GB2114188A - Subsea well completion system, a base template for the system and a method of establishing production capability from multiple subsea wellheads - Google Patents

Abstract

A subsea well completion system includes a fluid-tight work enclosure hull 13 containing manifold means and having a plurality of radially- disposed lateral penetration means 38 which extend through the hull 13 and are operatively connected to the manifold means. The system also includes a base template 11 having means for securing the template 11 to the marine floor in a substantially horizontal position and having a lower support structure for supporting the work enclosure hull. The template 11 is further provided with an upper guidance structure comprising a plurality of substantially vertical guide members 19 mounted in spaced radial array, the guide member 19 extending inwardly toward the center of the template and forming an opening at the central portion of the template for receiving the work enclosure hull, a portion 20 of the upper peripheral surface of each guide member 19 sloping downwardly toward the opening for guiding the hull 13 as it is lowered during installation of the hull onto the template. To establish production capability from multiple subsea wellheads 14 on the template 11, with the template being secured to the marine floor, the work enclosure hull 13 is lowered towards the template 11 from a position directly above the template. The upper guide structure then guides the hull 13 into the central cylindrical opening defined by the guide members 19 and, when the hull is in position, fluid communication is established between the wellheads 14 and the manifold means through respective penetration means 38. <IMAGE>

Description

SPECIFICATION Subsea well completion system, a base template for the system and a method of establishing production capability from multiple subsea weliheads This invention relates to a subsea well completion system, a base template for the system and a method of establishing production capability from multiple subsea wellheads.

Recent developments in the offshore oil and gas industry extend production to undersea areas, such as the outer fringes of the continental shelves and the continental slopes. A submarine production system is believed to be the most practical method of reaching the subaqueous deposits. Although hydrocarbons are the main concern at this time, it is contemplated that subaqueous deposits of sulfur and other minerals can be obtained from beneath the seas. While bottom-supported permanent surface installations have proved to be economically and technologically feasible in comparatively shallow waters, in deeper waters, such as several hundred to several thousand meters, utilization of such surface installations must be limited to very special situations.Installations extending above the water surface are also disadvantageous even in shallower water where there are adverse surface conditions, as in areas where the bottomsupported structure of the above-surface production platform is subject to ice loading.

Subsea systems are feasible for installing multiple well heads in relatively close proximity through the use of a drilling template secured on the marine floor. Such systems can be operated from remote, floating surface facilities using electrohydraulic control systems, with the subsea systems being connected to the surface facilities by flowlines for production fluids, injection fluids, hydraulic controls, electrical cables, and the like.

Habitable, subsea work enclosures, or satellites, can be maintained adjacent multiple, template-drilled wellheads for housing operating and/or maintenance personnel, as disclosed, for example in U.S. Patent No. 3,556,208. In such systems, the subsea satellite is independently connected to a number of surrounding subsea well heads and serves to control the production from, and maintenance of, the wellheads. The wells are drilled in a circular pattern through a template on the marine floor, the template serving also as a base upon which the satellite is installed.

The production/control passages of each well are connected to production equipment within the satellite by separate connector units which are independently lowered into place from a surface vessel and form portions of the flow paths between the wellheads and the production equipment within the satellite.

While the aforementioned subsea satellite systems prove generally satisfactory in water depths of 100 to 1 50 meters, the use of such systems at depths of 300 to 750 meters presents certain problems. For example, the utilization of guidelines and diver assistance for subsea installation of the components of the system becomes more complex with increasing water depths. In waters of such substantial depth, it becomes necessary to employ dynamic guidance systems, including remote television and/or sonar monitoring, during the installation process.

Furthermore, subsea installation of the satellite on the template in prior systems presents problems in terms of guidance of the satellite into proper position on the template and the need to fasten the satellite to the template. Also, prior art subsea well completion systems typically utilize submerged work enclosure hulls having vertically arranged hull penetrators. Such an arrangement of the penetrators produces undesirable hull stress conditions, particularly at depths in excess of 1 50 meters.

It is an objective of the present invention to alleviate the problems and disadvantges of the prior art by providing an improved subsea well completion system and template therefor capable of simplfied installation on the marine floor, as well as an improved subsea satellite installation procedure.

Accordingly, the invention resides in one aspect in a subsea well completion system for multiple subsea wells, comprising a fluid-tight work enclosure hull having a plurality of radiallydisposed lateral penetration means for establishing releasable fluid connection through the hull and a base template having a lower support structure for supporting the work enclosure hull and means for securing the template to a marine floor so that the lower support structure extends substantially horizontally, the template further having an upper guidance structure comprising a plurality of guide members extending substantially perpendicular to the lower support structure and mounted in spaced radial array, the guide members extending inwardly toward the center of the template and forming an opening at the central portion of the template for receiving the work enclosure hull, a portion of the upper peripheral surface of each guide member sloping downwardly toward the opening for guiding the hull into the opening during installation of the hull by lowering the hull onto the template.

In a further aspect the invention resides in a subsea base template for guiding marine floor well drilling equipment at multiple wells and supporting a subsea work enclosure hull and wellheads comprising: a lower support structure comprising a substantially horizontally aligned, open tubular framework and a plurality of substantially vertical well conductor pipes spaced around the peripheral portion of the framework and integral therewith, for aligning well drilling equipment, the upper section of each well conductor pipe terminating in a welihead, the central portion of the framework being adapted to support the subsea work enclosure hull and the peripheral portion being adapted to support the wellheads; and an upper guidance structure comprising a plurality of guide members rigidly mounted on, and extending vertically from, the lower support structure in spaced radial array, each guide member extending inwardly toward the center of the template, forming a substantially cylindrical opening at the central portion of the framework for receiving the work enclosure hull, a portion of the upper surface of each guide member sloping downwardly toward the cylindrical opening for guiding the work enclosure hull as it is lowered during installation thereof onto the template, the guide members further providing structural protection for the work enclosure hull and,the wellheads.

In yet a further aspect, the invention resides in a method of establishing production capability from multiple subsea wellheads on a base template secured to the marine floor, comprising: providing a work enclosure hull containing a manifold, the hull having a substantially cylindrical portion with a plurality of radiallydisposed lateral hull penetrators extending therethrough and operatively connected to the manifold; providing an upper guidance structure on the template comprising a plurality of substantially vertical guide members mounted in spaced radial array, each guide member extending inwardly from the outer periphery of the template, thereby providing a substantially cylindrical opening at the central portion of the template for receiving the work enclosure hull, a portion of the upper peripheral surface of each guide member sloping downwardly toward the cylindrical opening; lowering the work enclosure hull from a position directly above the template and directing the hull through the upper guidance structure into the cylindrical opening at the central portion of the template, the work enclosure hull being guided into its resting position on the template by the guide members; and establishing subsea fluid communication between the subsea wellheads and the work enclosure hull.

In the accompanying drawings, Figure 1 is a perspective view of a subsea well completion system according to a first example of the present invention for guidelineless installation; Figure 2 is a perspective view, in partial phantom, of the system of Figure 1, showing guidelineless installation of one of its components; Figure 3 is a perspective view of the marine floor base template of the system of Figure 1; Figure 4 is a plan view of the marine floor base template shown in Figure 3; Figure 5 is a perspective view of the subsea work enclosure hull of the system of Figure 1, showing the attached pipeline boom and pipeline; Figure 6 is a cross-sectional plan view of the upper control section of the work enclosure hull, showing internal monitoring and control equipment;; Figure 7 is a cross-sectional side elevation view of the lower service section of the work enclosure hull, showing a portion of the internal fluid handling apparatus; Figure 8 is a cross-sectional plan view, in partial phantom, of the lower service section shown in Figure 7; Figure 9 is a perspective view of a wellhead connector means and its associated protective alignment frame of the system of Figure 1; Figure 10 is a perspective view of a master valve assembly and associated protective alignment frame of the system of Figure 1; Figure 11 is a side elevation view of the master valve assembly and associated protective alignment frame shown in Figure 10; Figure 12 is a perspective view of a subsea well completion system according to a second example of the present invention, showing guideline installation of one of the system components.

Referring to Figure 1 , the subsea well completion system of the first example is represented generally by the numeral 10 and includes a base template, designated generally by the numeral 11, having a lower support structure for supporting a work enclosure hull 13, individual wellheads 14, and wellhead connector means 1 5. Wellheads 14 are mounted on well conductor pipes 16 forming a portion of the lower support structure of base template 11.

A semisubmersible drilling rig (not shown) lowers base template 11 to the marine floor on a drilling riser in a known manner. Drilling of each well through base template 11 is accomplished using a conventional blow out preventer (BOP) stack and conventional drilling procedures.

Preferably, base template 11 is constructed such that a BOP stack will be contained within its designated well location by vertical guides 19, thereby preventing overlap or entry into adjacent well locations. When a well is completed, a master valve assembly 50 (described below) is preferably lowered on a drilling riser (not shown) and operatively connected to welihead 14 to cap it. Work enclosure hull 13 is installed on base template 11 by lowering it on a riser from a semisubmersible drilling vessel and oriented by rotating the riser, using television cameras or sonar to determine the orientation. Installation of work enclosure hull 13 on base template 11 is preferably performed without the use of guidelines. Wellhead connector means 1 5 are then lowered from the drilling rig on a drill pipe and operatively connected between each master valve assembly and manifold means housed within work enclosure hull 13 via lateral penetration means 38 extending through the hull.

The manifold means, in turn, connects to pipelines and flow lines extending through work enclosure hull 13. Work enclosure hull 13 must land and lock on base template 11 within a determined rotational asimuth tolerance to allow lateral penetration means 38 to be within an acceptable reach of the corresponding wellhead connector means 1 5.

The well completion system 10 is operated from a remote surface production facility through the use of conventional electrohydraulic control systems, with the well completion system being connected to the surface facility by pipelines, fluid service lines, hydraulic lines, and electrical cables.

Production and control equipment inside work enclosure hull 1 3 is maintained by personnel brought to the chamber in a submersible or tethered transfer vehicle. Well repair is performed either by vertical reentry techniques from a floating drilling rig, or through the use of pumpdown tools (PDT) launched from inside work enclosure hull 13 and controlled from the remote surface facility.

Where desirable, e.g. for deeper water applications, all subsea components of the well completion system are installed on the base template 11 without the use of guidelines.

Wellhead connector means 1 5, master valve assemblies 50, and blow out preventer stacks (not shown) are preferably equipped with a specially designed bumper structure (described in detail below) to mate with a specially designed upper guidance structure section of base template 11.

Referring to Figure 2, the component, in this case a wellhead connector assembly 15, to be landed on base template 11 is lowered by drill pipe 61 to a point preferably outside the well bay, for safety in the event the component should be accidentally dropped, and is oriented by rotating the drill pipe using remote television or sonar to monitor the operation. Then the component is moved horizontally into the well bay structure and lowered for landing on wellhead 14 or master valve assembly 50, using running tools similar to those conventionally used for installing wet subsea trees.

Referring to Figures 1-4, the lower support structure of base template 11 also includes means for securing the template to the marine floor in a substantially horizontal position. As shown in Figure 4, the securing means includes conventional leveling pile guides 1 7 spaced about the periphery of the template and extending coaxially with well conductor pipes 1 6 for rigidly attaching base template 11 to the marine floor in a substantially horizontal position. Wellheads 14 and well conductor pipes 1 6 are of conventional construction.

Base template 11 further includes an upper guidance structure comprised of a plurality of substantially vertically extending guide members 1 9 mounted on the template in spaced radial array. Each vertical guide member 1 9 extends from the outer periphery of the base template inwardly, leaving a substantially cylindrical opening at the central portion of the template, defined by the respective vertical inner legs 21 of each guide member 19, for receiving the work enclosure hull 13. A portion 20 of the upper peripheral surface of each guide member 19 slopes downwardly towards the cylindrical opening to serve as a funnel or guideway.

Preferably, sloping portion 20 defines an angle of about 45 to the horizontal.

To install work enclosure hull 1 3 on the central portion of base template 11, the hull is lowered by a conventional drill string or riser (not shown) from a floating or semi-submersible vessel (not shown) above the template. The drill string may be connected to work enclosure hull 13 using a connector 1 8 (see Figure 12) coaxially secured to an upper portion of the hull. As work enclosure hull 1 3 contacts the upper guidance structure of base template 11, sloping portions 20 will serve to guide the hull 13 into the substantially cylindrical opening defined by legs 21 of the template upper guideance structure at the central portion of the template, thus ensuring proper positioning of the hull at the central portion of the template.

In j- addition to providing guidance to work enclosure hull 13 during guidelineless installation onto base template 11, the upper guidance structure of base template 11 provides protection against damage to the hull. As a result of its rigid construction, this structure serves as a protective cage surrounding work enclosure hull 1 3. Base template 11 is preferably constructed from rigid structural piping, using an open frame construction, as shown. In addition to its strength, such piping permits control of the buoyancy of the template, to aid in its installation on the marine floor.

Further guidance and orientation for the hull 13 is preferably provided by guide flanges 22 (Figure 3) on the template 11, which extend radially inwardly from legs 21 and have downwardly inclined upper surface portions 23.

While other shapes are possible, base template 11 is preferably circular in shape, when viewed from above, with wellheads 14 and well conductor pipes 1 6 spaced about its circumference, preferably at a common radial distance from the center of the template. In such a system, vertical guide members 19 are preferably spaced apart equidistantly.

The upper guidance structure of base template 11 also preferably possesses crosspieces 24 (Figure 1) of structural piping extending between adjacent vertical legs 21, and rigidly secured thereto. As will be explained below, crosspieces 24 serve as blocking means whereby the omission of a crosspiece 24 between a preselected pair of iegs 21 furtherfacilitates alignment and orientation of work enclosure hull 1 3 in its desired position during installation on base template 11.

Base template 11 may be provided with ballast tanks (not shown) for ease of handling during towing and installation of the structure.

Preferably, base template 11 is an open, welded metal structure with a tubular metal frame, crossbraced for strength.

Referring now to Figures 1 and 5, as mentioned, work enclosure hull 13 is installed on the subsea base template 11 by lowering it on a drill string without the use of guidelines. To further assist in aligning and orienting work enclosure hull 13 in the desired position at the central portion of base template 11, alignment means 25 (Figure 5) preferably extends from the periphery of work enclosure hull 13. As embodied herein, the alignment means 25 comprises a pipeline boom, within which are disposed one or more pipelines and flow lines 26 extending through work enclosure hull 1 3 to its interior (discussed in greater detail below). The external dimensions of pipeline boom 25 are selected so as to provide a close fit between the boom and adjacent vertical legs 21 of the upper guide structure of base template 11.During installation, the crosspieces 24 serve as boom blocking means, precluding the lowering of pipeline boom 25, so that the pipeline boom may only be lowered between the single pair of vertical legs 21 having no crosspiece 24, thereby ensuring the desired orientation of work enclosure hull 13.

As best shown in Figures 1 and 3, base template 11 preferably further comprises pipeline boom alignment bumpers 27 for providing finer alignment of boom 25 between the correct vertical guide members 19. Pipeline boom 25 preferably tapers toward a narrower end portion 25', and bumpers 27 are spaced along the periphery of base template 11 at a distance designed to ensure a close fit of this narrower end portion. As shown, bumpers 27 also preferably include downwardly sloping portions adapted to guide end portion 25' as it is lowered during installation on base template 11.

As shown in Figure 5, as least one laterally extending positioning stop 29 is preferably secured to the outer periphery of the cylindrical portion of work enclosure hull 1 3 for contacting vertical leg 21 of a guide member 19 to block movement of the hull when it is rotated during installation of the hull on base template 11, thus further facilitating orientation of the hull with respect to the template. Positioning stops 29 may also serve as lifting tabs or gussets for surface handling of work enclosure hull 13.

Utilizing the procedures discussed above, a work enclosure hull may be installed on a marine floor base template without the use of guidelines at water depths of 750 meters. Acoustic beacons and sonar reflectors, as well as remote television cameras may be used to monitor the position and orientation of the work enclosure hull relative to the base template during installation.

Referring now to Figures 5-7, the work enclosure hull 1 3 preferably comprises a vertically oriented, stepped cylinder. The upper, smaller cylindrical section 30, together with a complementary hemispherical end section 31 house a control section 32. The lower, larger cylindrical section 33 is topped by a complementary hemispherical section 34, which joins the lower end of the smaller cylindrical section 30. A further hemispherical section 35 extends from the bottom of cylindrical section 33 and completes the enclosure for a service section 36, which is supported by skirt member 37 having the flow line boom 25 extending therefrom.

Spaced about the periphery of cylindrical section 33, and extending generally horizontally therefrom, are lateral penetration means 38, for establishing well fluid communication through work enclosure hull 13. Horizontal alignment of lateral penetration means 38 through hull 13 provides significantly improved hull stress relief when compared with vertical alignment through upper hemispherical section 31.

Service section 36 (Figure 7) houses production manifold 39 which is operatively connected to one or more pipelines 26 extending through work enclosure hull 13, as shown in Figure 7.

A portion of the internal fluid handling system of a typical service section 36, as shown in Figures 7 and 8, operatively connects the manifold 39 to the internal terminations 40 of the integrally welded penetration means 38. Various produced petroleum streams, gas streams, water streams, chemical injection streams, test streams and hydraulic lines can be manifolded through their respective lines and valves individually according to the desired production schedules.

The manifolding and valving are preferably designed to permit the passage of pump-down tools (PDT) from the subsea work enclosure out to and down the individual wells. In such a case, a lubricator, to permit loading the pump-down tools into the system piping, must be connected to a power fluid supply line from a surface facility to satisfy the requirement for large pumping capability, metering, fluid treating and storage.

Capability is preferably provided to allow switching between the individual well functions (from production to test to service) during the operating life of the well. Internal valve means permit sequencing or combining fluids according to the desired production schedules. Remotelyactuated and/or manual valve operations are employed, as desired.

Figures 7 and 8 illustrate relevant portions of a typical system of internal piping and valving, including PDT capability, for establishing fluid flow between single penetration means 38 and manifold means 39. Substantialiy identical systems are provided for connecting each of the individual penetration means 38 spaced about work enclosure hull 13 to manifold means 39.

The complete details of such other systems have been omitted from Figures 7 and 8 for clarity. PDT servicing requires that at least a 1.52 meter bending radius be maintained on all piping bends through which pump-down tools will pass.

Service section 36 is provided with an explosion-inhibiting inert atmosphere, such as nitrogen. A structural bulkhead and purgable compartment 42 are provided for transferring personnel between service section 36 and control section 32, while keeping the two atmospheres in the respective sections separated and free from mixing through the use of conventional air lock transfer techniques. Plug-in type breathing equipment is utilized by personnel in service section 36.

Control section 32 (Figure 6) is provided with a breathable atmosphere, rendering the control section habitable. The life support systems for habitable control section 32, as well as the required remote controls and the like, may be connected to a remote surface facility by one or more conduits for providing air, exhaust, communications, power, and the like. These conduits may piggyback with or be within pipeline 26.

Control section 32 (Figure 6) is provided with a personnel transfer bell, or "teacup", 41 for transferring operating and maintenance personnel from a conventional submarine vessel (not shown) using atmospheric pressure transfer techniques.

Work enclosure hull 13 must be of sufficient strength to withstand the extremely high pressure at water depths up to 750 meters. It has been found that work enclosure hull 13 may be constructed so as to possess negative buoyancy, through proper weighting and ballasting. Such a construction avoids the necessity for any latching equipment to hold down the hull once it is installed on the marine floor base template.

Preferably, work enclosure hull 13 includes slips (not shown), which may be of conventional construction, and the base template 11 includes a centrally located mandrel 9 (see Figures 3 and 4) extending substantially vertically upward. In this embodiment, work enclosure hull 13 is retained on base template 11 by the force of gravity and by the slips attaching to mandrel 9.

Referring to Figures 1 and 9, the well completion system of the present invention further comprises wellhead connector means 1 5 for connecting a wellhead 14 to a work enclosure hull penetration means 38 to establish fluid communication therebetween. As embodied herein, welihead connector means 1 5 comprises a fluid connection assembly 49, and a conventional hydraulic connector (not shown), extending substantially vertically from the lower end of the assembly for operatively connecting it to well head 14. In a preferred embodiment, the hydraulic connector does not attach directly to wellhead 14, but is connected to a master valve assembly 50, secured to well head 14 for providing well shut-in capability and protection before the well is connected to work enclosure manifold 39.Master valve assembly 50, which may be of conventional construction, is installed on base template 11 before work enclosure hull 13 is installed. Master valve assembly 50 will be discussed in greater detail below.

Fluid connection assembly 49 also preferably includes a wye spool 51 extending from a diverter 52, which provides fluid communication between conventional swab valves 53 and the hydraulic connector. Swab valves 53 are preferably included for maintenance purposes, commonly referred to as "workover". In the preferred embodiment shown in Figure 9, swab valves 53, as well as the down hole production and service bores, may be vertically accessed from the surface or a submersible work vehicle via conventional connector mandrel 54 and piping 55. In order to provide for pump-down tool capability, wye spool 51 must be curved on a radius of at least 5 feet.Wye spool 51 is connected to the associated lateral penetration means 38 through the use of a suitable penetrator connector 56, with a mechanical linkage 57 being provided for movement of penetrator connector 56 onto operative connection with the penetration means. For a more complete description of the construction and operation of penetrator connector 56 and lateral penetration means 38, attention is invited to U.S. Patent No.

4,191,256.

Upon coupling the hydraulic connector of the wellhead connector means 1 5 to wellhead 14, or master valve assembly 50, and coupling of penetrator connector 56 to lateral penetration means 38, well fluids exiting wellhead 14 may be communicated through work enclosure hull 13 and into manifold means 39, thus establishing production capability. The wellhead connector means 1 5 shown in Figure 9, in combination with horizontal penetration means 38, permit significant reduction in the size of the well head connector means, when compared with prior structures, while still providing external production piping which is removable for maintenance.

Wellhead connector means 1 5 preferably further comprises a guide frame 60 for support and protection of the fluid communication assembly 49, which is rigidly secured thereto. As shown in figure 2, wellhead connector means 1 5 may be installed on base template 11 by lowering it on a riser 61, connected to upper mandrel 54 by conventional running total connectors. In water depths of 750 meters, conventional guideline installation may, however, not be possible.

Consequently, in one preferred embodiment of the invention, a specially-designed guide frame 60 serves not only as a protective cage for the connector means 15, but also faciiitates installation of connector means 1 5 on base template 11.

Specifically, in the embodiment shown in Figures 2 and 9, guide frame 60 is constructed as an open, wedge-shaped bumper structure designed to mate with a well bay defined by adjacent vertical guides 19 of base template 11 for facilitating approximate alignment and orientation of wellhead connector means 1 5 on the template. This bumper structure preferably extends the full height of fluid connection assembly 49, and is preferably comprised of heavy structural piping.

In the preferred embodiment shown in Figure 9, guide frame 60 comprises substantially symmetrical top and bottom support members 65, 66, with fluid connection assembly 49 aligned for inward, substantially horizontal connection to a mating lateral penetration means on work enclosure hull 13, and for downward, substantially vertical connection to a mating wellhead 14, either directly or via a master valve assembly 50. Top and bottom support members 65, 66 are vertically connected by substantially vertical structural members 67,68,69,70,71, 72, 73, 74, and have an inwardly-tapering outer dimension to facilitate alignment of guide frame 60 within a correspondingly tapered well bay section.Although the trapezoidal shape of top and bottom support members 65, 66, shown in Figure 9 is well-suited to provide the desired inwardly-tapering puter dimension of guide frame 60, it is by no means the only suitable shape. The important factor is that guide frame 60 has opposing side portions which are tapered similarly to the tapered sides of the well bay in which wellhead connector means 1 5 is to be mounted (as defined by adjacent vertical guide members 19), and which are sufficiently spaced apart and extend for a sufficient length and height to provide alignment of guide frame 60 in the well bay as it is moved laterally inwardly during installation on base template 11.In addition, the tapered side portions of guide frame 60 must taper to a narrow end width which is sufficiently narrow to permit the guide frame to fully enter the well bay, and thus position well head connector means 15, and particularly penetrator connector 56, sufficiently close to work enclosure hull 13, and particularly to penetration means 38, to permit their operative connection. Thus, the narrow end width defined by bumper members 75, 76, 77 must be small enough to be received adjacent to the work enclosure hull 1 3, as guide frame 60 is moved toward the center of base template 11 during installation.

In general, the desired orientation of well connector means 15 in the well bay may be achieved by making the width dimension of the radially outermost portion of guide frame 60, with respect to the center of base template 11, sufficiently large to prevent misorientation of guide frame 60. In the embodiment shown in Figure 9, this width dimension is defined by bumper members 78, 79. In such an alternative construction, radial positioning of wellhead connector means 1 5 is preferably assisted by making the width dimension of the radially innermost portion of guide frame 60 (defined by bumper members 75, 76, 77 in Figure 9) sufficiently small to be unobstructed by vertical guides 19, so as to be received adjacent work enclosure hull 13, and by proper radial positioning of fluid connection assembly 50 on guide frame 60, with respect to the end bumper members 75, 76, 77.

Guidelineless installation of wellhead connector means 1 5 is achieved by first lowering the connector to a depth which permits contact between guide frame 60 and the upper guidance structure of base template 11. For safety reasons, wellhead connector means 1 5 is preferably not lowered directly over the template. This reduces the risk, should the lowering riser fail or a mishap occur, resulting in the equipment being dropped.

Having reached the proper depth in the general vicinity of base template 11, wellhead connector means 1 5 is moved laterally in the general direction of the center of base template 11.

Monitoring of its movement may be by remote television cameras, sonar, submarines, etc. Guide frame 60 will contact one or more vertical guide members 19 of base template 11, and will be guided into the well bay between adjacent vertical guide members 19, thus insuring proper orientation of wellhead connector means 1 5.

Referring again to Figure 1, in the preferred embodiment shown, the vertical guide members 1 9 of the base template 11 are spaced equidistantly around the template so as to divide it into equally-sized, inwardly tapered well bays, all but one of which are adapted to receive correspondingly tapered wellhead connector means 15. Each of the lateral penetration means 38 are situated on work enclosure hull 13 so as to be aligned with a wellhead connector means 15, with the horizontal spacing between all but two of the lateral penetration means being equal.Such an arrangement, together with the arrangement of wellheads 14 at a common radial distance, permits the use of equally sized and shaped well connector means 15 and provides for improved utilization of space within service section 36 of work enclosure hull 13, in terms of the arrangement of the necessary production, testing and service intervals.

Referring now to Figures 2, 9 and 10, final alignment and operative connection of wellhead connector means 15 with wellhead 14, or preferably with master valve assembly 50 which is coupled to wellhead 14, is preferably achieved using conventional funneling alignment techniques. One such technique employs a large diameter, downwardly directed funnel 80 (Figure 9) connected to the bottom of fluid connection assembly 49 and/or guide frame 60. As wellhead connector means 1 5 is lowered, funnel 80 is guided over a mating alignment structure, e.g.

ring 81 (Figure 2), and the wellhead connector means is rotated into the final, aligned position.

Funnel 80 is then retracted upward, allowing well connector means 1 5 to operatively engage the mandrel of wellhead 14 (or master valve assembly 50) thereby establishing fluid communication.

Such a guide funnel technique may also be used to connect wellhead connector means 1 5 to drilling riser 61, with funnel 62 (Figure 2) being secured to the riser, or a running tool, and guided overlanding ring 62 on the wellhead connector means.

Master valve assembly 50, as shown in Figures 1, 2, 10 and 11, is generally of conventional construction to provide well shut-in capability after drilling is completed and protection before the well is connected to work enclosure manifold 39. It is installed after drilling and completing the well, but before work enclosure hull 13 is installed on base template 11. Master valve assembly 50 typically comprises a lower connector 82 to be attached to the wellhead, a master valve 83 in each string, and a top mandrel 84. A guide funnel technique, as described above in connection with wellhead connector means 15, is preferably utilized to guide master valve assembly 50 onto wellhead 14, if guidelineless installation is employed.Furthermore, guidelineless installation of master valve assembly 50 on base template 11 is preferably facilitated by incorporating a wedgeshaped, protective bumper structure, or guide frame, 90 into the master valve assembly. Except for obvious changes resulting from differences in size, the structure and functioning of guide frame 90 are substantially identical to guide frame 60, described above in connection with the installation of wellhead connector means 15, with the vertical guides 19 serving to direct guide frame 90 into position as it is moved laterally during its installation on base template 11.

As shown in Figure 1, to assist in guidelineless installation of master valve assembly 50, and to provide increased structural protection, base template 11 preferably further comprises bumpers 95 extending along the outer periphery of the template. The vertical height of bumpers 95 should approximate the height of master valve assembly 50. Installation of master valve assembly 50 requires that the assembly first be lowered to a depth no greater than the top of bumpers 19, then laterally moved into position over wellhead 14, and finally lowered the remaining distance to establish contact with wellhead 14. Master valve assembly 50 is then operatively connected to wellhead 14 via its lower connector 82.

Figure 12 illustrates an embodiment of the invention in which a conventional guideline technique is used for installing wellhead connector means 1 5. In this technique, guidelines 100 are affixed to a guide frame 101 secured in a well bay on base template 11, strung through vertical piping which forms the corner posts of the wellhead connector frame 60, and then placed under high tension. Wellhead connector means 1 5 is then lowered along guidelines 100 by riser 61. In such a system, the structure of base template 11 is essentially as described above for guidelineless installation (except for the presence of guide frame 101), and the procedure for installing subsea work enclosure 1 3 on the template is substantially unchanged from that already described.

Illustrative exemplary parameters for various system components of the present invention are discussed below.

The upper guidance structure of base template 11 is preferably sized and constructed such that, upon lowering, work enclosure hull 11 can be 1.8 meters off center in any lateral direction and will still be directed on target by the upper guidance structure, or up to 1 50 off in rotationai orientation and will still be properly oriented by the upper guidance structure. Of course, the more offset horizontally the work enclosure hull 13 is, the smaller the orientation misalignment that can be tolerated. Once the work enclosure hull 13 is within the portion of base template 11 formed by vertical legs 21, additional flanges or gussets 22 preferably align the hull within 7.6 cm of the desired alignment.When work enclosure hull 13 is fully lowered on base template 11, preferably only a 1 5.2 cm clearance will exist between pipeline boom 25 and alignment bumpers 27 at the free end of the boom. This is sufficient to orient work enclosure hull 1 3 to within plus or minus one-half degree in rotation.

The lower support system of base template 11 is preferably leveled to within plus or minus onehalf degree of horizontal.

With a 22-1/2 angular spacing of blow out preventer (BOP) envelopes around a circular base template 11 during drilling of the wells, and assuming the envelopes to be 3.7mx4.6m, the envelopes need not overiap each other, which is preferable. With such a BOP envelope spacing, a base template diameter of 1 8 meters is preferably the minimum diameter for the template.

In the present invention, for water depths in excess of 300 meters, the wells are spaced about base template 11 at a common radius from the center of the template.

In one practical embodiment of a well completion system designed for operation at water depths of 750 meters, base template 11 is circular in shape and has a diameter of 19.5 meters and an overall height (bottom of lower support structure to top of upper guidance structure) of 13.7 meters. Such a template, designed for up to 8 wells, has a weight of about 2x 105 Kg and a well spacing of 6.7 meters radially. The well to well spacing is 4.6 meters.

The upper guidance structure is 9.8 meters in height. While the lower support structure has a height of 3.96 meters. The structural members forming the upper guidance structure of the base template 11 comprise 50.8 cm outer diameter by 0.750 cm Wall structural tubing while those forming the template lower support structure are 76.2 cm outer diameter by 0.500 cm Wall structural tubing. Typically the wellheads of such a system are 42.5 cm and the leveling pile guides utilize three 106.7 cm outer diameter piles. The subsea work enclosure hull 13 has an overall height of 17.45 meters and overall outer diameter of 7.4 meters, with the outer diameter of the cylindrical section 30 of control section 32 being 3.7 meters. The outside radius of hemispherical section 31 is 182 cm and the outside radius of hemispherical sections 34, 35 is 370 cm. The weight of work enclosure hull 13 is 203,000 Kg (less the weight of skirt 37, boom 25 and the internal piping and equipment), and the total outfitted weight is 457,000 Kg. Sufficient ballast is added within chambers (not shown) in skirt 37 to make the submerged hull (overall) about 45,000 Kg heavy.

Claims (15)

Claims

1. A subsea well completion system for multiple subsea wells, comprising: a fluid-tight work enclosure hull having a plurality of radially-disposed lateral penetration means for establishing releasable fluid connection through the hull, and a base template having a lower support structure for supporting the work enclosure hull and means for securing the template to a marine floor so that the lower support structure extends substantially horizontally, the template further having an upper guidance structure comprising a plurality of guide members extending substantially perpendicular to the lower support structure and mounted in spaced radial array, the guide members extending inwardly toward the center of the template and forming an opening at the central portion of the template for receiving the work enclosure hull, a portion of the upper peripheral surface of each guide member sloping downwardly toward the opening for guiding the hull into the opening during installation of the hull by lowering the hull onto the template.

2. A subsea well completion system as claimed in claim 1, wherein the work enclosure hull includes alignment means extending laterally from the periphery of the work enclosure hull and the upper template guidance structure further comprises blocking means rigidly mounted between each, but one, pair of adjacent guide members, whereby said blocking means can only be received between said one pair of adjacent guide members as the hull is lowered during installation of the hull onto the template, thereby orienting the hull.

3. A subsea well completion system as claimed in claim 2, wherein the free end of the hull alignment means is smaller than the opposite end thereof, and the base template further comprises a pair of substantially vertically extending bumpers spaced along the periphery of the template at a distance permitting close fitting of said free end therebetween, the vertically extending bumpers having facing portions sloping downwardly for guiding the alignment means as the work enclosure hull is lowered during installation onto the template.

4. A subsea well completion system as claimed in any preceding claim wherein the lower support structure of the template includes a plurality of well conductor pipes which extend substantially vertically in use and which are spaced around the template at a common radial distance from the center of the template for aligning the individual wells during drilling, the upper section of each conductor pipe terminating in a wellhead.

5. A subsea well completion system as claimed in claim 4, further comprising wellhead connector means for releasably connecting a wellhead to one of the lateral penetration means to establish fluid communication therebetween, and wherein the vertical guide members are situated such that adjacent members define a radially inwardly tapered well bay for each wellhead.

6. A subsea well completion system as claimed in claim 5, wherein the wellhead connector means comprises a fluid connection assembly adapted for mounting in a well bay and a rigid, open guide frame surrounding the rigidly secured to the fluid connection assembly, the frame having opposing side portions which are tapered similarly to the radially aligned sides of the well bay in which the wellhead connector means is to be mounted, the tapered side portions being sufficiently spaced apart and extending for a sufficient length and height to provide alignment of the frame in the well bay as it is moved laterally during installation of the wellhead connector means onto the template, whereby a desired orientation of the fluid connection assembly can be achieved.

7. A subsea well completion system as claimed in claim 6, wherein the guide frame comprises substantially symmetrical upper and lower support members and open, vertical structural members connected between the upper and lower support members, the fluid connection assembly being aligned for inward horizontal connection to a mating lateral penetration means and downward vertical connection to a mating wellhead.

8. A subsea well completion system as claimed in any one of claims 5 to 7, further comprising at least one master valve assembly for providing fluid communication between a wellhead and the associated wellhead connector means, the master valve assembly including a rigid guide frame having opposing side portions which are tapered similarly to the radially aligned sides of the well bay into which the assembly is to be mounted, the tapered side portions being sufficiently spaced apart and extending for a sufficient length and height to provide alignment of the guide frame in the well bay as it is moved laterally during installation onto the template, whereby a desired orientation of the assembly can be achieved.

9. A subsea well completion system as claimed in claim 8, wherein the upper structure of the template further comprises substantially vertical bumpers extending along the outer periphery of the template for radially guiding and positioning the master valve assembly as it is lowered during installation onto the template, the vertical bumpers providing structural protection and alignment of the assembly.

10. A subsea well completion system as claimed in any preceding claim, wherein the work enclosure hull is divided into an upper control section having a breathable atmosphere and a lower service section having an inert, noncombustible, and substantially dry atmosphere, the service section having a substantially cylindrical portion and the penetration means extending laterally through the wall of said cylindrical portion, and the guide members forming a substantially cylindrical opening at the central portion of the template.

11. A subsea base template for guiding marine floor well drilling equipment at multiple wells and supporting a subsea work enclosure hull and wellheads, comprising: a lower support structure comprising a substantially horizontally aligned, open tubular framework and a plurality of substantially vertical well conductor pipes spaced around the peripheral portion of the framework and integral therewith, for aligning well drilling equipment, the upper section of each well conductor pipe terminating in a wellhead, the central portion of the framework being adapted to support the subsea work enclosure hull and the peripheral portion being adapted to support the wellheads; and an upper guidance structure comprising a plurality of guide members rigidly mounted on, and extending vertically from, the lower support structure in spaced radial array, each guide member extending inwardly toward the center of the template, forming a substantially cylindrical opening at the central portion of the framework for receiving the work enclosure hull, a portion of the upper surface of each guide member sloping downwardly toward the cylindrical opening for guiding the work enclosure hull as it is lowered during installation thereof onto the template, the guide members further providing structural protection for the work enclosure hull and the weliheads.

12. A subsea base template as claimed in claim 11 further comprising means for securing the template to the marine floor in a substantially horizontal position.

13. A method of establishing production capability from multiple subsea wellheads on a base template secured to the marine floor, comprising: providing a work enclosure hull containing a manifold, the hull having a substantially cylindrical portion with a plurality of radiallydisposed lateral hull penetrators extending therethrough and operatively connected to the manifold; providing an upper guidance structure on the template comprising a plurality of substantially vertical guide members mounted in spaced radial array, each guide member extending inwardly from the outer periphery of the template, thereby providing a substantially cylindrical opening at the central portion of the template for receiving the work enclosure hull, a portion of the upper peripheral surface of each guide member sloping downwardly toward the cylindrical opening;; lowering the work enclosure hull from a position directly above the template and directing the hull through the upper guidance structure into the cylindrical opening at the central portion of the template, the work enclosure hull being guided into its resting position on the template by the guide members; and establishing subsea fluid communication between the subsea wellheads and the work enclosure hull.

14. A method as claimed in claim 13, wherein the fluid communication between the work enclosure hull and the wellheads is established by operatively connecting a wellhead connector therebetween within a well bay defined by adjacent vertical guide members.

15. A method as claimed in claim 14, including the step of lowering the welihead connector in the vicinity of the template and laterally moving the well head connector into the well bay, the wellhead connector being guided into its resting position on the template by the adjacent vertical guide members defining the well bay.