Subsea Gas Release Research Articles

Numerical Estimation of Gas Release and Dispersion from a Submarine Pipeline

Submarine pipeline gas releases and dispersions can cause safety concerns such as fire and explosion, which can cause serious casualties and property losses. There are many existing studies on the impacts of the horizontal diffusion distances of natural gas leakages from subsea pipelines, but there is a lack of research on the impact of influencing factors on vertical diffusion distances. Therefore, a diffusion model of natural gas leakage from a submarine pipeline is established by using the computational fluid dynamics method (CFD). The influence law and degrees of factors such as water depth at the leakage point, leak orifice size, leak pressure and the ocean current’s velocity on the leakages and vertical diffusion distances of natural gases from submarine pipelines are systematically investigated. The results show that the leaked natural gas jet enters the sea water to form an air mass, which rises continuously under the action of the pressure in the pipe and the buoyancy of the sea water. The gas mass breaks into smaller bubbles affected by the interaction between the gas–liquid two phases and continues to float up and diffuse to the overflow surface. It is also found that the ocean current’s velocity will affect the offset of leakage gas along the current direction; the depth of the leakage water, the pressure in the pipe and the leakage aperture will affect the time when the gas reaches the sea surface and the release area after a submarine pipeline’s leakage. The research results would help to support risk assessments and response planning of potential subsea gas release accidents.

Modelling underwater dispersion of gas released from seabed soil considering current and wave

Subsea gas release incidents may result in catastrophic consequences, e.g., overturning of offshore floating structures, fire, and explosion. This paper developed a model to investigate the dispersion behavior of underwater gas released from the seafloor soil under combined action of current and wave. Eulerian-Eulerian model is used to track underwater gas dispersion trajectory. Porous model is utilized to describe the seafloor soil and simulate the penetration of gas released from seafloor soil. The numerical model is validated by comparing with small-scale experiments. The effect of release rate, current velocity and soil porosity is investigated. The parameters, e.g., rising time, horizontal dispersion distance and surfacing area are estimated. The uniqueness of this study is that underwater gas plumes are simulated considering the seafloor soil and the combined action of current and wave. The results indicate that the presence of seafloor soil has a significant effect on the migration shape and trajectory of underwater gas plume. The combined action of current and wave increases the dispersion distance of gas plume. This study can support risk assessment and emergency planning of subsea gas release accidents.

Modeling and assessment of accidental subsea gas leakage using a coupled computational fluid dynamics and machine learning approaches

All over the world, the oil and gas industries are the most important source of energy. The likelihood of subsea gas and oil leakage is increasing, which can cause threats and harmful impacts on the marine environment and potentially catastrophic events such as fires, explosives, and the loss of structural integrity of subsea infrastructure. Also, Physical models have usually been used to predict sea currents, but they are unstable to disturbances and hence incorrect over long periods of time. Machine learning approaches are more resistant than the physical models that have usually been used to predict sea currents. Also, Physical models have usually been used to predict sea currents. Nonetheless, they are not stable to disturbances and thus are not correct for long periods of time. Machine learning approaches are more resistant than the physical models that have usually been used to predict sea currents. Machine learning approaches are more resistant to change and perturbation. Therefore, the goal of this research is to assess the potential of hazards of the gas plume from subsea pipeline rupture till reaching the sea surface by changing the influence parameters on gas plume to assist petroleum companies in developing risk assessment strategies by assessing and simulating subsea gas release in order to contain the leakage by developing coupling models one for machine learning code which can predict the upcoming water current speed by using Multiple Linear Regression algorithm and hooked it by UDF to a second model which implements Computational Fluid Dynamics (CFD) model to study subsea gas release under current effects. Engebretsen’s Rotvoll experiment data is being used to validate the numerical computational fluid dynamics model. The rising time and fountain height and horizontal migration for gas release are the essential factors to be considered while evaluating the gas dispersion through our study by changing the influencing parameters such as leakage hole sizes, water current speeds, gas velocity, and water depths in the presence of water current in all cases. Also, applied our simulation to real case parameters for one of the Egyptian Petroleum Companies. These findings might aid in evaluating the hazards and response planning in the event of subsea gas leakage.

Numerical modelling of wind-influenced above sea gas dispersion and explosion risk analysis due to subsea gas release on multileveled offshore platform

Above-sea gas dispersion due to subsea release could lead to explosion on nearby offshore facility. Less congested single-deck offshore platform has been considered in past for numerical modelling of above-sea gas dispersion and deflagration. Offshore platforms are designed compactly and comprise of multiple decks due to space restrictions. The approaching flammable gas may disperse differently at each deck, and high overpressures could develop in event of explosion in confined decks causing severe damages. Therefore, investigating effect of above-sea gas release and dispersion and resulting vapour cloud explosion on equipment damage and human fatality in complex multi-deck platform is worth investigating. This paper presents above-sea gas dispersion and explosion modelling on realistic multileveled fixed offshore platform under varying wind speeds using FLACS. Simplified steps are provided to model gas release from large area sea surface gas pool along with atmospheric dispersion and subsequent explosion in FLACS. It was found that generally, lower decks had near-stoichiometry concentrations thus being most susceptible to explosion consequences. High wind speed increased flammable cloud accumulation, where 50-60% of decks were filled at 3m/s wind speed whereas 100% filled under 7m/s. It is suggested to have adequate ventilation on lower platform decks specially under high wind circumstances to avoid possible explosion hazard due to cloud accumulation. Congested and confined regions with low flammable concentration produced more overpressure than the areas with same concentration but no or low congestion and confinement. Stoichiometric concentration together with congestion produced incredibly high localised overpressure reaching 3.55-4 barg. The probability of equipment damage and human fatality was reaching 1 for explosions at base and deck 2 under 7 m/s wind speed. Since roof was open, the probability of equipment damage and human fatality was least.

Risk assessment of offshore fire accidents caused by subsea gas release

Subsea gas release is an industrial hazard that can impose fire hazards on offshore facilities near the gas surfacing area. However, risk assessment of the fire caused by subsea gas release is challenged due to inadequate recognition of the knowledge of subsea gas release mechanism and resulting hazards. At present, minimal researches involving risk assessment of offshore fire resulting from a subsea gas release were reported, and this paper is an extension of the previous works on subsea gas behavior. This paper focuses on modeling fire risk on offshore facilities due to subsea gas release. A numerical simulation is carried out using the Computational Fluid Dynamic technique of Fire Dynamics Simulator (FDS) to analyze fire propagation characteristics and assess the impact of fire on personnel and assets. A probit model is adopted to calculate the probabilities of injury or death caused by fire hazards. This study also investigates the effect of wind speed, gas release rate and the distance between gas pool and platform on fire impacts and casualty probabilities. The present study can support safety measure design to mitigate or avoid the impacts of offshore fire events from subsea gas release.

Underwater gas release modeling and verification analysis

Accidental subsea gas releases may cause an underwater gas plume migrating from the seafloor to the sea surface, which may pose offshore fire hazards or instability of ships. Numerical simulation is an efficient approach to model the underwater gas behavior and support risk assessment. To verify the availability of numerical modeling methods for the underwater gas release, this paper establishes a small-scale experiment system to simulate the underwater gas release, and several experiments with the typical conditions are conducted to obtain the plume parameters, e.g. shape, radium and fountain height. Two CFD models, i.e. Eulerian-Eulerian and Eulerian-Lagrangian approaches, are used to reproduce underwater gas plumes in the experimental conditions. The comparison between simulations and experiments is conducted to analyze the effectiveness and the rationality of numerical modeling methods. The results indicate that simulations with two methods are overall consistent with experiments. However, a detailed comparison reflects that Eulerian-Eulerian model cannot satisfactorily capture the transition of jet to plume and the entrainment during gas rising. In contrast, the results from Eulerian-Lagrangian model are better in agreement with experiments. This study verifies these two numerical modeling methods through a small-scale experiment. The validation against full scale tests is suggested in future work to use it as a reliable tool for risk assessment of subsea gas release incidents.

Summarizing an Eulerian–Lagrangian model for subsea gas release and comparing release of CO2 with CH4

A subsea gas release is a concern for both safety and environment. This can be assessed by mathematical models. The development of an Eulerian–Lagrangian modelling concept to study subsea gas release has taken place over many years and the piecewise enhancements have been documented in the open literature. The model in its current state is summarized in this article. Model simulations are shown to be consistent with different experiments varying in depth from 7 to 138 m. The model can be applied to estimate how gas surfaces into the atmosphere from a subsea source. This is vital input to risk assessments. Due to recent interest in subsea CO2 storage and transport, a comparison of CO2- and CH4-releases has been performed. Model results show that a much smaller fraction of released CO2 reaches the atmosphere than CH4 due to the high solubility of CO2 in water.

Analysis of underwater gas release and dispersion behavior to assess subsea safety risk.

Underwater gas release and dispersion characteristics are important to assess and manage potential risks. This paper presents an experimental and numerical investigation of underwater gas release and dispersion behavior. A small-scale experimental setup is designed and developed for underwater gas release and dispersion study. A series of release scenarios are carried out to study the effect of release size, leak pressure, and leak direction on dispersion behavior. The underwater gas dispersion behavior is analyzed from the risk assessment perspective. The considered parameters included plume offset, plume radius and fountain height for different scenarios. The experimental results are used to test and verify numerical computational fluid dynamics model using Eulerian-Lagrangian approach. The developed numerical model is subsequently used to analyze the gas plume in a full-scale scenario. The developed model would help to support risk assessment and response planning of potential subsea gas release accidents.

Simulation and assessment of underwater gas release and dispersion from subsea gas pipelines leak

Abstract Subsea gas release and dispersion can cause safety concerns such as fire, explosion or stability loss of floating installations. This paper presents a Computational Fluid Dynamics (CFD) based approach to describe the behavior of underwater gas release and dispersion from subsea gas pipelines leak. The uniqueness of the present study is the integration of estimating subsea gas release rate and predicting rising gas plume. The proposed approach is comprised of two submodels. An equivalent short pipeline model is established to calculate the subsea gas release rate, considering the change of hole size and environmental pressure. A 3D model based on Eulerian-Lagrangian modeling concept is built to predict the rising gas plume, in which bubbles are treated as discrete particles. The validation is carried out by comparing CFD results against experimental data. The underwater gas dispersion simulations include a matrix of scenarios for different gas release rates, water depths, ocean current speeds and leak positions, to study their effects on the behavior of underwater gas plume. The developed CFD model can provide some valuable outputs, e.g., gas release rate, rise time, horizontal dispersion distance and surfacing area size. These results could help to conduct the risk assessment and the emergency planning for accidental leakage of subsea gas pipelines.

Modelling subsea gas releases and resulting gas plumes using Computational Fluid Dynamics

A Computational Fluid Dynamics (CFD) model was developed to describe the behavior of a subsea gas release and the subsequent rising gas plume. Four numerical approaches were assessed for their suitability to capture the characteristic behaviors in a rising gas plume by comparing the CFD results with experimental data obtained from an underwater gas release experiment carried out in a towing tank basin with 10 m depth.The k-ε turbulence model was found to be unsatisfactory in capturing random wandering behavior of the subsea gas plume due to the inherent Reynolds-Averaged Navier-Stokes (RANS) nature of the approach. The result is an over-prediction of the plume central line velocity and an under-prediction of the plume width as there was no mechanism to distribute and dissipate the high momentum gained during the initial gas release phase. The results obtained using the Large Eddy Simulation (LES) approach show the inherently random wandering behavior of the plume is successfully captured and both the centerline velocity and the velocity profile are in much better agreement with the experimental data.The study was carried out using air as released gas. This was done to compare with the available experimental data where air was used as the source. However the CFD model developed is applicable for actual subsea gases.

Current understanding of subsea gas release: A review

AbstractIn this paper we review the current understanding of bubble plumes discharged from subsea sources related to oil and gas production, and show how CFD can be applied for risk assessments. A general introduction to causes and risks is given. This is followed by a discussion of the physics that need to be accounted for before giving a brief review of the different modelling approaches employed today. The empirical and experimental knowledge base is also summarized. An example of how CFD can be applied to study gas releases is given. At the end we outline what is needed to advance current understanding of such releases and model their interaction with the surroundings. The scope of the review is limited to the fate of the gas and the flow induced by the ascending bubble plume in the water column. Atmospheric dispersion of surfacing gas is not considered.

A parcel based modelling concept for studying subsea gas release and the effect of gas dissolution

A modelling concept for analysing the fate of a subsea gas release is presented. The concept is based on a coupled Eulerian–Lagrangian method. The gas bubbles are modelled and tracked as parcels in a Lagrangian Discrete Phase Model (DPM). The continuous water and atmospheric gas are covered by an Eulerian VOF model. The model accounts for compressible gas effects, bubble size, gas dissolution and is fully transient. It compares well with experiments from a release depth of 7 m. The concept is applied to a set of release scenarios and the results are presented.

CFD modeling of plume and free surface behavior resulting from a sub-sea gas release

A 3D, transient, mathematical model was developed to simulate the plume and free surface behavior resulting from a sub-sea gas pipe rupture. A coupled volume of fluid (VOF) and discrete phase model (DPM) approach was used to account for the multiphase aspects. Turbulence was modeled using the standard k – ε approach. The model was compared to experiments conducted in a 7 m deep test basin and successfully predicted a wide range of experimental measurements. The model was also applied to gas release at large ocean depths to verify that the model is applicable to studies of realistic scenarios.