A compaction front in North Sea chalk

P. Japsen, D.K. Dysthe, E.H. Hartz, S.L.S. Stipp, V.M. Yarushina, B. Jamtveit

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

Abstract

North Sea chalk shows a pronounced porosity drop, from 20% to <10% over a compaction front of less than 300 m. The position of the compaction front is closely tied to an effective stress of ∼17 MPa. These observations require a strongly nonlinear rheology with a marked increase in compaction rate at a specific effective stress. Grain-scale observations demonstrate that the front coincides with grain coarsening and recrystallization of fossils and fossil fragments. We propose that this nonlinear rheology is caused by stress-driven failure of the larger pores and the associated generation of reactive surface area by subcritical crack propagation away from these pores. Before the onset of this instability, compaction by pressure solution is slowed down by the inhibitory effect of organic compounds associated with the fossils. Although the compaction mechanism is mainly by pressure solution, the rheological response to burial may still be dominantly plastic and controlled by the rate of exposure of reactive surface area. The nonlinear compaction of chalk has significant implications for the evolution of petroleum systems in the central North Sea, both with respect to sea-floor subsidence above hydrocarbon-producing chalk reservoirs and for the formation of low-porosity pressure seals within the chalk.

Original languageEnglish
Title of host publication74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012
Subtitle of host publicationResponsibly securing natural resources
PublisherEuropean Association of Geoscientists and Engineers
Pages1462-1466
Number of pages5
Volume2
ISBN (Print)978-1-62993-790-8
Publication statusPublished - 2012
Event74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012: Responsibly Securing Natural Resources - Copenhagen, Denmark
Duration: 4 Jun 20127 Jun 2012

Conference

Conference74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012
Country/TerritoryDenmark
CityCopenhagen
Period4/06/127/06/12

Programme Area

  • Programme Area 2: Water Resources
  • Programme Area 3: Energy Resources

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