Safety Problems Caused by Hydrate Formation in Deepwater Production Operation

Although hydrate formation phenomenon has been identified for many years, this is still one of the most challenging problems in oil & gas industry as they are associated with flow assurance problems and safety issues. Although, many studies have focused on developing thermodynamic and kinetic models to understand and predict hydrate formation, this phenomenon is not fully understood and there is not a general methodology for the quantification of the risk that considers the uncertainty associated with key input parameters. Therefore, there is a need for developing risk assessment methodologies, which considers, not only the models for predicting hydrates, but also the organizational factors associated with the hydrate management system. In this work, a comprehensive framework was developed for estimating the risk of hydrate formation in a subsea production operation taking into consideration the effectiveness of the entire hydrate management system. The proposed framework was divided in three areas: 1) definition of causal and consequence models; 2) application of Bayesian Networks; and 3) sensitivity analysis of the thermodynamic or kinetic models. In order to probe the concept and illustrate the application of the proposed framework, a hypothetical case study was created based on literature data and inputs provided by flow assurance experts from academia and industry. Causal and consequence models were developed, including a visual representation of the preventive and mitigative measures. The hydrate equilibrium curves were generated using PVTsim Nova software, and the uncertainty analysis was done with Latin Hypercube Method and statistical iii calculations. The Bayesian Networks method was used to understand the complexities associated with the Hydrate Management System. This model solved with AgenaRisk software using discrete and continuous distributions. The results of this work include the visual representation of the probabilistic relationship between certain components and variables of a typical hydrate management system, which can affect the reliability of the control and preventive measures for hydrate control. The probability values calculated in this case study were in agreement with likelihood values typically used in a risk matrix, which probes that the proposed approach is a good starting point for future improvements to the proposed framework

Computational framework for real-time diagnostics and prognostics of aircraft actuation systems

Prognostics and Health Management (PHM) are emerging approaches to product life cycle that will maintain system safety and improve reliability, while reducing operating and maintenance costs. This is particularly relevant for aerospace systems, where high levels of integrity and high performances are required at the same time. We propose a novel strategy for the nearly real-time Fault Detection and Identification (FDI) of a dynamical assembly, and for the estimation of Remaining Useful Life (RUL) of the system. The availability of a timely estimate of the health status of the system will allow for an informed adaptive planning of maintenance and a dynamical reconfiguration of the mission profile, reducing operating costs and improving reliability. This work addresses the three phases of the prognostic flow - namely (1) signal acquisition, (2) Fault Detection and Identification, and (3) Remaining Useful Life estimation - and introduces a computationally efficient procedure suitable for real-time, on-board execution. To achieve this goal, we propose to combine information from physical models of different fidelity with machine learning techniques to obtain efficient representations (surrogate models) suitable for nearly real-time applications. Additionally, we propose an importance sampling strategy and a novel approach to model damage propagation for dynamical systems. The methodology is assessed for the FDI and RUL estimation of an aircraft electromechanical actuator (EMA) for secondary flight controls. The results show that the proposed method allows for a high precision in the evaluation of the system RUL, while outperforming common model-based techniques in terms of computational time.Comment: 57 page

Algal proliferation risk assessment using Vine Copula-based coupling methods in the South-to-North Water Diversion Project of China

The Middle Route of the South-to-North Water Diversion Project of China (MRSNWDPC), i.e., the longest inter-basin water diversion project (1,432 km) in the world, has delivered more than 60 billion m3 of water resources to North China and benefiting more than 100 million people since December 2014. However, the abnormal algal proliferation in the main canal under low nutrient background has seriously threatened the water quality safety of this mega project. In this research, 3 years of monitoring data matrix, including water temperature (WT), flow discharge (Q), flow velocity (V), dissolved oxygen (DO), and the algal cell density (ACD), from the main canal of the MRSNWDPC were analyzed. The nonlinear relationships were determined based on multiple regression models, and a composite risk analysis model was constructed by Latin hypercube sampling (LHS) method coupled with Vine Copula function. The impacts of different hydrological and environmental factors on algal proliferation were comprehensively analyzed by Bayesian theory. The results showed that the WT gradually decreased from upstream to downstream, with a narrow range of 16.6–17.4°C, and the annual average concentrations of DO showed a gradual increase from upstream to downstream. The flow velocity of MRSNWDPC had a tendency to increase year by year, and the maximum flow velocity exceeds 0.8 m/s upstream, midstream and downstream by 2018. The ACD accumulated along the main canal, and the annual average ACDs of downstream were the highest, ranging from 366.17 to 462.95 × 104 cells/L. The joint early-warning method considering both water temperature and flow velocity conditions is an effective way for algal proliferation risk warning management. When water temperatures of the upstream, midstream, and downstream were below 26, 26, and 23°C, respectively, the algal proliferation risk can be controlled under 50% by the flow velocity at 0.3 m/s; otherwise, the flow velocity needs to be regulated higher than 0.8 m/s. In order to keep the midstream and downstream avoid abnormal algal proliferation events (ACD ≥ 500 × 104 cells/L), the corresponding ACDs of the upstream and midstream need to be controlled lower than 319 × 104 cells/L and 470 × 104 cells/L, respectively. This study provides a scientific reference for the long-distance water diversion project’s algal control and environmental protection. The proposed coupling Vine Copula models can also be widely applied to multivariate risk analysis fields

The probabilistic solution of dike breaching due to overtopping

Disertační práce se zabývá analýzou spolehlivosti ochranných hrází na základě odhadu pravděpodobnosti poruchy hráze. Práce na základě teoretických poznatků, experimentálních a statistických výzkumů, matematických modelů a terénního šetření rozšiřuje soudobé znalosti analýzy spolehlivosti hráze ohrožené porušením v důsledku přelití. Tato práce obsahuje výsledky pravděpodobnostního řešení možné poruchy levobřežní ochranné hráze řeky Dyje v místě vesnice Ladná v České Republice v důsledku jejího přelití. V rámci práce byl navržen matematický model popisující proces přelití a proces eroze hráze. Proces přelití hráze byl popsán jednoduchými hydraulickými rovnicemi. Po začátku přelití hráze dojde k jejímu porušení za předpokladu překročení odolnosti povrchu hráze proti erozi vlivem proudící vody na vzdušním líci. Proces eroze hráze byl popsán jednoduchými rovnicemi pro transport sedimentů. Tyto rovnice obsahují parametry, které byly stanoveny s využitím údajů z minulých reálných poruch hrází. V rámci rozboru modelu byly stanoveny nejistoty ve vstupních datech a následně byla provedena citlivostní analýza s použitím „screening“ metody. Za účelem dosažení pravděpodobnostního řešení byly vybrané vstupní parametry uvažovány jako náhodné veličiny s různým rozdělením pravděpodobnosti. Pro generování sady náhodných hodnot pro vybrané vstupní veličiny byla použita metoda Latin Hypercube Sampling (LHS). V procesu porušení hráze v důsledku jejího přelití byly identifikovány čtyři typické fáze. Konečné výsledky této studie mají formu pravděpodobností vzniku jednotlivých typických fází porušení hráze.Doctoral thesis deals with reliability analysis of flood protection dikes by estimating the probability of dike failure. This study based on theoretical knowledge, experimental and statistical researches, mathematical models and field survey extends present knowledge concerning with reliability analysis of dikes vulnerable to the problem of breaching due to overtopping. This study contains the results of probabilistic solution of breaching of a left bank dike of the River Dyje at a location adjacent to the village of Ladná near the town of Břeclav in the Czech Republic. Within thin work, a mathematical model describing the overtopping and erosion processes was proposed. The dike overtopping is simulated using simple surface hydraulics equations. For modelling the dike erosion which commences with the exceedance of erosion resistance of the dike surface, simple transport equations were used with erosion parameters calibrated depending on data from past real embankment failures. In the context of analysis of the model, uncertainty in input parameters was determined and subsequently the sensitivity analysis was carried out using the screening method. In order to achieve the probabilistic solution, selected input parameters were considered random variables with different probability distributions. For generating the sets of random values for the selected input variables, the Latin Hypercube Sampling (LHS) method was used. Concerning with the process of dike breaching due to overtopping, four typical phases were distinguished. The final results of this study take the form of probabilities for those typical dike breach phases.

Methods for comparative assessment of active and passive safety systems with respect to reliability, uncertainty, economy, and flexibility

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.Includes bibliographical references.Passive cooling systems sometimes use natural circulation, and they are not dependent on emergency AC power or offsite power, which can make designs simpler through the reduction of emergency power supplying infrastructure. The passive system approach can lead to substantial simplification of the system as well as overall economic benefits, and passive systems are believed to be less vulnerable to accidents by component failures and human errors compared to active systems. The viewpoint that passive system design is more reliable and more economical than active system design has become generally accepted. However, passive systems have characteristics of a high level of uncertainty and low driving force for purposes of heat removal phenomena. These characteristics of passive systems can result in increasing system unreliability and may raise potential remedial costs during a system's lifetime. This study presents a comprehensive comparison of reliability and cost taking into account uncertainties and introduces the concept of flexibility using the example of active and passive residual heat removal systems in a PWR. The results show that the active system can have, for this particular application, greater reliability than the passive system. Because the passive system is economically optimized, its heat removal capacity is much smaller than that of the active system. Thus, functional failure probability of the passive system has a greater impact on overall system reliability than the active system. Moreover, considering the implications of flexibility upon remedial costs, the active system may more economical than the passive system because the active system has flexible design features for purposes of increasing heat removal capacity.by Jiyong Oh.Ph.D

Developing a workflow to represent fractured carbonate reservoirs for simulation models under uncertainties based on flow unit concept

International audienceDescription of fractured reservoir rock under uncertainties in a 3D model and integration with reservoir simulation is still a challenging topic. In particular, mapping the potential zones with a reservoir quality can be very useful for making decisions and support development planning. This mapping can be done through the concept of flow units. In this paper, an integrated approach including a Hierarchical Cluster Analysis (HCA), geostatistical modeling and uncertainty analysis is developed and applied to a fractured carbonate in order to integrate on numerical simulation. The workflow begins with different HCA methods, performed to well-logs in three wells, to identify flow units and rock types. Geostatistical techniques are then applied to extend the flow units, petrophysical properties and fractures into the inter-well area. Finally, uncertainty analysis is applied to combine different types of uncertainties for generating ensemble reservoir simulation models. The obtained clusters from different HCA methods are evaluated by the cophenetic coefficient, correlation coefficient, and variation coefficient, and the most appropriate clustering method is used to identify flow units for geostatistical modeling. We subsequently define uncertainties for static and dynamic properties such as permeability, porosity, net-to-gross, fracture, water-relative permeability, fluid properties, and rock compressibility. Discretized Latin Hypercube with Geostatistical (DLHG) method is applied to combine the defined uncertainties and create an ensemble of 200 simulation models which can span the uncertainty space. Eventually, a base production strategy is defined under operational conditions to check the consistency and reliability of the models created with UNISIM-II-R (reference model) as a real reservoir with known results. Results represent the compatibility of the methodology to characterize fractured reservoirs since those models are consistent with the reference model (used to generate the simulation models). The proposed workflow provides an efficient and useful means of supporting development planning under uncertainty

Comparison of Intake Gate Closure Methods At Lower Granite, Little Goose, Lower Monumental, And McNary Dams Using Risk-Based Analysis

The objective of this report is to compare the benefits and costs of modifications proposed for intake gate closure systems at four hydroelectric stations on the Lower Snake and Upper Columbia Rivers in the Walla Walla District that are unable to meet the COE 10-minute closure rule due to the installation of fish screens. The primary benefit of the proposed modifications is to reduce the risk of damage to the station and environs when emergency intake gate closure is required. Consequently, this report presents the results and methodology of an extensive risk analysis performed to assess the reliability of powerhouse systems and the costs and timing of potential damages resulting from events requiring emergency intake gate closure. As part of this analysis, the level of protection provided by the nitrogen emergency closure system was also evaluated. The nitrogen system was the basis for the original recommendation to partially disable the intake gate systems. The risk analysis quantifies this protection level

Comparison Of Intake Gate Closure Methods At Lower Granite, Little Goose, Lower Monumental, And Mcnary Dams Using Risk-Based Analysis

The objective of this report is to compare the benefits and costs of modifications proposed for intake gate closure systems at four hydroelectric stations on the Lower Snake and Upper Columbia Rivers in the Walla Walla District that are unable to meet the COE 10-minute closure rule due to the installation of fish screens. The primary benefit of the proposed modifications is to reduce the risk of damage to the station and environs when emergency intake gate closure is required. Consequently, this report presents the results and methodology of an extensive risk analysis performed to assess the reliability of powerhouse systems and the costs and timing of potential damages resulting from events requiring emergency intake gate closure. As part of this analysis, the level of protection provided by the nitrogen emergency closure system was also evaluated. The nitrogen system was the basis for the original recommendation to partially disable the intake gate systems. The risk analysis quantifies this protection level

Algal proliferation risk assessment using Vine Copula-based coupling methods in the South-to-North Water Diversion Project of China

The Middle Route of the South-to-North Water Diversion Project of China (MRSNWDPC), i.e., the longest inter-basin water diversion project (1,432 km) in the world, has delivered more than 60 billion m3 of water resources to North China and benefiting more than 100 million people since December 2014. However, the abnormal algal proliferation in the main canal under low nutrient background has seriously threatened the water quality safety of this mega project. In this research, 3 years of monitoring data matrix, including water temperature (WT), flow discharge (Q), flow velocity (V), dissolved oxygen (DO), and the algal cell density (ACD), from the main canal of the MRSNWDPC were analyzed. The nonlinear relationships were determined based on multiple regression models, and a composite risk analysis model was constructed by Latin hypercube sampling (LHS) method coupled with Vine Copula function. The impacts of different hydrological and environmental factors on algal proliferation were comprehensively analyzed by Bayesian theory. The results showed that the WT gradually decreased from upstream to downstream, with a narrow range of 16.6–17.4°C, and the annual average concentrations of DO showed a gradual increase from upstream to downstream. The flow velocity of MRSNWDPC had a tendency to increase year by year, and the maximum flow velocity exceeds 0.8 m/s upstream, midstream and downstream by 2018. The ACD accumulated along the main canal, and the annual average ACDs of downstream were the highest, ranging from 366.17 to 462.95 × 104 cells/L. The joint early-warning method considering both water temperature and flow velocity conditions is an effective way for algal proliferation risk warning management. When water temperatures of the upstream, midstream, and downstream were below 26, 26, and 23°C, respectively, the algal proliferation risk can be controlled under 50% by the flow velocity at 0.3 m/s; otherwise, the flow velocity needs to be regulated higher than 0.8 m/s. In order to keep the midstream and downstream avoid abnormal algal proliferation events (ACD ≥ 500 × 104 cells/L), the corresponding ACDs of the upstream and midstream need to be controlled lower than 319 × 104 cells/L and 470 × 104 cells/L, respectively. This study provides a scientific reference for the long-distance water diversion project’s algal control and environmental protection. The proposed coupling Vine Copula models can also be widely applied to multivariate risk analysis fields

Algal proliferation risk assessment using Vine Copula-based coupling methods in the South-to-North Water Diversion Project of China

The Middle Route of the South-to-North Water Diversion Project of China (MRSNWDPC), i.e., the longest inter-basin water diversion project (1,432 km) in the world, has delivered more than 60 billion m3 of water resources to North China and benefiting more than 100 million people since December 2014. However, the abnormal algal proliferation in the main canal under low nutrient background has seriously threatened the water quality safety of this mega project. In this research, 3 years of monitoring data matrix, including water temperature (WT), flow discharge (Q), flow velocity (V), dissolved oxygen (DO), and the algal cell density (ACD), from the main canal of the MRSNWDPC were analyzed. The nonlinear relationships were determined based on multiple regression models, and a composite risk analysis model was constructed by Latin hypercube sampling (LHS) method coupled with Vine Copula function. The impacts of different hydrological and environmental factors on algal proliferation were comprehensively analyzed by Bayesian theory. The results showed that the WT gradually decreased from upstream to downstream, with a narrow range of 16.6–17.4°C, and the annual average concentrations of DO showed a gradual increase from upstream to downstream. The flow velocity of MRSNWDPC had a tendency to increase year by year, and the maximum flow velocity exceeds 0.8 m/s upstream, midstream and downstream by 2018. The ACD accumulated along the main canal, and the annual average ACDs of downstream were the highest, ranging from 366.17 to 462.95 × 104 cells/L. The joint early-warning method considering both water temperature and flow velocity conditions is an effective way for algal proliferation risk warning management. When water temperatures of the upstream, midstream, and downstream were below 26, 26, and 23°C, respectively, the algal proliferation risk can be controlled under 50% by the flow velocity at 0.3 m/s; otherwise, the flow velocity needs to be regulated higher than 0.8 m/s. In order to keep the midstream and downstream avoid abnormal algal proliferation events (ACD ≥ 500 × 104 cells/L), the corresponding ACDs of the upstream and midstream need to be controlled lower than 319 × 104 cells/L and 470 × 104 cells/L, respectively. This study provides a scientific reference for the long-distance water diversion project’s algal control and environmental protection. The proposed coupling Vine Copula models can also be widely applied to multivariate risk analysis fields