Practical Aspects of Brine Extraction as a Storage Management Tool
Dr. Roland T. Okwen, Illinois State Geological Survey, Prairie Research Institute, University of Illinois Urbana-Champaign
Brine extraction can be used in developing and deploying commercial-scale carbon dioxide (CO2) storage to manage reservoir pressure and control CO2 plume in storage units, thus reducing the risks associated with reservoir pressure buildup and CO2 migration outside the injection zone. Major technical challenges of using brine extraction to manage storage include locating the extraction well and determining the efficacy of brine extraction. This study addresses these challenges and investigates the practical aspects of brine extraction for effective pressure and plume management by designing a brine exaction pilot at the Decatur CO2 storage site using numerical simulations. The simulated scenario at this site is a pre-existing, one-million tonne CO2 plume, a planned three-year CO2 injection via second, nearby injection well, and brine extraction planed for the second year of CO2 injection. A series of cases were simulated to determine the optimal extraction well type, well location, extraction rate (or injection-to-extraction ratio), and perforation interval. Differential pressure, CO2 storage efficiency, and the CO2 plume extent were used as metrics to evaluate brine extraction performance. Simulation results suggest that the pressure variations induced by brine extraction were of sufficient magnitude to be observed in multilevel monitoring well for all simulated brine extraction rates. With an injection-to-extraction ratio of 1:1 (volumetric balance), the optimal location for a vertical extraction well was (1) 0.5 mi (0.8 km) away from the injector, (2) in a direction perpendicular to high hydraulic connectivity direction, and (3) on the down-dip side, with perforation(s) within the injection zone. Alternatively, a horizontal well placed directly above the existing CO2 plume decreased the risk of drilling into the existing and new plume and reduce uncertainty in the geology. Compared to a vertical extraction well, a horizontal extraction well could manage pressure and CO2 plume at a lower extraction rate and had less impact on the lateral movement of the CO2 plume, which could result in higher CO2 storage efficiency and maintain the CO2 plume within an area of review. To minimize brine extraction and yet have a noticeable effect on reservoir pressure and movement of the CO2 plume, this study recommends injection-to-extraction ratios of 2:1 for a vertical well and 4:1 for a horizontal well, which correspond to extraction rates of 10,000 and 5,000 bbl/day (1,590 and 795 m3/day), respectively, when injecting 1 million tonnes of CO2 per annum (1.1 million tons of CO2 per annum). These findings demonstrate the practical approach to design a brine extraction research pilots that could lead to commercial storage applications requiring brine extraction to manage CO2 storage.
About the speaker
Dr. Okwen is a reservoir engineer at the Illinois State Geological Survey (ISGS), University of Illinois at Urbana-Champaign. As a member of ISGS, he has contributed to the Midwest Geological Sequestration Consortium’s Phase II pilot studies in the Illinois Basin. In addition to this project, he is assisting in the development of performance curves to act as screening tools for CO2 EOR floods. Previously, Dr. Okwen was a Postdoctoral Research Associate at Schlumberger Cambridge Research Center in the United Kingdom. He earned his PhD in Civil Engineering from the University of South Florida (2009), MS in Petroleum Engineering from Technical University of Denmark (2005), and BS in Chemistry from the University of Buea (1997). His research interests are in geological sequestration of carbon dioxide, enhanced oil recovery, reservoir geomechanics and data analytics.