Environment Report 2017

3.2 Produced Water When oil and gas are produced, water that lies under the ground is also brought to the surface. This produced water can make up over 95 per cent of produced liquids in some fields and is separated from the hydrocarbons before either being reinjected into the reservoir to increase production, or treated and discharged to sea. Operators gain approval for produced water discharges by applying for a permit. Produced Water Volumes The total amount of produced water handled on the UKCS follows the general trend of production and had therefore been declining since 2000 (see Figure 2 overleaf). Over time, however, the decline in production had been greater than the decrease in produced water generated. This is because, as the UKCS matures, hydrocarbons become harder to reach and extract, which, in the process, generates larger volumes of produced water per unit of production. Since 2014, the UKCS has reversed the production decline of the preceding 15 years resulting in a rise in total produced water to 203 million cubic metres in 2016 (accounting for 72 per cent of total well stream fluids). Despite this, the amount of produced water discharged to sea fell by 6 per cent from 165 million cubic metres in 2015 to 155 million cubic metres in 2016. This is because record levels of produced water were reinjected into suitable subsurface strata or the reservoir itself as an alternative to discharging to sea and, where technically feasible, to aid enhanced oil recovery (EOR). The amount of produced water reinjected to the subsurface increased to almost 48 million cubic metres last year, up 30 per cent from 2015. One project that is an exemplar of increased produced water reinjection is Apache North Sea’s Aviat gas field, brought online during 2016. The Aviat field is tied-back to the neighbouring Forties Field and provides fuel gas for generating power as offshore installations are not connected to the National Grid. The use of fuel gas brings environmental and financial benefits, namely significantly reduced diesel consumption and increased uptime of injection pumps on the Forties field, which in turn helps maximise produced water reinjection.

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