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Assessment of discharges, spills and emissions from offshore oil and gas operations on the United Kingdom Continental Shelf, 2016 - 2020

Executive Summary

This report presents the discharge, spill and emission data for UK offshore oil and gas operations during the period 2016 – 2020 and provides an assessment of that data. The annual data on which the assessment is based is provided in Appendix 2.

a. Level of Activity

The United Kingdom Continental Shelf (UKCS) is a mature oil and gas province within the OSPAR region which has been experiencing declining production for many years. Since 2016 production had declined 11% from 102,5 million toeq to 90,8 million toeq. (Fig. 1).

There has been a 12% decrease in the total number of installations mainly as a result of decommissioning of smaller southern North Sea gas installations. (Fig. 2).

Full Report

Oil and gas activity to maintain production levels and maximise economic recovery of reserves had resulted in an increase in number of wells drilled up to 2018, but that has since declined due to drop in oil prices in the later part of the period and the covid-19 pandemic resulting in a 17% drop in number of wells drilled in 2020 from 2018 (Fig. 3).

b.    Discharges & Spills of Oil

The total quantity of dispersed1 oil (aliphatic oil) discharged to the sea from produced water and displacement water increased during the assessment period, from 2 017 tonnes in 2016 to 2 426 tonnes in 2020, an increase of 20% (Fig. 5) and reversing the trend from the previous 5 years. The increase is due to a mix of some installations producing more water and increasing average oil concentrations.

As in previous years, produced water and displacement water are the main contributors to the oil discharges from offshore oil and gas activities, representing 97-98% of the total amount of oil discharged to the sea during the period 2016 - 2020. Flare drop-out is a minor source of oil discharge and is not covered by OSPAR measures, though it is reported in the UK as a spill should it occur.

It should be noted that dispersed oil in displacement water contributes less than 4% of the total dispersed oil discharged.

The annual average dispersed oil content in produced water has increased over the period between 13,0mg/l in 2016 to 17,8mg/l in 2020 (Fig. 5). While this is likely due to a deterioration in performance in produced water treatment it may also be affected by changes in analytical correlation factors.

Despite efforts made to reduce the number of installations which exceed the 30mg/l performance standard for the discharge of dispersed oil in produced water, in 2020 there were 17 installations that currently don’t meet the standard, up from 11 in 2016.  The amount of oil being discharged in excess of the performance standard has also increased from 5,7 tonnes in 2016 to 104 tonnes in 2020 (Fig. 6).  Over 80% of the excess oil discharged in 2020 is from 4 installations, one of which has since ceased production and the main contributor having significant process problems which were due to be rectified in 2021.  

The total number of spills of oil to sea over the period 2016-2020 appears to be decreasing, though due to the nature of spills there is no trend in the quantity spilled each year as spills are highly variable (Fig. 7).

c.    Chemicals

The use and discharge of chemicals have been regulated by OSPAR and UK national legislation since 2001, with the first national reports provided for 2003. The total quantity of chemicals used offshore decreased during the period 2016-2020 (Fig. 9). On average, during the period 2016-2020 less than 2% (by weight) of the total amount of chemicals used contains either substances on the OSPAR List of Chemicals for Priority Action (LCPA) or substances which are candidates for substitution.

The total quantity of chemicals discharged offshore has also varied year on year from a peak of 75 323 tonnes in 2019 and a low of 55 720 tonnes in 2020 (Fig. 9). On average almost 80% (by weight) of the chemicals discharged are on the OSPAR PLONOR list2 .

OSPAR Recommendation 2005/2 set environmental goals for the reduction of discharges of LCPA substances, and discharges were to be phased out by 2010. This was achieved in the UK by 2012 and other than a 3,4kg discharge of lead-based pipe dope in 2016 which was mistakenly permitted during drilling operations, there have been no discharges of LCPA since (Fig. 10).

OSPAR Recommendation 2006/3 set environmental goals on the phasing out of discharges of chemicals that are, or which contain, substances identified as candidates for substitution3 by 2017. The quantity of substances identified as candidates for substitution (other than LCPA substances) used during the period 2016-2020 has increased by 40%, however the discharge of such substances has decreased by 34%.  The difference in trends between use and discharge are mainly that while more substitution chemicals are used, particularly in well operations, that more are being shipped to shore, treated or disposed of downhole.  This latter option is particularly the case for the increasing number of decommissioning well operations, which have increased sharply over the period. 

d.    Atmospheric Emissions

Atmospheric emissions from offshore oil and gas activities are not regulated by OSPAR measures, but are reported annually by operators. Emissions to the atmosphere have generally decreased with the exception of nmVOC emissions predominantly from Floating, Production, Storage and Offloading (FPSO) operations. These increased substantially between 2016-18, but have started to decline again, though remain higher than in 2016 (Figure 14 and Figure 15).


1“Aliphatics” and “aromatics” are defined by the reference method set in OSPAR Agreement 2005-15 (Solvent extraction, Infra-Red measurement at 3 wavelengths). In that context, “aliphatics” and “dispersed oil” mean the same thing.

2Pose little or no risk to the environment - PLONOR

3Except for those chemicals where, despite considerable efforts, it can be demonstrated that this is not feasible due to technical or safety reasons. Demonstration of those reasons should include a description of the efforts.