Jeffrey Eppink, Enegis, LLC, Peter Geiser, G-O-Image LLC; Peter Malin, ASIR
Geologic carbon storage (GCS) is predicted to play a critical role in the reduction of global carbon emissions. The total number of global, large-scale facilities is projected to increase to over 2,000 by 2050 to reach emissions reduction goals. These projections reflect the need to sequester 5,600 million metric tons per annum, a 140-fold increase from current levels. To ensure their effectiveness for the public and storage developers, it is important that geologic carbon storage sites be assessed properly, maintain their technical integrity, are safe, and are developed at low cost. We are advancing a GCS technology—Ambient Seismic Imaging (ASI)—that facilitates easier, better, higher-resolution data acquisition and interpretation of what has been previously considered ambient seismic noise. ASI is distinct from microearthquake monitoring, instead detecting and locating fluid-and-gas filled fractures and fracture systems. ASI reduces the risks posed to carbon storage projects, both during the site characterization and monitoring phases, for a broad set of stakeholders. ASI can cost-effectively improve GCS mapping and monitoring. It does this by imaging fluid pathways and thereby increases the knowledge fluid movements. Critical for GCS, repeated fluid-pathway ASI surveys can directly detect and follow the development of initial and subsequent flow fluid in near real time.
ASI technology, similar to seismic emission tomography, passively listens to fluid-rock interactions using newly recognized seismic emissions from permeable rock. Our permeability field imaging for reservoir characterization, assessment of CO₂ behavior, evaluation of caprock failure and monitoring capabilities could make an important contribution to GCS. Because such maps are proportional to fracture density and fluid content, they provide direct evidence of the permeability field. The technical merit for the technology in GCS is achieved by establishing the existence of resonance signals (Krauklis waves generated by fluid filled fractures). Current 4D reflection seismic technology has some ability to locate fluids but falls well short of providing the permeability field imaging needed.
The current state-of-the-art in ASI technology comes from the oil and gas and mining industries. Pre-drill ASI maps have been verified by subsequent drilling. ASI maps have been used to target drilling and identify reservoirs for stimulation and to monitor fluid production. Analogous to GCS application is the use of ASI to monitor the injection of nitrogen as a miscible flooding gas in EOR operations. In a mining application, the location of an initial mine flood inflow was identified via a 4D time-lapse seismic reflection survey. Subsequently, about 9 months later when inflow had been reduced by two orders of magnitude, a blind test of ASI mapping showed a nearly 1:1 correspondence with the 4D mapping. Overall, the application of ASI technology could increase efficiency, enhance productivity and safety, reduce risk, increase regulatory certainty, and reduce costs.