Henrik Rye

DeepSpill––Field Study of a Simulated Oil and Gas Blowout in Deep Water

Abstract With the world’s increasing demand for oil and gas and dwindling onshore reserves, the need to exploit oil and gas has moved into deep water. This move brings with it the potential of accidental releases from well blowouts and pipeline or riser ruptures. While there is a low risk of such accident thanks to today’s technology, the oil industry has to be prepared. To better understand how oil and gas would behave during a deep water release, the DeepSpill experiment was conducted in the Norwegian Sea at the Helland Hansen site (65°00′N, 04°50′E) in 844 m of water roughly 125 km off the coast of central Norway. Four controlled discharges of oil and gas were made during late June 2000 amounting to a total of 120 m3 of oil and 10,000 standard m3 of natural gas. The main objectives of the experiments were to calibrate numerical models and to test methods of subsurface surveillance. Extensive observations were made of wind, currents, water density, surface and subsurface oil concentrations, and chemical and biologic samples in the water column. Results showed that the oil started reaching the surface about an hour after the release began and within a few hundred meters of the release site. Oil continued to surface for several hours after the release stopped. No gas hydrates were formed even though thermodynamic equilibrium suggested they should have. No gas bubbles reached the surface indicating that gas dissolution was complete but not as quickly as predicted by standard algorithms. The echo sounders on-board the research vessels were able to track the oil/gas plume as it rose through the water column. In general the surface slick was much thinner than a slick initially released at the surface would have been. Emulsified oil was observed at the surface after the crude oil discharge, with water content increasing with time after the oil came to the surface. An integral plume model [Spill Science and Technology Bulletin 6 (2000) 103] did a reasonable job of predicting the time to surface and the location of the slick though some tuning of the bubble/droplet sizes, gas dissolution rate, and hydrate formation were needed. Finally, the results showed that all gas was dissolved well beneath the surface suggesting that today’s safety restrictions governing surface vessel activity could possibly be revised.

A THREE-DIMENSIONAL OIL AND CHEMICAL SPILL MODEL FOR ENVIRONMENTAL IMPACT ASSESSMENT

ABSTRACT A comprehensive model of the dynamic, three-dimensional physical fates of contaminants in the marine environment has been developed. For oil spills, dissolution of aromatics from surface s...

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 m3 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.

Subsurface blowouts: Results from field experiments

Abstract A field experiment was carried out in June 1996 with a subsurface release of air and oil close to the Frigg Field in the North Sea. One of the purposes of this sea trial was to increase the knowledge concerning the behaviour of the oil and gas during a subsurface blowout. This was done by simulating a subsurface blowout at 106 m depth with a realistic gas oil ratio (GOR = 67) and release velocity of the oil/gas. In addition to the main oil release (43 m3 Troll crude), other releases with water and air (GOR = 7–65) were performed. Important and unique data were collected during these subsurface releases that can be used to improve numerical models for such releases. The main conclusions from these trials are: • • The field methodology used to study blowout releases in the field appears to be appropriate. • • The surface oil slick formed by subsurface releases is significantly wider and thinner than if it was caused by a surface release. • • Only 15–20% of the released oil was detected at the surface. This percentage is expected to depend on factors like depth, GOR, oil type and release velocity. • • Some discrepancies between existing models and field results were found. The field data may thus serve as a basis for model improvements.

Comparison of the ParTrack mud/cuttings release model with field data based on use of synthetic-based drilling fluids

A model for the calculation of the spreading and deposition of drilling mud and cuttings has been developed. The calculations are based on a Lagrangian particle approach, which means that the properties of the discharge are represented by moving particles in the model domain. The initialization of the particles is based on the output from an Eulerian near-field underwater plume model. In addition, the model applies external current fields for the horizontal advection of the particles. The paper explains details in a comparison made between measured barium concentrations in the sediment and the modeled deposition on the sea floor from the drilling of eight exploration wells and eight production wells for the development of an oil field in the North Sea.

Comparison of the ParTrack mud/cuttings release model with field data

Abstract The oil industry promotes the development of numerical models for prediction of impacts from their discharges to sea. A model for the simulation of the spreading and deposition of drilling mud and cuttings on the sea floor as well as the spreading of chemicals (and small-sized particles) in the water column has been developed. The simulation is based on a Lagrangian ‘particle’ approach, which means that the properties of the discharge are represented by moving ‘particles’ in the model domain. The initialization of the particles is based on the output from an Eulerian near field underwater plume model. In addition, the model applies external current fields for the horizontal advection of the particles. This paper presents a comparison between simulated and measured concentrations of barium (barite) in surface contaminated sediment in the vicinity of an oil production field. As a part of the regular surveillance of oil production sites on the Norwegian Continental Shelf, the barium content in surface sediments is measured. These data might therefore serve as an opportunity for comparing simulation results with measured depositions of barium (barite) on the sea floor. The paper explains details in the comparison made between the measured barium concentrations in the sediment and the simulated deposition on the sea floor from the drilling of three exploration wells and 18 production wells off the west coast of Norway.

Including impacts of particulate emissions on marine ecosystems in life cycle assessment: The case of offshore oil and gas production

Life cycle assessment is increasingly used to assess the environmental performance of fossil energy systems. Two of the dominant emissions of offshore oil and gas production to the marine environment are the discharge of produced water and drilling waste. Although environmental impacts of produced water are predominantly due to chemical stressors, a major concern regarding drilling waste discharge is the potential physical impact due to particles. At present, impact indicators for particulate emissions are not yet available in life cycle assessment. Here, we develop characterization factors for 2 distinct impacts of particulate emissions: an increased turbidity zone in the water column and physical burial of benthic communities. The characterization factor for turbidity is developed analogous to characterization factors for toxic impacts, and ranges from 1.4 PAF (potentially affected fraction) · m(3) /d/kg(p) (kilogram particulate) to 7.0 x 10³ [corrected] for drilling mud particles discharged from the rig. The characterization factor for burial describes the volume of sediment that is impacted by particle deposition on the seafloor and equals 2.0 × 10(-1) PAF · m(3) /d/kg(p) for cutting particles. This characterization factor is quantified on the basis of initial deposition layer characteristics, such as height and surface area, the initial benthic response, and the recovery rate. We assessed the relevance of including particulate emissions in an impact assessment of offshore oil and gas production. Accordingly, the total impact on the water column and on the sediment was quantified based on emission data of produced water and drilling waste for all oil and gas fields on the Norwegian continental shelf in 2008. Our results show that cutting particles contribute substantially to the total impact of offshore oil and gas production on marine sediments, with a relative contribution of 55% and 31% on the regional and global scale, respectively. In contrast, the contribution of particulate emissions to the total impact on the marine water column is of minor importance. We conclude that particles are an important stressor in marine ecosystems, particularly for marine sediment, and particulate emissions should therefore be included in a (life cycle) impact assessment of offshore oil and gas production.

An Intercomparison Between Field Measurements and Three Different Calculation Models for Estimates of Dilution Factors

Produced water releases have recently received increased attention due to its potential toxicity and its expected increase in the amounts on the Norwegian continental shelf for the years to come. Factors that govern the toxicity of the release when mixed into the recipient water becomes therefore essential. This paper deals with one such factor, namely the mixing rate of the release. When sufficiently mixed with the ambient water, the concentrations of the toxic components will fall below the:“No Effect Level” (NEC level), and harmful effects from the release are no longer expected. It is therefore of interest to determine how far off the release site (and how fast) this NEC level is surpassed for produced water releases.

Exposure of Fish Larvae to Hydrocarbon Concentration Fields Generated by Subsurface Blowouts

Abstract As the oil activity outside the Norwegian coast moves towards north, the potential for conflict with the fishing industry increases. Reasons for this are the presence of spawning areas for important fish stocks like herring and cod, and also the technical development of subsurface solutions for the oil exploration, increasing the risks for the occurrence of subsurface blowouts. The paper explains how this potential for conflict can be described by means of numerical modelling techniques. The Haltenbanken area outside the western coast of Norway is selected as a field case. The modelling work involves underwater plume modelling as well as 3D modelling of ocean currents. The results from these modelling works are then combined with the modelling of the far-field transport and dilution of the underwater plume, and also the modelling of the spreading and transport of larvae from spawning areas. By combining the calculation of the concentration fields with the spreading calculations of the larvae, the exposure of a total larvae population (one year stock) can be estimated. The paper concludes that under unfavourable conditions, the overlap between the hydrocarbon concentration fields and the geographical distribution of larvae at its most vulnerable stage may cause a significant impact on a population level.

Probable Effects of Langmuir Circulation Observed on Oil Slicks in the Field

Abstract Although the presence of Langmuir circulation (LC) cells is evident from observations in lakes, ponds, and coastal waters, the effects of these cells on oil slicks have received less attention. This paper considers the effects as inferred from field data of LC cells on oil slicks. Examples from observed experimental oil slicks in the field are presented. The importance of these LC cells is discussed from the point of view of oil spill contingency.