Produced Water – Introduction and Background

Almost all offshore oilfields produce large quantities of contaminated water that can have significant environmental effects if not handled properly.

Oil and gas reservoirs have a natural water layer (called formation water) that, being denser, lies under the hydrocarbons. Oil reservoirs frequently contain large volumes of water, while gas reservoirs tend to produce only small quantities. To achieve maximum oil recovery, additional water can be injected into the reservoirs to help force the oil to the surface and as a result both formation and injected water are eventually produced along with the hydrocarbons.

The OSPAR Recommendation 2001/1 for the Management of Produced Water from Offshore Installations, the purpose of which is to prevent and eliminate pollution by oil and other substances caused by discharges of produced water into the sea, was agreed in 2001. The recommendation requires the following:

• reduction of oil-in-produced water of 15% by the end of 2006 compared to a 2000 baseline (by country)
• achievement of 30 mg/l oil-in-produced water concentration by the end of 2006 (by installation)

The recommendation was amended in 2006 to stipulate a new analysis reference method and to prohibit dilution to achieve the standard.

Produced Water - Key Statistics and Commentary

The concentration of oil-in-produced water has continued to decline over recent years through investment in separation technologies which along with re-injection projects has seen the steady decline in total oil discharged from UK producing assets. Indeed, the UK achieved the OSPAR targets and by 2006 had actually made a 24% reduction (from the 2000 baseline) in the discharged oil-in-produced water.

During 2006, 104 installations discharged a total of 222,367,000 tonnes of Produced Water which contained 4355.11 tonnes of oil. This correlates to an average of 19.58ppm, significantly below the OSPAR target of 30ppm. This exceeds the offshore industry’s performance for 2005 where the average oil content of produced water was 20.5ppm, achieved from 71 discharging installations. Recently collated data suggests that the UKCS performance for 2007 is further exceeding the target.

Produced Water Discharges 2000-2006

Produced Water – Supplementary Statistics and Commentary

For more information, see the Supplementary Statistics Section.