Prompted by regulatory requirements to work towards “Zero harmful discharges” to the Norwegian Sector of the North Sea, the oil industry developed the “Environmental Impact Factor (EIF) Produced Water” risk management tool. This helps to identify best measures for reducing risk from the offshore discharge of produced water and is used by all operators in the Norwegian Continental Shelf for reporting continuous improvement. Its success has led to the application of the EIF concept as part of the risk evaluation for other types of discharge, both onshore and offshore. This paper presents the EIF Onshore Discharges tool and evaluates its use for application to hydraulic fracturing (HF) operations.

The EIF Onshore Discharges tool uses quantitative modelling techniques in combination with generic principles for environmental risk assessment to predict the volume of three receptor compartments (soil, groundwater and surface water) potentially impacted as a result of intentional or unintentional liquid discharges or releases. In this instance the tool has been used to predict potential impacts from a range of accidental release scenarios associated with hydraulic fracturing (HF) operations. These included surface and subsurface spills/leaks of HF fluids and flowback water. Various HF fluid blends were assessed using a variety of release locations to represent the range of key factors affecting risk. The purpose has been to raise awareness and identify proper risk mitigation measures.

The results indicated a large range in potential impacts arising from unmitigated accidental releases. This variation could be explained by differences in the release scenarios, HF fluid composition and variability in receiving environment conditions. The results also appear to be in line with impacts experienced from known spills, adding confidence to the tool's predictive ability.

Whilst the probability of such releases occurring is very low, the fact that some scenario/chemical combinations have the potential to cause significantly higher impacts than others helps identify key considerations for risk management decisions. In particular, the modelling demonstrated that some HF fluid blends posed significantly higher environmental risk than others, prompting consideration of chemical substitution as part of the overall risk management strategy for the HF operations. Other ways in which the tool aids risk management decisions include identifying higher risk locations where additional risk prevention and/or mitigation measures would be warranted and helping to define spill response measures.

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