HSE & Sustainability

ERA Acute: A New Method for Environmental Risk Assessment of Acute Offshore Oil Spills

The new standardized ERA Acute method provides quantitative assessment of environmental impact and risk of acute oil spills covering four environmental compartments: sea surface, shoreline, water column, and seafloor.

190540-hero.jpg
The cumulative oil slick of the Deepwater Horizon oil spill derived from field observation (satellite data). The color codes show the coverage of oil assumed to be above 2 μm and 10 μm.

Energy companies conduct environmental risk assessments (ERAs) as part of their risk-management processes to ensure acceptable environmental risk for all operations. In some parts of the world, ERAs are required by regulators to assess risk and as a basis for evaluating risk-reducing measures. The new standardized ERA Acute method has been developed that provides quantitative assessment of environmental impact and risk of acute oil spills covering four environmental compartments: sea surface, shoreline, water column, and seafloor. The method uses oil-drift simulations and valued-ecosystem-components (VECs) data as input. Based on a selection of relevant oil spills, impact and recovery times are calculated for VECs in all compartments using continuous functions. Several endpoints are provided, including a resource damage factor (RDF) that combines the extent of an impact with recovery time, the risk matrix, and a risk comparison tool (e.g., for quantifying effects of risk-reducing measures).

The methodology has been benchmarked and compared with the current industry standard ERA used on the Norwegian Continental Shelf, the MIRA method. The ERA Acute method also has been compared with data from real spills: Deepwater Horizon (Gulf of Mexico, 2010) and Exxon Valdez (Alaska, 1989). Estimated impact and recovery time of incidents (e.g., from post-spill monitoring of environmental impact and reconstructed oil exposure data from satellite) have been compared with ERA Acute calculations and oil-spill simulations.

Acknowledging that validation of the model is challenging, the results support the new impact algorithms and are within the range of expected uncertainties related to field observations. The continuous risk functions better discriminate the effect of small spills and of mitigation measures compared with the MIRA methodology, and details of the exposure mechanisms such as exposure time and specific behavior of surface species are also included. The validity and applicability of the new ERA Acute method are presented in the paper, including the benefits the industry obtains from a standardized methodology providing reliable environmental-risk estimations.

Introduction

ERAs are performed to assess and ensure acceptable environmental risk for oil and gas offshore operations. This is done through methodologies able to calculate the potential damage to the environment resulting from oil spills and the probability that this damage happens. The acceptability of the risk is assessed using predefined acceptance criteria, and risk reduction measures are applied until risk is deemed acceptable.

ERAs are mandatory in some companies and a regulatory requirement in most countries aiming to minimize risk to the environment. In that context, several ERA methodologies have been developed. One example is the MIRA methodology developed in Norway, which defines ranges of exposure to oil and corresponding ranges of potential damages on the basis of field observation of historical spill effects. Although this methodology has proved to be useful, the need to develop a more-standardized ERA methodology on the basis of continuous functions and better suited for quantitative risk assessment has been identified.

The ERA Acute method is in line with the guidelines developed by IPIECA and the International Association of Oil and Gas Producers on how to run ERAs and aims to offer the industry an easy way to apply them. It is geographically referenced and uses a grid-cell-based approach; thus, ERAs can easily be conducted anywhere. It offers a high degree of flexibility. Calculations can be made in two steps (i.e., impact at three levels of details in Level A and duration of impact determined by recovery times in Level B). Four environment compartments are considered: surface, water column, shoreline, and seafloor. Environmental exposure to oil is calculated through oil-drift modeling, and the results are used by continuous functions to calculate the impact for each environment compartment, considering their specificity. Further modeling and use of literature data allow estimation of the recovery time of the environment (i.e., the time required to return to prespill conditions, taking into account the natural variability). The damage is expressed finally as a combination of impact and recovery time of the environment and the related probability inferred along each calculation steps from oil exposure to final damage.

The final risk result can be expressed in different ways, depending on users’ needs (e.g., a fully quantitative number for each specific VEC or displayed as impact and recovery time data). Results can be presented in a risk matrix, a common tool used by industry for risk management. Comparing risk reduction by different oil-spill-response options can be assessed as an input to net environmental benefit analysis or spill impact mitigation analysis. Although validation is challenging because of the spatial scale and complexity of gathering field data, the method was benchmarked against MIRA and some past accidental spill events such as the Exxon Valdez and the Deepwater Horizon accidents.

Find paper SPE 190540 on the HSE Technical Discipline Page free for a limited time.

Find paper SPE 190540 on OnePetro.