Riser connector

A riser connector connects the upper portion of a riser (12) having a latching enlargement (32) to a receptacle (14) on a vessel (16), so the riser upper end (22) can connect to a fluid coupling (42) leading to a conduit (40) on the vessel. A double-click mechanism (88), with parts on the enlargement and on the receptacle, turns a load ring on the enlargement to latch the enlargement in place when it is lifted to an upper position and lowered to a latched position, and releases it by again lifting and lowering. A cable coupling (24) is temporarily mounted on the top of the riser to enable the riser to be lifted by a cable (26), the cable coupling being later removed to connect the riser upper end to the fluid coupling on the vessel.

BACKGROUND OF THE INVENTION

Risers, which are fluid-carrying conduits, are widely used in the production and transfer of hydrocarbons in offshore installations, such as to carry oil and/or gas from a sea floor well up to a vessel that floats at the sea surface. The connection and disconnection of the ends of risers can be time-consuming. One current method is to mount an enlargement on the riser near an upper end of the riser. The vessel carries a basket that can hold the enlargement. The riser is lifted until the enlargement lies above the level of the basket. The riser is moved sideward through a slot in the basket so the enlargement is directly over the basket. The enlargement is then lowered until it lies nested in the basket. Thereafter, the basket supports the enlargement and the upper end of the riser. This method is time consuming. In some situations, as where the riser upper end must be pulled up into an underwater opening in a turret of the vessel, considerable extra space must be provided, in addition to the awkwardness of shifting the enlargement through the slot before setting it down into the basket. It is desirable that no separate hydraulic or electrical actuator be required to latch the enlargement in the basket. A way of latching a lifted riser enlargement into a receptacle on a vessel, which minimizes the required space around the receptacle, which can be easily operated, and which does not require electric or hydraulic energized locks, would be of value.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a riser connector is provided for latching an enlargement on the upper portion of a riser, in a receptacle on a floating structure such as a vessel, which is simple to operate, minimizes the required space around the receptacle and avoids the need for electrically or hydraulically energized locking devices. The riser has an upper portion that extends above the enlargement. A cable coupling is attached to the top of the riser and a pull-in cable is attached to the coupling. The pull-in cable initially extends through the receptacle, and the cable can be pulled until the enlargement enters the receptacle and is then let down about a meter, to automatically latch the enlargement in place.

The automatic latching of the riser enlargement in the receptacle is accomplished by the use of a “double-click” mechanism. Double-click mechanisms are commonly used on ball-point pens, with a first push on a button latching the pen point in a projecting position, and a second push causing the penpoint to retract. U.S. Pat. No. 4,943,188 shows such a double-click mechanism on a tether that extends down from a floating structure to connect to a receptacle on the sea floor, so as to anchor the floating structure. Applicant's receptacle has a through hole, and the cable and then the upper portion of the riser are pulled up through the through hole. When the enlargement is latched in the receptacle, the cable coupling is removed from the riser upper end, and the riser upper end is connected to a fluid coupling on the floating structure. Then, fluid can flow through the riser.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates a system10wherein a riser12of about ten inches diameter, is being pulled up into a basket, or receptacle14. The receptacle is mounted on a fixed offshore tower, or to the side of a floating structure16that floats at the sea surface20, such as a vessel that produces hydrocarbons from an undersea reservoir or that flows hydrocarbons to or from a seafloor pipeline. In one example (FIG. 2), the lower end18of the riser has been connected to a fluid coupling21leading to a sea floor hydrocarbon well beneath the sea floor19, and the upper end22of the riser must be coupled to the vessel16to carry produced hydrocarbons to the vessel for processing (remove stones, sand and water, etc.) for later transfer to a tanker. A cable coupling24has been temporarily connected to the upper end of the riser, and a pull-in cable26(cable, rope, or other line) has been connected to the coupling. A sheave30(FIG. 1) directs the cable to a winch31on the vessel that pulls the cable and therefore also pulls up the riser. The cable extends through a through hole or passage36of the receptacle14. When the riser has been pulled in sufficiently for an enlargement, or latching enlargement32at the bottom of the riser upper portion23to move up into the receptacle14, the enlargement may engage a bumper or stop38in the receptacle and cannot move up further, or the enlargement is moved up to a predetermined height. The cable is then lowered by perhaps a meter, and the enlargement automatically becomes latched in the receptacle. Because the enlargement is latched, the riser that is attached to the enlargement, cannot move down. The receptacle14which is fixed to the vessel or other structure, and the enlargement32on the riser, can together be referred to as a riser connector34.

With the riser upper end fixed in the latched position shown in phantom lines at22A inFIG. 1, a conduit40on the vessel is connected to the top of the riser. This can be done by disconnecting the cable coupling24and connecting the riser upper end to a fluid or pipe coupling42at the adjacent end of the conduit. After the connection to the conduit coupling, hydrocarbons or other fluid or control elements can flow through the riser up to or down from the vessel. At a later time, the riser may have to be disconnected from the vessel, as when a large storm is approaching, for change out, for maintenance purposes, or when the riser is no longer required. Such disconnection can be accomplished by disconnecting the riser upper end (or a fluid connector thereon) from the fluid coupling42, reconnecting the cable coupling24, and lowering the cable with the winch after first raising it by about a meter.

FIG. 2shows that the enlargement32includes a body50and a load ring52that can rotate on the body about a riser axis54. The load ring52has six support lugs56with support surfaces60that will be supported by a corresponding surface on the receptacle. The support lugs also carry cam followers62that will engage cams on the receptacle to rotate the connector load ring.

FIG. 3shows details of the latching enlargement32and of the receptacle14, with the enlargement in a fully latched position. Only the left side of the figure, to the left of the primarily vertical riser axis54, shows the enlargement in section. The support surfaces60of the lugs that are part of the connector load ring52, bear against a receptacle supporting surface70. The supporting surface70lies at the top of a receptacle guiding portion72. The figure also shows cams74which engage the cam followers62on the lugs.

FIG. 4shows that the receptacle guide portion72has six slots80that receive the six lugs56on the load ring52. The slots have portions that receive the cam followers62to guide the six lugs into the six slots as the enlargement is raised in the receptacle. As mentioned above, the cam followers lie on the connector load ring52which can rotate on the enlargement body.

The cams on the receptacle and the cam followers on the enlargement form a “double-click” mechanism, that rotates the cam followers in steps as the enlargement on the riser moves up and down, and that alternately cause support and release of the enlargement. Such double click mechanism is widely used in ball-point pens with retracting tips.FIG. 5shows about 180° of the double click mechanism88, laid flat on the paper of the figure. The particular double click mechanism is one of the types shown in U.S. Pat. No. 4,943,188 for an anchor tether.

FIG. 5shows a cam follower62of the double click mechanism88as it moves through various positions with respect to the cam surfaces of cams74of the mechanism. The cams and cam followers form parts of the double click mechanism. The cam follower at62A moves up as the riser is pulled up into the receptacle. Cam surfaces90,92guide the cam follower into a slot80A. Near the top of its path the cam follower encounters a cam surface94that rotates the cam follower by 15° as it continues to move up until it reaches position62B. Instead of placing a stop at38, applicant provides vertical slots96that allow continued upward movement. Applicant stops upward movement by the bumper38(FIG. 1) or, preferably, by an operator stopping the winch when he sees the top of the riser at a certain level. The riser is then lowered and the cam follower encounters cam surface100that rotates the cam follower by another 150 to position62C. Rotation of the cam follower62on the enlargement32at the upper portion of the riser, involves twisting of the cable26that supports the riser. At62C the cam follower lies in a retained position wherein it is locked in rotational position and the lugs56(FIG. 3) are supported by a support surface70, and the riser is held in this position indefinitely while fluid flows through the riser. The cam follower62C lies above a bottom surface102.

FIG. 5shows that to later disconnect the riser, the cam follower is lifted from position62C to position62D while it and the load ring turn another 15°. Then the cam follower is lowered, and it moves down along slot80B to position62E where the cam follower is in a release position and the riser can be lowered out of the receptacle. The enlargement has six cams that engage six sets of the cam followers. The vertical movement of the cam followers is on the order of magnitude of a meter, and is usually about a meter. Compared to the riser entire length which is usually a plurality of 10's of meters, such vertical movement of about a meter to latch and unlatch can be referred to as a “slight” movement.

Referring again toFIG. 3, the riser includes a cupped end82that is clamped between a body abutment83and an elastomeric bearing ring84. This allows the riser portion86to deflect by as much as perhaps 20° with respect to the riser upper portion23. This is a known arrangement.

FIG. 6shows another system100wherein a riser102carries an enlargement104that must be pulled up into a receptacle106. The receptacle lies in a turret110that lies in a vessel112. The top of the riser is shown connected through a pipe120to a fluid swivel114on the turret. It can be seen that there is a considerable advantage in being able to pull a cable, followed by the riser and enlargement, directly into a receptacle passage116and latch the enlargement in the receptacle. If the enlargement had to be pulled up beside the receptacle and then moved over the receptacle and lowered, then a lot more room would be required. It also should be noted that the latching arrangement can be used to lower a riser lower end onto a connector on a platform on the sea floor. This is done by orienting the receptacle and riser enlargement upside-down and using the reverse vertical movements of the enlargement to latch it to the receptacle so the riser cannot move upward.

Although applicant shows the cam followers and support lugs on a rotatable load ring, it would be possible to instead use a rotatable load ring on the receptacle that holds its cams, or to mount the entire receptacle or entire enlargement so it can rotate.

FIG. 7shows a riser with a coupling120at its upper end that can be connected to a corresponding coupling on a floating structure conduit. The coupling120includes a plurality of eyelets121,122(and possibly a third one). An intermediate cable connector130formed by a plurality of cables131,132extend to a single cable140that is pulled up by a winch.

Thus, the invention provides a latching arrangement for latching a conduit used in offshore hydrocarbon transfers, such as a riser, to a structure such as one at the sea surface or sea floor. The latching arrangement enables the conduit to be pulled through a receptacle and then latched in place, by vertical movement of the riser and without requiring an energized actuator such as one energized by hydraulic fluid or electricity. A cable coupling is connected to a riser end and extends through a receptacle of the latching arrangement, to pull a cable and the riser until an enlargement on the riser enters the receptacle and small (on the order of a meter) vertical movement of the riser latches the enlargement in the receptacle. In some cases, an end of the riser that projects beyond the enlargement is disconnected from the cable coupling and connected to a pipe.