GB2129472A - A method for providing a horizontal support area at a subsea production site - Google Patents

Abstract

To provide a horizontal support area at a subsea production site, a single support pile is driven into the ocean floor and a support bracket is secured to the piling. The slope of the support bracket to the horizontal is determined and a wedge 20 is prefabricated so as to have the equal and opposite slope. The wedge 20 is then located on the bracket to define a horizontal seating for a subsea production template. <IMAGE>

Description

SPECIFICATION A method for providing a horizontal support area at a subsea production site The present invention pertains to a subsea production assembly wich connects a plurality of hydrocarbon producing wells with flowlines to transport hydrocarbons to storage facilities and more particularly to a method of providing a horizontal support area 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 multiple piling support cocept.

Accordingly the invention resides in a method for providing a horizontal support area at a subsea production site comprising the steps of determining the slope of the subsea production site prefabricating a wedge having a slope equal and opposite of the determined slope and placing the wedge on the subsea production site.

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 Figure 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 Figure 4.

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

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

Referring now to Figure 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 whenever monopile 1 2 is not installed perfectly vertical.

Monopile 12 may be of any commonly used support material. However, the preferred 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 Figure 1, a five degree deviation from vertical at the top of monopile 12 results in a deviation in excess of 2 feet (0.6 m) between corner 1 6 and opposite corner 1 8 of the ring girder 14. Ring girder 14 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 12 by standard methods such as welding.

Monopile 12 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 12 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, pumping 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 Figures 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 component, 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 (Figure 3) on the wafer 20.

Precise orientation is not critical, as an orientation error of 1 80 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 12 (see Figure 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 12 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 12 while misalignment of center slot 32 with respect to the center of monopile 12 may be as much as 4 feet (1.2 m). The funnel type arrangement of slot 32 ensures centering on monopile 12 and allows alignment with side walls of ring girder 14.

Wafer 20 is constructed to compensate for any deviation from vetical of monopile 12 which results in a slope from horizontal of the base of ring girder 14. As illustrated in Figure 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 orientation 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 circular 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 20A, 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 1 2 as the sole support for the template presents an additional problem in latching the template to the monopile 12. Thus the template must be securely fastened to the monopile 12 even when monopile 12 deviates from vertical. However, the wafer 20 allows the template to assume a level position, so that the center axis of template 40 is always substantially vertical, but will be at an angle with the center line of monopile 1 2 when it deviates from vertical.

Referring now to Figures 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 universal 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, compensation for deviation from the vertical by hydraulically operated slip latch 46 can only compensate for deviations within the 90 degree arc of universal joint 48, that is t 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 centre line 52. Thus, template 40 may be lowered upon wafer 20 and latched to monopile 1 2 despite its deviation from vertical.

Figure 5 illstrates 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 Figures 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 12 despite any forces exerted on template 40 or monopile 12. 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 transplated 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 12 and acts through universal connection 48, gimbaled ring 42 and universal connection 44 to provide secure mounting for template 40 to monopile 12.

Claims (3)

1. A method for providing a horizontal support area at a subsea production site comprising the steps of: determining the slope of the subsea production site; prefabricating a wedge having a slope equal and opposite of the determined slope; and placing the wedge on the subsea production site.

2. The method according to claim 1 wherein the prefabricating step includes providing first and second concentric, superimposed, generally circular wedge segments which are capable of relative angular movement, each wedge segment defining an angle between its upper and lower surfaces, and imparting relative angular movement to the segments so as to vary the angle between the upper surface of the first segment and the lower surface of the second segment.

3. The method of claim 1 or claim 2 and further comprising the steps of driving a single support pile into the ocean floor, securing a support bracket to the piling, and mounting a template on the support bracket with the prefabricated wedge being located between the bracket and the template.