rod 107 extends parallel to the axis of ducting 97 to a second bracket assembly 108 which is clamped to the outer circumference of ducting 97 a distance above flange 98 at least equal to the difference between the minimum shortened length of sleeve 96 and the maximum extended length of the sleeve.

A plurality of stay elements 109, such as stiff metal rods or woven wire cable, are connected to the exterior of tube 99 at selected locations along its length and extend radially of the tube to corresponding ones of a plurality of slip rings 110 which are loosely engaged about the circumference of guide rods 104. The stay elements maintain the tube generally concentric to drill string 18 regardless of the condition of extension or compression of the tube from its normal relaxed state.

As a floating drilling vessel, from which duct 97 is suspended, rises or falls relative to a submerged wellhead structure to which the lower end of ducting 28' is connected, ducting flange 98 moves away from or toward ducting flange 62, thereby elongating or shortening sleeve 96. During such movement, lugs 105 slide along guide rods 107 to maintain guide rods 104 in their desired position relative to each other, thereby assuring that tube 99 is maintained concentric to the drill string throughout such movement of the vessel. Holes 106 formed in lugs 105 are significantly larger in diameter than rods 107 with which they cooperate. Accordingly, the axis of ducting 97 can be moved angularly relative to the axis of ducting 28' without causing lugs 105 to bind upon rods 107 and without imposing bending moments upon either rods 104 and 107 sufficient to cause these rods to take a permanent nonlinear set. Therefore, it is apparent that riser structure 95 accommodates both lateral and vertical movements of a floating vessel relative to a submerged wellhead structure between which riser structure 95 is connected.

Each of riser structures 26 (see FIG. 1), 45 (see FIG. 2), 61 (see FIGS 3 and 4), 86 (see FIG. 5), and 95 is particularly useful in connection with drilling operations carried out from a floating drilling vessel moored in relatively shallow water depths. The riser structures described above do not suffer from the defects of the prior riser structures reviewed supra, and provide a continuous fluid flow path between the floating vessel and the submerged wellhead structure regardless of the vertical or lateral position of the vessel relative to the submerged wellhead structure. The present riser structures are simple to install and economical to fabricate, use and maintain.

The present invention has been described above with reference to various embodiments thereof. This description has been presented in furtherance of an explanation of the operative principles at work in this invention, rather than for the purposes of exhaustively cataloging structures which are considered to be within the scope and spirit of this invention. Accordingly, the foregoing description should not be considered as limiting the scope of this invention.

Claims

We claim:

1. An improved riser structure for use in drilling submarine oil wells and the like from floating vessels and the like comprising a first length of tubular and essentially rigid ducting and adapted at one end thereof for connection to a submerged wellhead structure, a second length of tubular and essentially rigid ducting adapted at one end thereof for connection to a floating drilling vessel, elongate laterally and longitudinally flexible sleeve means comprised of an elongate tube of reinforced elastomeric material including at least one ply of fabric material and connected at its opposite ends between the other ends of the ductings to define, in cooperation with the ductings, a fluid flow passage extending from the one end of the first ducting to the other end of the second ducting, a plurality of stay elements secured to the exterior of the tube in a predetermined pattern about the circumference of the tube at each of a plurality of stations spaced along the tube, means for adjusting the length of each stay element, and a slip ring connected to each stay element at the end thereof opposite from the tube.

2. An improved riser structure for use in drilling submarine oil wells and the like from floating vessels and the like comprising a first length of tubular and essentially rigid ducting and adapted at one end thereof for connection to a submerged wellhead structure, a second length of tubular and essentially rigid ducting adapted at one end thereof for connection to a floating drilling vessel, elongate laterally and longitudinally flexible sleeve means comprised of an elongate tube of reinforces elastomeric material including at least one ply of fabric material and connected at its opposite ends between the other ends of the ductings to define, in cooperation with the ductings, a fluid flow passage extending from the one end of the first ducting to the other end of the second ducting, the tube being defined by a plurality of contiguous hemitoroids disposed concave to the interior of the tube, a plurality of stay elements secured to the exterior of the tube in a predetermined pattern about the circumference of the tube at each of a plurality of stations spaced along the tube, and a slip ring connected to each stay element at the end thereof opposite from the tube.

3. An improved riser structure for use in drilling submarine oil wells and the like from floating vessels and the like comprising a first length of tubular and essentially rigid ducting adapted at one end thereof for connection to a submerged wellhead structure, a second length of tubular and essentially rigid ducting adapted at one end thereof for connection to a floating drilling vessel, elongate laterally and longitudinally flexible sleeve means comprised of an elongate tube of reinforced elastomeric material including at least one ply of fabric material and connected at its opposite ends between the other ends of the ductings to define, in cooperation with the ductings, a fluid flow passage extending from the one end of the first ducting to the other end of the second ducting, a plurality of stay elements secured to the exterior of the tube in a predetermined pattern about the circumference of the tube at each of a plurality of stations spaced along the tube, a slip ring connected to each stay element at the end thereof opposite from the tube, a first plurality of guide rods corresponding in number to the plurality of stay elements at each said station, means for mounting the guide rods to one of the ductings adjacent the sleeve means in correspondence to the predetermined pattern to extend parallel to each other through the slip rings to the other ducting a second plurality of guide rods, means for mounting the second guide rods to the other ducting adjacent the sleeve means in said pattern to extend parallel to the other ducting away from the sleeve means, and means slidably engaging each first guide rod with a corresponding one of the second guide rods.

4. An improved riser structure for use in drilling submarine oil wells and the like from floating vessels and the like comprising a first length of tubular and essentially rigid ducting adapted at one end thereof for connection to a submerged wellhead structure, a second length of tubular and essentially rigid ducting adapted at one end thereof for connection to a floating drilling vessel, elongate laterally and longitudinally flexible sleeve means comprised of an elongate tube of reinforced elastomeric material including at least one ply of fabric material and connected at its opposite ends between the other ends of the ductings to define, in cooperation with the ductings, a fluid flow passage extending from the one end of the first ducting to the other end of the second ducting, a plurality of stay elements secured to the exterior of the tube in a predetermined pattern about the circumference of the tube at each of a plurality of stations spaced along the tube, a slip ring connected to each stay element at the end thereof opposite from the tube, a plurality of elongate guide elements corresponding in number to the number of stay elements associated with each said station and extending through the slip rings for imparting lateral stability through the sleeve means, and means for mounting one end of each guide element fixedly to one of the ductings and for mounting the other end of each guide element to the other ducting for movement therealong toward and away from the sleeve means.