What Are the Discharge Permit Limits for Oil?

The Department of Energy and Climate Change (DECC) issues guidance addressed at all companies involved in offshore exploration and production where oil may be released into the sea or other water systems. In order to minimize damage to the environment, the Offshore Petroleum Activities Regulation imposes controls on levels of oil discharged by offshore faculties processing oil, gas or condensate fields.

All offshore installations are required to obtain a permit, an authorization granted by the DECC which sets out conditions of their activities. These include specific regulations on the oil concentration levels in discharged water along with the mass of oil emitted in produced water. 

Oil Discharge Permit Applications

Permit applications from companies engaged in practices which result in the emission of oil into the sea or other water systems must provide an assessment of Best Available Techniques (BAT) and Best Available Practice (BAP) outlining measures taken to minimize pollution and limit discharges.

The assessments should include an outline of the technologies investigated and in use, as well as any planned improvement programs to reduce oil discharge.

Existing discharge streams must demonstrate that they are using the Best Available Techniques (BAT) and Practices (BAP) by focusing on how the equipment in use is being managed to minimize discharged oil. There must be some justification for lack of intention to upgrade to more efficient technologies.

What are the permitted concentration levels?

The regulatory limit for concentration of oil in produced water discharged into the sea is set at a 30 mg/l performance standard.

This figure applies as averaged over a monthly period. At any one time the concentration must not exceed 100 mg/l.

What are the permitted quantity levels?

The regulatory limit for mass of oil in water discharged into the sea must not exceed 1 tonne in any 12 hour period.

Other limits

International regulatory limits relating to specific discharge streams will also be enforced through the Permit Conditions.

E.g. The limit for discharge of displacement water, drainage water, and ballast water is set at 40 mg/l performance standard.

Where there is no set regulatory limit for certain discharge streams (e.g. Sand and Scale Discharges, Pipeline Discharges and any discharge downhole), the producer is expected to provide an estimate of oil concentration and quantity levels based on data from previous discharges.

Most effective monitoring solutions for offshore facilities

The two most widely used inline monitoring systems are:

• UV fluorescence – measures light reflected from surface of water and calculates the concentration of oil in the water based on light intensity.
• Particle analysis – records density of oil in water through use of microscopes. 

Further information on different technology options and their respective advantages/disadvantages can be found in this article: Different Technology Options for Monitoring Oil in Produced Water – Inline Continuous Monitoring and IR Analysis.

As well as careful monitoring, systems which separate oil from water before water disposal should be checked regularly to ensure they are functioning properly and avoid exceeding discharge permit levels.