GB2127881A - Apparatus and method for attaching a template at a subsea production site - Google Patents

Abstract

Attachment of a template 40 at a subsea production site is effected through a single support piling (not shown) driven in the ocean floor. The template 40 is rotatably mounted on gimbal 42 which in turn provides a rotatable mounting for a latching arrangement 46 for securing the template 40 to the piling. <IMAGE>

Description

SPECIFICATION Apparatus and method for attaching a template at a subsea production site The present invention pertains to a subsea production assembly which connects a plurality of hydrocarbon producing wells with flowlines to transport hydrocarbons to storage facilities and more particularly to a method and apparatus for attaching a template at a subsea production site.

Present oil production is being directed to offshore areas located in water of up to 2,500 feet (762 m) deep. Subsea production is more economical if a plurality of wells are drilled from the same area with different slopes to achieve more efficient well production. A manifold structure is then used to combine the output of the plurality of wells in one or two flowlines to transport either liquid or gaseous hydrocarbons to storage facilities or a transfer vessel for further transportation to refining facilities. Typically, the manifold structure is supported on a template which is placed on a plurality of pilings, leveled by adjusting the heights of the respective pilings and securely fastened to each of the pilings.

The manifold structure also comprises several bays, the majority of which are used as connections to wellheads. One or two of the bays are used for connections to flowline bundles which carry the liquid or gaseous hydrocarbons to a remote destination.

The concrete pilings upon which the template is placed are usually prefabricated concrete and may be several hundred feet long.

The pilings are driven into the ocean floor with an underwater hammer. Once the concrete pilings are in place, they must be adjusted so that the template, which is typically 25 feet (7.6 m) in diameter, is level within 3 inches (7.6 cm) across its diameter. To appreciate the magnitude of this problem, it is to be noted that, for a 25 foot (7.6 m) diameter template, a slope of 5 degrees from the horizontal will result in a discrepancy of over 2 feet (0.6 m) from one side of the template to the opposite side.

As the depth increases down to 2,500 feet (762 m), leveling of the template becomes more and more of a problem particularly with the muitiple piling support concept.

Accordingly the invention resides in one aspect in an apparatus for attaching a template at a subsea production site by way of a single support piling comprising gimbal means rotatably mounted to the template and latch means rotatably mounted to the gimbal means for securing the template to the support piling.

In a further aspect, the invention resides in a method for attaching a template at a subsea production site comprising the steps of: driving a single support piling into the ocean floor; and latching the template to the piling so that the piling provides the sole support for the template.

In the accompanying drawings, Figure 1 is a diagrammatic side view of a monopile support.

Figure 2 is a plan view of a leveling wafer.

Figure 3 is a cut away side view of Fig. 2.

Figure 4 is a plan view of a template and a gimbal mounted latch system.

Figure 5 is a side view along lines 4-4 of Fig. 4.

Figure 6 is a plan view of a slip segment latching system.

Figure 7 is a partially cut away side view of Fig. 6.

Referring now to Fig. 1, a monopile support assembly is illustrated having monopile 12 with ring girder 14 attached thereto. Superimposed in phantom are monopile 1 2A and ring girder 1 4A depicting distance variations existing whenevenmonopile 1 2 is not installed perfectly vertical. Monopile 1 2 may be of any commonly used support material. However, the preferre embodiment uses steel pipe having an outer diameter of 6 feet (1.8 m) and a thickness of 2 inches (5.1 cm). This single support monopile 12 may be as long as 300 feet (91 m) of which only a few feet extend above the mudline of the ocean floor.

As illustrated in Fig. 1, a five degree deviation from vertical at the top of monopile 1 2 results in a deviation in excess of 2 feet (0.6 m) betweeh corner 16 and opposite corner 18 of the ring girder 14. Ring girder 1 4 may also be of any type currently used to initially support the weight of the template which will rest thereon. Ring girder 14 may be affixed to monopile 1 2 by standard methods such as welding.

Monopile 1 2 and its ring girder 14 are to be installed in 2,500 feet (762 m) of water, by driving with an underwater hammer. A tolerance on the verticality of the pile axis may be zero to five degrees omni-directionally. A ten bay template is preferably landed on the pile and made level to within one-half degree of horizontal to accommodate later operations. A more detailed description of a subsea template may be found in our published British Patent Application No.

2,114,188.

Normally, monopile 1 2 projects approximately 10 feet (3 m) above the ocean floor, and has a ring girder assembly 14 25 feet (7.6 m) in diameter fixed at the mudline. As previously stated, a five degree slope amounts to in excess of 2 feet (0.6 m) deviation across the 25 foot (7.6 m) base of the girder, whereas the template, when set down, must be leveled to + 2.62 inches (6.65 cm) across this same 25 foot (7.6 m) diameter. A significantly sloped surface presents drilling, pump ing and connection problems which, due to the depth at which the platform is operated, require many man hours and great expense to correct.

A nearly level template surface is a prerequisite for reliable, efficient operation of a subsea production system which contains connections to oil wellheads and production flowlines.

Referring now to Figs. 2 and 3, a template leveling wafer 20 is illustrated as having template orientation slot 22, handling eye 24, slope indicators 26 and lifting pins 38. The wafer 20 is a prefabricated structural compo- nent, which is constructed before the installation phase but is designed to be field adjustable. The wafer centers on the pile only loosely and provides a level top surface since its bottom surface is adjusted on site to compensate for the angle of ring girder plate 14.

The wafer does not need to be precisely centered, but it does require orientation with respect to monopile 12. This can be accomplished with a orientation pin 30 (Fig. 3) on the wafer 20. Precise orientation is not critical, as an orientation error of 180 degrees will produce an error of only 10 degrees from level. Therefore, an orientation error of a few degrees will result in a small leveling error.

A subsea platform is thus required to have no leveling machinery, as the foundation has already been made level. A large bearing area is also achieved. Separate orientation of a subsea platform is possible if done before the weight of the template is set on wafer 20. If compensating wafer 20 is set on ring girder 14 and found to be incorrect, it can be pulled back to the surface much easier and quicker than a large subsea platform base.

In operation, the deviation of monopile 1 2 (see Fig. 1) is measured and the slope of ring girder 14 is computed. Wafer 20 is prefabricated to compensate for the determined slope of ring girder 14. Wafer 20 may be lifted by lift pins 28 and lowered onto ring girder 14 on monopile 1 2 by methods currently used in subsea construction. Wafer 20 has a center slot 32 which defines a funnel from bottom to top. The top of center slot 32 is approximately 6 feet (1.8 m) in diameter and the bottom is approximately 10 feet (3 m) in diameter. This permits wafer 20 to be lowered on monopile 1 2 while misalignment of center slot 32 with respect to the center of monopile 1 2 may be as much as 4 feet (1.2 m).The funnel type arrangement of slot 32 ensures centering on monopile 1 2 and allows alignment with side walls of ring girder 14.

Wafer 20 is constructed to compensate for any deviation from vertical of monopile 1 2 which results in a slope from horizontal of the base of ring girder 14. As illustrated in Fig. 3, wafer 20 may consist of two concentric superimposed, mutually rotatable segments 20A and 20B. Each segment is in the form of a circular wedge, conveniently defining a 2 1/2 degree angle between its upper and lower surfaces so that, by varying the angular oriel tation of the segments, the angle between the top and bottom surfaces of the overall wafer can be adjusted from 0-5 degrees. Each segment is a steel plate fabrication with circu lar and radial stiffeners 39 being provided to give the wafer sufficient strength to transfer the compressive loads experienced in use.

Before the wafer 20 is lowered into place on monopile 12 and ring girder 14, the angular orientation of the segments 2OA, 20B is adjusted to compensate for slope existing in ring girder 14. After the wafer has been installed, the accuracy of this adjustment can be confirmed by visual inspection of the slope indicators 26.

Using the monopile 12 as the sole support for the template presents an additional prob lem in latching the template to the monopile 12. Thus the template must be securely fas tened to the monopile 12 even when mono pile 12 deviates from vertical. However, the wafer 20 allows the template to assume a level position, so that the center axis of tem plate 40 is always substantially vertical, but will be at an angle with the center line of monopile 12 when it deviates from vertical.

Referring now to Figs. 4 to 7, template 40 is illustrated as being connected to gimbaled ring 42 through universal connection 44 and having hydraulically operated slip latch 46 attached to gimbaled ring 42 through univer sal connection 48. Hydraulically operated slip ring latch 46 fits around monopile 12 and may rotate to compensate for any deviation from vertical in monopile 12. However, com pensation for deviation from the vertical by hydraulically operated slip latch 46 can only compensate for deviations within the 90 de gree arc of universal joint 48, that is + 45 degrees from center line axis 50 of universal joint 48.

Universal joint 44 connecting gimbaled ring 42 and template 40 is spaced 90 degrees from the center line 50 of universal joint 48 having a center line axis 52 perpendicular to axis 50. Universal joint 44 will compensate for deviations from the vertical in monopile 1 2 which are + 45 degrees from center line 52.

Thus, template 40 may be lowered upon wafer 20 and latched to monopile 12 despite its deviation from vertical.

Fig. 5 illustrates universal connection 44 to gimbaled ring 42 and universal connection 48 to hydraulically operated slip ring latch 46. As Illustrated, template 40 may be set on wafer 20 while hydraulically operated latch 46 slides down monopile 12. Template 40 will rest on wafer 20 while hydraulically operated latch 46 is configured to extend to a level slightly above wafer 20.

As shown in Figs. 6 and 7, hydraulically operated slip latch 46 includes slip segments 50, 50A having wedges 52, 52A located therein. Slip latch 46 also includes hydraulic cylinders 56 connected to wedges 52 and 52A in juxtaposition with slip segments 50 and 50A, respectively. Slip segments 50 and wedge 52 depict the elements in unlocked position and slip segment 50A and wedge 52A depict the elements in locked position.

Hydraulically operated slip latch 46 must be capable of being operated remotely and be capable of latching positively to monopile 1 2 despite any forces exerted on template 40 or monopile 1 2. This means that hydraulically operated slip latch 46 must not be susceptible to working itself loose when operational forces are applied. The combination of wedges 52 and slip segments provide a secure connection as required.

In operation, hydraulically operated slip latch 46 is lowered onto monopile 12, with the wedges and slip segments in their unlocked position. When the latch is in place, hydraulic cylinders 56 are actuated to force piston arm 58 against wedge 52A forcing it to slide slip segment against monopile 12.

Once in position, any radial or transverse forces exerted on either template 20 or monopile 1 2 will be translated into radial forces. By arranging that the angle of inclination of wedge 52 with respect to slip segment 50 is small, radial forces will be almost perpendicular to surfaces 60 and 60A of wedges 52 and 52A. As such, wedges 52 and 52A will maintain their position forcing slip segments 50 and 50A to remain tight against monopile 12.

Hydraulically operated slip latch 46 makes positive solid contact with monopile 1 2 and acts through universal connection 48, gimbaled ring 42 and universal connection 44 to provide secure mounting for template 40 to monopile 1 2.

Claims (5)

1. Apparatus for attaching a template at a subsea production site by way of a single support piling comprising: gimbal means rotatably mounted to the template; and latch means rotatably mounted to the gimbal means for securing the template to the support piling.

2. The apparatus according to claim 1 wherein the latch means includes means for gripping the support piling, wedge means slidably mounted in contact with the gripping means for urging the gripping means against the support piling and a hydraulically operated actuator connected to the wedge means for moving the wedge means to a position urging the gripping means against the support piling.

3. A method for attaching a template at a subsea production site comprising the steps of: driving a single support piling into the ocean floor; and latching the template to the piling so that the piling provides the sole support for the template.

4. The method according to claim 3 wherein the latching step includes the steps of: providing a gimbaled latch generally cen trally of the template; rotating the latch to compensate for any vertical deviation of the single support pil ing; and removably securing the template to the single support piling by way of the latch.

5. The method according to claim 4 wherein the step of removably securing includes the steps of providing slip segments slidably mounted in conjunction with wedge members operated by hydraulic actuators and actuating the hydraulic actuators to urge the wedge members against the slip segments and thereby urge the slip segments against the single support piling.