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Diagenetic modeling to assess the relative timing of quartz cementation and brittle grain processes during compaction

¹ Department of Geological Sciences, University of Texas at Austin, Austin, Texas 78712; present address: BP America, 501 Westlake Park Blvd., Houston, Texas 77079; Astrid.Makowitz{at}BP.com
² Geocosm LLC, 3311 San Mateo Drive, Austin, Texas 78738
³ Department of Geological Sciences, University of Texas at Austin, Austin, Texas 78712

Astrid Makowitz joined BP upon completion of her Ph.D. at the University of Texas at Austin (2004). Both M.S. (1999) and B.S. (1997) geology degrees were awarded from the Michigan State University. Astrid has enjoyed working as a reservoir quality specialist and is currently in the Onshore North American Gas production setting. Her love for geology remains with studying rocks on a pore to subpore scale.

Robert Lander coinvented Geocosm's Prism and Touchstone models and Geologica's Exemplar® model. Rob obtained a Ph.D. in geology from the University of Illinois in 1991 and was a senior research geologist at Exxon Production Research from 1990 to 1993. He then worked for Rogaland Research and Geologica in Stavanger, Norway. Rob cofounded Geocosm in 2000 and is a research fellow at the University of Texas at Austin.

Kitty Milliken has degrees in geology from Vanderbilt University (B.A.) and the University of Texas at Austin (M.A. degree, Ph.D.). At the University of Texas at Austin, she currently serves as a research scientist in the electron microbeam facility. Together with students, she pursues research projects that apply imaging and analysis to decipher the chemical histories of low-temperature systems. She is a coauthor of the recently released interactive teaching module Sandstone Petrology: A Tutorial Petrographic Image Atlas.

This study describes porosity reduction by brittle deformation and the application of Touchstone^TM sandstone diagenesis modeling software to assess the relative timing and interactions between grain fracturing and cement formation during burial compaction. Two examples from a previous study of compactional fracturing are used: the Oligocene Frio Formation, Gulf of Mexico Basin, and the Cambrian Mount Simon Formation, Illinois Basin, United States. Grain fracturing during compaction creates intragranular fracture surfaces that are favorable sites for quartz nucleation compared to external grain surfaces that may bear coatings that inhibit the nucleation and growth of quartz cement. Thus, the progress of brittle fracture processes during diagenesis affects quartz cementation. In turn, modeling of the quartz cementation process can serve to place fracturing into its proper context in burial history.

In the Mount Simon Formation, the extent of brittle deformation of quartz grains correlates with reconstructed effective stress at the onset of quartz cementation. For Frio Formation samples, however, the extent of brittle deformation does not correlate well with reconstructed effective stress obtained using a one-dimensional basin model that uses compaction disequilibrium as the dominant mechanism for overpressure generation. Judging from the observed degree of grain fracturing, significant fluid overpressures in the Frio may not have developed at the shallow depths indicated by our basin models. The degree of compactional fracturing in sandstones constitutes observable evidence that can be used to decipher the complexities of pressure history.

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				W. T. Parry, M. A. Chan, and B. P. Nash Diagenetic characteristics of the Jurassic Navajo Sandstone in the Covenant oil field, central Utah thrust belt AAPG Bulletin, August 1, 2009; 93(8): 1039 - 1061. [Abstract] [Full Text] [PDF]

				R. H. Lander, R. E. Larese, and L. M. Bonnell Toward more accurate quartz cement models: The importance of euhedral versus noneuhedral growth rates AAPG Bulletin, November 1, 2008; 92(11): 1537 - 1563. [Abstract] [Full Text] [PDF]