Focusing Future Exploration in Mature Basin: Maturation and Migration Models Integrated with Timing of Major Structural Events in Illinois

Donald F. Oltz, Joan E. Crockett

Exploration risk can be decreased by highgrading areas where the timing of structural events and maturation of source rocks are nearly coincident. Knowledge of migration fairways further aids in focusing exploration. Four burial-history models have been constructed to accommodate (1) a rift-fill sequence in excess of 24,000 ft, (2) a hypothetical Fairfield basin model, (3) a model using a deep well, and (4) a model on the Sparta shelf. These complex models, which use several variables including compaction, thermal conductivity, kerogen kinetics, and multiple unconformities, indicate a possibility for multiple hydrocarbon-generative events and show that linear geothermal gradients are ineffective in explaining maturation in Illinois. Periods of oil generation determined fr m the models can be compared with known timing of structural events to predict trapping potential. Depths to the oil phase-out zone are also significant.

Exploration risk can be reduced in Illinois by using a simple migration model that uses the basal Upper Devonian Sylamore Sandstone in central and western Illinois as a migration conduit and the New Albany Group as a source. Other migration conduits in the basin are discussed including faults associated with structures and fracture systems such as the Wabash Valley fault system.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.