Blowout Scenario Research Articles

Blowout Contingency Decision-Making Leveraging Reservoir/Wellbore Pressure Modeling: Cap-and-Restrain or Cap-and-Divert?

Summary After the MC 252–1 “Macondo Well” blowout on 20 April 2010 in the Gulf of Mexico, notable efforts were placed on subsea-well capping and containment to improve the industry’s response to offshore-blowout events. The thrust of this paper is an investigation of the role that forward modeling and monitoring of the reservoir and wellbore pressures can play in determining the best practice to kill a blown well. A novel workflow is presented for supporting blowout contingency by assisting decision-making across different post-blowout intervention strategies integrating reservoir simulation, wellbore mechanics, and the surface equipment’s operating limits. Caused by the unique set of challenges of each blowout incident, a well-intervention method proven effective in one scenario may not be optimal for the next—it could lead to failure, or be unimplementable. Proper response to a well-control event of this type is divided into two broad categories. The first category is “Cap-and-Restrain,” which requires forward modeling of the wellbore-pressure buildup, identifying the critical post-blowout discharge flowrates, above which it is safe to shut-in the subsea-capping stack (SCS). The second category is “Cap-and-Divert,” which requires the SCS to remain partially or completely open after its installation on the blown well’s damaged blowout preventer (BOP), with the flow being diverted to an external storage unit. The SCS is shut-in later once it is confirmed that the well’s integrity can handle the backpressure of the controlled discharge without any “underground blowouts” triggered by tensile failures on exposed locations along the wellbore. This work focuses on the methods and processes planned to contain a subsea blowout, either by Cap-and-Restrain or by Cap-and-Divert, using a workflow employing a generic, multipurpose, 3D, two-phase (water/oil) reservoir simulator [Program for Integrated Modeling of Petroleum Systems (PIMPS3D2P), written in MATLAB® of The MathWorks, Inc.]. Once the feasibility of SCS deployment and landing is evaluated, the implementation of a shut-in procedure becomes vital for reaching the static well conditions required. Our workflow has been applied a posteriori to the Macondo Well’s blowout scenario, as an illustrative example.

The tyre blow-out vehicle lateral pulling control using an active suspension system with comfort-lateral trajectory based control scheme.

When a tyre blows out, the vehicle’s trajectory deviates from the intended path, resulting in an accident and death. Because of its larger contact patch, applying more steering force to the flat tyre will cause the tyre to separate from the wheel. Also, improper braking effort causes rollover related issues due to the sudden vehicle’s centre of gravity (C.G.) displacement and weight transfer towards the blow-out tyre. Therefore, this research attempts to return the C.G. to its initial position through the suspension control. The force supplied between the sprung and unsprung masses of the flat tyre through suspension actuator is estimated and controlled by the model predictive control (MPC) scheme with respect to its input signals. For the non-linear simulation, the four-wheel passenger car vehicle dynamic model and the combined empirical model for the tyre inflation pressure effect are used. And the equivalent plant model is identified through a simple system identification method for the MPC design. The passive and active based suspension of standalone, roll-resistant interconnected and pitch-resistant interconnected systems, including the proposed comfort-lateral trajectory controlled standalone active suspension, were examined. To assess the effectiveness of each suspension and its control strategy in a tyre blow-out scenario, a vehicle was analysed with various longitudinal velocities along with and without steer input.

Wellbore Integrity After a Blowout: Stress Evolution Within the Casing-Cement Sheath-Rock Formation System

A robust evaluation of the casing-cement sheath-rock formation system is foundational in ensuring wellbore integrity throughout a well's lifecycle. Analytical theory for a multi-layer, thick-walled cylinder is used to evaluate the aggregate stress distributions within the casing-cement sheath-rock formation system, honoring boundary conditions of radial stress and displacement continuity. These stress distributions are adjusted for scenarios that a well may experience in its lifetime. Each layer of the casing-cement sheath-rock formation system is evaluated separately against various possible mechanical failure mechanisms, all of which can compromise wellbore integrity.A blowout scenario after a mismanaged loss-of-well-control situation induces high stress loads in the casing-cement sheath-rock formation system, with the wellbore pressure rapidly decreasing during post-blowout discharge, followed by a rapid increase following successful well capping. Casing and cement sheath failures can expose the surrounding rock formation to the pressurized fluid inside the wellbore, risking hydrocarbons broaching the surface, or the seafloor. The aggregate stress distribution model is applied on a case study performed using parameters from the MC 252–1 “Macondo Well” blowout from April 20, 2010 in the deepwater Gulf of Mexico. The stress evolution suggests stability against mechanical failure mechanisms within the casing (collapse/burst and tensile/compressive), cement-sheath (inner or outer debonding, and shear cracking), and rock-formation layers (longitudinal or transverse tensile fracture initiation, along with shear-slippage along pre-existing faults in the near-well vicinity), throughout the blowout aftermath. Nevertheless, tendencies towards radial cracking and disking (tensile) failures were indicated for the cement-sheath layer as the system reaches radial stress and displacement continuity, after cement setting.

Advanced monitoring and simulation for underground gas storage risk management

It is crucial to ensure the safety and integrity of underground gas storage (UGS) infrastructure for energy reliability in California, and many other places around the world. To address the risk management need in UGS industry, we take advantage of recent advances in downhole fiber optic monitoring and coupled well-reservoir simulation to provide unprecedented understanding of gas flow in wells at UGS sites. We have combined advanced monitoring and simulation of UGS operations into a decision-support system called the Integrated Risk Management and Decision Support System (IRMDSS). The IRMDSS framework includes three components: (i) mechanistic models, (ii) continuous and frequent monitoring data, and (iii) a supervisory interface for performing analyses using the models and monitoring data. The goal of the IRMDSS is to equip UGS operators with real-time monitoring data and simulation tools that can alert them to potential failures, detect early leakage, and support mitigation decision-making to prevent otherwise larger failures. We demonstrate an application of the IRMDSS by analyzing the temperature and pressure response to a hypothetical leak. Through a review of distributed temperature sensing (DTS) data collected at an operating UGS facility we show that DTS can uniquely and precisely identify the depth of the gas-water-contact in the well annulus, and that DTS can provide an early warning signal of upward gas flow as would occur in a well blowout scenario. When combined with modeling analysis, a rough leak rate can be roughly estimated to understand the severity of the leakage conditions and to support the mitigation decision needed. • Mechanistic models simulate system responses to UGS facility operations. • Advanced monitoring technologies provide continuous update status for UGS facilities. • DTS data can provide real-time well leakage detection and identify leaky location. • Combination of models and advanced monitoring benefits UGS risk management.

Engineering Challenges in Alloy Wheel Rim for Safety Simulations

<div class="section abstract"><div class="htmlview paragraph">Aluminum alloy wheels are being widely used in the automotive industry since the last decade due to its superior styling and performance. Alloy wheel rim is one of the critical components and plays an important role in a frontal crash scenario. The wheel rim failure prediction in safety simulation is essential to ensure robust safety performance. Determining failure characteristics of an alloy wheel poses many difficulties considering its brittle nature, porosity and inhomogeneity in material properties across different regions of wheel rim due to mold design, cooling rate and other process parameters of the low-pressure die casting process.</div><div class="htmlview paragraph">This paper describes the modelling and simulation methodology developed to predict accurate wheel behavior. The methodology addresses two distinct areas of challenges such as alloy wheel rim failure prediction and associated tire blow out.</div><div class="htmlview paragraph">Alloy wheel rim material is characterized considering the inhomogeneity of material properties at different regions such as the rim, spokes and hub. The material model is developed, considering strain rate sensitivity, anisotropy due to the state of loading, ductile normal and shear fracture aspects. Scatter function is developed to simulate material property variations.</div><div class="htmlview paragraph">Radial tire characterization is carried out with detailed modelling of constituents such as rubber, steel beads, body plies and steel belts. Various physical tests and digital correlation studies are carried out at coupon and tire assembly level to represent the stiffness and deformation of the tire accurately. A novel approach was developed using sensors in digital models to detect the alloy wheel rim failure in real-time. This triggers rapid air leakage in the tire to simulate the blowout scenario during the crash event. The methodology has been validated at the subsystem and full vehicle level by carrying out multiple physical tests. This approach can be used for digital development and validation of alloy wheel rim design to ensure robust crash safety performance.</div></div>

An Overview of Wellhead Burning: Fundamental Science to Burn Performance Prediction

ABSTRACTWhile wellhead burning has been an oil field hazard for generations, the development of capping response technologies and practices by industry experts has enabled the oil exploration community to shift its views of wellhead burning from a hazard to an oil spill response tool. This review covers some of the fundamental scientific aspects and technical issues of wellhead burning that engineers and policy makers will need to consider as this mitigation strategy is examined as a standard oil spill response tactic. For context, we examine a potential wellhead blowout scenario over a range of oil flows and examine the regimes of two-phase pipe flows, their dependence on wellbore velocities and gas-liquid ratios, and how those regimes will influence the burn efficiency with some insight from our experimental observations from two-phase spray burn testing. Among the critical findings that we present is that the worst-case discharge flow rate cannot be assumed to be the worst-case wellhead burning scenario.

Operational risk analysis of blowout scenario in offshore drilling operation

Offshore drilling is a complex and hazardous operation. The safety of the drilling operation is a strong function of many time-dependent parameters. The traditional risk analysis model fails to capture the impact of spatial and temporal variations of these parameters. This paper presents a Bayesian Network (BN) model for the offshore drilling operation. The model uniquely considers the evolution of hazards as a function of time and space, and failure of the safety barriers. The model development is explained using the bowtie approach, which is routinely used in the industry for risk management. The bowtie model is subsequently transformed into a BN model and simulated for the well blowout scenarios. The blowout risk is updated based on operational field observations. An uncertainty analysis is also conducted to capture the spatial variability of the parameters. The results of the BN model provide a dynamic risk profile of the blowout accident during the drilling operation. Other possible accident scenarios, such as lost circulation, can also be analyzed using the proposed model. The proposed BN model serves as a robust tool for risk management of offshore drilling operations.

Major CO2 blowouts from offshore wells are strongly attenuated in water deeper than 50 m

AbstractGrowing interest in offshore geologic carbon sequestration (GCS) motivates evaluation of the consequences of subsea CO2 well blowouts. We have simulated a hypothetical major CO2 well blowout in shallow water of the Texas Gulf Coast. We use a coupled reservoir‐well model (T2Well) to simulate the subsea blowout flow rate for input to an integral model (TAMOC) for modeling CO2 transport in the water column. Bubble sizes are estimated for the blowout scenario for input to TAMOC. Results suggest that a major CO2 blowout in ≥50 m of water will be almost entirely attenuated by the water column due to CO2 dissolution into seawater during upward rise. In contrast, the same blowout in 10 m of water will hardly be attenuated at all. Results also show that the size of the orifice of the leak strongly controls the CO2 blowout rate. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Natural bridging as a tertiary well control method in deep-water wells: A case study from Caspian Sea

Blowout is the uncontrolled flow of reservoir fluids into the well, which can cause different types of problems during the drilling operations. In high-pressure formations with low rock strengths, it is more likely to occur self-killing through bridging mechanisms. The underbalanced conditions that are induced during developing a kick, leading into sufficient instability in exposed formations such that the borehole bridges over and kick kills itself. In this research, the potential of natural bridging is studied in one of the deep-water wells in the Caspian Sea to figure out whether this natural phenomenon is able to terminate the uncontrolled influxes of formation fluids into the borehole. For the reason, a series of semi-integrated numerical simulators are employed to evaluate wellbore pressure profile and wellbore instability as a function of time under blowout conditions. Applied analyses to a particular blowout scenario indicated that rock fragments falling off the wellbore wall are suspended in the two-phase flow (a mixture of gas and drilling mud) during developing the kick. As a result, cavings settlement is less not probable to plug the wellbore. On the other hand, suspension of rock fragments gradually increases the solid concentration of fluid phase until it hits a critical value at a certain time after the beginning of the kick, thereby bridging occurs before developing the kick into a blowout.

Modelling oil plumes from subsurface spills

An oil plume model to simulate the behavior of oil from spills located at any given depth below the sea surface is presented, following major modifications to a plume model developed earlier by Malačič (2001) and drawing on ideas in a paper by Yapa and Zheng (1997). The paper presents improvements in those models and numerical testing of the various parameters in the plume model. The plume model described in this paper is one of the numerous modules of the well-established MEDSLIK oil spill model. The deep blowout scenario of the MEDEXPOL 2013 oil spill modelling exercise, organized by REMPEC, has been applied using the improved oil plume module of the MEDSLIK model and inter-comparison with results having the oil spill source at the sea surface are discussed.

How To Develop a Well-Specific Capping-Stack Blowout Contingency Plan

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 181393, “How To Develop a Well-Specific Blowout Contingency Plan That Covers Engineering Analysis of the Deployment, Installation, and Soft Shut-In of a Subsea Capping Operation,” by Ray T. Oskarsen, SPE, Morten H. Emilsen, SPE, and Amir S. Paknejad, Add Energy; Mike Cargol, Trendsetter Engineering; and Kwee Choong See, SPE, Shell International Exploration and Production, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed. The planning process for developing a well-specific subsea-capping contingency plan involves assessing the feasibility of deploying a capping stack from a floating vessel, determining the weight and stability of the capping stack to overcome the force of the blowout jet, and performing dynamic-flow simulations of closing the capping stack outlets without loss of well integrity. This process not only assesses the feasibility, complexity, and risk exposure of the capping operation but also may justify further planning, studies, or expenditure. Introduction Blowout-kill techniques can be classified as either surface-intervention or relief-well methods. Relief wells aim to kill a blowout from the bottom by injecting fluid into the wellbore until the influx of formation fluid is stopped and the well is static when pumping stops. In many cases, a relief well will be the safest intervention and have the highest likelihood of success, and often it is considered the last line of defense against a blowout. Surface interventions are kill attempts aimed at controlling the discharge at the wellhead or at the fluid-exit point. An example is to install a capping stack on top of the wellhead and close its openings, which can be gate valves, chokes, or rams. Blowout Contingency Planning. Blow-out contingency plans ensure that people understand and can manage risks, thus ensuring safe and sustainable operations at all times. All blowouts are inherently different; thus, it would be both impractical and impossible to attempt to cover every possible blowout scenario in a contingency plan. For source-control planning, an operator should, at a minimum, address a worst credible scenario to demonstrate how the well will be brought under control. This scenario may be different from the worst-case discharge, which is used to estimate spill potential and necessary resources for containment and cleanup. As an example, if there is uncertainty about the gas/oil ratio (GOR), a low-case GOR may cause more oil spill, while a high-case GOR may make source control more challenging.

Modelagem computacional 3D do blowout de poço de petróleo: revisão sobre requisitos ambientais e metodologia

Este artigo de revisão bibliográfica tem por finalidade apresentar as diferentes metodologias utilizadas na modelagem tridimensional da dispersão dos hidrocarbonetos originados do blowout de um poço de petróleo. São considerados os conceitos de sensibilidade e vulnerabilidade ambiental da costa, a importância destes para a priorização de áreas mais vulneráveis em casos de contingência, e a legislação pertinente. São levantados os questionamentos sobre a metodologia atualmente utilizada nos estudos ambientais de deriva do óleo, que considera a simplificação do vazamento em superfície, mesmo nos cenários de blowout de poços. Os esforços para o melhor entendimento do comportamento do óleo e do gás na coluna d’água e da modelagem tridimensional da trajetória ganharam força após o vazamento da Deepwater Horizon em 2010 no Golfo do México. Os dados coletados e observações realizadas durante o acidente foram amplamente utilizados para ajuste dos modelos, que buscaram incorporar os diversos fatores referentes às forçantes hidrodinâmicas e aos processos de intemperismo aos quais os hidrocarbonetos são submetidos em vazamentos de subsuperfície tais como: evaporação, dispersão, emulsificação, dissolução, oxidação, sedimentação e biodegradação. As dificuldades se apresentam ainda mais desafiadoras para o caso de blowouts em águas profundas, onde as incertezas são ainda maiores. Os estudos abordaram diferentes variáveis para realizar os ajustes dos modelos de dispersão do óleo e do gás ao longo da trajetória de subida, e, dentre os fatores que exercem forte influência, destacam-se: a velocidade das correntes de subsuperfície; a separação do gás da pluma principal; a formação de hidrato, a dissolução das gotículas de óleo e gás; as variações no diâmetro das gotículas; a intrusão das gotículas em profundidades intermediárias; a biodegradação; e a parametrização adequada dos perfis de densidade, salinidade e temperatura da água ao longo da coluna.

A framework to quantify uncertainty in simulations of oil transport in the ocean

AbstractAn uncertainty quantification framework is developed for the DeepC Oil Model based on a nonintrusive polynomial chaos method. This allows the model's output to be presented in a probabilistic framework so that the model's predictions reflect the uncertainty in the model's input data. The new capability is illustrated by simulating the far‐field dispersal of oil in a Deepwater Horizon blowout scenario. The uncertain input consisted of ocean current and oil droplet size data and the main model output analyzed is the ensuing oil concentration in the Gulf of Mexico. A 1331 member ensemble was used to construct a surrogate for the model which was then mined for statistical information. The mean and standard deviations in the oil concentration were calculated for up to 30 days, and the total contribution of each input parameter to the model's uncertainty was quantified at different depths. Also, probability density functions of oil concentration were constructed by sampling the surrogate and used to elaborate probabilistic hazard maps of oil impact. The performance of the surrogate was constantly monitored in order to demarcate the space‐time zones where its estimates are reliable.

Ultra-deepwater blowout well control analysis under worst case blowout scenario

Because of the high frictional pressure losses in kill lines in ultra-deep water wells, it is challenging to control the blowout under worst case blowout scenarios. The operational parameters need to be carefully controlled to avoid exceeding the operational limitations such as breaking the formation or exceeding available pump pressure limit. In this study, dynamic kill simulations of multiphase flow are carried out to evaluate the operational parameters during the kill process. The simulations account for transient changes including frictional pressure losses, u-tube effect and fluid density variations. By optimizing the operational sequence with regards to, kill mud density, pump flow rate, pump down staging, relief well drillstring and trajectory, blowout can be controlled without exceeding the operational window. This paper shows that 10,390 bbls of the kill mud, 8000 psi pump pressure limit, optimum flow rate arrangement, and minimum 270 min required to get full kill mud return to the sea floor during the well kill operation. Through the aid of advanced transient software models, assessment of the required capacity to kill a blowout enables development of realistic contingency plans to ensure that well control can be re-established in case of an ultra-deep water worst blowout scenario.

Wellbore-Stability Assessment for Self-Killing Blowouts

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 156330, ’A Wellbore-Stability Approach for Self-Killing-Blowout Assessment,’ by Stephen M. Willson, SPE, Apache Corporation, prepared for the 2012 SPE Deepwater Drilling and Completions Conference, Galveston, Texas, 20-21 June. The paper has not been peer reviewed. An analysis approach was developed to assess borehole stability following a hypothetical blowout from representative deepwater scenarios. It addresses whether imposed underbalanced conditions cause sufficient instability that the borehole bridges over and the well kills itself. Analyses applied to a typical deepwater blowout scenario suggest that bridging leading to self-killing can occur only in a few situations. This finding differs from widely published data from shallow-water Gulf of Mexico shelf wells that show that self-killing is likely in shallow-hazard scenarios. Introduction Uncontrolled influxes of formation fluids into a borehole (a kick) develop into a blowout when the drilling fluid is fully displaced from the well and the formation fluid exits the well. In the case of subsea deepwater wells, the wellhead is at the seafloor and is connected to the drill rig by a marine riser. Depending upon the integrity of the well and riser following a blowout, hydrocarbon discharge may be at the seafloor, at the rig floor, or at some point in between. An influx of hydrocarbons, especially gas, is more severe than an influx of overpressured water. Occurrences of overpressured water (i.e., shallow water flows) or shallow-gas influx are well understood from a shallow- hazards perspective. Another possible route for hydrocarbons to reach the mudline is by way of an underground blowout. An underground blowout occurs when the hydrostatic pressure in the borehole exceeds the fracture gradient of exposed formations. In these circumstances, the increased borehole pressure from actuating the blowout preventer (BOP) to stop flow up the wellbore can cause fracturing of the formation and, depending on the overburden geology, can result in fractures propagating around the wellbore to seabed. As a kick develops, drilling fluid is displaced from the wellbore by the influx of less-dense fluids that have a formation pressure greater than the hydro-static pressure exerted by the drilling fluid. Thereby, the bottomhole pressure (BHP) in the wellbore decreases during the developing kick, which accelerates the influx. When all the drilling fluid is displaced from the wellbore, unrestricted open flow occurs (i.e., a column of hydrocarbon fluid to the wellhead) and the blowout continues until terminated by natural causes or external intervention. Natural causes that terminate a blowout include depletion (depressurization) of the formation, water breakthrough (particularly in shallow-hazard gas blow-outs), wellbore collapse, or bridging at choke points resulting from an accumulation of produced formation solids in the hydrocarbon flow. The size, productivity, and overpressured nature of many deepwater reservoirs preclude depletion and water breakthrough as viable self-killing methods within acceptable time scales.

Nonlinear gyrofluid computation of edge localized ideal ballooning modes

Three dimensional electromagnetic gyrofluid simulations of the ideal ballooning mode blowout scenario for tokamak edge localized modes (ELMs) are presented. Special emphasis is placed on energetic diagnosis, examining changes in the growth rate in the linear, overshoot, and decay phases. The saturation process is energy transfer to self generated edge turbulence which exhibits an ion temperature gradient (ITG) mode structure. Convergence in the decay phase is found only if the spectrum reaches the ion gyroradius. The equilibrium is a self consistent background whose evolution is taken into account. Approximately two thirds of the total energy in the edge layer is liberated in the blowout. Parameter dependence with respect to plasma pressure and the ion gyroradius is studied. Despite the violent nature of the short-lived process, the transition to nonlinearity is very similar to that found in generic tokamak edge turbulence.

Strike-slip faulting as a trigger mechanism for overpressure release through piercement structures. Implications for the Lusi mud volcano, Indonesia

Piercement structures such as hydrothermal vent complexes, pockmarks, and mud volcanoes, are found in various geological settings but are often associated with faults or other fluid-focussing features. This article aims to investigate and understand the mechanisms responsible for the formation of piercement structures in sedimentary basins and the role of strike-slip faulting as a triggering mechanism for fluidization. For this purpose four different approaches were combined: fieldwork, analogue experiments, and mathematical modeling for brittle and ductile rheologies. The results of this study may be applied to several geological settings, including the newly formed Lusi mud volcano in Indonesia (Mazzini et al., 2007). Lusi became active the 29th of May 2006 on the Java Island. Debates on the trigger of the eruption rose immediately. Was Lusi triggered by the reactivation of a fault after a strong earthquake that occurred two days earlier? Or did a neighbouring exploration borehole induce a massive blow-out? Field observations reveal that the Watukosek fault crossing the Lusi mud volcano was reactivated after the 27th of May 2006 earthquake. Ongoing monitoring shows that the frequent seismicity periodically reactivates this fault with synchronous peaks of flow rates from the crater. Our integrated study demonstrates that the critical fluid pressure required to induce sediment deformation and fluidization is dramatically reduced when strike-slip faulting is active. The proposed shear-induced fluidization mechanism explains why piercement structures such as mud volcanoes are often located along fault zones. Our results support a scenario where the strike-slip movement of the Watukosek fault triggered the Lusi eruption and synchronous seep activity witnessed at other mud volcanoes along the same fault. The possibility that the drilling contributed to trigger the eruption cannot be excluded. However, so far, no univocal data support the drilling hypothesis, and a blow-out scenario can neither explain the dramatic changes that affected the plumbing system of numerous seep systems on Java after the 27-05-2006 earthquake. To date (i.e. April 2008) Lusi is still active.

The Complex Neutral Gas Dynamics of the Dwarf Starburst Galaxy NGC 625

We present new multiconfiguration H I aperture synthesis imaging of the nearby dwarf starburst galaxy NGC 625 obtained with the Australia Telescope Compact Array. Total H I column density images show gas well aligned with the optical major axis and low column density H I extending to greater than 6 optical scale lengths. The H I velocity field, on the other hand, is highly disturbed, with neutral gas at nearly all detected velocities within the central region. After considering various interpretations, we find that a blowout scenario most accurately describes the data. Since at our resolution we do not detect any large evacuated holes in the H I disk, we interpret this blowout to be the result of the extended (both spatially and temporally) star formation event that NGC 625 has undergone in the last 100 Myr. This is one of the clearest examples of H I outflow detected in a dwarf galaxy. We find no obvious external trigger for this extended star formation event. We detect strong radio continuum emission from the largest H II regions; comparing to our Hubble Space Telescope and ground-based Hα fluxes suggests either appreciable amounts of extinction toward the star formation regions or the contribution of nonthermal sources to the radio continuum luminosity.

Oil Spill Contingency and Response (OSCAR) Analysis in Support of Environmental Impact Assessment Offshore Namibia

The work reported here encompasses analyses of specific potential spill scenarios for oil exploration activity planned offshore of Namibia. The analyses are carried out with the SINTEF Oil Spill Contingency and Response (OSCAR) 3-dimensional model system. A spill scenario using 150 m 3 of marine diesel demonstrates the rapidity with which such a spill will dissipate naturally, even in light winds. Vertical and horizontal mixing bring subsurface hydrocarbon concentrations to background levels within a few days. A hypothetical 10 day blowout scenario releasing 11,000 bbl per day of light crude oil is investigated in terms of the potential for delivering oil to selected bird and marine mammal areas along the Namibian coast. Worst case scenarios are selected to investigate the potential mitigating effects of planned oil spill response actions. Mechanical recovery significantly reduces, and in some cases eliminates, potential environmental consequences of these worst case scenarios. Dispersant application from fixed wing aircraft further reduces the potential surface effects. The analysis supplies an objective basis for net environmental analysis of the planned response strategies.