SeaStar Mini TLP Paper

August 13, 2017 | Author: Sean Middleton | Category: Gas Compressor, Pump, Hvac, Pipeline Transport, Buoyancy
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OTC 14123 Typhoon SeaStar TLP R. B. Matten, M.J.Provost, Atlantia Offshore Limited, S. Pastor, BHP Billiton Petroleum (Americas) Inc and W. S. Young , Chevron

Copyright 2002, Offshore Technology Conference This paper was prepared for presentation at the 2002 Offshore Technology Conference held in Houston, Texas U.S.A., 6 –9 May 2002. This paper was selected for presentation by the OTC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviejed by the Offshore Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Offshore Technology Conference or its officers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented.

Abstract This paper describes the design, fabrication, installation and hook-up and commissioning of the Typhoon SeaStar. The Typhoon SeaStar TLP was installed in 2097’ water depth in Green Canyon 236/237 and produced First Oil on July 28th 2001, just eighteen months after project sanction. The Atlantia scope of project was completed on budget and on schedule. A reimbursable contract with a cost based management fee proved to be effective in maintaining alignment between Owner and Contractor to minimize changes and avoid cost growth. Detailed planning and execution of onshore precommissioning was key to achieving the very fast schedule. Repeat of a proven design with incentives to improve the design where possible was key to the successful outcome Introduction The Typhoon SeaStar is the third SeaStar TLP to be installed in the Gulf of Mexico, and follows the Sir Douglas Morpeth Seastar (installed 1998) and the Allegheny SeaStar (installed 1999). Both platforms have been trouble free in operation since installation. The SeaStar TLP design features a monocolumn hull with 3 pontoons radiating outwards at the base. The platform stability against overturning is provided by 6 near neutrally buoyant tendons which run vertically from the top connectors mounted on tendon porches located at the extremities of each pontoon to piles driven in the seabed. The tendon system also acts as the station keeping system. In principle, the buoyant pontoons tension the tendons and the column buoyancy supports the topsides payload to minimize the moment transfer at the pontoon/ column connection.

The four-legged deck is supported on the hull and incorporates a K braced jacket structure to transmit the shear loads. The SeaStar is relatively transparent to the crests of extreme waves, thereby avoiding “ringing” loads experienced by other TLPs. The Typhoon deck is comprised of two main levels, a grated main deck and a plated production deck, which provide support for the process and auxiliary equipment, an under deck truss, a small cellar deck, a support frame for the quarters building and a flare/vent boom. The deck’s design is based on a conventional deck structure consisting of commonly available tubular sizes and wide flange members. It is supported by four main columns arranged in a square pattern to align with the hull’s outer diameter of 58-ft. The under-deck truss, located beneath the Cellar deck, frames into the deck legs in a cross pattern to provide support for the deck’s wing sections and provide bracing to the deck. Between deck levels, the legs have been designed to minimize diagonal bracing wherever possible to allow for clear unobstructed equipment access Health, Safety, Environmental, and Regulatory concerns impacted nearly every aspect of the design. Equipment layouts and deck surface selection were no exception. The deck surfaces were selected to optimize containment and ventilation Two stairways provide access between the main and production deck levels and a stairway and ladder provide access between the production and cellar deck levels and cellar deck and top of the hull utility space (H.U.S.). Two stairs on the living quarters that also provide access between the main and production deck levels. The platform’s 50’ x 50’ helideck, designed for a Sikorsky S-76 helicopter, has been incorporated into the quarters building’s structure and is located on top of the building. The deck is designed for a single point lift for loadout and offshore installation onto the hull. After the hull has been installed, the deck is lifted and stabbed into the hull’s jacket section and welded out at the four connection points. The Typhoon SeaStar TLP comprising hull and deck structures and marine equipment is classed under the ABS Guide for Building and Classing Floating Production, Storage



and Offloading Systems, as XA1 Floating Offshore Installation (TLP). Project Execution Strategy Joint venture cowners Chevron USA and BHP selected a local surface facility in preference to an extended subsea tie-back due to concerns regarding flow assurance and to maximize the hydrocarbon recovery from the reservoir. Atlantia’s experience with previous SeaStar platforms was key to the concept selection as it minimized technical risk and enabled an aggressive schedule to be planned with confidence. The Atlantia scope of work comprised Engineering design, Procurement, Construction and hook-up and commissioning of the platform including deck, facilities, hull, tendon system and foundation with handover to the Owners at production start-up. Atlantia provided assistance as required to Company’s Installation Contractor, i.e. an EPCi contract. The Typhoon SeaStar development project was spilt into the Front End Engineering and Design phase (FEED) and the Execution phase. Project sanction for the Execution Phase was conditional upon establishing a cost budget and schedule that met Partners commercial criteria. The FEED was reimbursed according to a conventional lump -sum contract while the Execution Phase was reimbursable with a Cost Based Management Fee (CBMF). The value of the CBMF was to be increased in the event that the project was completed under budget – shared savings - or reduced if over budget – shared cost - in order that Owners and Contractor were aligned in minimizing project cost. The FEED lasted 5 months from September through January 2001 and met the defined objectives of finalizing the execution phase schedule and identifying the Target Cost Budget within +/-10%. In fact, the final execution cost identified was within less than 1% of the Target Cost Budget identified during FEE. Establishment of the cost and schedule was dependent upon completion of about 25% of the detailed engineering, award of purchase orders for long-lead equipment, and issue of material take-off drawings to facilitate early material order. Selection of the hull and topsides fabrication contractors and development of contracts ready for award on project sanction was another key element. A small integrated team was established for the topsides facilities design. This was lead by Atlantia and included key representatives from the Partners, Chevron and BHP. Mustang Engineering provided the facilities detailed engineering design support. Key to the effort was the development of the Design Basis, establishing the topside facilities equipment list, finalizing the facilities layout and defining the corresponding weight budget. Typhoon Facilities Design Production capacity for Typhoon was defined at the onset of the Front End Engineering and Design (FEED) phase as 40,000 bopd, 60 mmscfd, and 15,000 bwpd. An objective for the Typhoon facilities design team was to maximize leverage

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off of previous SeaStar facilities and Chevron’s Genesis project designs, in effect minimizing engineering effort, cost, and cycle time. The general facilities configuration was established early using this objective as a guiding principle. The gathering and production facilities included an inlet manifold for four subsea wells, expandable to six. A three phase low pressure (LP) inlet separator operating at 200 psig and a two phase intermediate pressure inlet separator operating at 600 psig process bulk production from the inlet manifold. Crude from the LP separator is routed through a crude heater and electrostatic treater with integral degasser for processing to oil export pipeline quality specifications of less than 1% bs&w. Crude moves from the treater to a dry oil storage tank operating at 1 psig where the last flash is made to meet the 10 psig Reed Vapor Pressure (RVP) specification. Finally, crude is pumped from the dry oil storage tank using two vertical can type centrifugal charge pumps through Lease Automatic Custody Transfer (LACT) meters and on to two 800 hp electric motor driven multistage centrifugal export oil pipeline pumps. The export oil pipeline pumps are constant speed and export rate is controlled with recycle. Control of the pipeline pump recycle loop was redesigned to include operator selectable level, pressure, or combination control. Produced water treating on Typhoon is handled by hydrocyclones with a vertical column floatation unit. Unlike most other parts of the plant, this system was rigorously redesigned to increase its performance and reliability over previous designs. Several features were scrutinized and enhanced in the produced water treating system including LP separator control level changes, chemical injection point additions and changes, redesign and optimization of control functionality across the hydrocyclones, incorporation of dual stage sparging and coalescing in the vertical column, addition of online backwash and sparger tube change out capability, and optimization of column slenderness ratio and internal design. Gas processing and handling on Typhoon includes an 800 hp electric motor driven three stage reciprocating vapor recover unit (VRU) compressor moving gas from the wet and dry oil storage tanks at 1 psig and the crude treater at 45 psig to the suction stage of the export compressor at 200 psig. A 5500 hp (site rated) turbine engine driven two body tandem centrifugal export compressor handles gas from the VRU and the low pressure inlet separator at 200 psig and gas from the intermediate pressure inlet separator at 600 psig. Design rates for the compressor are 25 mmscfd through the LP body and 60 mmscfd through the hp body. A conventional TEG gas dehydration system receives and dries the gas from the export compressor to less than 4 pounds of water per mmscf. The gas is then metered using standard orifice metering and routed to the gas export pipeline. One aspect of gas handling on Typhoon (in the export pipeline) that proved challenging was retrograde condensate. During FEED, process simulation and flow assurance work identified condensate dropout in the export line could range from one to 5 bbl/mmscf. Several options were considered to handle the rich gas stream condensate including installing a

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condensate recovery system on Typhoon, operating the pipeline at pressures in the dense phase region, and frequent pigging to sweep the pipeline. The condensate recovery system and higher operating pressure on the export pipeline were cost prohibitive. The flow assurance team established design criteria for downhole, subsea, and topsides chemical injection during FEED. Significant challenges facing the team included high asphaltene content crude management, hydrate mitigation associated with 40 degree Fahrenheit seafloor temperatures, subsea flow modeling, arrival temperature prediction, and modeling / management of condensate dropout in the export gas stream. Utility systems on Typhoon are of conventional design. Electric power is provided by a dual fuel turbine engine driven 4.2 megawatt generator. A decision was made during FEED to eliminate the backup main generator to cut cost. An 800 kw diesel engine driven generator provides essential and emergency power. Fuel gas for the main generator and export compressor is taken from either dehydrated gas upstream of sales meters, wet gas from the 600 psig intermediate pressure system, or bought back from the gas export pipeline. The high pressure flare and relief system is sized for 90 mmscfd instantaneous and 60 mmscfd continuous rates. A separate low pressure cold vent system was included with the vent tip terminating half way up the 160 ft. flare boom. The drains and sump system were redesigned to enhance performance. New features included bubble capped drain troughs and a four inch per hour rainfall rate criteria. A combination process heating and cooling system uses water as the heat transfer medium with input heat as required from an electric emersion heater for heating and cooling and an air cooler for cooling. The instrumentation and control system is primarily PLC based with an enhanced graphical user interface. The electrical distribution system includes 4160 V, 480 V, and 120 V networks. Hull Engineering and Design The facilities weight grew during FEE as a consequence of the decision by the Operator to maximize the life cycle value of the asset by provision of future capacity for operation of the platform as a host facility. This was accommodated by the introduction of the column extension, a buoyancy compartment which extends the main column below the underside of the pontoon keel. The structural design of the column extension is dictated solely by resisting hydrostatic loads, with minimal dynamic loads resulting from wave action. As a consequence, various heights of column extension were carried through FEE and the final height was defined at the end of FEE when the facilities weight budget was frozen. The column extension is not only a cost-effective means to increase the payload of the hull but also improves the overall global performance of the platform. Lateral accelerations are reduced due to the increased mass. Tendon loads are reduced due to the lowering of the vertical center of


gravity. All ballast being located in the column extension, the only permanent buoyancy tank in the Typhoon hull, facilitates internal inspection. A deep center of gravity is a benefit to the performance of all floating vessels. In addition to the design of the column extension, substructure engineering during FEE focused on optimization of the structural design of the hull. The hull was analyzed using a large finite element model using SESAM. Scantling design according to ABS Rules has been developed for shallow draft free floating structures subject primarily to direct wave action. The pontoon plating of TLP hulls are subject to significant tensile and compressive loads due to moments applied by tendon tensions in addition to increased hydrostatic loads. Consequently, design according to scantling rules is non-conservative for the pontoon keel plate and is over-conservative in other areas. In addition, fatigue is an extremely important aspect of design at special connections, such as the tendon porch and at the column/pontoon basenode intersection as well as at changes of plate thickness. Constructability was a major consideration in the design optimization. Excessive numbers of changes of plate thickness to save material were avoided in order to maximize ease of construction. The additional material cost was more than compensated for the saving in hull fabrication schedule. The Typhoon hull is considered to be a second generation SeaStar hull design as a consequence of the structural optimization. This effort could not be attemp ted during the ‘design-while -build’ execution of the Morpeth/ Allegheny Projects. Inclusion of the column extension provides flexibility to accommodate weight growth during facilities engineering. This avoids the conventional concern about sensitivity of TLPs to facilities weight growth. Execution Phase The fabrication contracts for hull and deck were awarded to J. Ray McDermott in Morgan City based upon the evaluation on Safety, Quality, Cost and Schedule. The project schedule was planned to be 16 months, 2 months shorter than the 18 months achieved previously by the smaller Morpeth and Allegheny platforms. Fabrication contracts were placed in February 2000 and material was ordered. Engineering was well advanced and early opportunities for savings in cost and time were identified and implemented. However, as usual, unexpected events raised cost and slowed progress. For example, repeated failures by a single source mill to deliver special shapes ordered for the hull necessitated a change in fabrication sequence and substitution by alternative sections. The substitution was facilitated by reanalysis using the SESAM finite element model but still resulted in fabrication starting in July, some 2 months later than the planned start. Hull fabrication had now to be accomplished in 10 months. Topsides fabrication was planned to ensure the maximum productivity by installing the maximum of pipe spools prior to floating decks. This was successfully achieved by close



cooperation between the topsides teams to ensure timely delivery of engineering drawings. Fabrication proceeded without an incident for several months with more than 100,000 manhours. However, following the good start, there was suddenly a spate of accidents. A major initiative was launched to strive for an incident and injury free commitment from the work force. The safety performance thereafter improved significantly as a consequence. The lesson learned was that the safety initiative should to be implemented at the start of fabrication. Weight Control is of fundamental importance for all floating structures and was meticulously executed from FEED through fabrication and into operation of the platform. An example of one weight trend graph is shown in Fig. The final weighed weight was 2.5% below the original budget. Detailed engineering weight take-offs were confirmed by load cell weighings for the major packages and with truck weighing for the smaller skids. The PDMS piping model was used as the basis for piping weight. The hull and deck were each weighed immediately prior to loadout and the predicted weights were found to be within the accuracy of the loadcell measurement. The weight reconciliation after installation was also excellent without the need to introduce a “phantom weight” correction to the weight reporting system. Installation The Typhoon foundation piles were installed by the DB50 in September 2000. The early installation removed critical path work and provided greater time for soil set-up after driving, enabling the pile length and corresponding drive time to be reduced. A persistent strong eddy current event delayed the installation of the export pipelines, which in turn delayed the start of the platform installation by 1 week. The Typhoon tendons, fabricated at Aker Gulf Marine, Brownsville Texas, were loaded out, sailed to field on May 30th and were installed in 4 days between June 3rd and June 13th , with delays due to waiting on weather and maintenance work on the DB50. Meanwhile the hull was lifted by the 5,000 ton shear leg crane on to the MD500 barge on May 29th where it waited until he tendons were installed. The hull sailed to field on June 13th and again after waiting on weather was installed in four days from June 16 to 19. The oil and gas export Steel Catenary Risers (SCRs) were picked up and set in porches on the hull on June 20 and 21. The topsides was lifted on to the I 404 barge on June 12th,and sailed to field on June 20th Typhoon HUC Planning and Execution On Saturday June 23, 2001 at 1:38am, the Typhoon topside was installed onto the awaiting hull. Twenty-eight hours after setting the topsides, the entire Typhoon hookup crew boarded and occupied the platform. The DB50 left the field a few hours later, leaving the Typhoon platform an independently occupied offshore floating installation with all utilities and

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safety systems in operation. The USCG arrived the next morning to make their inspections and approve the installation. Thirty-six days after setting the topsides, first oil was produced. Seventy-seven days after setting the topsides, all Typhoon wells were open and flowing full design production rates. The excellent achievements above are attributable to the extensive planning and diligent execution of hookup and commissioning (HUC). For the Typhoon project, HUC was defined as the quality assurance activities conducted to ensure rapid and safe facilities startup. HUC, as defined for Typhoon, did not include fabrication or construction activities. The integrated HUC Management team consisted of approximately six personnel from Chevron, BHP, and Atlantia. The execution team consisted of two Atlantia supervisors and labor assistance from Chevron Operations, Atlantia Inspectors, Atlantia subcontractors, and equipment vendors. One of the key factors of success was the objective to achieve a single topside lift with as much equipment installed and operable as possible. The single lift design was ensured by keeping the deck size and weight within the lifting limits of the lift barge. Weight data was carefully monitored throughout the design and fabrication effort to meet this objective. The single lift afforded a very simple offshore installation with only four stab points between the topside and hull. The operability of the topsides after installation was ensured by a thorough effort to maximize onshore HUC. This was accomplished through the aforementioned wellexperienced and committed team. The focus on achieving habitable quarters, which includes all livable and utility systems in accordance with USCG requirements, and the desire for earliest first oil resulted in a detailed onshore execution plan. The general philosophy was to maximize onshore HUC, minimize offshore HUC, to achieve the most efficient and cost-effective startup. The HUC activities consisted of three separately defined areas: Mechanical Completion, Precommissioning, and Commissioning Mechanical Completion was inspection (static) activities confirming that all equipment and systems were of correct design in accordance with the project specifications without testing their function or operation. Typical activities included: visual inspection of equipment against data sheets, visual inspection of piping systems against P&IDs, visual inspection of vessel internals, control cable continuity checks, power cable insulation checks, and pipe hydrotesting. Resources used for these activities were mainly Atlantia Inspectors, the fabrication subcontractor, and the E&I subcontractor. Precommissioning was activities confirming that the function of individual equipment items were in accordance with the project specifications. Precommissioning also included the preparation of general systems for operation. Some typical activities included: motor rotation confirmation, instrument function checks, checking and filling lubricants, checking and adjusting shaft alignments, and pipe systems cleanout. Resources used for precommissioning were mainly the fabrication subcontractor, the E&I subcontractor, and

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equipment vendors. Special contractors were called in to complete such activities as pipe systems cleanout. Commissioning was considered activities where equipment and systems were operated. In some cases, systems were operated under simulated conditions. Examples of these activities are: operating the oil pump system with water, testing the glycol pumping and heating systems without flowing gas, and running the heat medium systems pumps and heaters. In other cases, the systems were operated under actual conditions, essentially confirming startup. Examples of these activities are: operating and testing the emergency generator under load, operating and testing the main generator under load, running the air compressors and using them for testing instruments, operating the platform crane by assisting construction activities, and operating the survival craft in the nearby water slip. The philosophy adopted for HUC was to maximize value while minimizing overhead. This was accomplished in part by utilizing a custom designed database by Atlantia called PRISM that separates the planned (HUC) activities from the non-planned (Punchlist) activities while maintaining relationships. The database is designed to track progress only and does not record detailed design data for asset management. Each activity in the database identified all tagged items applicable to that activity. As each activity was performed, the tagged items were recorded as complete in the database. If any problems were found during the activity, a punchlist item was recorded in the database referencing the applicable tagged item(s). This allowed separate and controlled management of progressing the HUC activities vs. the punchlist. This also allowed an automated review of all previous activities for applicable tagged items in preparation of commissioning, ensuring that any non-completed activities or punchlist items were addressed. The database proved to be a valuable asset in assisting the team in staying on schedule. All HUC activities were carefully planned to provide maximum assurance of a safe and trouble-free startup in the quickest amount of time after installation. Each activity was associated with project schedule activities for assisting with time and resource management. The use of the project schedule proved very effective in the integration of HUC activities with normal fabrication and construction activities. Additionally, the team effort of especially Chevron Operations, the fabrication subcontractor, and the E&I subcontractor helped to assure success. Conclusions A relatively short Front End Engineering phase can provide extremely accurate cost and schedule estimates for application of a well proven concept Detailed planning and well-managed execution of hookup and commissioning of facilities is key to achieving early First Oil within budget without excessive offshore hookup A reimbursable contract with Cost Based Management Fee enables alignment between Owner and Contractor to their mutual benefit and to the benefit of the Project


Safety performance needs to be emphasized from the start of fabrication if performance goals are to be met. Acknowledgements Appreciation is extended to ChevronTexaco and BHP Billiton for their permission and support in compiling this paper. Recognition is made to the Typhoon project team.



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Fig: 2 SeaStar® Installations

Typhoon SeaStar® Fig: 1 Table 1 Typhoon SeaStar Final forecast cost 100.50% 100.00%

99.00% 98.50% 98.00% 97.50% 97.00%

















96.50% Mar-00

% Budget


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Table: 2

Weight Trend Deck Lift

8000 7000 6000 5000 4000 3000

Assigned Margin Current Estimate


2000 1000 0 Oct-99










RB MATTEN, M.J. PROVOST, S.PASTOR, S.W. YOUNG Typhoon Hull Transport

Fig: 3 Typhoon Hull Installation

Fig: 4

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