Modelling seismic response from North Sea chalk reservoirs resulting from changes in burial depth and fluid saturation

O.V. Vejbæk, R. Rasmussen, P. Japsen, A. Bruun, J.M. Pedersen, G. Marsden, I.L. Fabricius

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingspeer-review

13 Citations (Scopus)


Changes in seismic response caused by variation in degree of compaction and fluid content in North Sea chalk reservoirs away from a wellbore are investigated by forward modelling. The investigated seismic response encompasses reflectivity, AVO and acoustic impedance. Synthetic seismic data are calculated on the basis of well data from the South-Arne and Dan fields, Danish North Sea and compared to field records. Seismic response predictions are based on three main tools: (1) saturation modelling, (2) compaction/decompaction modelling and (3) rock physics. Hydrocarbon saturation in North Sea chalk is strongly affected by capillary forces and transition zones in the order of 50m are common. Advanced saturation height modelling is applied, which has proved robust for the prediction of saturation profiles in Danish chalk. Compaction modelling relies on exponential decay of porosity with depth, where abnormal fluid pressures are accounted for. A new set of compaction parameters is presented based on a normal velocity-depth trend and a velocity-porosity transform for North Sea chalk. The parameters appear to allow fairly precise predictions of abnormal fluid pressures from observed average porosity. Based on this, the relative contribution to porosity preservation by abnormal fluid pressure and early hydrocarbon invasion may be estimated. Rock physics theory is applied to obtain all necessary parameters for the complete set of elastic parameters for seismic modelling. Modelling results of importance in the search for subtle traps include: (1) correlation of reflectivity with porosity; (2) primary sensitivity of acoustic impedance is to porosity variation rather than hydrocarbon saturation; (3) the Poisson ratio is very sensitive to hydrocarbon saturation at high porosity, depending on fluid density contrasts. In addition, compaction modelling shows a clear effect of porosity preservation by hydrocarbons in the South-Arne Field, whereas this effect is negligible in the Dan Field. In both fields seismic signatures in field records originating from fluid changes are identified.

Original languageEnglish
Title of host publicationPetroleum Geology: North-West Europe and Global Perspectives. Proceedings of the 6th Petroleum Conference London
EditorsA.G. Doré, B.A. Vining
PublisherGeological Society of London
Number of pages13
ISBN (Print)1-86239-164-5
Publication statusPublished - 2005
Event6th Petroleum Geology Conference - Queen Elizabeth II Conference Centre, London, United Kingdom
Duration: 6 Oct 20039 Oct 2003

Publication series

SeriesPetroleum Geology Conference series


Conference6th Petroleum Geology Conference
Country/TerritoryUnited Kingdom


  • Chalk
  • Compaction
  • North sea
  • Oil-water contact
  • Reservoir properties
  • Seismic attributes

Programme Area

  • Programme Area 3: Energy Resources


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