The Biological Implications For The Filtration Of North Sea Injection Water

Abstract

As a result of core injectivity tests and alternative filtration trials carried out on Forties platforms it became apparent that certain components of the North Sea biomass have a direct bearing upon the ultimate quality of North Sea injection water. This view is substantiated by the continuous monitoring of the fine filters currently in use in the Forties Water Injection System. This paper discusses those species which according to test data and observations of the fine filters are considered most likely to influence water quality. Their seasonal frequency and lateral and vertical distribution in the North Sea are also commented upon. The conclusion is drawn that filtration of North Sea Water is necessary prior to well injection Introduction Sea Water injection of the Forties oilfield commenced in December 1976 and is currently going ahead at a rate of approximately 125,000 b/d for each of the four platforms. The details of the Forties water injection system have been published and will not be mentioned here in any detail. published and will not be mentioned here in any detail. Suffice to say that the sea water is won from a depth of 200 ft below sea level and is filtered before being pumped down to the aquifer at a well-head pressure of 1,200 psi. An initial coarse filtration of the water is obtained by a 80 um stainless steel screen. Fine filtration down to 5 um is achieved by backwashable. Plenty cartridge filters containing replaceable fibre elements which are positioned upstream of the main injection pumps. The decision to filter the sea water prior to injection was based upon information gained from numerous on-site tests which in turn were followed by filtration trials to ensure the selection of the most efficient fine filter element available for use in the Forties environment. The current paper which is a sequel to one published in 1978 is limited to a discussion of the organic content of the injection water and its relationship to the fine filters.