The Role of Existing Seismic Reflection Data in Evaluating Sites for CO₂ Sequestration and Natural Gas Storage in the Illinois Basin

By

MCBRIDE, J. H., and KOLATA, D. R.

Illinois State Geological Survey and Department of Geology, University of Illinois at Urbana-Champaign, IL

NELSON, W. J

Illinois State Geological Survey, Champaign, IL

LEETARU, H. E.

Illinois State Geological Survey and Department of Geology, University of Illinois at Urbana-Champaign, IL

     For the past several years, the Illinois State Geological Survey (ISGS) has pursued a vigorous program of procuring seismic reflection data from the Illinois Basin previously acquired by the petroleum exploration industry.  The availability of these data have been used to leverage acquisition of grant and contract funds from, e.g., the U. S. Geological Survey and the National Science Foundation through the Mid-America Earthquake Center.  Such funds are used to support processing, interpretation, and archiving of seismic data at the ISGS.  Although most of these data remain proprietary and are used only according to the owner’s specification, ISGS researchers may use the data for non-commercial purposes, such as scientific studies of the structural and stratigraphic framework of the basin, seismic hazard evaluation, and detailed analysis of specific geologic features (e.g., anticlines and domes).  2-D and 3-D seismic reflection data are received in varying formats, including paper and film copies and/or digital records of raw or stacked and migrated data.  The ISGS has excellent hardware, software, and personnel resources that enable us to scan, reprocess, and create state-of-the-art in-house databases, which allows incoming data to be fully integrated with a great variety of ancillary geological, geophysical, and GIS data.  Our reprocessing and data integration capability effectively increases the value of the original seismic data for both the ISGS researcher and for the original data owners.  For example, the results of reprocessing and mapping of reflection profiles currently available over the major folds and monoclines of the Illinois Basin reveal deep-seated faults penetrating lower Paleozoic strata and underlying basement that propagate up into the cores of folds.  The pervasiveness and pattern of deep fracturing beneath folds are critical factors for evaluating the viability of a structure in Paleozoic strata for CO₂ or other gas storage.  The asymmetry of some folds in Mississippian and Pennsylvanian strata suggests the possible presence of a deeper, facilitating reverse or thrust fault.  A distinct forward hinge typically appears at the top of Precambrian basement beneath folds mapped in Paleozoic strata.  Truncated and offset intra-basement reflectors below this hinge imply a reverse fault within Precambrian rocks.  Reprocessed long-record reflection profiles reveal seismic facies with a sedimentary character below the basal Mt. Simon Sandstone (Cambrian), which are bounded by strong, laterally continuous reflectors expressed as broad “basinal” packages that become areally more restricted with depth.  At least four highly coherent, layered, unconformity-bounded seismic stratigraphic sub-Mt. Simon sequences that could total several thousand meters in thickness can be mapped in three dimensions over distances in excess of 200 km.  The shallowest part of these sequences may host reservoirs capable of storing natural gas or sequestering CO₂.  Ultimately the selection of a suitable structure for gas injection will require new 3-D seismic coverage; however, available 2-D profiles can provide a cost-effective means for sifting through the multitude of possible structures in the Illinois Basin.