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Characterisation of the effect of CO2 on the reservoir properties of the Navajo Sandstone (Green River, Utah)


In July 2012 a well was drilled into the natural CO2 system at Green River, Utah by Shell. A sequence of reservoir-, cap- and fault rocks of about 300 meters was cored. This unique core material enables studying the long-term effect of CO2-charged brines on different lithotypes. CIM, as part of an international multi-disciplinary research-team, is in charge of the mineralogical and petrological part of the research.
This thesis will focus on the Navajo Sandstone formation (Jurassic). This eolian sandstone constitutes the main CO2 reservoir at the Green River site. It contains several reservoir sandstone intervals as well as tighter siltstones. The latter were identified as barriers to the upward migrating CO2-charged fluids. During drilling of the borehole substantial pressure differences were observed across the tighter horizons. These are expected to correspond to vertical gradients of the CO2-induced alteration of the reservoir's mineralogy.
The goal of this study is to characterise and quantify these gradients by means of a sediment-petrological and mineralogical study. The principal methods will be microscopy (polarised light, cathodoluminescence, SEM) and X-ray diffraction. The former will enable detailed identification of the CO2-induced alterations and evaluation of their impact on rock texture, while X-ray diffraction, using the advanced rietveld procedures developed at CIM, allows for accurate quantification of the mineralogical variation. The role of CO2 in the vertical mineralogical/textural variation observed in the cores from the well will be evaluated by comparison to outcrop samples from locations away from the CO2-migration pathways.


Start of work: Asap
Supervision: Pieter Bertier, Helge Stanjek, Chris Hilgers
Project partners: Shell, Cambridge University, Bonn University, Delft University, Oak Ridge National Laboratory
Level: MSc


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