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

Publikation: Bidrag til bog/rapport/konferenceproceedingsKonferenceartikel i proceedings

11 Citationer (Scopus)

Abstrakt

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.

OriginalsprogEngelsk
TitelPetroleum Geology: North-West Europe and Global Perspectives. Proceedings of the 6th Petroleum Conference London
RedaktørerA.G. Doré, B. Vining
ForlagGeological Society of London
Sider1401-1413
Antal sider13
DOI
StatusUdgivet - 2005
Begivenhed6th Petroleum Geology Conference - Queen Elizabeth II Conference Centre, London, Storbritannien
Varighed: 6 okt. 20039 okt. 2003

Publikationsserier

NavnPetroleum Geology Conference series
ForlagGeological Society. London.
Vol/bind6

Konference

Konference6th Petroleum Geology Conference
Land/OmrådeStorbritannien
ByLondon
Periode6/10/039/10/03

Programområde

  • Programområde 3: Energiressourcer

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