Environment Report 2015

Produced Water Composition While producedwater mainly consists of water, it does accumulate small amounts of naturally occurring substances through contact with the reservoir rock, including dispersed oil, dissolved organic compounds and naturally occurring radioactive material (NORM). Trace production chemicals are also present. If discharged with produced water, these chemicals rapidly dilute within the marine environment. The type and composition of chemicals is determined by the reservoir geology, maturity and production life stage. Oil in Produced Water In 2014, around 2,000 tonnes of oil were discharged with produced water, making up just over 0.001 per cent of the total mass of produced water discharged. This is similar to the 2013 value, showing consistent management. Produced water is sampled and analysed for hydrocarbon concentrations on a daily basis offshore and this is recorded in the EEMS database. OSPAR Recommendation 2001/1 requires that individual installations do not exceed an average annual oil in water concentration of 30 milligrammes per litre (mg/l). In 2014, the average concentration across the industry was less than half of this, at 12.8 mg/l, measured using the GC-FID method 7 . This is the lowest annual average on record since 2000 (see Figure 3 below). There were slight variations in the average monthly concentrations of oil in water discharged over 2014 from 11.7 to 14.1 mg/l, with a rise during September coinciding with some hydrocarbon production coming back on-stream after the summer maintenance period. IOGP reports that the global average oil content in produced water from offshore installations in 2013 was 13.4 mg/l. Norske Olje & Gass reports that a total of 1,542 tonnes of oil were discharged with produced water on the Norwegian Continental Shelf (NCS) in 2013, with an average concentration of 12.1 mg/l of oil in water. The 2013 UKCS average concentration was 14.4 mg/l, and is largely comparable to both the global and Norwegian values, as is the 2014 UKCS value of 12.8 mg/l.

1

2

3

4

5

6

Figure 3: Oil Discharged with Produced Water to Sea

Oil Discharged with Produced Water

Average Oil Content with IR Method

Average Oil Content with GC-FID Method

Oil in Water Concentration Limit

7

7,000

35

6,000

30

5,000

25

4,000

20

3,000

15

2,000

10

1,000

5

Oil Discharged with Produced Water (Tonnes)

0

0

Oil in Water Content (Milligrammes per Litre)

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Source: EEMS June 2015

7 Up to 2006, oil concentration in produced water was measured using the infrared method (IR). The IR method measures, in solvent, both the dispersed and dissolved hydrocarbons extracted. This method can, however, include other organic chemicals, giving an artificially high result and can also underestimate dissolved hydrocarbons. To rectify this and to provide a more accurate analysis of hydrocarbon content, OSPAR agreed (Agreement 2005-15) the use of a new method for oil in water analyses, based on a modified version of the ISO 9377-2 (GC-FID) method.

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