Philip Christie¹, Pal Kristiansen², Jack Bouska³, Andrew O'Donovan³, Peter Westwater³, Ed Thorogood⁴

(1) Schlumberger, Tulsa, OK
(2) Schlumberger
(3) BP
(4) Shell

ABSTRACT: Foinaven 4D: Repeatability and Reservoir Impact of Two Designer Time-Lapse Surveys

Time-lapse, or 4D, seismic has been demonstrated as a cost-effective tool for reservoir management several recent case studies. Conceptually, the technique analyses differences between two seismic surveys over the same field to image changes in the reservoir which can be related to changes in saturation, phase or pressure. Most studies have used "legacy" datasets in relatively mature fields, where the reference 3D survey was acquired to improve imaging in a reservoir which had been under production for some time. These studies have often succeeded in imaging large changes in the reservoir and are useful in managing the reservoir by, for example, guiding the selection of in-fill drilling targets.

Foinaven, the first producing field West of Shetlands, is the laboratory for two designer 4D surveys. Deepwater reservoirs, like Foinaven, are produced through flexible risers to FPSO facilities which makes re-entry for surveillance logging prohibitively expensive and motivates 4D as a surveillance technique. Both towed streamer and Ocean-Bottom Hydrophone surveys were acquired in Foinaven to evaluate the benefit of 4D seismic in this area and to compare the two technologies. Because the time-lapse signal must be detected from a background of non-repeatable seismic noise, comparisons of repeatability between towed and OBH data will help evaluate their relative utility in future 4D surveys.

This paper presents the two 4D results in Foinaven, reviews their impact on understanding the dynamic behaviour of the reservoir, compares the repeatability of the two technologies and offers some pointers for future surveys.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado