NERI Technical report no. 536: Aromatic Hydrocarbons in Produced Water from the Offshore Oil and Gas Industry. Test of Sampling Strategy. Hansen, A.B. 2005. 41 pp.
Summary
In co-operation with the Danish EPA, the National Environmental Research Institute (NERI) has carried out a series of measurements of aromatic hydrocarbons in produced water from an offshore oil and gas production platform in the Danish sector of the North Sea as part of the project "Testing of sampling strategy for aromatic hydrocarbons in produced water from the offshore oil and gas industry". The purpose of this project has been to test the sampling strategy, and the measurements included both volatile (BTEX: benzene, toluene, ethylbenzene and xylenes) and semi-volatile aromatic hydrocarbons: NPD (naphthalenes, phenanthrenes and dibenzothiophenes) and selected PAHs (polycyclic aromatic hydrocarbons).
In total, 12 samples of produced water were sampled at the Dan FF production platform located in the North Sea by the operator, Mærsk Oil & Gas, as four sets of three parallel samples from November 24 - December 02, 2004. After collection of the last set, the samples were shipped to NERI for analysis.
The water samples were collected in 1 L glass bottles that were filled completely (without overfilling) and tightly closed. After sampling, the samples were preserved with hydrochloric acid and cooled below ambient until being shipped off to NERI. Here all samples were analysed in dublicates, and the results show that for the BTEX, levels were reduced compared to similar measurements carried by NERI in 2002 and others. In this work, BTEX levels were approximately 5 mg/L while similar studies showed levels in the range 0,5 - 35 mg/L. For NPD levels were similar, 0,5 - 1,4 mg/L, while for PAH they seemed elevated; 0,1 - 0,4 mg/L in this work compared to 0,001 - 0,3 mg/L in similar studies.
The applied sampling strategy has been tested by performing analysis of variance to the analytical data. The test of the analytical data has shown that the mean values of the three parallel samples collec-ted in series constituted a good estimate of the levels at the time of sampling; thus, the variance between the parallel samples was not significanly (95%) different from the analytical variance (from replicate samples). However, the variance between samples colleceted at different days was significantly different from that within parallel samples, but not all average values for each day were significantly different for all measured components. The relative standard deviation between the four different sampling times varies between 6 and 47%, lowest for BTEX and highest for phenanthrenes. In conclusion, it seems possible to track variations in the content of aromatic hydrocarbons in produced water over time by applying the tested sampling strategy.
Full report in pdf format (494 kB).
