The impact of sub-seismic shale layers on the reservoir's stress sensitivity

Colin MacBeth, Karl Stephen, Andy Gardiner

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Citations (Scopus)

Abstract

In most clastic reservoirs experiencing pressure depletion due to production, the hydraulically connected sands in the reservoir naturally compact to some degree. As a consequence, the much lower permeability reservoir shales may experience mechanical tension. The effective seismic response of the reservoir interval is thus a mix of both hardening and softening reservoir components. This phenomenon alters the predicted overall stress sensitivity from that anticipated for a homogeneous, fully connected reservoir interval. The time period over which this effect might be observed is influenced by the rate at which the shales reach pressure equilibrium with the surrounding sands. This work indicates that sub-seismic shale layers of approximately 1m thickness take less than 12 months to equilibrate, whilst thicker shale layers of 8m can take over 10 years. It is concluded that the mechanical and dynamic response of sub-seismic reservoir shale must be considered when quantitatively assessing the 4D seismic signature from frequently shot time-lapse surveys with a periodicity of 6 to 12 months, but also perhaps, for conventional 4D seismic surveys shot over 5 to 10 years. These conclusions are strongly affected by the permeability of the shale layers, the stress state, and are also a function of net to gross and depositional environment.

Original languageEnglish
Title of host publication78th Society of Exploration Geophysicists International Exposition and Annual Meeting
PublisherSociety of Exploration Geophysicists
Pages3209-3213
Number of pages5
ISBN (Print)9781605607856
DOIs
Publication statusPublished - 2008
Event78th Society of Exploration Geophysicists International Exposition and Annual Meeting 2008 - Las Vegas, United States
Duration: 9 Nov 200814 Nov 2008

Conference

Conference78th Society of Exploration Geophysicists International Exposition and Annual Meeting 2008
Abbreviated titleSEG 2008
CountryUnited States
CityLas Vegas
Period9/11/0814/11/08

Keywords

  • 4D
  • Monitoring
  • Reservoir characterization
  • Rock physics
  • Time-lapse

ASJC Scopus subject areas

  • Geophysics

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