Upgrading Offshore Wellhead Platforms

Abstract

Systems and methods for upgrading an offshore wellhead platform include identifying existing wells on an offshore wellhead platform that are capable to produce hydrocarbons for a specified time period; determining that an existing platform structure of the offshore wellhead platform is unable to accommodate additional loads from new equipment and upgrades when at least 50% of the existing wells on the offshore wellhead platform are capable to produce hydrocarbons for the specified time period; determining that the existing platform structure is unable to accommodate addition of two piles to support the additional loads from new equipment and upgrades; determining that the existing wells will handle horizontal loads when the existing platform structure is removed; and performing a slipover platform upgrade to the offshore wellhead platform when the existing wells will handle horizontal loads.

Claims

1. A method for upgrading an offshore wellhead platform, the method comprising: identifying existing wells on an existing offshore wellhead platform that are capable to produce hydrocarbons for a specified time period; determining that an existing platform structure of the existing offshore wellhead platform is unable to accommodate additional loads from new equipment and upgrades when at least 50% of the existing wells on the existing offshore wellhead platform are capable to produce hydrocarbons for the specified time period; determining that the existing platform structure is unable to accommodate addition of two piles to support the additional loads from new equipment and upgrades; determining that the existing wells will handle horizontal loads when the existing platform structure is removed; and performing a slipover platform upgrade to the existing offshore wellhead platform when the existing wells will handle horizontal loads.

2. The method of claim 1, wherein determining the ability of the existing wells to handle horizontal load comprises determining the ability of the existing wells to handle the horizontal loads using clamps to strengthen the existing wells.

3. The method of claim 1, wherein performing the slipover platform upgrade comprises: demolishing the existing offshore wellhead platform while maintaining the existing wells in place; removing the existing platform structure; installing a new slipover platform structure; and installing a new production deck module on the new slipover platform structure.

4. The method of claim 3, further comprising installing new piles to support the slipover platform.

5. The method of claim 4, wherein installing the new piles comprises installing the new piles with safe distances from existing piles and/or in a same direction as the existing piles to avoid clashing between the new piles and the existing piles.

6. The method of claim 1, further comprising: determining that the existing platform structure is able to accommodate the additional loads from new equipment and upgrades; and performing an in-place platform upgrade when the existing platform structure is able to accommodate the additional loads.

7. The method of claim 6, wherein performing the in-place platform upgrade comprises installing new equipment on the existing offshore wellhead platform; and upgrading topside piping for the existing wells.

8. The method of claim 7, wherein the new equipment comprises one or more of an electric switchgear, topside electric submersible pump equipment, transformers, and chemical injection systems.

9. The method of claim 1, further comprising drilling new wells and constructing a new platform structure at a new location when the existing wells are unable to handle the horizontal loads or when fewer than half of the wells are capable to produce hydrocarbons for the specified time period.

10. The method of claim 9, further comprising plugging and abandoning the existing wells on the existing offshore wellhead platform; and removing the existing offshore wellhead platform to free the space for future development or undergo a de-commissioning phase.

11. The method of claim 1, further comprising: determining that the existing platform structure is able to accommodate the two additional piles to support the additional loads from the new equipment and upgrades; and performing a two additional piles upgrade to the existing offshore wellhead platform when the existing platform structure is unable to accommodate the additional loads and the existing platform structure is able to accommodate the two additional piles.

12. The method of claim 11, wherein performing the two additional piles upgrade comprises installing two piles on a side of the existing offshore wellhead platform to redistribute a current loading and support a new loading; and constructing a new portion for the existing offshore wellhead platform supported by the two additional piles.

13. The method of claim 1, further comprising performing an auxiliary platform upgrade when the existing platform structure is unable to accommodate the additional loads from new equipment and upgrades, the existing platform structure is unable to accommodate the two additional piles, and the existing wells are unable to handle horizontal loads.

14. The method of claim 13, wherein performing the auxiliary platform upgrade comprises building a new structure near the existing offshore wellhead platform to house new equipment for the existing offshore wellhead platform, wherein the new structure comprises a bridge to connect the new structure with the existing offshore wellhead platform.

15. A method for upgrading an offshore wellhead platform, the method comprising: identifying existing wells on an existing offshore wellhead platform that are capable to produce hydrocarbons for a specified time period; determining that half or more of the existing wells are capable to produce hydrocarbons for a specified time period; performing a slipover platform upgrade when a construction risk for performing the slipover platform upgrade is less than a threshold risk, wherein performing the slipover upgrade comprises: demolishing the existing offshore wellhead platform while maintaining the existing wells in place; removing an offshore wellhead platform structure; installing a slipover platform structure; and installing a new production deck module on the slipover platform structure.

16. The method of claim 15, further comprising installing isolation plugs in the existing wells prior to performing the slipover platform upgrade.

17. The method of claim 15, further comprising drilling additional wells to increase production of hydrocarbons.

18. The method of claim 17, further comprising installing a temporary conductor guide to assist conductor installations on the additional wells.

19. The method of claim 17, further comprising installing clamps to group well conductors for the existing wells prior to demolishing the existing offshore wellhead platform.

20. The method of claim 17, wherein installing the slipover platform comprises: lifting the slipover platform; and moving the slipover platform into place over the existing wells.

Description

DESCRIPTION OF DRAWINGS

[0007] FIG. 1 illustrates an offshore wellhead platform (WHP).

[0008] FIG. 2 is a flow chart for determining the appropriate option for upgrading an offshore WHP.

[0009] FIG. 3 illustrates a WHP upgraded in place.

[0010] FIG. 4 illustrates a WHP with two additional piles added to support a platform upgrade.

[0011] FIG. 5 illustrates an auxiliary platform upgrade.

[0012] FIG. 6 illustrates a slipover platform for upgrading an offshore WHP.

[0013] FIGS. 7A-7B illustrate examples of well clamp designs to strengthen well conductors during a slipover platform upgrade.

[0014] FIG. 8 illustrates an example of a lifting operation for lifting a support structure for a WHP.

[0015] FIG. 9 illustrates an example of a cutout in a slipover structure to accommodate existing well conductors.

[0016] FIG. 10 illustrates an example of the placement locations of new piles for a slipover structure relative to existing piles.

[0017] FIG. 11 illustrates an example of a pile clash study.

[0018] FIG. 12 illustrates an example a temporary well conductor guide.

[0019] FIG. 13 illustrates an example a frame infill around well conductors.

[0020] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0021] This disclosure provides an approach to upgrading offshore wellhead platforms (WHPs) to maintain hydrocarbon production from wells with significant productive life remaining. One of these upgrade techniques can be used to upgrade the wellhead platform (WHP) including an in-place upgrade, an additional two piles upgrade, an auxiliary platform upgrade and a slipover upgrade. The appropriate technique for upgrade can be determined based on several factors including the percentage of existing wells that can continue to produce hydrocarbons at target rates for a new design life of the upgraded facility; the structural integrity of the existing WHP; whether additional wells are needed to extract the hydrocarbons from the target formation; risk management during offshore construction activities; and/or a cost analysis of the various upgrade techniques. After determining an appropriate upgrade technique, the offshore WHP can be upgraded using the determined technique.

[0022] The approach of this disclosure includes identifying existing wells on an offshore WHP that are capable to produce hydrocarbons at target rates for a specified time period (e.g., 20 years). The existing platform of the offshore wellhead platform and the existing wells are assessed to determine that the existing platform structure is unable to accommodate additional loads from new equipment and upgrades when at least 50% of the existing wells are capable to produce hydrocarbons for the specified time period; the existing platform structure is unable to accommodate addition of two piles to support the additional loads from new equipment and upgrades; and the existing wells will handle horizontal loads when the existing platform structure is removed. A slipover platform upgrade is performed for the offshore wellhead platform when the existing wells will handle the horizontal loads, and a cost of performing the slipover platform upgrade is less than a cost of building a new offshore wellhead platform.

[0023] FIG. 1 is a schematic of an example offshore wellhead platform (WHP) 100. The WHP 100 includes a topside portion 102 and a jacket portion 104. The topside portion 102 is above the waterline 106, and the majority of the jacket portion 104 is below the waterline 106. The topside portion 102 includes a Production Deck Module (PDM) 108. The PDM 108 can include for example a hydrocarbon production (on main deck) 107, an electrical equipment (on mezzanine deck) 110, liquid collection (on cellar deck) 109, a boat landing 111 and a helideck 113. Mezzanine deck 110 can include electrical topside equipment such as electric switchgear, topside ESP equipment and transformers. Main deck 107 can include topside equipment such as hydrocarbon production manifold, metering, scraping (pigging) launcher and chemical injection system. Cellar deck 109 can include a slop tank and slop pumps.

[0024] The jacket portion 104 includes a subsea structure 112. Piles 114 are driven into the seabed 115 to anchor the WHP 100 in place. Multiple wells 116 are drilled into the subsurface formation to reach a hydrocarbon producing zone. The WHP 100 can be connected to a pipeline 120 to transport hydrocarbons extracted from the hydrocarbon producing zone to a different location for refinement and processing. The WHP 100 can be connected to a composite subsea power cable (with fiber optic) 121 to receive electric power from a nearby electrical distribution platform.

[0025] FIG. 2 is a flow chart of a method 200 for upgrading a wellhead platform (WHP). The method 200 evaluates well health, the existing WHP structure, and costs to determine a type of WHP upgrade to perform. Types of WHP upgrades include an in-place platform upgrade, a two additional piles upgrade, an auxiliary platform upgrade, and a slipover platform upgrade. In some cases, it may not be cost effective to upgrade the existing WHP, and a new platform can be constructed at a new location to produce hydrocarbons from a subsurface reservoir and the existing wells can be abandoned along with removing the existing WHP.

[0026] The method 200 begins by evaluating a WHP candidate to determine the best platform upgrade option (201). An existing WHP is a candidate for upgrade when for example, the existing WHP has a structural integrity problem and/or an artificial lift installation such as an electric submersible pump (ESP), gaslift, etc. is to be installed to extend the productive life of the existing wells at target rates. The artificial lift installation introduces additional topside equipment that requires space and introduces additional load to the existing WHP. Upgrading the existing WHP spends capital to extend the life of facilities either with upgrading existing structure or installing a new structure.

[0027] The health of existing wells at the WHP upgrade candidate are assessed (202). The existing wells can be assessed to determine production potential from the well for an upgraded facility design life (e.g., 10 years or more, 20 years or more). Some of the existing wells may have integrity, restriction or limitation during this extension time period. Example classifications of the wells include healthy wells, healthy wells that require one or more side-tracts to access a new target zone, and unhealthy wells. Healthy wells include wells that are capable to produce hydrocarbons at target rates for a specified time period (e.g., upgraded facility design life) without any well integrity issue. Healthy wells can include wells that may need one or more side-tracts to maintain hydrocarbon production for the specified time period. Unhealthy wells can be wells that may not be able to produce hydrocarbons at target rates for the specified time period. For example, an unhealthy well may have a well integrity problem such as a casing integrity issue that may require installing smaller casing preventing the installation of a larger ESP or be a slim well which cannot meet specified target rates. The un-healthy well can require plug & abandonment (P&A), slot recovery or slot replacement, and drilling new wells from the same well slot on the WHP using a deflecting conductor sleeve (DCS).

[0028] At block 204, if at least half of the existing wells at the WHP are identified as healthy and the wells can sustain hydrocarbon production for the facility design life, then the method 200 proceeds to block 206. If half or more of the wells are determined to be unhealthy or the wells cannot sustain hydrocarbon production for the facility design life, then a new WHP can be constructed, and new wells drilled from the new WHP (208). When the majority of existing wells are unhealthy, then the benefit of upgrading an existing WHP is diminished, and upgrading existing WHP can be more expensive than constructing a new WHP. The new platform structure can be constructed at an adjacent location to the existing WHP with the same or new subsurface targets as the existing WHP. When a new WHP is constructed, existing wells undergo P&A and the existing WHP structure is removed to free the space for future development or a decommissioning phase.

[0029] At block 206, the existing wells are further assessed to determine costs for drilling and workover operations (DWO) on existing wells, drilling new wells from a new WHP and the cost removal of the existing offshore structure after P&A existing wells. DWO and facilities costs include (a) workover healthy wells including side tracts, (b) drilling on unhealthy well slots with slot recovery or slot replacement technique after the unhealthy well P&A, (c) drilling all new wells from a new WHP at adjacent location with the same subsurface targets, and (d) workover costs for P&A of existing wells and removal of the existing WHP structure.

[0030] At block 210, the costs for DWO (a+b) are compared with the costs for (c) drilling all new wells from a new WHP at an adjacent location with the same subsurface targets and (d) workover costs for P&A of existing wells and removal of the existing offshore WHP structure. When the costs for DWO are less than the costs for drilling new wells from a new WHP and removal of the existing WHP (e.g., a+b<c+d), then the method 200 proceeds to block 212. Otherwise, the method 200 proceeds to block 208 where a new WHP is constructed, and new wells are drilled from the new WHP. Installing or constructing a new WHP also includes P&A of existing wells and demolishing and removing the existing WHP. Assessing the costs in this way can realize savings from DWO activities by avoiding potentially unnecessary costs of P&A of existing wells and removal of the existing WHP.

[0031] At block 212, the existing WHP structure is assessed to determine whether the structure can accommodate additional loads (e.g., vertical and horizontal loads) from new equipment and structural upgrades (e.g., topside piping, deck extension, boat landing, helideck, etc.). The WHP structure can be assessed according to industry standards such as the API Recommended Practice 2A-WSD (Planning, Designing, and Constructing Fixed Offshore Platforms-Working Stress Design). For example, a structure that can accommodate the additional loads from new equipment and structural upgrades includes each pile on the structure having a factor of safety (FOS) above the minimum FOS value specified in the API RP 2A-WSD based on a threshold amount of additional loading.

[0032] At block 214, if the existing WHP structure is able to accommodate new loads, then the method 200 proceeds to block 216. When the existing WHP cannot support new loads, then the method 200 proceeds to block 222.

[0033] At block 216, costs (e) associated with performing an in-place (in-situ) upgrade of the existing WHP are determined. An in-place WHP upgrade includes adding new equipment and upgrading facilities such as topside piping, deck extensions, a boat landing, a helideck at the existing WHP without upgrading or strengthening the existing structure. An in-place upgrade of the existing WHP will be discussed in more detail in reference to FIG. 3.

[0034] At block 218, the costs for performing an in-place upgrade (a+b+e) are compared with the costs for constructing a new platform, drilling new wells from the new platform, and removing the existing structure (c+d). If the costs for performing the in-place upgrade are less than the costs for installing a new platform (a+b+e<c+d), then the in-place platform upgrade is performed (block 220). If the costs for the in-place upgrade are greater than the cost for installing a new platform, then the method 200 proceeds to block 208 where a new WHP is constructed, and new wells are drilled from the new WHP.

[0035] In some implementations, an in-place platform upgrade can be the cheapest platform upgrade option; however, an in-place upgrade can have longer WHP shutdown for offshore activities. In these implementations, the cost of lost production from the WHP can be included in the cost comparison by estimating the shutdown period for the in-place upgrade compared with the shutdown period for the new platform.

[0036] At block 222, the feasibility and cost (f) of structurally strengthening the existing WHP is determined. In some cases, strengthening the structure of the existing WHP may be required for some corroded and/or cracked structural members. In this case, installing clamps can include diving operations to strengthen the structure members beneath the water's surface.

[0037] At block 224, when strengthening the WHP structure is feasible and the costs of strengthening the existing WHP structure and performing an in-place platform upgrade are less than the costs for installing a new platform and removing the existing structure (a+b+e+f<c+d), the method 200 proceeds to block 220 where the in-place platform upgrade is performed. When strengthening the existing WHP structure is not feasible or the costs of strengthening the existing WHP structure and performing the in-place platform exceed the cost for installing a new platform, the method proceeds to block 226.

[0038] At block 226, the existing WHP is assessed to determine if two additional piles can be added to the existing WHP structure to accommodate new loads and redistribute the load on existing piles (e.g., by changing the center of gravity of the existing WHP and reducing the loads on the overloaded piles toward the two new piles).

[0039] At block 228, when two additional piles can be added to the existing WHP structure to accommodate new loads, then the method 200 proceeds to block 230. If the two additional piles cannot be added to the existing WHP structure, then the method 200 proceeds to block 236.

[0040] At block 230, the cost (g) for adding the two additional piles is determined along with the costs for upgrading the existing topside equipment on the existing WHP or the cost of installing a new production deck module. In some implementations, a new production deck module can be fabricated onshore to reduce offshore construction work and costs.

[0041] At block 232, the costs of adding the two additional piles are compared with the costs for installing a new WHP. When the costs of adding the two additional piles is less than the cost for installing a new WHP and removing the existing structure (a+b+g<c+d), then the method proceeds to block 234 where the two additional piles upgrade is performed. If the cost for adding the two additional piles exceeds the cost for installing a new platform, the method 200 proceeds to block 236.

[0042] At block 236, the existing wells are assessed to determine if the wells can sustain horizontal loads associated with a slipover platform upgrade. Existing wells may not have been designed to sustain horizontal loading in the offshore environment without a WHP structure. In implementations where a deflecting conductor sleeve (DCS) has been installed during a slot recovery operation, the DCS can cause additional horizontal loadings that cause a potential twisting force on the existing wells when the existing WHP is demolished and removed. In some implementations, a strengthening clamp can be designed to keep the existing well conductors in a group before demolishing the existing structure to improve the horizontal loading capability of the existing wells.

[0043] At block 238, when the existing wells with the strengthening clamps are capable of withstanding a threshold amount of horizontal loading, the method 200 proceeds to block 246. When the existing wells with the strengthening clamps are unable to withstand the threshold amount of horizontal loading, the method 200 proceeds to block 240.

[0044] At block 240, the cost (h) for performing an auxiliary platform upgrade is determined. An auxiliary platform upgrade can include upgrading the existing topside equipment on the platform, installing the auxiliary platform including a boat landing and helideck, and a bridge connection between the auxiliary platform and the existing WHP. The bridge connection provides personnel, boat, and helicopter access to the existing platform. Generally, an auxiliary platform upgrade can be more expensive than slipover platform upgrades; however, the auxiliary platform upgrade can be performed at an existing WHP that otherwise could not be upgraded due to horizontal loading during the upgrade process or offshore construction risk cannot be managed.

[0045] At block 242, the cost of performing an auxiliary platform upgrade is compared with the cost of building a new WHP and drilling new wells from it. When the cost of performing the auxiliary platform upgrade is less than the cost of installing a new WHP, drilling new wells and removing the existing structure (a+b+h<c+d), then the method 200 proceeds to block 244 to perform the auxiliary platform upgrade. If the cost of performing the auxiliary platform upgrade exceeds the cost of installing a new WHP, drilling new wells and removing the existing structure, the method 200 proceeds to block 208 to construct a new WHP and drill new wells.

[0046] At block 246, a slipover structure is designed to replace the existing WHP. The design of the slipover structure can avoid clashing with existing piles. The structure design can also include safe clearances with existing wells to minimize offshore construction risk during slip-over the new structure over existing wells. Offshore construction risk of performing the slipover structure can also be assessed with the installation contractors. For example, for deeper water depth, the offshore construction risk can be assessed for two lifting methods (1) a single lift and (2) a multi-lift based on the capacity and/or length of crane barges available during the estimated construction window.

[0047] At block 248, the offshore construction risk is determined to be either manageable or unmanageable. If the offshore construction risk is determined to be unmanageable, then the method 200 proceeds to block 240 to assess costs for an auxiliary platform upgrade. If offshore construction risk can be managed, then the method proceeds to block 250. An example of offshore construction risk includes when the hazards associated with lifting the new slip-over structure over existing wells which have been plugged previously.

[0048] At block 250, the cost (i) for performing a slipover upgrade is determined based on the slipover design and offshore construction risk. The cost benefit (j) of having additional spare well slots with the slipover platform (as compared with the existing WHP) can offset a portion of the cost (i) for performing the slipover upgrade.

[0049] At block 252, the cost for performing the slipover upgrade is compared with the cost of installing a new WHP and drilling new wells and removing the existing structure. If the cost for performing the slipover upgrade is less than the cost for installing a new platform and drilling new wells and removing the existing structure (a+b+ij<c+d), then the method 200 proceeds to block 254 to perform the slipover platform upgrade. If the cost for performing the slipover upgrade exceeds the cost for installing a new WHP and drilling new wells, then the method 200 proceeds to block 240 to assess the cost of performing an auxiliary platform upgrade.

[0050] FIG. 3 illustrates an example in-place upgrade 300. The in-place upgrade 300 includes a new partial production deck 302 and a new helideck 304 which can be fabricated at the onshore fabrication yard. The new partial production deck 302 and helideck 304 are attached to and supported by the existing main deck structure 306. Alternatively, or additionally, an in-place upgrade can include installing all new equipment and upgrading the topside piping offshore. The new equipment can include electric switchgear, topside electric submersible pump (ESP) equipment, transformers and chemical injection system. The topside upgrade can include upgrading topside piping, emergency shutdown (ESD) and supervisory control and data acquisition (SCADA) equipment.

[0051] FIG. 4 illustrates an example two additional piles upgrade 400. The two additional piles upgrade includes adding new piles 402 in the south side of the existing platform to support new loads. The new piles 402 can be tied to existing structure 404 to reduce the stress on overloaded piles. New structure 406 can be installed toward the new piles 402 to house new modules and equipment. A helideck 408 can also be installed toward the new piles 402 to facilitate transportation of personnel or materials via boat and helicopter.

[0052] FIG. 5 illustrates an example auxiliary platform upgrade 500. In the auxiliary platform upgrade 500, a new auxiliary platform 502 is constructed near the existing WHP 504. The new auxiliary platform 502 houses new equipment, modules, and a helideck 506. The auxiliary platform 502 is connected to the existing WHP 504 by a bridge 508. The bridge 508 can facilitate movement of personnel, equipment, piping, etc. between the auxiliary platform 502 and the existing WHP 504.

[0053] FIG. 6 illustrates an installed slipover platform upgrade 600. The slipover platform upgrade includes demolishing the existing topside WHP while keeping existing wells 601 in place, removing the existing structure, installing a new slipover structure 602 along with new boat landings 603, and installing a new production deck module 604 along with a helideck 605.

[0054] The slipover platform upgrade technique can be the most cost-effective option for upgrading an existing WHP when the following conditions are met: more than 50% of existing wells are healthy and able to sustain hydrocarbon production at target rates for the specified facility design life of the new structure, the existing offshore structure is not able to accommodate additional loads (e.g., from topside, boat landing and helideck upgrades) and it cannot be upgraded by strengthening, and additional wells or slots can be utilized on the WHP upgrade candidate.

[0055] The slipover platform upgrade can be feasible when certain technical challenges can be resolved. For example, the existing well conductors are able to handle horizontal load from offshore environment, clash between existing piles and new piles can be avoided, and high-risk offshore construction activities can be managed.

[0056] In some implementation, existing well conductors are not designed to withstand horizontal loading in an offshore environment when the WHP is removed. If a DCS is present on a slot recovery, further horizontal loads can be applied to the well conductors resulting in potential twisting of the existing wells when the existing WHP is demolished and removed before the new slipover structure is installed. To strengthen the existing wells, a clamp can be installed on the existing well conductors to group the well conductors together before demolishing the existing WHP.

[0057] To reduce clashes between existing WHP piles and new piles for the slipover structure, the new slipover structure can be designed with enough clearance with existing wells to allow safe slipover structure deployment. The slipover structure can be lifted and slipped over the existing wells during deployment. The size and location of the slipover structure can be designed to reduce clashing with existing piles. Also, the direction of the new piles can be designed to follow the direction of the old piles to reduce clashing.

[0058] During installation of the slipover structure, the high-risk offshore construction activities can be managed to reduce the likelihood of damage to the existing wells while the new structure is lifted and slipped over the existing wells. For example, isolation plugs can be installed in each well before starting the offshore construction activities and all lift attachment points (e.g., pad-eyes) can be checked with non-destructive testing (NDT) methods to verify structural integrity to safely lift the existing WHP and the new slipover structures over the existing wells.

[0059] Performing a slipover platform upgrade in deep water can include significant risks. An offshore constructability and risk assessment can be performed to determine whether to use a long crane barge for a single lift or use a smaller crane barge using dual lifts to reduce the risks.

[0060] New well conductors can be installed from the new slipover platform after the slipover platform upgrade has been completed. For example, the new slipover platform structure can be positioned with a safe clearance distance from the existing well conductors to reduce the likelihood of damaging the existing well conductors during the slip over operation. A safe clearance distance includes, for example, a distance that reduces the likelihood of contact between the new slipover platform structure and the existing well conductors during installation of the new slipover platform structure. After the new slipover structure is close to the seabed, the safe clearance can be utilized and the new slipover structure can be moved slightly to the north, south, west or east direction depending on desired locations to install one or more new well conductors. After the new slipover structure sits on the seabed, the area created for the safe clearance distance can be used to install the additional well conductors. For example, if additional well conductors are in the south side, then the new slipover structure can be moved slightly to the south side to provide space for additional well conductor installations. Temporary topside conductor guides can also be installed to assist the installation of additional well conductors. The location of the conductor guide will depend on the location of the additional conductors (e.g., north, south, east or west of the WHP). The location of additional well conductors may lead to the possibility of installing permanent conductor guides as part of the new slipover structure which will reduce offshore construction time and costs. After removal of the temporary conductor guide, the temporary conductor guide can be used for another slipover upgrade at a different location.

[0061] Demolition of an existing WHP platform includes performing a subsea survey to plan the deployment of the cutting tools and divers as well as checking for any unforeseen items that could potentially hamper the demolition and installation operations. The survey can also confirm the existing pile batters and pile locations relative to the existing well conductors.

[0062] Any additional structural strengthening that might be required for the removal of the existing topside and/or the structure can be designed and fabricated (e.g., installing temporary clamps to connect all conductors together and enhance their structural stiffness for the period during which the well conductors will be free standing until the installation of the new structure. FIGS. 7A-7B show examples of clamp designs 700, 710 installed on existing well conductors 702, 712, respectively.

[0063] Risers and pipelines are disconnected from the existing structure and existing topside frames are demolished locally around the well trees 704 providing sufficient clearance to allow the safe removal of the existing topside and structure without compromising the integrity of the existing well conductors.

[0064] The helideck is removed using existing pad-eyes where available. The existing pad-eyes can be assessed using NDT and analysis to verify the safe removal of the helideck. If necessary, new lifting aids can be designed and fabricated for the removal operations.

[0065] Structural members around the well conductors above and below the water level are removed. Sufficient clearance can be provided between the well conductors and the structural framing to allow for the structural removal without compromising the integrity of the conductors and/or well trees.

[0066] Marine growth (MG) is removed to allow divers to cut the steel work as necessary and remove any debris that could potentially hamper the demolition and/or installation operations. The piles can be cut at approximately 1.5 meters below the mudline. Pits as a result of the structure and pile removal can be re-filled and levelled using the material from the seabed.

[0067] The locations of the removed piles can be marked using markers or pegs. These markers can be positioned such that they clearly indicate the exact positions of the removed piles above the mudline. These markers or pegs can be used to help position the slipover structure at the required location and away from the existing piles below the mudline. Once the jacket has been installed and piles driven, the markers can be removed.

[0068] Lift the structure using existing pad-eyes where available after performing all the necessary NDT work to ensure the integrity of the existing lifting aids. New lifting aids can be designed and fabricated as necessary. FIG. 8 illustrates an example of lifting an existing structure 800 using a spreader bar 802. The removed topside and existing structure can be offloaded onto a material barge, sea-fasting as necessary and transported safely to an onshore collection yard.

[0069] The seabed can be inspected to verify that it is free from debris and an even condition following the removal of the existing structure. Subsea surveys can be performed to verify that the seabed is suitable for the installation of the new slipover structure.

[0070] A new slipover structure installation starts by lifting the slipover structure over the existing well conductors and lowering the slipover structure into position with the well conductors located central to a cut-out portion until the structure clears the well trees in a vertical plane. FIG. 9 illustrates an example of cutouts 902 in the well structure 900 and the clearance to the existing well conductors 904.

[0071] Once the structure has cleared the well trees, the structure can be maneuvered in the horizontal plane until it reaches the sitting position. The structure can be re-oriented to allow for the installation of additional well conductors. The new slipover structure can be moved slightly to the north, south, west or east direction depends to where several new well conductors will be installed.

[0072] Once the structure has been positioned with installation tolerances to avoid pile clashing. The orientation of the new slipover structure can be similar to the demolished structure. FIG. 10 illustrates an example of the existing location of four old piles 1002 and the installation location of four new piles 1004 including installation tolerances to avoid clashing between the old piles 1002 and the new piles 1004. Safe clearance distances are used between the old piles 1002 and the new piles 1004 to avoid contact between the new piles 1004 and the old piles 1002.

[0073] FIG. 11 illustrates an example of a pile clash study to confirm the safe position of the new slipover structure 1100. The pile clash study considers the locations of the existing piles 1102, the new piles 1104, the existing conductors 1106, and new conductors 1108.

[0074] The new piles can be driven into the seabed to the designed penetration depths. Once the new structure is firmly in position, the pile crown connection can be welded in place. Additional well conductors can be installed and driven into the seabed to the required penetration depths.

[0075] FIG. 12 illustrates an example of a temporary conductor guide 1200 that can be used to guide the installation of new well conductors 1202.

[0076] FIG. 13 illustrates an example of infill frame 1300 that can be installed to fill the cutout 1302 on the deck 1304 after the additional conductors 1306 are installed, the topside slipover platform structure 600 can then be installed on the slipover structure 602 as shown in FIG. 6.

[0077] A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

EXAMPLES

[0078] In an example implementation, a method for upgrading an offshore wellhead platform includes identifying existing wells on an existing offshore wellhead platform that are capable to produce hydrocarbons for a specified time period; determining that an existing platform structure of the existing offshore wellhead platform is unable to accommodate additional loads from new equipment and upgrades when at least 50% of the existing wells on the existing offshore wellhead platform are capable to produce hydrocarbons for the specified time period; determining that the existing platform structure is unable to accommodate addition of two piles to support the additional loads from new equipment and upgrades; determining that the existing wells will handle horizontal loads when the existing platform structure is removed; and performing a slipover platform upgrade to the existing offshore wellhead platform when the existing wells will handle horizontal loads.

[0079] In an aspect combinable with the example implementation, determining the ability of the existing wells to handle horizontal load includes determining the ability of the existing wells to handle the horizontal loads using clamps to strengthen the existing wells.

[0080] In another aspect combinable with any of the previous aspects, performing the slipover platform upgrade includes demolishing the existing offshore wellhead platform while maintaining the existing wells in place; removing the existing platform structure; installing a new slipover platform structure; and installing a new production deck module on the new slipover platform structure.

[0081] Another aspect combinable with any of the previous aspects includes installing new piles to support the slipover platform.

[0082] In another aspect combinable with any of the previous aspects, installing the new piles includes installing the new piles with safe distances from existing piles and/or in a same direction as the existing piles to avoid clashing between the new piles and the existing piles.

[0083] Another aspect combinable with any of the previous aspects includes determining that the existing platform structure is able to accommodate the additional loads from new equipment and upgrades; and performing an in-place platform upgrade when the existing platform structure is able to accommodate the additional loads.

[0084] In another aspect combinable with any of the previous aspects, performing the in-place platform upgrade includes installing new equipment on the existing offshore wellhead platform; and upgrading topside piping for the existing wells.

[0085] In another aspect combinable with any of the previous aspects, the new equipment includes one or more of an electric switchgear, topside electric submersible pump equipment, transformers, and chemical injection systems.

[0086] Another aspect combinable with any of the previous aspects includes drilling new wells and constructing a new platform structure at a new location when the existing wells are unable to handle the horizontal loads or when fewer than half of the wells are capable to produce hydrocarbons for the specified time period.

[0087] Another aspect combinable with any of the previous aspects includes plugging and abandoning the existing wells on the existing offshore wellhead platform; and removing the existing offshore wellhead platform to free space for future development or undergo a de-commissioning phase.

[0088] Another aspect combinable with any of the previous aspects includes determining that the existing platform structure is able to accommodate the two additional piles to support the additional loads from the new equipment and upgrades; and performing a two additional piles upgrade to the existing offshore wellhead platform when the existing platform structure is unable to accommodate the additional loads and the existing platform structure is able to accommodate the two additional piles.

[0089] In another aspect combinable with any of the previous aspects, performing the two additional piles upgrade includes installing two piles on a side of the existing offshore wellhead platform to redistribute a current loading and support a new loading; and constructing a new portion for the existing offshore wellhead platform supported by the two additional piles.

[0090] Another aspect combinable with any of the previous aspects includes performing an auxiliary platform upgrade when the existing platform structure is unable to accommodate the additional loads from new equipment and upgrades, the existing platform structure is unable to accommodate the two additional piles, the existing wells are unable to handle horizontal loads.

[0091] In another aspect combinable with any of the previous aspects, performing the auxiliary platform upgrade includes building a new structure near the existing offshore wellhead platform to house new equipment for the existing offshore wellhead platform, where the new structure includes a bridge to connect the new structure with the existing offshore wellhead platform.

[0092] In another example implementation, a method for upgrading an offshore wellhead platform includes identifying existing wells on an existing offshore wellhead platform that are capable to produce hydrocarbons for a specified time period; determining that half or more of the existing wells are capable to produce hydrocarbons for a specified time period; performing a slipover platform upgrade when a construction risk for performing the slipover platform upgrade is less than a threshold risk, where performing the slipover upgrade includes demolishing the existing offshore wellhead platform while maintaining the existing wells in place; removing an existing offshore wellhead platform structure; installing a slipover platform structure; and installing a new production deck module on the slipover platform structure.

[0093] An aspect combinable with the example implementation includes installing isolation plugs in the existing wells prior to performing the slipover platform upgrade.

[0094] Another aspect combinable with any of the previous aspects includes drilling additional wells to increase production of hydrocarbons.

[0095] Another aspect combinable with any of the previous aspects includes installing a temporary conductor guide to assist conductor installations on the additional wells.

[0096] Another aspect combinable with any of the previous aspects includes installing clamps to group well conductors for the existing wells prior to demolishing the existing offshore wellhead platform.

[0097] In another aspect combinable with any of the previous aspects, installing the slipover platform includes lifting the slipover platform; and moving the slipover platform into place over the existing wells.