1887
Volume 24 Number 4
  • ISSN: 0263-5046
  • E-ISSN: 1365-2397

Abstract

During the last 10 years, time-lapse or 4D seismic has become a valuable means for improving the understanding of many North Sea reservoirs and establishing better drainage strategies (Landrø and Strønen 2003, Calvert 2005). In this study we demonstrate how time-lapse seismic has contributed to improving the drainage strategy at the Heidrun field and how working in integrated teams helps exploit the full potential of the methodology. We also show how Statoil’s time-lapse seismic inversion procedure has improved the interpretation of intra-reservoir production changes. The Heidrun oil field was discovered in 1985 off the coast of mid-Norway (Figure 1) and has total reserves of 180 million Sm3 of oil and 41.6 billion Sm3 of gas. Approximately 107 million Sm3 of the oil have been exported since production began in 1995. Seismic monitoring is an integral part of an improved oil recovery (IOR) campaign to exploit the remaining reserves. Time-lapse seismic surveys were carried out over the southern part of the Heidrun field (Figure 1) in 2001 and 2004 (Furre et al., 2003 and 2005, respectively), the base survey stemming from 1986. The 2004 survey, however, covered a slightly larger area to gain information to the west of the production platform where an additional production well was to be drilled. The results not only provided a better understanding of the reservoir but also permitted the drainage strategy to be significantly upgraded. The Heidrun field comprises late Triassic to early/mid Jurassic fluvial, deltaic, and shallow marine sandstones of the Åre and upper Tilje formations and the overlying Fangst Group (Figure 2). The field is a heavily faulted horst block and has to be produced in general by draining separate compartments. The aim of the 2004 repeated survey was to better understand the reservoir and improve the drainage strategy for the Fangst and Upper Tilje units which were favourably disposed to time-lapse seismic because of their location and production properties. The seismic data were acquired in September 2001 and June 2004, a time difference of just less than three years (i.e. about half that compared with more than six years of production in the period between the 1986 base line survey and the 2001 repeat survey). The overall drainage strategy for the field is reservoir pressure maintenance by up-flank gas and down-flank water injection - the first row of productions wells being placed accordingly. However, time-lapse seismic was used to optimize the location of new up-flank targets as the wells started to water out. The remaining reserves for each target presently range between 0.25-0.5 million Sm3. The 2001 time-lapse seismic survey results proved valuable for locating four new production wells, while the results from the 2004 survey helped to optimize the positioning of at least one new production well and three new injection wells. The repeated seismic surveys also improved our general understanding of the field’s drainage and helped to increase the knowledge of multi-disciplinary staff engaged in generating flooding maps.

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/content/journals/10.3997/1365-2397.2006008
2006-04-01
2024-03-28
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http://instance.metastore.ingenta.com/content/journals/10.3997/1365-2397.2006008
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  • Article Type: Research Article
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