Upgrading Offshore Wellhead Platforms

This disclosure generally relates to upgrading offshore wellhead platforms.

Offshore wellhead platforms are offshore structures with facilities to extract hydrocarbons from subsurface formations beneath the seabed. Offshore wellhead platforms can have multiple wells to extract the hydrocarbons from the target subsurface formations. Harsh offshore conditions can cause deterioration of an offshore wellhead platform after a period of time that may be shorter than the productive life of the wells supported by the offshore wellhead platform. In later stages of the wells' lifecycles, the wells may require additional topside artificial lift equipment to extend the productivity of the wells which the existing offshore wellhead platform structure may not be able to support.

This disclosure provides an approach to upgrading offshore wellhead platforms (WHPs) to maintain hydrocarbon production from wells with productive life remaining. Upgrade techniques that can be used to upgrade the offshore WHP include 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 specified design life of the upgraded facility; the structural integrity of the existing offshore WHP; whether additional future wells are needed to extract the hydrocarbons from the target formation; risk management of 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.

The approach of this disclosure includes identifying existing wells on an offshore wellhead platform that are capable to produce hydrocarbons 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.

Implementations of the systems and methods of this disclosure can provide various technical benefits. For example, this approach uses a holistic assessment of the existing WHP to determine a suitable and cost effective upgrade option considering factors including the hydrocarbon producing potential of existing wells, the structural integrity of the existing platform, and the offshore construction risks for installing a new heavy structure over existing wells. The cost for each of the upgrade techniques can be compared to the total cost of installing a new WHP, drilling new wells to the same subsurface targets, workover for Plug & Abandon (P&A) for existing wells, and the cost of removing the existing WHP.

The details of one or more embodiments of this approach are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of this approach will be apparent from the description and drawings, and from the claims.

Like reference symbols in the various drawings indicate like elements.

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.

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.

is a schematic of an example offshore wellhead platform (WHP). The WHPincludes a topside portionand a jacket portion. The topside portionis above the waterline, and the majority of the jacket portionis below the waterline. The topside portionincludes a Production Deck Module (PDM). The PDMcan include for example a hydrocarbon production (on main deck), an electrical equipment (on mezzanine deck), liquid collection (on cellar deck), a boat landingand a helideck. Mezzanine deckcan include electrical topside equipment such as electric switchgear, topside ESP equipment and transformers. Main deckcan include topside equipment such as hydrocarbon production manifold, metering, scraping (pigging) launcher and chemical injection system. Cellar deckcan include a slop tank and slop pumps.

The jacket portionincludes a subsea structure. Pilesare driven into the seabedto anchor the WHPin place. Multiple wellsare drilled into the subsurface formation to reach a hydrocarbon producing zone. The WHPcan be connected to a pipelineto transport hydrocarbons extracted from the hydrocarbon producing zone to a different location for refinement and processing. The WHPcan be connected to a composite subsea power cable (with fiber optic)to receive electric power from a nearby electrical distribution platform.

is a flow chart of a methodfor upgrading a wellhead platform (WHP). The methodevaluates 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.

The methodbegins by evaluating a WHP candidate to determine the best platform upgrade option (). 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.

The health of existing wells at the WHP upgrade candidate are assessed (). 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).

At block, 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 methodproceeds to block. 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 (). 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.

At block, 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.

At block, 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 methodproceeds to block. Otherwise, the methodproceeds to blockwhere 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.

At block, 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.

At block, if the existing WHP structure is able to accommodate new loads, then the methodproceeds to block. When the existing WHP cannot support new loads, then the methodproceeds to block.

At block, 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.

At block, 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). If the costs for the in-place upgrade are greater than the cost for installing a new platform, then the methodproceeds to blockwhere a new WHP is constructed, and new wells are drilled from the new WHP.

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.

At block, 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.

At block, 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 methodproceeds to blockwhere 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.

At block, 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).

At block, when two additional piles can be added to the existing WHP structure to accommodate new loads, then the methodproceeds to block. If the two additional piles cannot be added to the existing WHP structure, then the methodproceeds to block.

At block, 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.

At block, 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 blockwhere 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 methodproceeds to block.

At block, 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.

At block, when the existing wells with the strengthening clamps are capable of withstanding a threshold amount of horizontal loading, the methodproceeds to block. When the existing wells with the strengthening clamps are unable to withstand the threshold amount of horizontal loading, the methodproceeds to block.

At block, 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.

At block, 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 methodproceeds to blockto 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 methodproceeds to blockto construct a new WHP and drill new wells.

At block, 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.

At block, the offshore construction risk is determined to be either manageable or unmanageable. If the offshore construction risk is determined to be unmanageable, then the methodproceeds to blockto assess costs for an auxiliary platform upgrade. If offshore construction risk can be managed, then the method proceeds to block. 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.

At block, 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.

At block, 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+i−j<c+d), then the methodproceeds to blockto 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 methodproceeds to blockto assess the cost of performing an auxiliary platform upgrade.

illustrates an example in-place upgrade. The in-place upgradeincludes a new partial production deckand a new helideckwhich can be fabricated at the onshore fabrication yard. The new partial production deckand helideckare attached to and supported by the existing main deck structure. 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.

illustrates an example two additional piles upgrade. The two additional piles upgrade includes adding new pilesin the south side of the existing platform to support new loads. The new pilescan be tied to existing structureto reduce the stress on overloaded piles. New structurecan be installed toward the new pilesto house new modules and equipment. A helideckcan also be installed toward the new pilesto facilitate transportation of personnel or materials via boat and helicopter.

illustrates an example auxiliary platform upgrade. In the auxiliary platform upgrade, a new auxiliary platformis constructed near the existing WHP. The new auxiliary platformhouses new equipment, modules, and a helideck. The auxiliary platformis connected to the existing WHPby a bridge. The bridgecan facilitate movement of personnel, equipment, piping, etc. between the auxiliary platformand the existing WHP.

illustrates an installed slipover platform upgrade. The slipover platform upgrade includes demolishing the existing topside WHP while keeping existing wellsin place, removing the existing structure, installing a new slipover structurealong with new boat landings, and installing a new production deck modulealong with a helideck.

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.

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.

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.

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.

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.

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.

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.

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.

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.show examples of clamp designs,installed on existing well conductors,, respectively.

Risers and pipelines are disconnected from the existing structure and existing topside frames are demolished locally around the well treesproviding sufficient clearance to allow the safe removal of the existing topside and structure without compromising the integrity of the existing well conductors.