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Giles G.R.,III | Poll P.,Houston Offshore Engineering LLC | Converse R.,Williams | Park Y.C.,Williams | Mao C.,Williams
Proceedings of the Annual Offshore Technology Conference | Year: 2015

Historically, Spar platforms have utilized both riser porches and riser pull tubes for interfacing steel catenary risers (SCRs) to the floating system. The riser porch requires a stress joint at the hang-off end of the SCR to withstand tension and bending loads at the fixed connection. The pull tube requires special hardware (e.g., a double-tapered stress joint) near the keel of the Spar where platform motions are first transferred to the riser system. Each of these options for the riser interface has advantages and disadvantages. The Gulfstar FPS utilized both pull tubes and a riser porch for riser interfaces. This paper evaluates the experience designing and building the two different types of riser interfaces for the Gulfstar FPS and the experience offshore during installation of the risers. The paper quantifies the structural appurtenances required for each interface in addition to the equipment required for riser installation, which is significantly different for each interface type. The evaluation results in important lessons learned and recommendations for both types of riser interface strategies. The paper also summarizes the keel interface utilized on the Gulfstar FPS. The Gulfstar FPS incorporates a different approach for the keel interface with the pull tube support compared to other recent Spar projects in the Gulf of Mexico. The results demonstrate the compatibility of the riser keel interface with the platform motions. The information and results presented in this paper are applicable to engineers, designers and fabricators when evaluating riser interface options for floating systems, particularly Spar platforms. Copyright © (2015) by the Offshore Technology Conference All rights reserved.


Zou J.,Houston Offshore Engineering LLC | Poll P.,Houston Offshore Engineering LLC | Park Y.,The Williams Companies | Converse R.,The Williams Companies | And 3 more authors.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

Waves, winds and currents increased considerably in the latest central GoM metocean criteria which posted tremendous challenges on designing floating production systems in the region. Since Gulfstar is first time introduced to oil and gas industry, a series of model tests have been launched to investigate Gulfstar global responses in central GoM irregular seas. Due to the limitations of test facility, moorings and SCRs have to be truncated in order to have a reasonable scale for hull with adequate hull external appurtenance details. The polyester mooring has distinct stiffness characteristics such as installation stiffness (or called static stiffness) and storm stiffness (or called dynamic stiffness). In general, ratio of the storm stiffness and installation stiffness is about 2~3. For simplicity, one has to choose only one polyester stiffness for tests. Because of truncation of moorings and SCRs and simplified polyester stiffness selection, the measured results can not be directly compared to the prototype predictions. Guidelines must be established that ensure the measured results are interpreted and utilized correctly for design. The enhanced hybrid approach has been developed to account for lumping and truncation and polyester mooring stiffness variation. This paper presents validation of Gulfstar global responses with the emphasis on maximum heave motions, heeling angles, minimum air gaps and maximum accelerations by both numerical analysis and wave basin model tests. Wave peak period variations and wave spreading effects on global responses are also investigated and identified. The developed guidelines on mooring/SCR truncation and highlighted correlation analysis procedure are generally applicable for all floaters in deep/ultra deep waters with polyester mooring system. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).


Zou J.,Houston Offshore Engineering LLC | Poll P.,Houston Offshore Engineering LLC | Park Y.,The Williams Companies | Converse R.,The Williams Companies | And 2 more authors.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

The Gulfstar Standard Floater hull is circular cylindrical shaped with 25.91 m (85 ft) diameter and 154.84 m (508 ft) draft with slender ratio around 6, it is susceptible to Vortex-induced Motions, or VIM. VIM has been characterized as a difficult subject with a complicated structural-hydrodynamic interaction. The physical mechanics is generally less well understood and numerical prediction is generally less reliable. Model testing has become an important and widely accepted design procedure for optimizing strake configuration and deriving A*/D and Cd values. Since Gulfstar standard floater is the first time introduced to oil and gas industry, extensive VIM tests have been executed to investigate the importance of strake configurations, external appurtenances and current heading on VIM motions. VIM tests have been performed with different strakes, appurtenances, and at various headings and various reduced velocities in two different strake heights and two different water depths. The measured A*/D and Cd values for the above mentioned various aspects have been derived for global performance, mooring and riser analysis. From the VIM tests, the generalized A*/D and Cd curves are relatively lower which indicated the effectiveness of the optimized strake configuration on mitigating VIM motions. The measured Strouhal number and transverse (lift) coefficients have been derived and compared with those published results of bare cylinders. Considerably different response characteristics have been observed and more in-depth researches are called to explore the intrinsic mechanics of cylinder with strakes and develop practical analysis tool for offshore industry to design efficient strake configuration in addition to VIM model tests. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).


Iyerusalimskiy A.,ConocoPhillips | Gu G.,ConocoPhillips | Zou J.,Houston Offshore Engineering LLC | Chianis J.,Houston Offshore Engineering LLC | And 2 more authors.
International Conference and Exhibition on Performance of Ships and Structures in Ice 2012, ICETECH 2012 | Year: 2012

The Arctic offshore may hold the largest undiscovered oil deposits which could account for up to 25% of the world's undiscovered hydrocarbons based on Gautier et al (2009). Access to the deepwater deposits in the Arctic Ocean presents a special challenge. In the past four decades only shallow water drilling campaigns have been executed in relatively mild ice environments and have accumulated valuable drilling experience. To drill an exploratory well at a deepwater Arctic location, a floating drilling platform is required. Floating platform design poses significant challenges given the harsh ice loading conditions and the demand on the hull and mooring system strengths. In most of the deep water Arctic regions, the winter season is characterized by the presence of first-year ice, multi-year ice, and in some areas ice islands and icebergs. Compared to the environmental loads due to waves, winds and currents, ice actions (both forces and moments) are considerably higher and are the governing loads for deepwater Arctic systems. The capability of a floater mooring system to withstand ice loads is limited as compared to gravity based structures. One of the solutions is a disconnectable system utilizing the ability to disconnect the floater from the mooring system and move off site when the ice loads are forecasted to approach the design limit. As of today, several disconnectable floating system concepts have been proposed, such as disconnectable FPSO, non ship-shaped circular FPSO, Arctic Spar and semi-rigid floater. These concepts are either intended for relatively mild Arctic ice conditions or require long durations for disconnection and re-connection. This paper presents an innovative disconnectable floating platform concept for deepwater Arctic, which can perform exploratory, development drilling and potentially year-round production in various deep water Arctic locations. This design, like many other similar concepts, by limiting the design ice loads to a pre-defined level, enables reasonable hull and mooring system configurations within existing technology limits for an environment where the environmental loading seems to approach infinity in practical terms, if unmanaged. In the event of an excessive ice feature approaching, the innovative platform can be quickly disconnected and towed away, and can then be quickly re-connected once the ice feature has passed. Copyright ©2012 ICETECH 12. All rights reserved.


Antony A.,Houston Offshore Engineering LLC | Vinayan V.,Houston Offshore Engineering LLC | Holmes S.,Redwing Inc. | Spernjak D.,Los Alamos National Laboratory | And 2 more authors.
Proceedings of the Annual Offshore Technology Conference | Year: 2015

Dry-tree semisubmersible concepts have been studied under multiple RPSEA funded projects since 2009. As hull forms used for dry tree applications have a deeper draft, vortex induced motion (VIM) can be an area of concern that needs to be addressed during design stage. The VIM model testing that was conducted during prior RPSEA study phases indicated that VIM exists and can impact the platform mooring and riser integrity. The current RPSEA funded project is aimed at improving overall mooring system safety and riser system integrity by testing design parameters of deep draft column stabilized floaters (DDCSF) to determine the ones that have the most impact on VIM. The study utilizes computational fluid dynamics (CFD) analysis and model testing to determine the sensitivity of VIM responses to DDCSF geometric parameters. The project studies both a four-column DDCSF and a multi-column DDCSF, specifically, the paired-column DDCSF developed by Houston Offshore Engineering (HOE). The CFD tools used are AcuSolve™ from Altair Engineering, Fluent™ from ANSYS and STAR-CCM+™ from CD-adapco. In this study existing VIM model test data is used to validate/verify the CFD tools, and the results are discussed in the paper. Some observations from the validation study are also discussed in the paper. More VIM model tests will be conducted during the later phase of the ongoing RPSEA project to correlate the CFD predictions with experimental data. The study results are part of "Vortex Induced Motion Study for Deep Draft Column Stabilized Floaters", a study funded by Research Partnership to Secure Energy for America (RPSEA), under the project number 11121-5404-03. Copyright © (2015) by the Offshore Technology Conference All rights reserved.


Zou J.,Houston Offshore Engineering LLC
Proceedings of the 17th Offshore Symposium: Pushing Boundaries in the Global Industry | Year: 2012

Mega oil and gas reservoirs have been discovered in deep and ultra-deep offshore Brazil. These Pre-Salt discoveries are remotely located at water depths ranging from 2200m (∼7,200 ft) to 2600 m (∼8,500 ft). Offshore Brazil has unique metocean conditions with long swell periods which present challenges on floating platforms such as Spars and Semis. In addition, the remoteness of location and the associated high cost of vessel mobilization add further pressure on economics and risk. Quayside integration is thus a desired feature of the hull concept in order to eliminate offshore mating and the associated risk to cost and schedule. To explore these pre-salt complicated ultra-deepwater reservoirs usually require large drilling rig and drilling variable payload which result in very large topsides in both size and weight. Spars and TLPs are the only two proven dry tree hull forms in deep and ultra-deep waters in the GOM. However the TLP becomes cost prohibitive if the water depth is beyond 1,524 m (5,000 ft). For large payload systems requiring a large drilling rig, a suitable Spar size creates a challenge for transportation and installation. The semi-submersible hull form is known to offer advantages over Spars such as larger deck space and quayside integration which are essential to reducing offshore commissioning time and risk as well as cost and schedule. Maturation of the dry tree semi-submersible solution in GoM ultra-deepwater (2,400m) had been undertaken by RPSEA and dry tree Paired Column Semisubmersible (PC Semi) platform, developed by Houston Offshore Engineering, was selected by the RPSEA committee in 2009. Extensive wind tunnel tests and wave basin model tests including 1,000-year central GoM hurricanes were successfully completed in 2010. PC Semi hull configuration, TTR stroke, the analytical results and simulation tools had been fully validated. This paper presents validation analysis results of a dry tree PC semi developed with conventional RAM style tensioners, in 2,400m ultra-deepwater of Offshore Brazil Pre-Salt carrying same topsides payloads as RPSEA. The validation analysis was performed by the correlated analysis tools and established analysis procedures. The design efficiencies including payload, steel weight and production efficiencies of PC Semis for BPS and central GoM are addressed and discussed. Highly efficient PC Semi for BPS has been developed, validated and became "market ready".


Jun Z.,Houston Offshore Engineering LLC | Poll P.,Houston Offshore Engineering LLC | Antony A.,Houston Offshore Engineering LLC | Das S.,Houston Offshore Engineering LLC | And 3 more authors.
Proceedings of the Annual Offshore Technology Conference | Year: 2014

The Paired-Column Semisubmersible (PC Semi) concept was selected as a dry tree alternative for ultra-deep water development by RPSEA in 2009. Since then, RPSEA continuously supported maturation of PC Semi. The PC Semi platform has relatively deeper draft and smaller columns compared to those of a generic Deep Draft Semisubmersible (DD Semi) platform. Due to its larger column slenderness ratio, it might be suspected to have a pronounced VIM response. VIM response characteristics of a floater are the key measures of its performance. It is an essential step to explore VIM response characteristics during concept maturation. An extensive VIM model test program funded by RPSEA was performed at MARIN in June, 2013. Key results are summarized and presented in this paper. Since the VIM response of a floater (Spar or Semi) is a controlling factor for mooring fatigue, VIM induced mooring fatigue analysis was followed by employing the measured test results. A typical loop current scatter diagram for the GoM was considered and the resultant fatigue damage was analyzed and highlighted. A parallel study for VIM induced mooring fatigue of a generic dry tree DD Semi was also carried out to establish a baseline for comparison of the PC Semi response features and mooring fatigue. Copyright © 2014, Offshore Technology Conference.


The U.S. Beaufort Sea may hold the largest undiscovered oil deposits which could account for up to 25% of the world's undiscovered hydrocarbons based on the article of "Science". Therefore, there are strong interests for oil and gas industry to explore these enormous reserves of oil and natural gas in order to meet the long term increasing energy demands. In Beaufort Sea, an averaging water depth is about 800m which is normally called deep waters. An exploratory well typically takes about five to six months for continuously drilling in shallow waters. Beaufort Sea has an average two-month open water window, thus an exploratory well will take two to three years to complete if only seasonal drilling is considered. In deep waters, it is much more complicated and challenging and will take a few times longer than drilling in shallow waters. Seasonal drilling for deep waters is practically and economically prohibited. Year-round drilling capability is a truly required feature. To have year-round drilling ability, hull and mooring has been designed to withstand ice actions of first-year ice, ridge and up to multi-year ridges depending on disconnection criteria. In Beaufort Sea, it is practically impossible to design the floater to stay in-place for 30-year service life for any ice actions. Thus, dis-connectable ability is another desired feature when a sizable iceberg or unmanageable ice feature is approaching. As of today, there are a few dis-connectable concepts had been proposed, such as disconnectable FPSO, non-ship-shaped circular FPSO, arctic Spar and semi-ridge floater. These concepts are either designed for benign ice conditions or intended just for seasonal drilling and production. So far, no floating drilling and production facility has been installed with year-round operation capability in Beaufort Sea. It strongly calls for development of alternative dis-connectable arctic floating platform concept to explore mega reserves in deep waters of cold regions. This paper presents HOE persisting efforts for developing innovative arctic floating platform concept having above mentioned features in past six years. A preliminary disconnection procedure of HOE arctic floater for drilling and production is outlined as an example.


Zou J.,Houston Offshore Engineering LLC
19th Offshore Symposium 2014: Emerging Technologies in Offshore Drilling and Production | Year: 2014

It is well known that VIM response of a floater (Spar or Semi) significantly affects fatigue of moorings. VIM response characteristic of a floater is a key measure of its performance. A dry tree Paired-Column Semisubmersible (PC-Semi) platform has deeper draft and smaller columns compared to those of a traditional Deep Draft Semisubmersible (DD-Semi) platform. PC-Semi might have more pronounced VIM response due to its larger column slenderness. Thus, there is strong interest for us to explore VIM response characteristics of the PC-Semi and how these key features are compared to the other floaters. HOE performed a small scale VIM model tests at the UC Berkeley towing tank on May, 2012. This paper presents the key testing results and compares them against other floater VIM response curves. A typical loop current scatter diagram in GoM was employed and the measured VIM test results were adopted and applied for mooring fatigue analysis. A traditional DD-Semi was considered and analyzed to establish the base to gauge VIM performance feature of the PC-Semi. The comparison results of the PC-Semi and DD-Semi on VIM responses as well as the corresponding effects on mooring fatigues are addressed and highlighted. Copyright © (2014) by the Society of Naval Architects and Marine Engineers Texas Section All rights reserved.


Udoh I.E.,Houston Offshore Engineering LLC | Zou J.,Houston Offshore Engineering LLC | Vinayan V.,Houston Offshore Engineering LLC
19th Offshore Symposium 2014: Emerging Technologies in Offshore Drilling and Production | Year: 2014

Tender-Assisted Drilling (TAD) Semisubmersible closely moored with a Tension Leg Platform (TLP) for deepwater ield development is becoming a popular scenario for benign environmental regions, such as Offshore Indonesia/Malaysia and Offshore Africa. To ensure a reliable and safe development and operation, it is crucial to thoroughly explore hydrodynamic response characteristics of TLP and TAD moored in close proximity in various environmental conditions. Due to drilling, lifting and transfer operation requirements, TAD may require to longitudinally and transversely offset relative to TLP. This paper presents a study on hydrodynamic interactions of TLP and TAD by varying separating distances in longitudinal and transverse directions to cover possible operational positions. Our results show that although hydrodynamic coupling exists between the floaters for the scenarios considered, the magnitudes are low and of modest practical significance. Our effort as presented in this paper is part of a broader scope of studies designed to address hydrodynamic and mechanical coupling between TLP and TAD. Copyright © (2014) by the Society of Naval Architects and Marine Engineers Texas Section All rights reserved.

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