Chalk background velocity: Influence of effective stress and texture

Peter Japsen, Gary Mavko, Lars Gommesen, Ida L. Fabricius, Finn Jacobsen, Ole Vejbæk, Rasmus Rasmussen, Christian Rau Schiøtt

Publikation: Bidrag til bog/rapport/konferenceproceedingsKonferenceartikel i proceedingspeer review

8 Citationer (Scopus)

Abstrakt

The relative variations in acoustic impedance and hence porosity may be determined by inversion of seismic data. The estimation of the absolute level of these parametres, however, requires a priori knowledge about the low-frequent, background velocity. We find that the background velocity of the North Sea chalk is primarily controlled by effective stress: velocity and porosity log data for chalk in two wells plotted versus effective depth match published reference lines for normally compacted chalk above c. 1.8 km. Effective depth is depth corrected for the effect of overpressure. Below that depth we observe a significant drop in porosity and an increase in velocity that possibly may be explained by a decrease in the Biot factor leading to an increase in effective stress and hence in pore-filling cementation originating from pressure dissolution along stylolites. Moreover, we observe different velocity-porosity relation for the chalk in the two wells leading to differences in porosity of some 5% for identical values of velocity for apparently pure chalk. These variations may be related to differences in contact cementation between the poorly cemented and suffer pore shapes (possibly affected by quartz-overcoating). The non-unique velocity-porosity relation for chalk will lead to variability in the estimation of porosity from seismic data because one impedance value may represent a range of porosities.

OriginalsprogEngelsk
Titel67th European Association of Geoscientists and Engineers, EAGE Conference and Exhibition, incorporating SPE EUROPEC 2005 - Extended Abstracts
ForlagSociety of Petroleum Engineers
Sider1829-1832
Antal sider4
ISBN (Trykt)9073781981, 9789073781986
StatusUdgivet - 2005
Begivenhed67th European Association of Geoscientists and Engineers, EAGE Conference and Exhibition, incorporating SPE EUROPEC 2005 - Extended Abstracts - Feria de Madrid, Spanien
Varighed: 13 jun. 200516 jun. 2005

Publikationsserier

Navn67th European Association of Geoscientists and Engineers, EAGE Conference and Exhibition, incorporating SPE EUROPE2005 - Extended Abstracts
Vol/bind67th European Association of Geoscientists and Engineers Conf...

Konference

Konference67th European Association of Geoscientists and Engineers, EAGE Conference and Exhibition, incorporating SPE EUROPEC 2005 - Extended Abstracts
Land/OmrådeSpanien
ByFeria de Madrid
Periode13/06/0516/06/05

Programområde

  • Programområde 3: Energiressourcer

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