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     Report: The University of Texas at Austin Susan D. Hovorka

Subject: Monitoring CO2 injection in brine formation

Time: 16:30pm March 31, 2010

Place: New Geology Building 3325 Room

Reporter: Susan D. Hovorka

 

Brief introduction of the reporter:

Susan Hovorka is interested in application of geological techniques to environmental problems, particularly focusing on the issue of permeability in both tight and very transmissive systems. This interest has lead led her to work on diverse problems, from characterization of salt as a containment material to analysis of carbonate fabrics to better understand flow in karst aquifers. Currently she is leading a team in a field pilot CO2 injection to assess the cost, safety, and effectiveness of geologic sequestration as a mechanism for reducing atmospheric greenhouse gas emissions (http://www.beg.utexas.edu/environqlty/co2seq/dispslsaln.htm).

She is also working on several projects to evaluate recharge processes and karst permeability on the Edwards aquifer.

She also is committed to facilitating exchange between the applied scientists and citizens, focusing on middle school students (http://www.beg.utexas.edu/mainweb/edu01.htm).

 

Monitoring CO2 injection in brine formation

Abstract

Geologic sequestration of CO2 in an oil reservoir is generally considered a different category than sequestration in formations that contain only brine. In this paper, the significance and validity of this conceptualization are examined by comparing the performance of CO2 injected into a depleted oil and gas reservoir with the performance of similar injection into non-oil-bearing sandstones using a field test at Cranfield field, Mississippi, as a case study. Residual oil and gas in the reservoir under miscible conditions reduces CO2 breakthrough time and rate of pressure buildup as compared to a reservoir containing only brine. Dense wells provide improved assessment of oil reservoir quality, leading to improved prediction, as well as verification of CO2 movement in this reservoir as compared with the sparsely characterized brine leg. Assessment of the difference made by the presence of residual oil and gas requires a good understanding of reservoir properties to predict oil and gas distribution. Stratal slicing, attribute analysis, and petrographic analyses are used to define the reservoir architecture. Real-time pressure response at a dedicated observation well and episodic pressure mapping have been conducted in the reservoir under flood since mid2008; comparison measurements are planned for 2009 in downdip environments lacking hydrocarbons. Model results using a CMG-GEM compositional simulator compare well in general to measured reservoir response under CO2 flood; imperfections in the model match of flood history document uncertainties. Time-lapse Reservoir Saturation Tool (RST) logging is under way to validate fluid composition and migration models. Monitoring performance of the wells during injection of CO2 suggests at this site that the value of wells for characterization exceeds the risk of leakage.
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