Floating Production Platform Research Articles

Fatigue assessment of fillet welded doubling plates using different methods

Analysis results using finite elements are compared with strain measurements and laboratory fatigue testing of doubling plates used in floating production platforms. Circular and quadratic doubling plates of thickness 10 mm with diameter and length equal to 150 mm fillet welded to a main plate of thickness 20 mm were fatigue tested. The testing was performed until crack growth through the plate thickness and the number of test cycles was compared with design standards. Finite element analyses of the doubling plates were performed using different methods for hot spot stress derivation in combination with relevant S-N curves. Analyses were performed using 8-node shell elements and 20-node solid elements. Hot spot stresses were based on calculated surfaces stresses at the weld toe. Also stresses through the thickness of the main plate were used for assessment of the hot spot stress. For purpose of analyses the main attention was made to the weld toe. However, the main reason for performing the fatigue testing was related to concern for crack growth from the weld root. This failure mode was found to be less critical than fatigue crack growth at the weld toe. The results from this work are being used for developing more reliable analysis methods to be included in design standards.

Dynamic Response Analysis and Positioning Performance Evaluation of an Arctic Floating Platform Based on the Mooring-Assisted Dynamic Positioning System

The Arctic region is rich in oil and gas resources, but exploitation of resources there is always facing great challenge. Floating offshore platform is considered as a practical choice for oil and gas exploration in the Arctic deep water regions. One of the key technologies is positioning system design under harsh arctic sea loads. In this paper, a comprehensive design of the positioning system is investigated. A coupled numerical model composed of a mooring-assisted dynamic positioning system and the Kulluk platform is established. 16 different positioning combination forms are selected and investigated. The positioning capability of the coupled system is evaluated by analyzing the platform motion response under different environmental loads, including wave, level ice, and broken ice floes. Wave load is calculated using potential flow theory. Computation of ice load is compared with the finite element method (FEM) and discrete element method (DEM). The dynamic analysis of the mooring system is carried out by using the slender finite element method. The control system of dynamic positioning adopts proportional-integral-derivative (PID) control methodology. It is found that a better positioning system design can reduce the offset by more than 50%, including surge, sway and yaw motion. The results of this study will provide a good reference for the positioning system design of an arctic floating production platform.

Gulf of Mexico Operators Transition to Faster, Cheaper Developments as Production Decrease Looms

The US Gulf of Mexico (GOM) has long been a sound investment opportunity for operators looking for world-class oil fields, stable government regimes, and predictable regulatory requirements. Since the 1980s, the region’s deeper waters have been populated by fresh infrastructure as commercial discoveries were made, appraised, and developed. Today, more than two dozen floating production platforms and miles of export and transport pipelines populate the area, with more on the way as producers continue successful exploration programs in the area. There have been nearly 90,000 offshore wells drilled in the GOM to date. The GOM arena has experienced a few bumps in the road over the past few years due to both COVID-19 and the challenges to the most recent lease sale that was revoked, then later reinstated. While GOM oil production dipped from its peak in 2019 due in part to the global pandemic, the area is still an appealing region for operators. Operators used that period to focus on short-cycle and low‑cost recompletions, infills, and tiebacks rather than larger, capital‑intensive projects. According to a report released by the US Bureau of Energy Management (BOEM), GOM production is expected to experience growth and multiple record years of total oil production, despite off‑trend production levels in 2020 and 2021. Gas production is expected to experience moderate increases but is not expected to rebound near previous highs. The growth in annual oil production predicted in the following years is supported by a strong project queue as deferred projects will now be executed. From 2022 through 2024, oil production is forecast to have strong growth, followed by a relative plateau (until 2027) and a gradual decline through 2031, the end of the forecast period (Fig. 1). Around 70% of new GOM production in 2023 is expected to come from just three projects: BP’s Argos, Shell’s Vito, and Murphy’s King’s Quay. The predicted decline may be due in part to the number of new wells being drilled in the area. The well count for the GOM in general had a decade’s peak back in 2018; however, the count has trended down ever since. According to analysts at Enverus, industry averaged almost 30 ultradeepwater wells per quarter during 2018 and 2019. Last year, that number was around 15. With fewer wells come fewer discovery opportunities. With fewer discoveries backfilling the queue of potential developments, the GOM could be headed for a lull in new project commitments. Additionally, Wood Mackenzie research found that net discovered resource by company in the GOM fell from more than 1 billion bbl in 2017 to around 250 million bbl in 2021. Research from Rystad Energy showed just two deepwater GOM hub-based developments received a green light in 2021 (Shenandoah and Whale), while so far in 2022, only one (Salamanca) has been approved (Fig. 2). Counter to that, several subsea tiebacks are in the queue. While these historically represent smaller production volumes, they also represent significantly reduced cycle times from inception to first oil.

E&P Notes (July 2022)

E&P Notes (July 2022)

The Marriage of the Octopus and the Hammerhead Shark and How That Relates To Making Money on Old Offshore Fields

PetroRio is a young, Brazilian independent oil producer whose acquisitions tend to raise the same question: “How do you make money from old brownfields? That is the question we have always heard,” said Iuri Rossi, subsea coordinator at PetroRio. The answer has existed since small companies began buying the discards from big oil companies looking for the next giant field—cut costs and invest some of the earnings to extend the productive life of the existing platform. At this year’s Offshore Technology Conference (OTC), Rossi provided an example by describing how PetroRio acquired two nearby fields in the Campos Basin to create a single, profitable unit (OTC 31900). It began with the acquisition of the Polvo field (Portuguese for “octopus”) in 2016, shortly after the launch of the privately owned company. The purchase from BP included a floating production platform and a costly leased floating, production, storage, and offloading (FPSO) vessel capable of handling many times the 8,000 B/D output of the aging field. The value of the Octopus field became apparent only in 2020 after the company made two more acquisitions: First, it purchased an FPSO on the nearby field Tubarão Martelo (Portuguese for “hammerhead shark”); later that year it also bought the field. Those deals offered a solution—build a pipeline from the Polvo platform to the Tubarão Martelo FPSO and dump the leased FPSO. The $45 million spent to marry the field saved $50 million a year, generating cash to support a future that will include more drilling, Rossi said. The cost-cutting moves also included small deals such as buying an obsolete drilling rig for $1.00, then getting it running again and using it to work over wells. “We bring a new mindset; so, we say, ‘let’s try it,’” Rossi said. New thinking and more investment in the Campos are what Brazil needs as Petrobras and other big companies sell off smaller holdings in the rich basin that made the country a major oil producer before the ultradeepwater pre-salt play in the Santos Basin eclipsed it. But there is a lot of oil left in the Campos. Equinor reported that its partnership with Petrobras has a goal of adding 1 billion bbl of production to the Roncador field alone (OTC 31729). Still, at age 40 it is a mature play, along with the North Sea and the US Gulf of Mexico (GOM). Petrobras recently announced it would allocate $5 billion to work in the Campos from a $20-billion fund to provide the infrastructure needed to promote offshore development. “The Campos Basin plays a very strategic role for Petrobras in the future. Two-thirds of the production [there] in 2026 will come from investments made right now,” said Eduardo Bordieri, executive strategy manager for Petrobras, while presenting a paper on the future of the Campos at an OTC session (OTC 31883).

Assessment of Station Keeping Capability for Dynamically Positioned Offshore Supply Vessel

Abstract Dynamic positioning capability (DPCap) assessment is essential during the preliminary investigation of the positioning ability of a newly designed dynamic positioning system (DPS). Operational safety is always the first consideration in the design and operation of a new DPS. To be able to plan a safe and efficient operation, it is important to know the maximum environmental conditions that the DP vessel can withstand. The main objective of this article is to present a developed tool capable of conducting the DPCap analysis for offshore supply vessels based on the DNVGL methodology. The article describes the background studies, methodology, and mechanism associated with the formulation and development of the tool. The optimization of the design variables for the station-keeping criteria targets the highest capability at the lowest possible energy expenditure. Finally, the results are presented in the form of standard capability polar plots to show the application of the computational assessment procedure. The accuracy and reliability of the DPCap tool are validated by comparing with the results of the commercial one for the same case study ship at multiple simulation cases. Introduction Many offshore operations require the vessel to be kept in a position to face environmental loads from wind, waves and current. This can be achieved using Dynamic Positioning System (DPS) by using thrusters (Sørensen 2011). Station keeping ability is used in different types of vessels with varying operational requirements. Cruise vessels and mega yachts use it in the form of virtual anchoring to avoid the environmental impact of anchoring in the sensitive estuaries they often ply. The importance of DPS is growing because of the increase in the number of offshore construction sites requiring DPS for their operations (Mehrzadi et al. 2020). Over the last four decades, dynamic positioning (DP) in deep water has been used in the marine sector, oil and gas industries, and military services in many tasks such as drilling, oil and gas floating production platform, cable, and pipe laying, docking and towing, firefighting, supply, search and rescue, surveying, and mobile offshore bases (MOB). Each of these operations benefits from a DP system’s ability to include precise position-keeping, freedom from the restrictions of mooring spread systems, the ability to move quickly from one site to another, and track-keeping capabilities (Elkafas et al. 2021; Mahfouz 2007).

Floating catenary riser system concept for brownfield application

The expansion of a deepwater brownfield may become necessary to increase the production of hydrocarbons. Such expansion often requires the installation of additional risers to the existing floating production platform. However, the seabed footprint of the existing facilities may be congested with existing subsea pipelines and structures. Tying back of risers such as steel catenary riser (SCR) to the floating platform becomes challenging. Floating catenary riser (FCR) is a novel riser solution with floating bends or ‘waves’ close to the seabed. The FCR is engineered to extend its touch down point (TDP) far beyond the nominal TDP of the SCR and away from the congested seabed footprint. The riser sections before the nominal SCR TDP is configured to float by installing buoyancy modules. The multiple wave buoyant sections also provide the FCR with the capability to decouple its touch down zone (TDZ) from the floating platform motion. This can result in a significant reduction in the stress and fatigue damage around the riser TDP. Presented in this paper are the FCR configuration development and global responses to vessel offsets, current drag load impact, combined load, and wave fatigue loads, simulated to demonstrate the FCR feasibility.

Event-triggered [formula omitted] control for networked spar-type floating production platforms with active tuned heave plate mechanisms and deception attacks

The service life of floating production platforms can be substantially shortened due to undesirable excessive vibrations caused by dynamic loads. It is thus necessary to develop effective vibration reduction methods for floating production platforms. This article proposes a network-based active control approach for a spar-type floating production platform (SP) against wave exciting loads and deception attacks. First, a novel active tuned heave plate (ATHP) mechanism based on the concept of the active tuned mass damper is developed for the SP. Second, in the context of networked control of the SP-ATHP system, an event-triggering transmission mechanism is introduced to significantly improve communication efficiency. Meanwhile, a Bernoulli distribution and a nonlinear function are employed to character possible deception attacks in shared communication channels. Then, by modelling the network-based closed-loop SP-ATHP system as a time-delay stochastic system, its stability and H∞ performance analysis is derived. Besides, some criteria are obtained to co-design the triggering mechanism and the H∞ controller. Finally, simulation studies demonstrate that compared with some existing heave plate mechanisms, the designed event-triggered H∞ controllers under this ATHP mechanism are more effective to suppress heave motions of the platform and save network resources and control expenditure. Furthermore, even though there are deception attacks, the proposed scheme can still guarantee satisfactory system performance.

Tensile Response of a Flexible Pipe With an Incomplete Tensile Armor Layer

Abstract Unbonded flexible pipes are widely utilized in the exploitation of offshore oil and gas resources. They are connected to two of the most critical types of system: floating production platforms and underwater production systems. However, if some tensile armor wires are substituted by cables or broken, the tensile armor layer will be incomplete, which seriously reduces the safety and reliability of the flexible pipe. In the present study, models of a flexible pipe with a complete tensile layer and with the tensile layer partially missing were established. The error for the tensile stiffness obtained by the finite element model of an intact flexible pipe was only 1% compared with experimental results. Because the load borne by the inner tensile armor layer is larger under tension than that borne by the outer tensile armor layer, the loss of inner tensile armor wires has a greater impact on the tensile properties. The maximum axial elongation of the flexible pipe increases with the number of missing inner tensile armor wires as a cubic polynomial. If the distribution of the missing armor wires is too dense, a stress concentration and local bending may occur, which will reduce the tensile strength of the flexible pipe.

Novel Quantitative Risk Assessment Interface for Fixed Offshore Oil and Gas Exploration Platforms

Abstract Light, sweet crude oils are depleting, forcing oil and gas companies to explore and operate in increasingly deeper waters, remote geographical locations, and harsher environmental conditions with higher safety risks. This paper analyzed the common misuse and errors of typical quantitative risk assessments (QRAs) during identification, assessment, approval, and project implementation stages of a project for the case of optimization of facilities and manning fixed offshore oil and gas platform, as well as the scenario of a gas leak from riser pipeline of a floating production platform. The lessons learned were then applied to design an optimized QRA process for a real case, preproject assessment for a proposed addition of a riser platform (R-A) to a fixed offshore oil and gas platform complex using individual risk per annum (IRPA) and potential loss of life (PLL) analyses. Findings reveal that applying the standard hazard and effects management process (HEMP) and as low as reasonably practicable (ALARP) guidelines and tools alone are insufficient. The application of practical lessons learned from the past oil and gas disasters using IRPA and PLL parameters has helped this research to produce an optimized QRA. The optimized QRA process is a live process which could be further improved with future lessons learned.

Effect of Axial Compression and Wet Collapse Loads on Torsional Response of Flexible Pipe

Flexible pipes connect the two critical systems of the floating production platform and underwater production, which play an important role in the transportation of oil and gas as well as water injection. However, flexible pipes are often subjected to multiple loads that threaten their stability in the service process. In this study, a model of a flexible pipe containing practical cross section in all layers is established to study the effects of axial compression and wet collapse loads on clockwise and anticlockwise torsional responses. The results of calculation show that the axial compression and radial expansion of the flexible pipe are caused by the axial compression load, which reduces clockwise torsional stiffness. The wet collapse load induces the bending deformation of the flexible pipes in clockwise and anticlockwise torsion, where the bending deformation of clockwise torsion is significantly affected by the change in the Young’s modulus of the tensile armor layers. This study shows that clockwise torsional stiffness is small and exhibits a trend of axial compression. Clockwise torsion has poor stability in combination with axial compression and wet collapse loads, respectively. Therefore, to prevent instability in flexible pipes, clockwise torsion load, or which coupled with axial compression and wet collapse load, should be avoided.

How Reliable Is Your Uninterruptible Power System?: Eliminating Single Points of Failure

Industrial Uninterruptible Power Systems (UPSS) on floating offshore oil and gas platforms supply power to critical loads and require extremely high reliability and uptime. UPS configuration or topology can have a major impact on reliability and uptime, and although several UPS topologies are available on the market, space constraints can limit the options. It is important to understand topology and how the components that make up a UPS operate and impact reliability. We detail a specific UPS topology chosen for a floating production platform with high reliability requirements and space constraints. We also identify particular reliability concerns associated with that topology and outline different solutions, with their associated advantages and disadvantages.

Development of Fatigue Design Standards for Marine Structures

Abstract Fatigue design standards for offshore structures became needed with development of offshore structures in harsh environments like the North Sea during the 1970s. The need for fatigue design of ship structures became increased as more high strength steel was being used in these structures during the 1970s. New types of structures and structural components have been developed such as tension leg platforms and floating production platforms and support structures for wind turbines. These structures are subjected to significant dynamic loading such that fatigue design becomes the main issue and relevant fatigue design standards are needed. This paper gives an overview of the development of fatigue design standards for marine structures over the last 40 years.

Numerical modelling of acoustic pressure fields to optimize the ultrasonic cleaning technique for cylinders

Fouling build up is a well-known problem in the offshore industry. Accumulation of fouling occurs in different structures, e.g. offshore pipes, ship hulls, floating production platforms. The type of fouling that accumulates is dependent on environmental conditions surrounding the structure itself. Current methods deployed for fouling removal span across hydraulic, chemical and manual, all sharing the common disadvantage of necessitating halting production for the cleaning process to commence. Conventionally, ultrasound is used in ultrasonic baths to clean a submerged component by the generation and implosion of cavitation bubbles on the fouled surface; this method is particularly used in Reverse Osmosis applications. However, this requires the submersion of the fouled structure and thus may require a halt to production. Large fouled structures such as pipelines may not be accommodated. The application of high power ultrasonics is proposed in this work as a means to remove fouling on a structure whilst in operation. The work presented in this paper consists of the development of a finite element analysis model based on successful cleaning results from a pipe fouled with calcite on the inner pipe wall. A Polytec 3D Laser Doppler Vibrometer was used in this investigation to study the fouling removal process. Results show the potential of high power ultrasonics for fouling removal in pipe structures from the wave propagation across the structure under excitation, and are used to validate a COMSOL model to determine cleaning patterns based on pressure and displacement distributions for future transducer array design and optimization.

Numerical study of the coupled motion responses in waves of side-by-side LNG floating systems

The paper presents a numerical and experimental study of multi-body systems composed of two floating structures floating side-by-side in head seas. This type of arrangement is being investigated for the operation of liquefied natural gas (LNG) transfer from a floating production platform to a shuttle tanker in an offshore environment. The floating structures are moored amongst themselves and floating in close proximity. The objective is to investigate the first order relative motions of side-by-side moored floating structures and the loads on the mooring lines and fenders, and to validate the existing numerical method by comparing to experimental results. Two case studies are analyzed. The first consists of two similar tankers moored together in intermediate water depth (80m). The second configuration considers a floating production storage and offloading system for production of LNG (FLNG), with a side moored shuttle tanker. The experimental work was carried out in two offshore wave basins with scaled models subjected to irregular operational seastates. The measured responses include the motions of the two floating structures and the loads in the mooring lines connecting them. A Green's function panel method is used for the hydrodynamic calculations.

Axial dispersion of suspended sediments in vertical upward pipe flow

The increasing pressure on earth׳s raw material resources forces the search for alternatives. An alternative source of raw materials is deep sea deposits. The mining of deep sea deposits comes with many challenges, one of them being the vertical transport of excavated material from the seafloor to a floating production platform at the surface. Material can be transported vertically by means of suspending the material in an upward flow of water in a riser. When the riser is fed irregularly by intermittent batches of solids, accumulation of solids can occur that in turn can result in riser blockage. The accumulation process is counteracted by axial dispersion of the batches. In this paper the vertical hydraulic transport of batches is experimentally explored to get insight in the influence of solids on the axial dispersion process. By analysis of the decrease in volume fraction, the axial dispersion coefficient for the vertical transport of batches of sand, gravel and plastic grains relative to the Taylor dispersion coefficient for dissolved matter in turbulent pipe flow is determined. The analysis shows that the presence of solids attenuates axial dispersion such that it plays a minor role in the transport process, particularly for coarse sediments.

Stress analysis of the subsea dynamic riser baseprocess piping

Thesubsea dynamic riser base (SDRB) is an important piece of equipment for the floating production platform mooring system. One end is connected to the rigid pipeline, carrying a rigid pipeline thermal expansion load and the other end is connected to a flexible riser, carrying the dynamic load of the flexible riser, so its function is a transition connection between the flexible riser and the rigid pipeline which fixes the flexible riser on the seabed. On the other hand, as a typical subsea product, the design will satisfy the requirements of the standards for subsea products. By studying the stress analysisphilosophy of the topside piping and subsea pipeline, a physical model and procedure for piping stress analysis of the SDRB have been established. The conditions of the adverse design load have been considered, and a combination of the static load from the rigid pipeline and the dynamic load flexibility has also been optimized. And a comparative analysis between the AMSE, DNV and API standards for piping stress with the checking rules has been done. Because the SDRB belongs to the subsea pipeline terminal product, the use of DNV standards to check its process piping stress is recommended. Finally, the process piping stress of the SDRB has been calculated, and the results show that the jacket pipe and the carrier pipe stress of the SDRB process piping satisfy the DNV standards as a whole.The bulkhead cannot be accurately simulated by the AutoPIPE software which uses the FEA software ANSYS in the detailed analysis, but the checking results will still meet the requirements of the DNV standards.

Floating production platforms and their applications in the development of oil and gas fields in the South China Sea

This paper studies the current available options for floating production platforms in developing deepwater oil fields and the potential development models of future oil and gas exploration in the South China Sea. A detailed review of current deepwater platforms worldwide was performed through the examples of industry projects, and the pros and cons of each platform are discussed. Four types of platforms are currently used for the deepwater development: tension leg platform, Spar, semi-submersible platform, and the floating production system offloading. Among these, the TLP and Spar can be used for dry tree applications, and have gained popularity in recent years. The dry tree application enables the extension of the drilling application for fixed platforms into floating systems, and greatly reduces the cost and complexity of the subsea operation. Newly built wet tree semi-submersible production platforms for ultra deepwater are also getting their application, mainly due to the much needed payload for deepwater making the conversion of the old drilling semi-submersible platforms impossible. These platforms have been used in different fields around the world for different environments; each has its own advantages and disadvantages. There are many challenges with the successful use of these floating platforms. A lot of lessons have been learned and extensive experience accumulated through the many project applications. Key technologies are being reviewed for the successful use of floating platforms for field development, and potential future development needs are being discussed. Some of the technologies and experience of platform applications can be well used for the development of the South China Sea oil and gas field.

Development planning of deepwater gas fields: the application of floating production platforms

Producing North West Australia (NWA) deepwater hydrocarbon reserves, particularly gas reserves to LNG plants, poses unique challenges. These include extreme metocean conditions, unique geotechnical conditions, long distances to infrastructure and LNG plants, as well as high reliability/availability of supply. This extended abstract addresses important technical, commercial, and regulatory factors that drive the field development planning, including the selection of suitable production facilities for these deepwater hydrocarbon developments off NWA. While all-subsea developments have been an inspiration for offshore engineers for a few decades, subsea gas compression, dehydration, power supply, and control are still technically and commercially demanding, especially for long distance tie-backs. Subsea well intervention and facility maintenance requirements also favour the application of dedicated floating platforms. A wet or dry-tree floating production platform, therefore, is required in most cases. Whereas Semisubmersible, TLP, Spar, FPSO, and FLNG (or LNG FPSO) designs all have the attributes to be a host gas production facility or a part of a production system, only oil FPSOs have been installed in this region to date. Linkages between key reservoir and fluid characteristics and surface facility functionalities are discussed in this extended abstract. Advantages and disadvantages of various platform designs are compared. A focus is on the influence of regional drivers and site characteristics, in particular, metocean and geotechnical conditions and remoteness of the NWA fields. The differentiation between oil and gas developments are addressed. It is emphasised that platform applicability and compatibility should be assessed in the context of field development planning for individual projects to achieve optimum risked life cycle financial values.

Process Design of Natural Gas Liquid Recovery Processes

This research was supported by a Floating Production Platform Topside Systems and Equipment Development Grant from the MOTIE (Ministry of Trade, Industry and Energy) of the Korean government.