4D seismic monitoring of CO2 sequestration

Abstract

W e are about to face a surge in the need for geophysical characterization and monitoring of subsurface reservoirs and aquifers for CO 2 sequestration projects. Global energy demand is rising signifi cantly, expected to double over the next 20-30 years, driven by world population increase and the rapid growth of emerging economies. At the current rate of development of alternate energy sources, it is possible that the world may have to rely even more heavily on carbonbased fuels than at present to meet the impending energy demand (Figure 1). With global oil production near its peak or perhaps already in decline, this will place an increased emphasis on coal and LNG (liquid natural gas) in the carbonbased energy mix, and on unconventional hydrocarbon resources like tight gas, coal-bed methane, and heavy-oil tar sands. All of these carbon-based energy sources, especially coal-fi red power plants, LNG, and tar-sand operations, will create a growing supply of excess CO 2 . Irrespective of whether man-made CO 2 emissions are a signifi cant cause of global climate change, or simply well-correlated with global temperature rise, there will be increasing pressure from world governments to reduce the amount of CO 2 emissions to the atmosphere, via policy change (e.g., Kyoto, Copenhagen) or via fi nancial measures (e.g., carbon tax, cap and trade). Capturing industrial CO 2 at its various sources and injecting it into deep geologic formations for longterm storage (sequestration) appears to be one of the most promising methods to achieve signifi cant reductions in atmospheric CO 2 emissions.Th e basic CO 2 sequestration approach will be to capture it at a source (e.g., coal-fi red power plant, LNG facility, or tar-sands operation) and inject it into a deep geologic formation located nearby. Subsurface storage targets include depleted hydrocarbon reservoirs, and saline aquifers. A massive undertaking has already started to locate and rank subsurface reservoir candidates for CO 2 sequestration among the world's sedimentary basins, and future work will require detailed geologic and geophysical site characterization of these reservoirs/aquifers in terms of better defi ning storage capacity (volume, porosity), injectivity (permeability, pressure regime, etc.), and sealing effi ciency (permeability barriers, structural and stratigraphic traps, fault seal, CO 2 trapping mechanisms, CO 2 capillary pressures, geochemistry, etc.). Australia has recently become the fi rst nation in the world to open up off shore exploration leases specifi cally for the purpose of locating potential subsurface CO 2 storage sites in preparation for a future market in CO 2 sequestration ( Figure 2). Th e role for seismicIn addition to site characterization, there will be a huge demand for geophysical monitoring and verifi cation technol-

Seismic Monitoring in the Framework of the Pilot Project CLEAN

“…They suggest that not exclusively direct reflections from the top reservoir, but also multiples and reflectins from layer boundaries below, which passed through the region with changed rock properties at least once, were migrated. This can lead to the wrong conclusion of CO 2 accumulations in greater depth as it was also shown by Lumley (2010).…”

Determining changes in CO2 saturation from time-lapse measurements using ghost reflections retrieved by seismic interferometry

“…Time-lapse seismic measurements have proven their merit in monitoring changes in the reservoirs layer during CO 2 sequestration (Arts et al, 2002;Chadwick et al, 2010;Lumley, 2010;Ivanova et al, 2012). Results at the Sleipner underground storage site in the North Sea show a very strong time-lapse seismic response, both in terms of high seismic amplitudes as well as strong timeshifts (Arts et al, 2004b).…”

Feasibility of time-lapse gravity monitoring of producing gas fields in the Northern Carnarvon Basin, Australia

“…Repeat (time-lapse) geophysical surveys, especially gravity, seismic or electromagnetic methods, may remotely detect changes in gas saturation over time (Lumley, 2009, Lumley, 2010. Gravity data has the benefit of being directly related to changes in subsurface density, which is a strong linear function of gas saturation (Figure 1).…”