Subsea Production System Research Articles

A resilience-driven emergency maintenance operation scheme optimization method based on risk

System failure caused by unexpected disruptions is unavoidable and can lead to catastrophic consequences. To complete the emergency maintenance operation safely and efficiently, a well-formulated emergency maintenance scheme is crucial. A resilience-driven optimization methodology for the emergency maintenance operation scheme with considering maintenance operational risk is proposed. The maintenance operational risk is assessed by combining Job Safety Analysis, Bayesian networks and the matter element theory. A graphical evaluation and review technique (GERT) model is established based on the informed maintenance operational risk to evaluate the emergency maintenance scheme. According to derived results of the GERT model, the expected time and the expected risk are preliminarily optimized. A re-optimization model focusing on the system resilience is established to optimize the suitable maintenance operation time for each equipment and the reasonable equipment maintenance sequence for the system. The emergency maintenance scheme optimization for the subsea production system is utilized to demonstrate the proposed method.

Intelligent full-stage stable fault diagnosis method for subsea production system

Subsea production system is a large slowly changing system. Through fault diagnosis, the state of it can be got in time, and this can ensure the smooth production of oil and gas. When the training data is insufficient, the performance of data driven methods is poor. Influenced by slow changes, the performance of model-based fault diagnosis methods may fluctuate. For long-term stable monitoring of subsea production system, an intelligent full-stage stable fault diagnosis method for subsea production system is proposed. A fault diagnosis framework with both digital and model drives is proposed. Model-based diagnostic model is used to achieve accurate diagnosis under insufficient data. Data driven model is trained continuously to achieve stable diagnosis. A dynamic digital twin model is proposed to accelerate the process of training. A case from the South China Sea is used to study the performance of this method. The results show that this method is stable over a long period.

A grouping module assessment method for ocean engineering systems: Subsea tree system as a case

In the ocean engineering environment, the quality failure data of complex systems are difficult to obtain due to the high experiment cost. In addition, using a single model to analyze risk, reliability, availability, and maintainability is a big challenge. Based on the fault tree, Dynamic Bayes and Markov models, a state assessment method for ocean engineering systems with multiple maintenance modes is proposed in this paper. This method gives full play to the advantages of the three methods, and comprehensively analyzes the risk, reliability, availability and maintainability. This method uses fault tree and Markov model to pre-process fault data, and then inputs the pre-processed fault data into the multi-state degradation model based on dynamic Bayesian theory. Considering the maintenance strategies of no repair, perfect repair, imperfect repair and preventive repair, the model is iterated and adjusted until the model has processed all the event data and the updated model can best reflect the state of the system. The method is verified by taking the subsea tree of the subsea production system as an example. The obtained tree reliability index (mean time without failure) is basically consistent with the failure statistics of offshore and onshore reliability databases, which verifies the accuracy of the proposed method.

A Method for Recognition and Coordinate Reference of Autonomous Underwater Vehicles to Inspected Objects of Industrial Subsea Structures Using Stereo Images

To date, the development of unmanned technologies using autonomous underwater vehicles (AUVs) has become an urgent demand for solving the problem of inspecting industrial subsea structures. A key issue here is the precise localization of AUVs relative to underwater objects. However, the impossibility of using GPS and the presence of various interferences associated with the dynamics of the underwater environment do not allow high-precision navigation based solely on a standard suite of AUV navigation tools (sonars, etc.). An alternative technology involves the processing of optical images that, at short distances, can provide higher accuracy of AUV navigation compared to the technology of acoustic measurement processing. Although there have been results in this direction, further development of methods for extracting spatial information about objects from images recorded by a camera is necessary in the task of calculating the exact mutual position of the AUV and the object. In this study, in the context of the problem of subsea production system inspection, we propose a technology to recognize underwater objects and provide coordinate references to the AUV based on stereo-image processing. Its distinctive features are the use of a non-standard technique to generate a geometric model of an object from its views (foreshortening) taken from positions of a pre-made overview trajectory, the use of various characteristic geometric elements when recognizing objects, and the original algorithms for comparing visual data of the inspection trajectory with an a priori model of the object. The results of experiments on virtual scenes and with real data showed the effectiveness of the proposed technology.

Subsea Production System Allows Safe and Successful Gas Hydrate Plug Remediation

Subsea Production System Allows Safe and Successful Gas Hydrate Plug Remediation

Life Cycle Structural Integrity Design Approach for the Components of Subsea Production System: SCSSV as a Case Study

Life Cycle Structural Integrity Design Approach for the Components of Subsea Production System: SCSSV as a Case Study

Целесообразность создания пилотной площадки по отработке безопасной эксплуатации технико- технологических средств для освоения длительнозамерзающих акваторий арктических морей

The Russian sector of the Arctic shelf to the east of the Kara Sea has been very poorly studied by seismic exploration and drilling. It is conditioned by several causes, one of which is the short ice-free period in combination with the remoteness from the shore bases, which significantly hampers operations making them extremely expensive and resource-consuming. The development of natural resources in conditions specific to the Kara Sea and to the east of it is restricted by the depths of the use of ice-resistant platforms and remoteness from the shore bases for subsea production systems. Various experts consider the perspective solutions of the implementation of subsea manned and unmanned drilling and production systems as concepts. At the same time, the existing technologies and the deep drilling technique are creatively reconsidered; the conclusion regarding the inapplicability of the currently used solutions for subsea wellhead drilling has been made. A specific focus has been made on the safety of the future oil and gas production facilities in the Arctic, considering both the operation of highly hazardous and complex manned underwater engineering facilities and the current strained geopolitical situation and the threats of terrorism. It is supposed that testing of perspective engineering solutions and technologies will be more efficient not only in conditions of plant testing laboratories and centers but also at the test site with maximally realistic conditions of the future operation. The analysis of potential test sites in accordance with selected criteria has chosen the Murmansk gas field in the southeast part of the Barents Sea as a prospective facility. Due to the large scale and complexity of the long-term challenge (20–30 years), a conclusion is made about the role of the state as an initiator and coordinator of the project involving the oil and gas companies concerned (Rosneft, Gazprom), scientific centers, and equipment manufacturers.

Deep learning-driven optimization design for the configuration of lazy-wave umbilical cables

Umbilical cables are essential components of subsea production systems for deep sea oil and gas exploration. Umbilical cables are often set to specific configurations that compensate for the motion of the floating body resulting from harsh environmental loads during operation to ensure structural safety and proper functioning. However, the optimization design of the umbilical cable configuration is a challenging problem owing to highly nonlinear relationship between loads and structural responses as well as the huge computational cost of evaluating numerous sea state combinations. This study proposes a deep learning-driven optimization design framework based on the residual artificial neural network to address the configuration design of lazy-wave umbilical cables. A parallel accelerated computation method based on Adam optimizer was established for the generation of the database. The transfer learning technique was also introduced into the deep learning model to build a configuration design prediction model based on small samples, which significantly reduced the cost of model building and training. Based on the above optimization design framework, a combination of tensile and bending optimization for a lazy-wave umbilical cable configuration was achieved, verifying the effectiveness and practicality of the proposed approach. This study provides an important reference for the rapid engineering design of umbilical cables.

Flow assurance analysis in Front End Engineering Design (FEED) of Subsea Flowline and Riser

Innovative subsea production systems (SPS) are required for deep-water oil and gas exploration in order to transport multiphase fluids—a complex mixture of water, gas, and oil—across long distances under challenging conditions. Significant technological challenges confront these systems, such as flow assurance, which ensures continuous fluid flow through pipelines, flowlines, and wells. Flow assurance issues can significantly impact production and incur costly downtime. This paper emphasizes the critical role of flow assurance analysis during the crucial Front-End Engineering Design (FEED) stage of SPS development. By utilizing industry-standard simulation tools like PIPESIM™, engineers can proactively identify and mitigate potential flow assurance problems that could hinder productivity. These analyses are crucial as FEED decisions significantly impact project cost-effectiveness. To illustrate the practical application of flow assurance principles, the paper presents a case study of a subsea architecture design for a specific manifold system. Considering operator requirements, flow assurance simulations were employed to guide critical decisions regarding material selection and optimal sizing of risers and flowlines. This demonstrates how flow assurance considerations during FEED directly influence cost-effective and optimized SPS design.

Challenges and strategic solutions in commissioning and start-up of subsea production systems

The commissioning and start-up of subsea production systems represent critical phases in offshore oil and gas operations, where meticulous planning and execution are essential for success. This abstract presents an overview of the challenges encountered during these phases and proposes strategic solutions to address them effectively. Environmental factors such as deepwater operations and subsea geology pose significant challenges to commissioning and start-up activities. Technical challenges include ensuring equipment reliability and seamless integration of control systems in harsh underwater conditions. Operational challenges such as remote monitoring and intervention and personnel safety further compound the complexities of these operations. Strategic solutions to mitigate these challenges include advanced planning and simulation using digital twin technology and scenario planning. Enhanced risk management strategies, including contingency planning and early detection systems, are vital to anticipate and manage potential issues effectively. Collaborative partnerships between stakeholders, including suppliers and cross-disciplinary teams, foster innovation and enhance project resilience. Drawing from successful case studies and lessons learned, this abstract emphasizes the importance of proactive planning, risk mitigation, and collaborative approaches in ensuring the successful commissioning and start-up of subsea production systems. By implementing these strategic solutions, operators can enhance operational efficiency, minimize downtime, and improve safety outcomes, ultimately contributing to the long-term viability and sustainability of offshore energy production.

DESIGN OF A 3/2-WAY SELF-RETAINING (SELF-LOCKING) INDIRECT-ACTING ELECTRO-HYDRAULIC VALVE AND ITS MATHEMATICAL MODEL

A current topic of scientific research and development for the subsea production system, minemill industry, for the nuclear industry and other industries that require the use of hydraulic distributors operating in conditions of limited electrical power and/or explosive environment is currently the problem of designing self-retaining (self-locking) indirect-action electro-hydraulic valves (distributors). The article describes the created design of a 3/2-way self-retaining (self-locking) indirect-acting electro-hydraulic valve (distributor). The principle of operation of the distributor is described in detail. Its basic hydraulic diagram is given. The developed object-oriented nonlinear mathematical model of a 3/2-way self-retaining (self-locking) indirect-acting electro-hydraulic valve is presented. Dynamic equations are presented that describe the movements of the shut-off and control element (SCE) of the main distributor and two pilot valves; equations describing the flow of liquid through the main distributor's SCE and the law of changes in the overlap area of the main distributor's SCE flow sections; equations that determine the dynamic characteristics of an electromechanical converter (EMC). Transient processes were obtained and presented, with the help of which the dynamic quality indicators of the created a 3/2-way self-retaining (self-locking) indirect-acting electro-hydraulic valve were found. Based on the analysis, appropriate conclusions were drawn. The scientific novelty of the work includes the created object-oriented nonlinear mathematical model and the developed design of a 3/2-way self-retaining (self-locking) indirect-acting electro-hydraulic valve.

Reliability-Based Preventive Maintenance Strategy for Subsea Control System

The subsea control system, a pivotal element of the subsea production system, plays an essential role in collecting production data and real-time operational monitoring, crucial for the consistent and stable output of offshore oil and gas fields. The increasing demand for secure offshore oil and gas extraction underscores the necessity for advanced reliability modeling and effective maintenance strategies for subsea control systems. Given the enhanced reliability of subsea equipment due to technological advancements, resulting in scarce failure data, traditional reliability modeling methods reliant on historical failure data are becoming inadequate. This paper proposes an innovative reliability modeling technique for subsea control systems that integrates a Wiener degradation model affected by random shocks and utilizes the Copula function to compute the joint reliability of components and their backups. This approach considers the unique challenges of the subsea environment and the complex interplay between components under variable loads, improving model accuracy. This study also examines the effects of imperfect maintenance on degradation paths and introduces a holistic lifecycle cost model for preventive maintenance (PM), optimized against reliability and economic considerations. Numerical simulations on a Subsea Control Module demonstrate the effectiveness of the developed models.

Combinatorial reasoning-based abnormal sensor recognition method for subsea production control system

The subsea production system is a vital equipment for offshore oil and gas production. The control system is one of the most important parts of it. Collecting and processing the signals of subsea sensors is the only way to judge whether the subsea production control system is normal. However, subsea sensors degrade rapidly due to harsh working environments and long service time. This leads to frequent false alarm incidents. A combinatorial reasoning-based abnormal sensor recognition method for subsea production control system is proposed. A combinatorial algorithm is proposed to group sensors. The long short-term memory network (LSTM) is used to establish a single inference model. A counting-based judging method is proposed to identify abnormal sensors. Field data from an offshore platform in the South China Sea is used to demonstrate the effect of the proposed method. The results show that the proposed method can identify the abnormal sensors effectively.

High-Pressure Separation: New Technology in the Subsea Toolbox

_ Subsea production systems have come far in the more than 60 years since the first deployment in the US Gulf of Mexico, helping many countries unlock their offshore hydrocarbon riches in the years that followed. For Brazil, it was a combination of advances in subsea technologies and floating production, storage, and offloading vessel (FPSO) designs that supported the growth of its offshore oil and gas prowess. From those first forays into the Sergipe-Alagoas basin in the northeast during the 1970s, the country’s offshore oil and gas footprint has grown significantly, with today’s production from the pre-salt Campos and Santos basins—located farther from shore and in much deeper water—launching state-run oil company Petrobras to a top spot among the ranks of global producers. The ongoing development of its offshore fields will continue to boost the country’s oil and natural gas production in 2024. Since December 2022, five FPSOs have been brought online, with four installed in 2023 delivering record output. The fifth one—the FPSO Sepetiba—delivered a New Year’s Day surprise when it came online at Mero 2 oil field on 31 December 2023. HISEP, a new subsea technology currently being readied for pilot testing, could potentially ensure continued future production of the Mero field and others by capturing CO2-rich dense gases directly from the wellstream and reinjecting it into the reservoir. The technology also frees up much-needed space and reduces weight on the FPSO’s topside by moving the separation process to the seafloor. Challenges and Solutions Brazil’s challenging offshore pre-salt region—first explored by Petrobras in 2005—contains estimated reserves of 30 to 40 billion BOE and comes with an extensive list of development challenges. Its Santos Basin, for example, lies in ultradeep water with hydrocarbon reservoirs located at extreme depths ranging from 5500 to 7600 m below sea level and under salt layers more than 2000 m thick. But the challenges do not end there. Managing the basin’s high gas/oil ratio (GOR) and CO2 content leaves a significant operational footprint. In OTC 29762, authors from Petrobras noted that developing the pre-salt reservoirs requires “large production facilities with complex gas processing plants that limit the oil processing and storage capacities.” In the paper presented at the 2019 Offshore Technology Conference (OTC) Brasil, the authors said that the gas processing plants for some pre-salt fields with high production indexes, GOR, and CO2 content account for nearly 60% of the total FPSO topsides area. The Santos Basin is home to the Mero oil field, the country’s third-largest pre-salt field and the first under a production-sharing contract awarded to the Petrobras-led Libra Consortium. The field is considered one of the largest hydrocarbon discoveries in the past decade, covering about 320 km2 of the Libra block and with a net pay zone reaching 420 m filled with 29 °API oil and high productivity, according to Ana Luiza Neder, et al. (OTC 32784).

Sealing Degradation Modeling and Reliability Analysis Method of Deep‐Water Pipeline Connector Based on the Two‐Phase Nonlinear Wiener Process

The deep‐water pipeline connector (DPC) is a key piece of equipment for the connection of multiple facilities located in different positions of the subsea production system. Establishing a DPC sealing degradation model considering the internal corrosion can provide a basis for its structural design and maintenance. Considering the characteristics of nonlinear and multiphase for the DPC degradation process, a two‐phase nonlinear Wiener process is applied to establish a DPC degradation model. It can reasonably consider the commonly encountered situation that a change point locates among the test times. DPC reliability analysis and lifetime prediction methods are constructed after a maximum likelihood method is employed to estimate the hyperparameters of the established degradation model. Finally, a subsea Christmas tree wellhead connector is taken as an example to verify the reasonability and effectiveness of the method. The results indicate that the proposed method can describe the nonlinear time‐varying properties caused by the DPC internal corrosion more accurate and reasonable than other traditional classic methods, and a more reasonable lifetime assessment result can be obtained.

Optimization of subsea production facilities layout based on cluster manifold system considering seabed topography

High investment in deep-water development highlights the importance of optimizing the subsea layout, a properly optimized subsea production system reduces costs and contributes to production performance. Aiming at the minimum total construction cost of a subsea cluster manifold system, an integrated mathematical model considering the combination of subsea well grouping, cluster manifold layout, connection relationships, pipe routes and seabed topography is developed in this study. A modified adaptive particle swarm optimization (MAPSO) algorithm coupled with A-star algorithm, clustering algorithm and minimum spanning tree algorithm is used to solve the model by using a newly proposed process. The feasibility and practicality of the model is verified by designing the layout of a deep-water oil field, and the influence of manifold number and seabed topography is demonstrated by the difference in suggested cost. The model provides a new method which can be used to estimate costs more reliably.

Investigation on the Erosion Characteristics of Liquid–Solid Two-Phase Flow in Tee Pipes Based on CFD-DEM

Tee pipes are widely utilized in pipeline transportation, especially in subsea production systems and the chemical industry. The purpose of this research is to study the influences of gravity direction, conveying parameters and particle properties on the erosion distribution in tee junctions. Investigation using the CFD-DEM coupled method is conducted on the flow mechanisms and erosion characteristics in a tee junction under different flow conditions. Firstly, numerical calculations of liquid–solid two-phase flow in a vertical cylindrical pipe are performed, and the comparison between simulation results and experimental results is carried out. Then, the verified lift and erosion models are used for the numerical calculations of tee pipes. Flow mechanisms and erosion characteristics are numerically investigated through analysis of the velocity profiles, streamlines, and erosion contours. The results indicate that the gravity direction has a nonnegligible influence on the cross-sectional velocity profiles, particularly under the condition of high velocity and high particle concentration. The region with the maximum erosion rate occurred at the branch pipes, about three fourths of the pipe diameter away from the tee junction.

Cross-validation enhanced digital twin driven fault diagnosis methodology for minor faults of subsea production control system

A subsea production system is essential for the subsea production of oil and gas. Real-time monitoring can ensure safe production. A subsea production control system is the core of the subsea production system and the top priority to be monitored. Minor faults refer to faults with weak characteristics and are difficult to be found. They are common and pose significant risks in subsea production system. Safe operation of the system can be guaranteed to the greatest extent with a timely detection and handling of minor faults. Digital Twin driven fault diagnosis is an effective method to monitor the subsea production control system. However, the combination of digital twin and fault diagnosis is not comprehensive, especially in data interaction. It leads to the fact that digital twin cannot improve fault diagnosis accuracy significantly, mainly when a minor fault occurs. A cross-validation enhanced digital twin-driven fault diagnosis methodology for minor faults of the subsea production control system is proposed to achieve high accuracy. Control, loss and fault parameters are presented and used for building a digital twin model. Bayesian Networks are used to construct a fault diagnosis model. Single and cumulative errors are used to measure the difference between digital twin models and physical systems. A verification feedback method is used to check the diagnosis results. Data of four days of a subsea production system in the South Sea of China is used to demonstrate the proposed methodology. The results show that the method can improve the diagnosis accuracy for minor faults effectively.

Mechanical Behavior and Sealing Performance Study of Subsea Connector Core-Sealing Components under the Combined Action of Internal Pressure, Bending Moment, and Axial Load

A complete subsea production system (SPS) is assembled by interconnecting subsea manufacturing facilities through subsea connectors. To ensure the reliability and longevity of the SPS, it is imperative to thoroughly investigate the mechanical behavior and sealing performance of the subsea connector’s core-sealing components. In this study, the loading conditions of the subsea clamp connector are examined to analyze the load transfer relationship between its components under different modes. A mathematical model for the load transfer between locking torque and sealing contact pressure is developed for the preloading mode, and the concept of mechanical transfer efficiency is introduced. Another mathematical model for the load transfer between the locking torque and the design pressure is developed for the operation mode. Furthermore, a three-dimensional full-size finite element model of the subsea clamp connector is established to analyze the effects of complex loads on the mechanical behavior and sealing performance of its core-sealing components. The simulation results indicate that internal pressure loading positively affects the sealing of the subsea connector, and that the stress distribution in the core-sealing components under bending moment loading exhibits significant asymmetric characteristics. Additionally, the superposition of axial tensile loads reduces the effect of the bending moment on the strength of the core seal member but further weakens the seal. Finally, an experimental system is designed to validate the simulation results.

Design-to-Cost Approach Increases Project Value of Troll Phase 3

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30954, “Troll Phase 3: The Next Step for a Groundbreaking Giant,” by Bjørn Laastad, Knut Ellevog, and Roger Oen Jensen, Equinor, et al. The paper has not been peer reviewed. Copyright 2021 Offshore Technology Conference. Reproduced by permission. _ An important driver for maximizing value creation for the Troll Phase 3 gas project offshore Norway was to identify ways to reduce the pressure drop in the value chain from the reservoir to the onshore terminal. Using a design-to-cost approach in the concept-selection phase has affected design of the wells, subsea production system, pipeline, and a new inlet separator on the platform. The final design has enabled a significant increase of project value by accelerated gas deliveries, reduction of energy consumption, and lowered CO2 emissions. Troll Phase 3 Business Case and Development Concept The Troll Phase 3 business case is to develop the vast gas reserves in Troll West, thus recovering approximately 340 billion std m3 gas over a 40‑year period. Production from Troll West will be commingled with Troll East gas production at Troll A. The Troll West volumes will supply approximately 40% of the total Troll A delivery and enable a 5‑year continuation of the current high plateau production level of 36 billion std m3/yr and an extension of field lifetime by 15 years until 2062. A prerequisite for the Phase 3 project is that the annual summer/winter swing production will be from the Troll A wells. Consequently, Troll West production will be stable and not affected by seasonal variations in market demand. Following a comprehensive concept‑selection analysis made from the perspective of the field’s life cycle, it was decided in May 2017 to develop Troll Phase 3 as a subsea tieback to the Troll A platform. The subsea design facilitates possible future Troll West gas building blocks. The first section of the complete paper is devoted to a discussion of the flow‑assurance aspects of the development; this component is not included in this synopsis. Troll Phase 3 Well Design During the feasibility and concept‑selection phases, an important opportunity to maximize value creation was found to be improving individual well performance by enlarging the tubing size. The standard 7‑in. tubing would have been a considerable production restriction. By enabling a larger tubing size, the production from each well could be increased and the required number of wells could be reduced. The big-bore completion design was new to the operator but had been implemented successfully in other high‑rate gas fields in the industry. Using a design‑to‑value process, the tubing size for Troll Phase 3 was increased to 9⅝ in. Comparison of a big‑bore well to a standard 7‑in. well in 2030 gives a reduced pressure drop of more than 12 bars/well, with an increased production potential for the big‑bore well of greater than 1000 std m3/d. Consequently, the required number of wells could be reduced by approximately 40% (from 14 to eight). Factoring in the total cost of the final gas producers, six saved wells equals a total cost savings of $150 million ($300 million including the subsea facilities).