Wed 11th November 2020 @ 9:00 am on Webex (Meeting #: 176 783 7775, password: J2XrX8PRnP7)

Abstract:

Quartz cementation is a major factor in the evolution of bulk properties in the common sandstone types of conventional reservoirs (quartzo-feldspathic sandstones). Is the same true of unconventional reservoirs? High-resolution compositional imaging such as EDS elemental mapping and cathodoluminescence imaging by field-emission scanning electron microscopy allows the examination of mudrock components at scales appropriate for discriminating different forms of quartz in mudrocks. Results from a growing number of case studies show that silt-size detrital quartz of extrabasinal origin is the dominant form of quartz in mudrocks overall.  Locally however, grain assemblages in organic-rich mudrocks, especially ones deposited under conditions of relatively slow sediment accumulation, may contain biogenic silica of intrabasinal origin that is prone to dissolve and re-precipitate as grain-binding microquartz cement. Where present, such cement tends to be abundant (30-40% of rock volume). A given unit however, typically contains a mix of cemented and uncemented muds. This talk will illustrate the relative simplicity of discriminating and quantifying detrital versus authigenic pore-filling quartz using examples of mudrocks that are and are not prospective for oil and gas. Similar to quartz cement content in sandstone, quantitative estimates of cement content to can be used to partition the causes of porosity decline in mudrocks.

Short bio:

Kitty L. Milliken is a Senior Research Scientist at the Bureau of Economic Geology, University of Texas at Austin. She received a B.A. in geology (1975) from Vanderbilt University and M.A. (1977) and Ph.D. (1985) degrees from UT Austin. Her research focuses on diagenesis of siliciclastic sediments and the evolution of rock properties in the subsurface. She has authored and co-authored over 100 peer-reviewed papers and also digital resources for teaching sedimentary petrography. Her current work is focused on the application of electron microbeam imaging and analysis to interpret chemical and mechanical histories of mudrocks (oil and gas shales).