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Agate As from Analog for Porosity Preserving Microquartz in Deep Clastic Reservoirs

French, Marsha W.1
 Worden, Richard H.2
 Lee, David R.2
 Lamberti, Previous HitWilliamNext Hit A.3
 Horn, Previous HitWilliamTop C.3

1ExxonMobil Upstream Research Company, Houston, TX.
Earth and Ocean Sciences,
University of Liverpool, Liverpool, United Kingdom.
ExxonMobil Corporate Strategic Research Company,
Annandale, NJ.

Understanding growth mechanisms in the formation of agates can be used as an analog for understanding microcrystalline quartz growth, which preserves porosity in deep clastic reservoirs. Agates of volcanic origin contain a range of microcrystalline silica phases; cryptocrystalline silica, chalcedony and quartz. These are arranged in concentric bands in agate and can be identified in natural microquartz examples, as well. Researchers disagree whether the range of microcrystalline silica minerals form from silica rich fluid pulses or by crystallization of a silica gel. Several advanced analytical techniques including Electron Backscatter Diffraction (EBSD), cathodoluminescence (CL), Fourier Transform Infrared (FT-IR) spectroscopy, Raman Spectroscopy, and Secondary Ion Mass Spectrometry (SIMS) were used to characterize the silica minerals present in the agates and microquartz and investigate the relationship between the minerals and layering of the different silica phases.

Integrating the results from these advanced analytical techniques in agates has helped us develop our understanding of the processes controlling the formation of different silica phases in agates similar to microcrystalline quartz and improved our ability to reconstruct the diagenetic history and /or trace element impact on microcrystalline quartz growth.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil