CA1212099A - Method of installing one or more subsea templates - Google Patents
Method of installing one or more subsea templatesInfo
- Publication number
- CA1212099A CA1212099A CA000490014A CA490014A CA1212099A CA 1212099 A CA1212099 A CA 1212099A CA 000490014 A CA000490014 A CA 000490014A CA 490014 A CA490014 A CA 490014A CA 1212099 A CA1212099 A CA 1212099A
- Authority
- CA
- Canada
- Prior art keywords
- template
- hoisting apparatus
- rig
- seabed
- hull
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Earth Drilling (AREA)
- Placing Or Removing Of Piles Or Sheet Piles, Or Accessories Thereof (AREA)
Abstract
Abstract The present invention relates to a method of installing one or more subsea templates at preselected sites on a seabed. The method is comprised of the steps of providing a column stabilized variable draft semi-submersible drilling rig having at least one submersible hull including a unit for supporting a template on the hull, a derrick, primary apparatus associated with the derrick for raising and lowering a riser through a moon pool on the rig spaced laterally from the hull, and secondary hoisting apparatus on the rig including a cable unit adapted to be connected to the template. At least one submersible template is adapted to have controllable positive and negative buoyancy. The steps further include loading the template on the support unit for the template using a crane and at least one of the hoisting apparatus to position the template over the support unit; lowering the template onto the support unit and ballasting the template to shift the weight of the template to the support unit; and transporting the template to a predetermined site on the seabed with the drilling rig. The method further includes the steps of connecting the template to the primary and secondary hoisting apparatus; venting ballast from the template to float the template free of the support unit while controlling the position of the template with the hoisting apparatus; taking up the primary hoisting apparatus and slacking off the secondary hoisting apparatus to position template under the moon pole; and lowering the template to the seabed with the hoisting apparatus.
Description
~2:1Z09~
A Method of Installi~gLOne or More Subsea Templates _._ This is a division of copending Canadian Patent Application Serial number 420,393 which was filed on January 27, 1983.
Field of the Invention The present invention pertains to a method and apparatus for installing and levelling subsea drilling and/or foundation templates and the like using a semi-submersible drilling rig equipped with a heave compensator.
lQ Background In the art of developing subsea installations for production of hydrocarbons from formations below the seabed there have been numerous types of installations placed on the seabed including structures known as templates and the like. These structures are typically characterized by large skeletal frames which are used for supporting well-head components and other apparatus used in conjunction with drilling and producing hydrocarbons from subsea wells.
- There are several problems associated with hand-ling the relatively large structures known as templates.
The process of loading, transporting and installing a sub-sea template using a semi-submersible drilling rig or other floating structure has presented several problems in the overall procedure of handling the templates from the point of embarkation to the final installation and levelling procedure.
In particular, it is difficult to properly position or level a subsea template from a floating structure unless sea conditions are totally calm, a rare 3~2~2(~9~
occurrence in many offshore oil fields, particularly areas such as the North Sea. The levelliny procedure is, however, desirable and necessary in order that the tem plate or other related structure be properly oriented with respect to a floating drill rig, for example, which will be working through and utilizing the template. Moreover, a levelling procedure using a floating vessel such as a semi-submersible drilling rig, which may be constantly changing its elevation with respect to the seabed as a lQ result of sea conditions, has presented several problems in the art of installing subsea templates. However, the present invention provides an improved method and apparatus for installing and properly levelling a subsea template or the like using a floating drilling rig or a similar floating vessel equipped with hoisting apparatusO In particular, the present invention pertains to an improved method and apparatus using a semi-submersible floating drilling rig equipped with a heave- compensator or the like.
~'JM~RY OF THE INVENTION
In accordance with an aspect of the invention there is provided a method of installing one or more sub-sea templates at preselected sites on a seabed comprising the steps of providing a column stabilized variable draft semi-submersible drilling rig having at least one sub-mersible hull including means for supporting a template on said hull, a derrick, primary hoisting apparatus associated with said derrick for raising and lowering a riser through a moon pool on said rig spaced laterally from said hull, and secondary hoisting apparatus on said rig including cable means adapted to be connected to said template; at 1212~9~
least one submersible template adapted to have controllable positive and negative buoyancy; loading said template on said support means for said template using a crane and at least one of said hoisting apparatus on said rig to position said template over said support means; lowering said template onto said support means and ballasting said template to shift the weight of said template to said support means; transporting said template to a predeter-mined site on said seabed with said drilling rig; con-necting said template to said primary and secondary hoisting apparatus; venting ballast from said template to float said template free of said support means while controlling the position of said template with said hoisting apparatus; taking up said primary hoisting apparatus and slacking off said secondary hoisting apparatus to position said template under said moon pool;
and lowering said template to said seabed with said hoisting apparatus.
The present invention taken in conjunction with 20. the invention described in copending Canadian Patent Application Serial number 420,393 which was filed on January 27, 1983, will be described in detail hereinbelow with the aid of the accompanying drawlngs, in which:
Figure 1 is a plan view illustrating a template being loaded on to a semi-submersible column stabilized drilling rig with its main deck structure removed;
Figure 2 is a side elevation illustrating an intermediate step in loading the template on the drilling rig;
30. Figure 3 is a view similar to Figure 2 showing 1;~12099 the template being set on a hull of the drilling rig;
Figure 4 is a cutaway plan view of the semi-submersible drilling rig showing the location of several templates in their loaded positions;
Figure 5 is a view taken along the line 5-5 of Figure 4;
Figure 6 is a section view taken along the lines 6-6 of Figure 4;
Figure 7 is a side elevation showing a center loade`d template being lowered into position on the seabed;
Figure 8 is a perspective view of a portion of the drilling rig illustrating the levelling procedure;
Figure 9 is a plan view of the tensioning winch assembly taken from the line 9-9 of Figure 8;
Figure 10 is a side elevation showing one of the templates being unshipped from a hull of the semi-submersible drilling rig;
Figure 11 shows the installation of the template unshipped in Figure 10 at a predetermined site on the seabed;
~L2~1~Q9~
~igurc 12 is a central section view of a pile slip assembly uscd in conjunction with the template levelling procedure of the prcsent invention; and I;igure 13 is a section view taken along the line 13-13 of figure 12.
DESCRIPTION OF TlIE PREFERRED E~PODI~ENTS
In the description which follows like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawings are not neccssarily to scale and certain features of the invention may be e~caggerated in scale or shown in schematic form in the interest of clarity and conciseness.
Referring to Figures 1 through 3 there is illustrated a floating drilling rig of the type known in the art as a column stabilized semi-submersible rig and which is generally designated by the numeral 20. The rig 20 is of the variable draft type and comprises spaced apart longritudinal submersible hulls 22 which are interconnected by a suitable framework including a main deck structure 24 and spaced apart vertical corner columns 26. The rig 20 is adapted to include a drilling derrick 28, one or more deck mounted boom cranes 30 and n plurality of deck mounted powered drum type winches 32. The rig 20 is also adapted to include conventional drilling rig hoisting and drill stem rotating apparatus which will be described in further detail herein.
The hoisting apparatus may include a suitable dra~vworks, generally designated by the numeral 34 in Figures 2 and 3. In the views of l;igures 1 through 3 the drilling rig 20 has prcviously been positioned over a template 36 and has londed the template to be suspended from the derrick 28 by the aforcmentioned hoisting nppnrntus nlld betweell the spaced apart hulls 22. The template 36 is a skelctnl frnme type ~21209~9 structure which will be described in some further detail hercin in conjunction l~lith Figurc 8. The procedure of loading and securing the template 3G is described in tlle above referenced copcnding application which is assigneà to the assignee of the present invention.
Referring further to Figures 1 through 3 there is illustrated a procedure for loading additional templates, each designated by the numeral 38, which may be, for e~cample, foundation templates for a tension leg platform or may comprise further drilling templates or other suitable support structures to be deposited on and secured to the seabed. As shown in Figure 1, with the rig 20 suitably anchored in a calm harbor or other anchorage, the templates 38 are loaded on to the rig by transferring the templates from a barge 40 utilizing a floating crane 42. Referring briefly to Figures 5 and 6 the hulls 22 of the drilling rig are provided with support frames 44 on which are mounted spaced apart pinlike stab guides 46 which are adapted to receive in locating and supporting relationship spaced apart pile sleeves 48 forming part of the framework of the templates 38. Each of the guide sleeves 48 is provided with a downwardly facing cone portion 49 to facilitate location and interengagement of the stab guides with the respective sleeves. The templates 38 may also be provided ~vith preinstalled stab guides 50, Figure 6, locatable in stab receiving cones 51 welded to the framework 44.
Figure 2 illustrates the floating crnne 42 in position for loading a terrplate 38 on to one of the support frames on a hull 22 using a sling 60 as indicated. The template 38 is preferably provided with suitable fair leads, not shown, througll wllich guide cables 54 an(l 56 are run from respective ones of the winches 32 to tlle SUppOl't fl'Elme 44. A third one of the winches 32 includes a tuggcr line 58 sccured to ~2~ 39 the templnte 38 to uid in positioning the template over the support frame 44. us shovrn in Figure 3 the starboard side deck crane 30 is also brought into operation by bcillg connected to the tcmplate 38 during the final positioning process on the hull 22. The tcmplates 38 are of a type which include buoyant hull structures which may be floodable to control the buoyancy of the templates, respcctively.
Accordingly, the hulls 22 rmay be su~)merged to a point whcrein as each of the templates 38 is lowered into position on its associated support framing 44 the templnte is submerged to a floating position. At this point a suitable ballast control line is connected to the template and the template is ballasted until it is securely disposed on the frame 44 and until a certain amount of negative buoyancy is obtained. This may be measured by suitable weight indicator apparatus associated with the starboard deck crane 30.
After each respective one of the templates 38 are located in position on the associated hulls 22 the sling 60 associated Wit]l each template is left with the template for use by the rig hoisting apparatus to remove the template for installation at the preferred site. Each template 38 is loaded out from the barge 40 by the floating crane 42 and positioned on the rig 22 in the general arrangement indicated in figure 4. ~Vhen the rig 20 is loaded with tlle requisite number of templates including a template 36 suspended from the derriclc hoisting apparatus and also supported by suitable hanger apparatus, not shown, the rig can proceed to the offshore site for installation of the templates. Upon reaching the predetermined site for installation of the templates the rig 20 is anchored and deballasted in accordance with procedures known in the art, and dependent on sea conditions, preparatory to installation of the templates 36 and 38.
~LZ~2~99 Upon reaching the predetermined site for install-ation of the template 36, for example, the aforementioned template hanger mechanism is disconnected from the template and the template is lowered to a predetermined site on the seabed 17, as shown in Figure 7.
referring to Figure 8 the templa'ce 36 is shown in posltion on the seabed 17 suspended from the derrick 28 by apparatus lncluding an elongated riser string 62 and a flexible sling 6~ connected to respective points on the template 36 equidistant Erom t6e riser string and such that the center of gravity of the template 36 is substantially coaxial with the longitudinal axis of and below the riser string 62. The template 36 is provided with suitable inclinometer or other level indicating units generally designated by the numeral 37 positioned on the corners of the templates 36 adjacent spaced apart vertical pile receiving sleeves 39. The template 36 is also provided with an improved slip assembly associated with each of the pile sleeves 39, generally designc.ted by the numeral 41, for gripping respective elongated support columns or plles 43 which extend through the pile sleeves 39 and are driven and/or, cemented into the seabed 17. The template 36 is also provided with a hydraulic control pod and receptacle arrange-ment of a type known in the art oE subsea well apparatus and generally designated by the numeral 65 which is adapted to supply pressure Eluid to each of the slip assemblies 41 by way of a hose bundle or umbilical 66 lowered from the rig 20.
The procedure of lowering the template 36 into po.sition, and inserting the piles ~3 into the pile sleeves is described in United States Patent No 4,~35,108 which issued to J.E. Hampton on March 6, 19~ The aforernentioned application also describes a preferred method of positioning the template 36 prior to drilling and/or driving ~LZ~Z1~99 the piles 43. ~Yith the piles in position as shown in figure 8 and with the umbilical 66 run from the rig 20 to the template so that control of the slip assemblies 41 May be exercised from on board the rig 20, from a suitable submersible vessel, not shown, or by divers positioned to view the level condition of the template, the levelling procedure of the present invention can be carried out using improved upparatus in accordance with the present invcntion.
Refcrring further to Figure 8 it will be noted that the drill rig 20 is provided with a drill stem heave or motion compensator, generally designated by the numeral 70. The heave compensator 70 is of a type which is commercially available and one type of compensator which will operate in conjunction with the apparatus and method of the present invention is a heave or motion compensator manufactured by NL
Rig Equipment Division of NL Industries, Inc., Houston, Texas, under the trademark RllC~ER. The heave compensator 70 is suspended from the derrick hoisting apparatus including a crown block, not shown, and a cable arrangement reeved through a travelling block 71 connected to the compensator. The motion compensator 70 includes a hook 72 from which spaced apart elevator links or bails 74 are suspended and are connected to a suitable riser elevator 76. The riser string 62 is suspended from the elevator 76 and the upper end of the riser string also supports a unique tensioner assembly generally designated by the numeral 78.
The tensioner assembly 78 comprises a generally rectangular frame 79, see Figure 9, along one side of which is secured a short section of drill collar or sub 80. The frame 79 also supports a motor driven drum type winch or so called air tugger unit generally designated by the numeral 81. The winch 81 includes a winch _g _ ~Z~;21)99 drum on ~vhicll an elongntctl tensioner cable 82 is wound ond extcnds from the winch downwnrd through a rotary table 83, supported Oll the rig platrorm 33 with its kelly buslling removed. Thc riser string 62 nnd the cnble 82 extend downward through a moon pool 84 formed in the main declc 24 and the cable ~2 is trained over a sheave 85 suitably connected to structure associated with the deck 24 in the vicinity of the moon pool. As illustrated in Figure 8, the cable 82 extends downward from the rig 20 and is connected to one of the piles 43. The winch 81 is of a type having a pressure fluid operated motor 87 which is opePable to exert a substantially constant torque on the winch drum to maintain a constant predetermined tension in the cable 82. The winch motor 87 is adapted to be connected to a source of pressure air such as a compressor ~9 by way of a suitable flow control valve 99 indicated schematically in Figure 8. The tensioner assembly 78 is adapted to be supported by the the riser string 62 by suitably coupling the sub 80 to the upper end of the riser string. Accordingly, the tensioner assembly 78 is adapted to move with the riser string 62 relative to the rig 20 in response to movement of the heave compensator 70 to compensate for motion of the rig under certain sea conditions.
The improved levelling procedure previously mentioned is carried out after the piles 43 have been inserted in the pile sleeves 39 and the rig 20 is suitably positioned substantially over the center of the template 36 and the rig mooring system is norr~alized. ~Vith the rig 20 properly positioned the riser string 62 is run to a point above the template 36 and the sling assembly 64 i5 connected to the templnte.
The sling assembly 64 may be connected to the tcmplate by submarine divers dispatched from thc rig 20 or a suitable surface or submarine support vessel. The riser string 62 is disconnected from the heave ~2~2~g9 compcnsatol 70 nssuring tllat thcre is enough slnck in thc lifting slings G4 and set on a spider or slip ussembly, not shown, suitably sul)portcd by the rotary table 83.
At this point, an underwater television camera 91 can be run from the rig 20 on suitable guidelines 93 and focused on one of the piles 93 which is provided with suitable indicia such as spaced apart bench murks 94 so that movement of the template relative to the pile can be observed. Thc inclinometer units 37 can also be viewed by a television camera or the units may be of a type which are capable of transmitting signals directly to a suitable receiver on the rig 20, for example, to indicate the level condition of the template 36.
Chile divers are positioning the television camera 91 and/or the sling assembly 64 the tensioner assembly 78 can be suitably connected to the riser string witll the sub 80. The heave compensator 70 is then louvered to permit connection of the links 74 to the hool; 72 and the tensioner assembly 78 together with the riser string 62 is picked up by the rig hoisting apparatus 34. With the riser string 62 and the tensioner assembly 78 attached to the hook 72 the rig hoisting apparatus is raised until there is approximately, for example, eight feet of slack in the sling assembly 64. At this time, the tensioner line 82 may be lowered through the rotary table B3 to the moon pool, trained over the sheave 85 and run to the template 36 using, for example, a guideline, not shown, for the hydraulic control pod 65. The tensioner line 82 is then connected to one of the piles 43, as illustrated in Figure 8, and pressure air supplied to the hoist motor 87 at a pressure sufficient to support the weight of the tensioner line 82.
At this point, if the control pod 65 is not alretldy connected for supplying pressure fluid to the slip assemblies 41 this procedure is ~2~ 099 carried out in accor(lance with known tcchniques for connecting subsea hydraulic conncctor assemblies such ns the control pod 65 to mnting pod receptacles. The template 36 is now ready for the final levelling process whic}l comprises pressurizing the hydraulic system of the heave compensator 70 to position the compensator at about mid length its wor]cing stroke at which point it will normally tale up the weight of the template 36. The compensator 70 is then additionally pressurized until the template 36 is in a level plane as indicated by the inclinometer units 37. The tclevision camera 91 is then focused on the refcrence pile including the aforementioned indicia or bench marks 94 and movement of the template 36 relative to the pile is observed. The pressure air supply to the winch motor 87 is increased to increase the tension in the line 82 while observing the dampening effect on the relative movement between the template 36 and the aforementioned reference pile. Tension in the line 82 is adjusted until there is no relative movement between the template and the reference pile whereupon the template is level and motionless .
At this point the signals from the inclinometer units 37 are rechecked to ensure that the template is level within the allowable tolerance. If the template is level within tolerance the slip assemblies 41 are activated to grip the piles 43 to secure the template 36 to the piles. After activation of the slip assemblies 41 the rig hoisting apparatus is slacl;ed off to allow the weight of the template to be transferred on to the piles to set the slip assemblies and the inclinometer readings are rechecked to determine if tlle template is still level within tolerance. If the template level is not within tolerance the rig hoisting apparatus is operated to pick up on the travellillg block and the heave compensator 70 to take the weight of the template. The l2~Lza.~
slips 41 nre thcn activated to retract and thc ubove described procedure is carried out until the templatc is level and locked. At this time, the hydrnulic control pocl 65 can be retrieved and divers can be jumped to disconnect the sling assembly 64 and the tensioning line 82.
The tensioning line 82 may be reshncl~led to thc aforementioned guideline for the control pod 65 and retrieved to the moon pool then removed from the guideline and pulled back through the rotary table 83 by rotating the drum of the winch assembly 81. The riser string 62 and slings 64 may then be retrieved in a conventional manner.
Referring briefly to Figures 12 and 13 one of the slip assemblies 41 is illustrated in longitudinal central section view and wherein the figure illustrates to the left of the longitudinal centerline the slip assembly in its actuated position and to the right in its retracted position. The slip assembly 41 is described and claimed in a copending application filed concurrently herewith. However, certain features of the slip assembly will be described hereinbelow to facilitate a better understanding of the operation of the slip assemblyO
The slip assembly 41 is adapted to surround a pile 43 and to grippingly engage the pile as will be evident from the following description. The slip assembly 41 includes a frame comprising upper and lower ring shaped abutment plates 151 and 153, respectively, which are secured to and spaced apart by a cylindrical tubular wall member 152. An annular slip bowl 154 is disposed within the enclosure formed by the frame plates 151 and 153 and includes upper and lower plates 155 and 157 which are spaced apart by an outer cylindrical wall 158 and a conically tapered inner wall 160. The slip bowl 154 fits loosely between the plates 151 and 53 and is operable to center itself radially with respect to the longitudinal central axis 147 of the slip assembly.
~212099 The slip bowl 154 is also opcrnble to move axially and to tilt with respect to the central axis of the slip ussembly within the limits imposed by the frame plates 151 nnd 153 to accommodate some skew rnisalignmcnt of the pile Witll respect to the slip assembly.
S The lower plate 153 is supported by a cylindrical tubular frame member 161 which is sccured to a mounting ring 163 and defines a receptacle 145 in which the pile 43 is disposed together with an actuator for the slip assembly to be described hercin. The mounting ring 163 is supported by and secured to a base plate 164. The base plate 164 is supported on and secured to a sleeve 166 and a mounting flange 141 by a plurality of radially extending gusset plates 168. The slip assembly 41 is also provided with a cylindrical outer housing member 172 disposed around the frame portion formed by the plates 151 and 153 and fixed thereto by a plurality of radially projecting gusset plates 165. The gussets 165 are also secured to lower and upper conical plates 173 and 174, disposed below and above the housing member 172, as shown. The conical plate 174 forms a guide funnel for guiding a pile into the central receptacle in the frame of the slip assembly .
, The slip assembly 41 is also provided with a plurality of slip segments 176 which are disposed generally within the tapered slip bowl wall 160 in surrounding relationship to a pile. The segments 176 are p,referably formed of case hardened steel and are arranged to engage a pile as shown by the position of one of the slip segments on the left side of the central axis of the slip assembly in Figure 12. The slip segments 176 are each in the form of a circular segment or sector portion, are preferably provided eight in number and are interconnectcd and biascd outwnrdly ngainst the wall l60 by suitable 1212~99 annular resllicnt rctaining springs 175 fitted in cooperating grooves in the inner wall surfaces of the slip segments. The springs 175 may be formed as n resilient steel split ring, for example, not unlike a piston ring and operable to bias the slip scgments radially outward with respect to the axis 147 against the inner wall 160 of slip bowl. The segments 176 include a sloping outer wall 179 and a cylindrical inner wall 131, the latter being provided with a series of gripping teeth or serrations for gripping the outer surface of a pile. The segments 176 are also provided with slots 177 formed in the opposed sidewalls of the segMents. The slots 177 are adapted to rcceive oppositely projecting trunnions 178 which are attached to spaced apart brackets 180 mounted on a circular guide ring 182.
The slip assembly 41 further includes hydraulic actuator means comprising an annular hydraulic cylinder 183 having a lower head member 184 which is supported on an anti-friction ball bearing assembly including a ball housing 186 supported on the base plate 164 and adapted to include bearing elements 187. The cylinder 183 is adapted to form a chamber 185 having an annular piston 188 disposed therein and connccted to a piston rod portion 189 which is vertically extelldable and retractable with respect to the cylinder through an upper head member 190 nnd is in supportive relntionship with the guide ring 182.
Pressure fluid is supplied to cylinder 182 to act on opposed faces of the piston 188 through suitable conduits 191 and 192, which are connected to the receptacle of control pod 65.
In response to application of pressure fiuid into thc portion of annular cylinder cllamber 185 formed below the piston 188, the guide ring 182 is movcd upwardly which in turn movcs thc slip scgments 176 against the tapered inner wa}l 160 to force the scgments radially 121~C199 inwardly into gripping engagement with the outer circumferential surface of the pile 122. Moreover, the weight of the template acting through the slip segments 17G tends to self energize the segments into tighter gripping engagement with the pile.
The templates 38 may also be installed and levelled utilizing the procedure dcscribed above for installation and levelling of the template 36. However, the procedure for locating the templates 38 on the seabed is somewhat different due to their initial stowed position on respective ones of the hulls 22. After the rig 20 is located in a predetermined position for installation of one of the templates 38 the hulls 22 are controllably ballasted to be sure that the drnft of the, rig is sufficient to permit floating of the templates 38 after venting ballast from the respective ballast compartments and these templates.
Referring to Figures 10 and 11, one of the templates 38 is shown with a ballast vent line 100 connected thereto for venting ballast from one or more of the aforementioned compartments and a snubbing line 101 is run from the starboard deck crane 30, for example, and is connected to the template 38 utilizing sling assembly 60 similar to the sling 64. The snub line 101 is trained through a suitable opening in the deck 24 and over a deck mounted sheave, no shown. A lifting line 105 is run to the sling 60 from the lower end of the riser string 62, which is suspended from the rig hoisting apparatus, and is pulled up into the a-rea of the moon pool and suitably tensioned.
The template 38 is positioned under the moon pool by venting template ballast until the template floats free of the supporting and locating structure previously described and the lifting line 105 is tal;en up as the snub line 101 is slacked off until the template is in position under the moon pool. Additional transverse snub lines may be required ~212C~9~
depending on sea and current conditions. ~lowever, it is contemplate that it is possible to hold the template 38 in position by running a very tight lift assembly with five to ten foot seas and a slick tide condition.
The guidelines 54 and 56 are adjusted during the template positioning procedure nnd disconnectcd and cleared from the template prior to lowering the template to the seabed. The template 38 is then lowered into a predetermined position on the seabed 17 generally using the same procedure as used for positioning the template 36. The templates 38 may be levelled in the same manner as described above for the template 36 and also utilizing level instrumentation disposed on each one of the templates 38 in generally the same manner as used for the template 36.
Alternatively, the templates 38 may be levelled screw jacks, not shown, and a drill string lowered frc,m the hoisting apparatus of the rig 20 and the rotary table 83 and including a scre~l jack stinger assembly and bumper sub connected to the drill string with one drill collar connected to the string below the bumper sub. The riser string 62, lifting line 105 and sling 60 are first disconnected from the template "8 and derigged. The drill string may then be tripped down to the template on preinstalled guidelines, not shown, and an offset frame, also not shown. The levelling instrumentation is consulted to select the low point of the template and the drill collar is stabbed in and rotated until the template is levelled. The sequence is then repeated until the template is within .50 degrees of level, preferably. The drill string and screw jack stinger are then recovered and rigging fvr a pile driving hammer or other pile insertion procedures in commenced.
- All of the tcmplates 38 are installed using basicnlly the same procedure with modifications as required depending on the position of 12:1~0~
the declc cranes 30 with rcspcct to the locntion of the templates on the hulls 22.
Those slcilled in the art will apprcciate from the foregoing description that improvcd methods and apparatus have been developed for locating and levelling subsea structures such as drilling and foundation templates and other structures wllich must be held motiunless in preferrecl attitude on the seabed and installed by a floating vessel such as a semi-subMersible drilling rig or other vessel which is in a buoyant mode in or on the sea. f~lthough preferred embodiments of the invention have been described in detail herein those skilled in the art will also recognize that various substitutions and modifications may be made to the methods and apparatus of the invention without depnrting from the scope and spirit of the invention as recited in the appended claims .
A Method of Installi~gLOne or More Subsea Templates _._ This is a division of copending Canadian Patent Application Serial number 420,393 which was filed on January 27, 1983.
Field of the Invention The present invention pertains to a method and apparatus for installing and levelling subsea drilling and/or foundation templates and the like using a semi-submersible drilling rig equipped with a heave compensator.
lQ Background In the art of developing subsea installations for production of hydrocarbons from formations below the seabed there have been numerous types of installations placed on the seabed including structures known as templates and the like. These structures are typically characterized by large skeletal frames which are used for supporting well-head components and other apparatus used in conjunction with drilling and producing hydrocarbons from subsea wells.
- There are several problems associated with hand-ling the relatively large structures known as templates.
The process of loading, transporting and installing a sub-sea template using a semi-submersible drilling rig or other floating structure has presented several problems in the overall procedure of handling the templates from the point of embarkation to the final installation and levelling procedure.
In particular, it is difficult to properly position or level a subsea template from a floating structure unless sea conditions are totally calm, a rare 3~2~2(~9~
occurrence in many offshore oil fields, particularly areas such as the North Sea. The levelliny procedure is, however, desirable and necessary in order that the tem plate or other related structure be properly oriented with respect to a floating drill rig, for example, which will be working through and utilizing the template. Moreover, a levelling procedure using a floating vessel such as a semi-submersible drilling rig, which may be constantly changing its elevation with respect to the seabed as a lQ result of sea conditions, has presented several problems in the art of installing subsea templates. However, the present invention provides an improved method and apparatus for installing and properly levelling a subsea template or the like using a floating drilling rig or a similar floating vessel equipped with hoisting apparatusO In particular, the present invention pertains to an improved method and apparatus using a semi-submersible floating drilling rig equipped with a heave- compensator or the like.
~'JM~RY OF THE INVENTION
In accordance with an aspect of the invention there is provided a method of installing one or more sub-sea templates at preselected sites on a seabed comprising the steps of providing a column stabilized variable draft semi-submersible drilling rig having at least one sub-mersible hull including means for supporting a template on said hull, a derrick, primary hoisting apparatus associated with said derrick for raising and lowering a riser through a moon pool on said rig spaced laterally from said hull, and secondary hoisting apparatus on said rig including cable means adapted to be connected to said template; at 1212~9~
least one submersible template adapted to have controllable positive and negative buoyancy; loading said template on said support means for said template using a crane and at least one of said hoisting apparatus on said rig to position said template over said support means; lowering said template onto said support means and ballasting said template to shift the weight of said template to said support means; transporting said template to a predeter-mined site on said seabed with said drilling rig; con-necting said template to said primary and secondary hoisting apparatus; venting ballast from said template to float said template free of said support means while controlling the position of said template with said hoisting apparatus; taking up said primary hoisting apparatus and slacking off said secondary hoisting apparatus to position said template under said moon pool;
and lowering said template to said seabed with said hoisting apparatus.
The present invention taken in conjunction with 20. the invention described in copending Canadian Patent Application Serial number 420,393 which was filed on January 27, 1983, will be described in detail hereinbelow with the aid of the accompanying drawlngs, in which:
Figure 1 is a plan view illustrating a template being loaded on to a semi-submersible column stabilized drilling rig with its main deck structure removed;
Figure 2 is a side elevation illustrating an intermediate step in loading the template on the drilling rig;
30. Figure 3 is a view similar to Figure 2 showing 1;~12099 the template being set on a hull of the drilling rig;
Figure 4 is a cutaway plan view of the semi-submersible drilling rig showing the location of several templates in their loaded positions;
Figure 5 is a view taken along the line 5-5 of Figure 4;
Figure 6 is a section view taken along the lines 6-6 of Figure 4;
Figure 7 is a side elevation showing a center loade`d template being lowered into position on the seabed;
Figure 8 is a perspective view of a portion of the drilling rig illustrating the levelling procedure;
Figure 9 is a plan view of the tensioning winch assembly taken from the line 9-9 of Figure 8;
Figure 10 is a side elevation showing one of the templates being unshipped from a hull of the semi-submersible drilling rig;
Figure 11 shows the installation of the template unshipped in Figure 10 at a predetermined site on the seabed;
~L2~1~Q9~
~igurc 12 is a central section view of a pile slip assembly uscd in conjunction with the template levelling procedure of the prcsent invention; and I;igure 13 is a section view taken along the line 13-13 of figure 12.
DESCRIPTION OF TlIE PREFERRED E~PODI~ENTS
In the description which follows like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawings are not neccssarily to scale and certain features of the invention may be e~caggerated in scale or shown in schematic form in the interest of clarity and conciseness.
Referring to Figures 1 through 3 there is illustrated a floating drilling rig of the type known in the art as a column stabilized semi-submersible rig and which is generally designated by the numeral 20. The rig 20 is of the variable draft type and comprises spaced apart longritudinal submersible hulls 22 which are interconnected by a suitable framework including a main deck structure 24 and spaced apart vertical corner columns 26. The rig 20 is adapted to include a drilling derrick 28, one or more deck mounted boom cranes 30 and n plurality of deck mounted powered drum type winches 32. The rig 20 is also adapted to include conventional drilling rig hoisting and drill stem rotating apparatus which will be described in further detail herein.
The hoisting apparatus may include a suitable dra~vworks, generally designated by the numeral 34 in Figures 2 and 3. In the views of l;igures 1 through 3 the drilling rig 20 has prcviously been positioned over a template 36 and has londed the template to be suspended from the derrick 28 by the aforcmentioned hoisting nppnrntus nlld betweell the spaced apart hulls 22. The template 36 is a skelctnl frnme type ~21209~9 structure which will be described in some further detail hercin in conjunction l~lith Figurc 8. The procedure of loading and securing the template 3G is described in tlle above referenced copcnding application which is assigneà to the assignee of the present invention.
Referring further to Figures 1 through 3 there is illustrated a procedure for loading additional templates, each designated by the numeral 38, which may be, for e~cample, foundation templates for a tension leg platform or may comprise further drilling templates or other suitable support structures to be deposited on and secured to the seabed. As shown in Figure 1, with the rig 20 suitably anchored in a calm harbor or other anchorage, the templates 38 are loaded on to the rig by transferring the templates from a barge 40 utilizing a floating crane 42. Referring briefly to Figures 5 and 6 the hulls 22 of the drilling rig are provided with support frames 44 on which are mounted spaced apart pinlike stab guides 46 which are adapted to receive in locating and supporting relationship spaced apart pile sleeves 48 forming part of the framework of the templates 38. Each of the guide sleeves 48 is provided with a downwardly facing cone portion 49 to facilitate location and interengagement of the stab guides with the respective sleeves. The templates 38 may also be provided ~vith preinstalled stab guides 50, Figure 6, locatable in stab receiving cones 51 welded to the framework 44.
Figure 2 illustrates the floating crnne 42 in position for loading a terrplate 38 on to one of the support frames on a hull 22 using a sling 60 as indicated. The template 38 is preferably provided with suitable fair leads, not shown, througll wllich guide cables 54 an(l 56 are run from respective ones of the winches 32 to tlle SUppOl't fl'Elme 44. A third one of the winches 32 includes a tuggcr line 58 sccured to ~2~ 39 the templnte 38 to uid in positioning the template over the support frame 44. us shovrn in Figure 3 the starboard side deck crane 30 is also brought into operation by bcillg connected to the tcmplate 38 during the final positioning process on the hull 22. The tcmplates 38 are of a type which include buoyant hull structures which may be floodable to control the buoyancy of the templates, respcctively.
Accordingly, the hulls 22 rmay be su~)merged to a point whcrein as each of the templates 38 is lowered into position on its associated support framing 44 the templnte is submerged to a floating position. At this point a suitable ballast control line is connected to the template and the template is ballasted until it is securely disposed on the frame 44 and until a certain amount of negative buoyancy is obtained. This may be measured by suitable weight indicator apparatus associated with the starboard deck crane 30.
After each respective one of the templates 38 are located in position on the associated hulls 22 the sling 60 associated Wit]l each template is left with the template for use by the rig hoisting apparatus to remove the template for installation at the preferred site. Each template 38 is loaded out from the barge 40 by the floating crane 42 and positioned on the rig 22 in the general arrangement indicated in figure 4. ~Vhen the rig 20 is loaded with tlle requisite number of templates including a template 36 suspended from the derriclc hoisting apparatus and also supported by suitable hanger apparatus, not shown, the rig can proceed to the offshore site for installation of the templates. Upon reaching the predetermined site for installation of the templates the rig 20 is anchored and deballasted in accordance with procedures known in the art, and dependent on sea conditions, preparatory to installation of the templates 36 and 38.
~LZ~2~99 Upon reaching the predetermined site for install-ation of the template 36, for example, the aforementioned template hanger mechanism is disconnected from the template and the template is lowered to a predetermined site on the seabed 17, as shown in Figure 7.
referring to Figure 8 the templa'ce 36 is shown in posltion on the seabed 17 suspended from the derrick 28 by apparatus lncluding an elongated riser string 62 and a flexible sling 6~ connected to respective points on the template 36 equidistant Erom t6e riser string and such that the center of gravity of the template 36 is substantially coaxial with the longitudinal axis of and below the riser string 62. The template 36 is provided with suitable inclinometer or other level indicating units generally designated by the numeral 37 positioned on the corners of the templates 36 adjacent spaced apart vertical pile receiving sleeves 39. The template 36 is also provided with an improved slip assembly associated with each of the pile sleeves 39, generally designc.ted by the numeral 41, for gripping respective elongated support columns or plles 43 which extend through the pile sleeves 39 and are driven and/or, cemented into the seabed 17. The template 36 is also provided with a hydraulic control pod and receptacle arrange-ment of a type known in the art oE subsea well apparatus and generally designated by the numeral 65 which is adapted to supply pressure Eluid to each of the slip assemblies 41 by way of a hose bundle or umbilical 66 lowered from the rig 20.
The procedure of lowering the template 36 into po.sition, and inserting the piles ~3 into the pile sleeves is described in United States Patent No 4,~35,108 which issued to J.E. Hampton on March 6, 19~ The aforernentioned application also describes a preferred method of positioning the template 36 prior to drilling and/or driving ~LZ~Z1~99 the piles 43. ~Yith the piles in position as shown in figure 8 and with the umbilical 66 run from the rig 20 to the template so that control of the slip assemblies 41 May be exercised from on board the rig 20, from a suitable submersible vessel, not shown, or by divers positioned to view the level condition of the template, the levelling procedure of the present invention can be carried out using improved upparatus in accordance with the present invcntion.
Refcrring further to Figure 8 it will be noted that the drill rig 20 is provided with a drill stem heave or motion compensator, generally designated by the numeral 70. The heave compensator 70 is of a type which is commercially available and one type of compensator which will operate in conjunction with the apparatus and method of the present invention is a heave or motion compensator manufactured by NL
Rig Equipment Division of NL Industries, Inc., Houston, Texas, under the trademark RllC~ER. The heave compensator 70 is suspended from the derrick hoisting apparatus including a crown block, not shown, and a cable arrangement reeved through a travelling block 71 connected to the compensator. The motion compensator 70 includes a hook 72 from which spaced apart elevator links or bails 74 are suspended and are connected to a suitable riser elevator 76. The riser string 62 is suspended from the elevator 76 and the upper end of the riser string also supports a unique tensioner assembly generally designated by the numeral 78.
The tensioner assembly 78 comprises a generally rectangular frame 79, see Figure 9, along one side of which is secured a short section of drill collar or sub 80. The frame 79 also supports a motor driven drum type winch or so called air tugger unit generally designated by the numeral 81. The winch 81 includes a winch _g _ ~Z~;21)99 drum on ~vhicll an elongntctl tensioner cable 82 is wound ond extcnds from the winch downwnrd through a rotary table 83, supported Oll the rig platrorm 33 with its kelly buslling removed. Thc riser string 62 nnd the cnble 82 extend downward through a moon pool 84 formed in the main declc 24 and the cable ~2 is trained over a sheave 85 suitably connected to structure associated with the deck 24 in the vicinity of the moon pool. As illustrated in Figure 8, the cable 82 extends downward from the rig 20 and is connected to one of the piles 43. The winch 81 is of a type having a pressure fluid operated motor 87 which is opePable to exert a substantially constant torque on the winch drum to maintain a constant predetermined tension in the cable 82. The winch motor 87 is adapted to be connected to a source of pressure air such as a compressor ~9 by way of a suitable flow control valve 99 indicated schematically in Figure 8. The tensioner assembly 78 is adapted to be supported by the the riser string 62 by suitably coupling the sub 80 to the upper end of the riser string. Accordingly, the tensioner assembly 78 is adapted to move with the riser string 62 relative to the rig 20 in response to movement of the heave compensator 70 to compensate for motion of the rig under certain sea conditions.
The improved levelling procedure previously mentioned is carried out after the piles 43 have been inserted in the pile sleeves 39 and the rig 20 is suitably positioned substantially over the center of the template 36 and the rig mooring system is norr~alized. ~Vith the rig 20 properly positioned the riser string 62 is run to a point above the template 36 and the sling assembly 64 i5 connected to the templnte.
The sling assembly 64 may be connected to the tcmplate by submarine divers dispatched from thc rig 20 or a suitable surface or submarine support vessel. The riser string 62 is disconnected from the heave ~2~2~g9 compcnsatol 70 nssuring tllat thcre is enough slnck in thc lifting slings G4 and set on a spider or slip ussembly, not shown, suitably sul)portcd by the rotary table 83.
At this point, an underwater television camera 91 can be run from the rig 20 on suitable guidelines 93 and focused on one of the piles 93 which is provided with suitable indicia such as spaced apart bench murks 94 so that movement of the template relative to the pile can be observed. Thc inclinometer units 37 can also be viewed by a television camera or the units may be of a type which are capable of transmitting signals directly to a suitable receiver on the rig 20, for example, to indicate the level condition of the template 36.
Chile divers are positioning the television camera 91 and/or the sling assembly 64 the tensioner assembly 78 can be suitably connected to the riser string witll the sub 80. The heave compensator 70 is then louvered to permit connection of the links 74 to the hool; 72 and the tensioner assembly 78 together with the riser string 62 is picked up by the rig hoisting apparatus 34. With the riser string 62 and the tensioner assembly 78 attached to the hook 72 the rig hoisting apparatus is raised until there is approximately, for example, eight feet of slack in the sling assembly 64. At this time, the tensioner line 82 may be lowered through the rotary table B3 to the moon pool, trained over the sheave 85 and run to the template 36 using, for example, a guideline, not shown, for the hydraulic control pod 65. The tensioner line 82 is then connected to one of the piles 43, as illustrated in Figure 8, and pressure air supplied to the hoist motor 87 at a pressure sufficient to support the weight of the tensioner line 82.
At this point, if the control pod 65 is not alretldy connected for supplying pressure fluid to the slip assemblies 41 this procedure is ~2~ 099 carried out in accor(lance with known tcchniques for connecting subsea hydraulic conncctor assemblies such ns the control pod 65 to mnting pod receptacles. The template 36 is now ready for the final levelling process whic}l comprises pressurizing the hydraulic system of the heave compensator 70 to position the compensator at about mid length its wor]cing stroke at which point it will normally tale up the weight of the template 36. The compensator 70 is then additionally pressurized until the template 36 is in a level plane as indicated by the inclinometer units 37. The tclevision camera 91 is then focused on the refcrence pile including the aforementioned indicia or bench marks 94 and movement of the template 36 relative to the pile is observed. The pressure air supply to the winch motor 87 is increased to increase the tension in the line 82 while observing the dampening effect on the relative movement between the template 36 and the aforementioned reference pile. Tension in the line 82 is adjusted until there is no relative movement between the template and the reference pile whereupon the template is level and motionless .
At this point the signals from the inclinometer units 37 are rechecked to ensure that the template is level within the allowable tolerance. If the template is level within tolerance the slip assemblies 41 are activated to grip the piles 43 to secure the template 36 to the piles. After activation of the slip assemblies 41 the rig hoisting apparatus is slacl;ed off to allow the weight of the template to be transferred on to the piles to set the slip assemblies and the inclinometer readings are rechecked to determine if tlle template is still level within tolerance. If the template level is not within tolerance the rig hoisting apparatus is operated to pick up on the travellillg block and the heave compensator 70 to take the weight of the template. The l2~Lza.~
slips 41 nre thcn activated to retract and thc ubove described procedure is carried out until the templatc is level and locked. At this time, the hydrnulic control pocl 65 can be retrieved and divers can be jumped to disconnect the sling assembly 64 and the tensioning line 82.
The tensioning line 82 may be reshncl~led to thc aforementioned guideline for the control pod 65 and retrieved to the moon pool then removed from the guideline and pulled back through the rotary table 83 by rotating the drum of the winch assembly 81. The riser string 62 and slings 64 may then be retrieved in a conventional manner.
Referring briefly to Figures 12 and 13 one of the slip assemblies 41 is illustrated in longitudinal central section view and wherein the figure illustrates to the left of the longitudinal centerline the slip assembly in its actuated position and to the right in its retracted position. The slip assembly 41 is described and claimed in a copending application filed concurrently herewith. However, certain features of the slip assembly will be described hereinbelow to facilitate a better understanding of the operation of the slip assemblyO
The slip assembly 41 is adapted to surround a pile 43 and to grippingly engage the pile as will be evident from the following description. The slip assembly 41 includes a frame comprising upper and lower ring shaped abutment plates 151 and 153, respectively, which are secured to and spaced apart by a cylindrical tubular wall member 152. An annular slip bowl 154 is disposed within the enclosure formed by the frame plates 151 and 153 and includes upper and lower plates 155 and 157 which are spaced apart by an outer cylindrical wall 158 and a conically tapered inner wall 160. The slip bowl 154 fits loosely between the plates 151 and 53 and is operable to center itself radially with respect to the longitudinal central axis 147 of the slip assembly.
~212099 The slip bowl 154 is also opcrnble to move axially and to tilt with respect to the central axis of the slip ussembly within the limits imposed by the frame plates 151 nnd 153 to accommodate some skew rnisalignmcnt of the pile Witll respect to the slip assembly.
S The lower plate 153 is supported by a cylindrical tubular frame member 161 which is sccured to a mounting ring 163 and defines a receptacle 145 in which the pile 43 is disposed together with an actuator for the slip assembly to be described hercin. The mounting ring 163 is supported by and secured to a base plate 164. The base plate 164 is supported on and secured to a sleeve 166 and a mounting flange 141 by a plurality of radially extending gusset plates 168. The slip assembly 41 is also provided with a cylindrical outer housing member 172 disposed around the frame portion formed by the plates 151 and 153 and fixed thereto by a plurality of radially projecting gusset plates 165. The gussets 165 are also secured to lower and upper conical plates 173 and 174, disposed below and above the housing member 172, as shown. The conical plate 174 forms a guide funnel for guiding a pile into the central receptacle in the frame of the slip assembly .
, The slip assembly 41 is also provided with a plurality of slip segments 176 which are disposed generally within the tapered slip bowl wall 160 in surrounding relationship to a pile. The segments 176 are p,referably formed of case hardened steel and are arranged to engage a pile as shown by the position of one of the slip segments on the left side of the central axis of the slip assembly in Figure 12. The slip segments 176 are each in the form of a circular segment or sector portion, are preferably provided eight in number and are interconnectcd and biascd outwnrdly ngainst the wall l60 by suitable 1212~99 annular resllicnt rctaining springs 175 fitted in cooperating grooves in the inner wall surfaces of the slip segments. The springs 175 may be formed as n resilient steel split ring, for example, not unlike a piston ring and operable to bias the slip scgments radially outward with respect to the axis 147 against the inner wall 160 of slip bowl. The segments 176 include a sloping outer wall 179 and a cylindrical inner wall 131, the latter being provided with a series of gripping teeth or serrations for gripping the outer surface of a pile. The segments 176 are also provided with slots 177 formed in the opposed sidewalls of the segMents. The slots 177 are adapted to rcceive oppositely projecting trunnions 178 which are attached to spaced apart brackets 180 mounted on a circular guide ring 182.
The slip assembly 41 further includes hydraulic actuator means comprising an annular hydraulic cylinder 183 having a lower head member 184 which is supported on an anti-friction ball bearing assembly including a ball housing 186 supported on the base plate 164 and adapted to include bearing elements 187. The cylinder 183 is adapted to form a chamber 185 having an annular piston 188 disposed therein and connccted to a piston rod portion 189 which is vertically extelldable and retractable with respect to the cylinder through an upper head member 190 nnd is in supportive relntionship with the guide ring 182.
Pressure fluid is supplied to cylinder 182 to act on opposed faces of the piston 188 through suitable conduits 191 and 192, which are connected to the receptacle of control pod 65.
In response to application of pressure fiuid into thc portion of annular cylinder cllamber 185 formed below the piston 188, the guide ring 182 is movcd upwardly which in turn movcs thc slip scgments 176 against the tapered inner wa}l 160 to force the scgments radially 121~C199 inwardly into gripping engagement with the outer circumferential surface of the pile 122. Moreover, the weight of the template acting through the slip segments 17G tends to self energize the segments into tighter gripping engagement with the pile.
The templates 38 may also be installed and levelled utilizing the procedure dcscribed above for installation and levelling of the template 36. However, the procedure for locating the templates 38 on the seabed is somewhat different due to their initial stowed position on respective ones of the hulls 22. After the rig 20 is located in a predetermined position for installation of one of the templates 38 the hulls 22 are controllably ballasted to be sure that the drnft of the, rig is sufficient to permit floating of the templates 38 after venting ballast from the respective ballast compartments and these templates.
Referring to Figures 10 and 11, one of the templates 38 is shown with a ballast vent line 100 connected thereto for venting ballast from one or more of the aforementioned compartments and a snubbing line 101 is run from the starboard deck crane 30, for example, and is connected to the template 38 utilizing sling assembly 60 similar to the sling 64. The snub line 101 is trained through a suitable opening in the deck 24 and over a deck mounted sheave, no shown. A lifting line 105 is run to the sling 60 from the lower end of the riser string 62, which is suspended from the rig hoisting apparatus, and is pulled up into the a-rea of the moon pool and suitably tensioned.
The template 38 is positioned under the moon pool by venting template ballast until the template floats free of the supporting and locating structure previously described and the lifting line 105 is tal;en up as the snub line 101 is slacked off until the template is in position under the moon pool. Additional transverse snub lines may be required ~212C~9~
depending on sea and current conditions. ~lowever, it is contemplate that it is possible to hold the template 38 in position by running a very tight lift assembly with five to ten foot seas and a slick tide condition.
The guidelines 54 and 56 are adjusted during the template positioning procedure nnd disconnectcd and cleared from the template prior to lowering the template to the seabed. The template 38 is then lowered into a predetermined position on the seabed 17 generally using the same procedure as used for positioning the template 36. The templates 38 may be levelled in the same manner as described above for the template 36 and also utilizing level instrumentation disposed on each one of the templates 38 in generally the same manner as used for the template 36.
Alternatively, the templates 38 may be levelled screw jacks, not shown, and a drill string lowered frc,m the hoisting apparatus of the rig 20 and the rotary table 83 and including a scre~l jack stinger assembly and bumper sub connected to the drill string with one drill collar connected to the string below the bumper sub. The riser string 62, lifting line 105 and sling 60 are first disconnected from the template "8 and derigged. The drill string may then be tripped down to the template on preinstalled guidelines, not shown, and an offset frame, also not shown. The levelling instrumentation is consulted to select the low point of the template and the drill collar is stabbed in and rotated until the template is levelled. The sequence is then repeated until the template is within .50 degrees of level, preferably. The drill string and screw jack stinger are then recovered and rigging fvr a pile driving hammer or other pile insertion procedures in commenced.
- All of the tcmplates 38 are installed using basicnlly the same procedure with modifications as required depending on the position of 12:1~0~
the declc cranes 30 with rcspcct to the locntion of the templates on the hulls 22.
Those slcilled in the art will apprcciate from the foregoing description that improvcd methods and apparatus have been developed for locating and levelling subsea structures such as drilling and foundation templates and other structures wllich must be held motiunless in preferrecl attitude on the seabed and installed by a floating vessel such as a semi-subMersible drilling rig or other vessel which is in a buoyant mode in or on the sea. f~lthough preferred embodiments of the invention have been described in detail herein those skilled in the art will also recognize that various substitutions and modifications may be made to the methods and apparatus of the invention without depnrting from the scope and spirit of the invention as recited in the appended claims .
Claims
1. A method of installing one or more sub-sea templates at preselected sites on a seabed comprising the steps of:
providing a column stabilized variable draft semi-submersible drilling rig having at least one sub-mersible hull including means for supporting a template on said hull, a derrick, primary hoisting apparatus associated with said derrick for raising and lowering a riser through a moon pool on said rig spaced laterally from said hull, and secondary hoisting apparatus on said rig including cable means adapted to be connected to said template;
at least one submersible template adapted to have controllable positive and negative buoyancy;
loading said template on said support means for said template using a crane and at least one of said hoisting apparatus on said rig to position said template over said support means;
lowering said template onto said support means and ballasting said template to shift the weight of said template to said support means;
transporting said template to a predetermined site on said seabed with said drilling rig;
connecting said template to said primary and secondary hoisting apparatus;
venting ballast from said template to float said template free of said support means while controlling the position of said template with said hoisting apparatus;
taking up said primary hoisting apparatus and slacking off said secondary hoisting apparatus to position said template under said moon pool; and lowering said template to said seabed with said hoisting apparatus.
providing a column stabilized variable draft semi-submersible drilling rig having at least one sub-mersible hull including means for supporting a template on said hull, a derrick, primary hoisting apparatus associated with said derrick for raising and lowering a riser through a moon pool on said rig spaced laterally from said hull, and secondary hoisting apparatus on said rig including cable means adapted to be connected to said template;
at least one submersible template adapted to have controllable positive and negative buoyancy;
loading said template on said support means for said template using a crane and at least one of said hoisting apparatus on said rig to position said template over said support means;
lowering said template onto said support means and ballasting said template to shift the weight of said template to said support means;
transporting said template to a predetermined site on said seabed with said drilling rig;
connecting said template to said primary and secondary hoisting apparatus;
venting ballast from said template to float said template free of said support means while controlling the position of said template with said hoisting apparatus;
taking up said primary hoisting apparatus and slacking off said secondary hoisting apparatus to position said template under said moon pool; and lowering said template to said seabed with said hoisting apparatus.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8202491 | 1982-01-28 | ||
| GB8202491A GB2094856B (en) | 1981-01-28 | 1982-01-28 | Slip assembly for subsea template |
| CA000420393A CA1203228A (en) | 1982-01-28 | 1983-01-27 | Installation and levelling of subsea templates |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000420393A Division CA1203228A (en) | 1982-01-28 | 1983-01-27 | Installation and levelling of subsea templates |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1212099A true CA1212099A (en) | 1986-09-30 |
Family
ID=25669920
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000490015A Expired CA1212100A (en) | 1982-01-28 | 1985-09-04 | Method of installing, levelling and securing a subsea template |
| CA000490014A Expired CA1212099A (en) | 1982-01-28 | 1985-09-04 | Method of installing one or more subsea templates |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000490015A Expired CA1212100A (en) | 1982-01-28 | 1985-09-04 | Method of installing, levelling and securing a subsea template |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1212100A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109515737B (en) * | 2018-03-16 | 2022-04-19 | 陕西飞机工业（集团）有限公司 | Aircraft wing surface leveling device |
-
1985
- 1985-09-04 CA CA000490015A patent/CA1212100A/en not_active Expired
- 1985-09-04 CA CA000490014A patent/CA1212099A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1212100A (en) | 1986-09-30 |
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