Technology Focus: CO2 Applications (July 2013)
Authors: Rogers John D. 
Published: February 2015

Technology Focus
Research-and-development modeling has shown that CO2 can diffuse a small distance into the thick shale caprocks above brine aquifers used for sequestration and cause migration of siderite (iron carbonate), magnesite (magnesium carbonate), calcite, and other precipitates back into the target zone, which is what is wanted for mineral sequestration of CO2. I bring this up because, eventually, the industry may want to enhance the oil recovery from fractured shale oil (e.g., Bakken, Niobrara, and Monterey). A keynote speaker at the 2013 SPE Unconventional Reservoir Conference in The Woodlands, Texas, suggested that the industry may eventually want to improve recovery of the Bakken by waterflooding. CO2 might also be an enhanced-oil-recovery direction for shale oil and effect a dual benefit of storage of CO2. Shale (and other mudstones) has significantly more mineral components with iron and other metals (e.g., clays and pyrite) than do typical clastic and carbonate oil reservoirs. As a result, the geochemical reactions and adsorption will be more complex than the typical CO2 floods have shown over the last 30-plus years. A university laboratory effort was published in this focus area in 2011 and also in the SPE Journal on using organic-rich shale for CO2 storage.
Today, reservoir simulators are robust and give the user great comfort in predicting how recovery performance will be affected by CO2 injection and, to a limited degree, geomechanical alterations. However, the industry currently has no functional true 3D reactive transport simulator that can help engineers efficiently model the CO2 flooding in shale where geochemical reactions and thermodynamic phase transitions take place simultaneously. Reservoirs that have rock assemblages consisting of a few mineral components have been modeled to a limited degree but are difficult to simulate beyond a teaching/research-and-development level. Very few truly reactive transport reservoir simulators exist. The few reactive reservoir simulators that are available are fairly good at 1D, possibly 2D, models but fail as a fast robust general engineering tool when large mineral assemblages with large orders-of-magnitude differences in kinetic reaction rates are to be modeled in three dimensions. A fast reactive transport simulator tool will need to be in place for engineering purposes for CO2 storage, as well as for EOR engineering studies, in shale.
As an additional side note, the 2014 US president’s budget submitted to the US Congress has cut the carbon-storage program by approximately 47% but has increased the carbon-capture research side of the program (by approximately 43%), which is the economic bottleneck of the carbon capture, utilization, and storage process, especially for power plants. Whether the US Congress will go along with this is yet to be determined because there is some opposition, especially from congress members from coal states.
Recommended additional reading at OnePetro: www.onepetro.org.
SPE 157136 Evaluating a Depleted Oil and Gas Field in the East Coast of Trinidad for Disposal of Carbon Dioxide by D.J. Jaggernauth, Petrotrin
SPE 156983 Enhanced CO2 Storage in Deep Saline Aquifers by Nanoparticles: Numerical-Simulation Results by Harpreet Singh, The University of Texas at Austin, et al.
SPE 157396 Sustainable Production of Biochemicals and Biofuels Based on Biofixation of Carbon Dioxide by Microalgae by W.A.P. van den Bos, TNO, et al.