DEVELOPMENT OF DTI GUIDANCE NOTES ON SAMPLING AND ANALYSIS OF PRODUCED WATER AND OTHER HYDROCARBON DISCHARGES

摘要

Historically the discharge of produced water is monitored in terms of a performance standard, e.g. 40 mg/l. To check if the produced water treatment systems meet the performance standard, produced water samples are taken regularly and measured according to an OSPAR agreed measurement method [1], which is based on solvent extraction and infrared quantification. Recently due to a ban on the use of Freon and also on the use of Tetrachloroethylene (TTCE) in some North Sea countries, a new reference method based on Gas Chromatography and Flame Ionisation Detection (GC-FID) was recommended by OSPAR in 2003 [2]. The new reference method will be implemented from 1 January 2007. Compared to the infrared based methods, the newly recommended GC based oil in water analysis reference method is relatively complicated, and requires the use of compressed gas and more skilful personnel. Challenges are therefore expected for the implementation of the new reference method. For the purpose of checking against the performance standard, the use of an alternative oil in water analysis method has been permitted by OSPAR [3]. The prerequisite condition is that such a method must be calibrated against the approved reference method. However there is little detailed information on how such a calibration should be carried out, on what basis the method can then be accepted. In the UK the new Offshore Petroleum Activities (Oil Pollution Prevention and Control) (OPPC) Regulations 2005 [4,5] came into force in August 2005. The new Regulations have been designed to more effectively regulate the offshore oil and gas industry for the discharge of hydrocarbons during the course of offshore operations. The Regulations introduce a permitting system for oil discharges and strengthen the powers to inspect and investigate oil discharges. The issue of permits under these new Regulations will be on a lifetime basis or for the duration of an activity covered. With regard to the discharge of oil in produced water, the new regulations stipulate that the monthly average concentration of dispersed oil in produced water does not exceed the 40 mg/l performance standard during the period between permit issue and 31 December 2005, and does not exceed 30 mg/l after 1 January 2006. The maximum concentration of dispersed oil in the discharge shall not exceed 100 mg/l. In addition to the analysis of dispersed oil in produced water, produced water samples shall also be collected on a bi-annual basis, at approximately six montly intervals and analysed for aliphatics, aromatics, total hydrocarbons, BETX (benzene, Toluene, Ethyl Benzene, Xylene), NPD (Napthalene, Phenanthrene and Dibenzothiophene, including C1-C3 Alkyl Homologues); 16 EPA PAHs (excluding Napthalene and Dibenzothiophene); organic acids; and heavy metals. The new OPPC Regulations also require operators to investigate the installation of an on-line oil in water monitor for platforms that discharge more than 100 tonnes of dispersed oil via the discharge of produced water to sea. In addition to the discharges of produced water, the OPPC Regulations also cover the discharge of hydrocarbons via the discharges of oil contaminated sand/scales, drainage water etc.