# AAPG Bulletin

Abstract

AAPG Bulletin, V. 86, No. 5 (May 2002), P. 745-778.

## Material-balance assessment of the New Albany-Chesterian petroleum system of the Illinois basin

### M. D. Lewan,1 M. E. Henry,2 D. K. Higley,3 J. K. Pitman4

1U.S. Geological Survey, P.O. Box 25046, Denver Federal Center, Denver, Colorado, 80225; email: mlewan@usgs.gov
2U.S. Geological Survey, P.O. Box 25046, Denver Federal Center, Denver, Colorado, 80225; email: henry@usgs.gov
3U.S. Geological Survey, P.O. Box 25046, Denver Federal Center, Denver, Colorado, 80225; email: higley@usgs.gov
4U.S. Geological Survey, P.O. Box 25046, Denver Federal Center, Denver, Colorado, 80225; email: jpitman@usgs.gov

## AUTHORS

Michael D. Lewan is a petroleum geochemist and geologist for the U.S. Geological Survey. His research is focused on generation and expulsion processes responsible for oil and gas accumulations. He previously worked for Amoco Production Company at their Tulsa Research Center (1978-1991) and for Shell Oil Company at their New Orleans Exploration and Production Office (1972-1975). He received a Ph.D. from the University of Cincinnati (1980), an M.S. degree from Michigan Technological University (1972), and a B.S. degree from Northern Illinois University (1971).

Mitchell E. Henry is a geologist for the U.S. Geological Survey. His research interests are in the area of application of remote sensing to petroleum prospecting. Recent assignments have been focused on resource evaluation in the United States and Canada. He earned a B.S. degree in biology at Midwestern University, Wichita Falls, Texas (1969) and an M.S. degree (1974) and Ph.D. (1982) in oceanography from Texas A&M University.

Debra K. Higley is a petroleum geologist for the U.S. Geological Survey. Her research interests include reservoir characterization, thermal maturation, and petroleum resource assessment. Her background includes uranium exploration (1976-1981) and petroleum geology and geochemistry with the U.S. Geological Survey (1982-present). Her Ph.D. in geology (1994) and M.S. degree in geochemistry (1982) are from the Colorado School of Mines, and her B.S. degree in geology (1977) is from Mesa State College, Grand Junction, Colorado.

Janet Pitman is a research geologist in the Geologic Division of the U.S. Geological Survey. As a member of the Central Energy Team, she has applied sandstone diagenesis and reservoir quality analysis in domestic and world energy studies. Her present research interests include petroleum system modeling and basin history reconstruction. She is a member of AAPG and SEPM.

## ABSTRACT

The New Albany-Chesterian petroleum system of the Illinois basin is a well-constrained system from which petroleum charges and losses were quantified through a material-balance assessment. This petroleum system has nearly 90,000 wells penetrating the Chesterian section, a single New Albany Shale source rock accounting for more than 99% of the produced oil, well-established stratigraphic and structural frameworks, and accessible source rock samples at various maturity levels. A hydrogen index (HI) map based on Rock-Eval analyses of source rock samples of New Albany Shale defines the pod of active source rock and extent of oil generation. Based on a buoyancy-drive model, the system was divided into seven secondary-migration catchments. Each catchment contains a part of the active pod of source rock from which it derives a petroleum charge, and this charge is confined to carrier beds and reservoirs within these catchments as accountable petroleum, petroleum losses, or undiscovered petroleum. A well-constrained catchment with no apparent erosional or leakage losses is used to determine an actual petroleum charge from accountable petroleum and residual migration losses. This actual petroleum charge is used to calibrate the other catchments in which erosional petroleum losses have occurred. Petroleum charges determined by laboratory pyrolysis are exaggerated relative to the actual petroleum charge. Rock-Eval charges are exaggerated by a factor of 4-14, and hydrous-pyrolysis charges are exaggerated by a factor of 1.7. The actual petroleum charge provides a more meaningful material balance and more realistic estimates of petroleum losses and remaining undiscovered petroleum. The total petroleum charge determined for the New Albany-Chesterian system is 78 billion bbl, of which 11.4 billion bbl occur as accountable in place petroleum, 9 billion bbl occur as residual migration losses, and 57.6 billion bbl occur as erosional losses. Of the erosional losses, 40 billion bbl were lost from two catchments that have highly faulted and extensively eroded sections. Anomalies in the relationship between erosional losses and degree of erosion suggest there is potential for undiscovered petroleum in one of the catchments. These results demonstrate that a material-balance assessment of migration catchments provides a useful means to evaluate and rank areas within a petroleum system. The article provides methodologies for obtaining more realistic petroleum charges and losses that can be applied to less data-rich petroleum systems.

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