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Norne Field, in the southern part of the Nordland II area in the Norwegian Sea approximately 100 km north of Aasgard Field, is producing from an FPSO. The main field is a horst block approximately 9 ǂ 3 km (Figure 1). The reservoir rocks are sandstones of Lower and Middle Jurassic age. The hydrocarbon reserves consist of a gas cap (75 m), mainly situated in Garn Formation, and an oil leg (110 m), mainly situated in Ile and Tofte formations. The sandstones are very good quality with porosities and permeabilities of 25-32% and 200-2000 mD, respectively. Net-to-gross is close to 1 for most reservoir zones. Oil production started in 1997. The first 4D seismic survey was acquired in 2001, and 4D information has been actively used in subsequent reservoir management. This paper will focus on the importance of tight integration of all disciplines for achieving good quality and repeatable 4D seismic data that can optimize new drilling targets and help obtain a more reliable reservoir simulation model.

A B S T R A C TSea-bed diffractions are frequently observed for several of the fields in the Norwegian Sea and the Barents Sea. This is a challenge in time lapse seismic analysis, since diffracted multiples are difficult to remove by processing and therefore is a major source of poor time lapse data quality. In this work we test if the diffractions can be used for enhanced 4D interpretation. By analysing the time-shift of the sea-bed diffraction hyperbola between the base and monitor it is tested if changes in water velocity and tides can be estimated.Two models using time lapse diffraction analysis are tested: the first one simply adds time-shifts for the two branches of the diffraction hyperbola and this average time-shift is then used to estimate the water velocity change. The other method uses an inversion method based on the diffraction equation for a point diffractor to estimate the velocity change. In-line common-midpoint shifts are estimated by subtracting the time-shifts of both hyperbola branches followed by direct inversion. The diffraction based time-shifts are compared to time-shifts estimated by standard cross-correlation of the sea-bed reflection. The averaging method gives slightly higher uncertainties, while the inversion using an exact traveltime equation gives similar uncertainties compared to the sea-bed reflection method.

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