Identification and Assessment of Alternative Disposal Options for Radioactive Oilfield Wastes

Identification and Assessment of Alternative Disposal Options for Radioactive Oilfield Wastes
UKRSR07

EXECUTIVE SUMMARY

1. BACKGROUND

Scales containing naturally occurring radioactive material are a by-product of hydrocarbon extraction. In the Scottish area of the North Sea the dominant nuclides in these scales are radium 226 and its daughters and radium 228 and its daughters. Typically all the daughters down to lead 210 are present in varying degrees of equilibrium. In the southern sector of the North Sea the radioactivity is mainly due to the presence of lead 210 and its daughters which are deposited by a different mechanism.

The scales are normally found on installations where injected water has mixed with water present in the formation. Barium sulphate is formed and precipitated as well fluids are brought to the surface. Some barium is substituted by radium and the precipitate is therefore radioactive. Naturally Occurring Radioactive Material (NORM) can be found as hard, insoluble scales adhering to equipment or as contaminated sand and silt inside vessels.

Installations are authorised to dispose of NORM as solid or liquid waste. Solid waste includes contaminated equipment sent to land for decontamination. Liquid waste includes solids in suspension discharged to sea. The UK Strategy for Radioactive Discharges 2001-2020 states that these discharges will continue to be tightly controlled and reduced wherever practicable. The Strategy also includes the statement that [authorisation holders] will be expected to manage their wastes in ways that minimise discharges to the environment.

Currently there is only one onshore facility which routinely disposes of NORM waste is Scotoil Services in Aberdeen.

2. PROJECT AIMS

This research aimed to:

Investigate factors influencing the production of NORM waste.
Determine the amount of NORM waste likely to be produced by installations operating in the UKCS during the operational and decommissioning phases.
Assess the availability, potential for development and utility of existing and novel waste minimisation techniques and disposal options.
Provide guidance to industry and regulators on minimisation and disposal of NORM waste.

3. PROJECT OUTPUTS

Four separate reports have been produced from this research:

Technical Summary Report: provides a synthesis of the findings of Phases 1 and 2 plus a discussion of capacity issues. This is the main project reference including the summary guidance.
Phase I Technical Report: provides details on NORM origins, occurrence in oil and gas processing and quantification (from a variety of data sources).
Phase II Technical Report: provides details on the legislation relevant to NORM disposal, NORM prevention and waste volume reduction, NORM removal techniques, NORM disposal routes and risk ranking of the disposal routes.
Summary Guidance: contains an overview of the issues discussed in the three main project documents above. The intended users of this document are likely to be: well informed in at least some of the issues associated with oilfield NORM; and have access to Radiation Protection Advisor (RPA) services and advice on current NORM disposal practice.

4. KEY FINDINGS

NORM origins and quantification
Amounts of NORM waste produced on the United Kingdom Continental Shelf (UKCS) were quantified and predictions made of potential arisings from future production and during decommissioning. Data obtained from operators, decontamination contractors, literature review, disposal outlets and the regulators has been included in the estimates.

NORM contaminated deposits in oil and gas production occur in two main forms:

As mineral scales, and sludges of particulate scale, containing radium and its decay products;
As thin coatings and “black sludges” in gas and condensate processing equipment, mainly containing decay products from Radon-222, predominantly Lead-210 and Polonium-210.

The estimates of the current arisings have been prepared and are summarised in section 4.4.6 of this report. The main findings are summarised in the points below:

The total activity discharged in produced water is relatively high due to the volumes produced.
The largest arising of solid NORM occurs through offshore decontamination, either through routine cleanout and descaling operations or from decommissioning. Terminal vessel sludges and pigging waxes account for the bulk of NORM solids dealt with onshore.
Onshore equipment decontamination accounts for a small fraction of the total activity and volume of solids discharged to sea.
The masses of solids from decommissioning are small in comparison to offshore decontamination. In all of the cases reviewed the actual amount of NORM solids disposed of from decommissioning has been significantly lower than original predictions.
The general trend in solid NORM is a slight increase in operational arisings in the next 2-3 years, as new facilities outpace decommissioning, followed by a steady decline as decommissioning increases in pace. Total arisings peak in about 2007 and are sustained by decommissioning arisings until around 2012, after which there is a sharp decline. By 2040, mass and activity via all disposals is estimated to be between 5-10% of its current value.
The total activity in produced water is also predicted to peaks in 2007 but falls steadily thereafter. By 2040, mass and activity via all disposals is estimated to be between 5-10% of its current value. Produced water discharged to sea is predicted to have already peaked and is in decline.

The Phase II Report (SNIFFER 2004b) investigated NORM waste minimisation and disposal options for the NORM from the UKCS and produced a ranking of potential disposal options.

NORM prevention, removal methods and waste reduction
A review of methods is presented. Of the NORM prevention methods, the only method widely used on the UKCS is chemical scale inhibition and to a lesser extent sulphate removal from injection water. NORM removal onshore and offshore is predominantly by mechanical means, mainly water jetting (with and without abrasives).

Waste reduction of solid NORM arisings is not routinely carried out on the UKCS as most NORM is discharged to sea. There is currently no reliable method for reducing the overall amount of radioactivity transferred from the subsurface in oil and gas production.

There are some chemical waste reduction methods at different stages on development but none are currently in use on UKCS. There needs to be financial backing and regulatory impetus for their development for use on the UKCS. There are some novel methods at the pilot stage particularly waste reduction by chemical concentration.

NORM disposal options
There is a wide variety of disposal options that are available in principle and feasible options are discussed. Different options are suited to different types of NORM waste and a mixture of options may be the best solution.

From discussions with waste contractors it emerges that some degree of financial security or guaranteed customer base is required for development of new onshore disposal facilities along with an indication of regulatory support. Even with such assurances, the relatively small predicted amounts of NORM arisings for onshore disposal under the current regulatory regime, even at the peak of decommissioning, suggest that a multi-industry LLW disposal facility would be the viable option.

None of the disposal routes appears to present a significant occupational or public radiation exposure risk apart from landspreading. Consequently, factors other than dose may be equally important in determining acceptability.

A generic risk ranking of disposal alternatives for the UKCS has been carried out.

Capacity
Although the current disposal routes present no immediate capacity problems, there is the potential for future pressure on existing oilfield NORM disposal routes, for example OSPAR and EU targets to reduce discharges of naturally occurring radionuclides to sea to background levels by 2020. If this were to mean that offshore discharge was discontinued and solid NORM waste had to be brought onshore for disposal there would be insufficient capacity (currently none in Scotland for some of the wastes).

If the UK continues to rely on a single site (Drigg) as the main onshore disposal route for non-exempt NORM waste, some assurance will need be sought by the regulators that oil and gas NORM waste will continue to be accepted.

If nothing is done to provide alternative onshore disposal routes there is the potential for stockpiling and consequent problems with public relations, licensing and ultimate disposal. The UK oil and gas industry is reliant on a single nearshore discharge to dispose of almost all NORM from onshore decontamination and on a single disposal facility for non-exempt wastes. Currently, the total amounts are low and appear to be within existing capacities, but this assumes that the capacity is available if required and this cannot be guaranteed at present. It also assumes that there will not be regulatory changes which discontinue the current practice of offshore disposal of most of the NORM waste.

Each report is available separately in electronic format at £20.00 + VAT.
Hard copy available at the following prices:
UKRSR07/TS Technical Summary Report (January 2005) £25.00
UKRSR07/Ph.l Phase 1 Technical Report (September 2004) £25.00
UKRSR07Ph.ll Phase 2 Technical Report (November 2004) £35.00
UKRSR07/SG Summary Guidance(March 2005) £10.00

All prices less 20% to FWR members.

N.B. The report is available for download from the SNIFFER Website