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Using Modern Cave Systems as Analogs for Paleokarst Reservoirs

Charles T. Feazel
ConocoPhillips, Houston, Texas ([email protected])

Abstract

Karst processes, hydrology, dimensions and architecture are useful in understanding karsted rocks that serve as reservoirs for oil and natural gas. Three-dimensional cave surveys can be used to assign properties to “karst” cells in geocellular models. Surveys of long karst passages (e.g. Yucatan flooded caves) can be used to infer connectivity (i.e. how many “karst” cells can be neighbors?).

Karst processes ranging from surface weathering to deep burial dissolution have affected numerous karst intervals that host petroleum accumulations. Recognition and prediction of subsurface paleokarst from seismic or borehole information involves addressing the following concerns:

  • Does the layer in question consist primarily of carbonate rocks?
  • Is there evidence to suggest subaerial exposure of the carbonates?
  • Can a humid paleoclimate be documented?
  • What was the paleo-relief?
  • Does the tectonic history include episodes of jointing, faulting, or fracturing that would focus flowing water in the paleo-hydrologic setting?
  • Is there reason to suspect burial dissolution?
  • Did karst dissolution pre-date petroleum migration?
  • What differences would karsting make to wellbore deliverability, well spacing, drilling operations, injection strategies and production profiles?
  • Analogs and regional studies incorporating the elements of this list can be used in the exploration and production workflow to identify potential problems and opportunities, to constrain geo-model input, and to improve communication of subsurface risks and uncertainties.

    AAPG Search and Discovery Article #90086 © 2008 AAPG Foundation Distinguished Lecturer Series 2008-2009