ABSTRACT: Stratigraphic Influence on Reservoir Rock Quality in the Mount Simon Gas Storage Reservoir, Pontiac Field, Illinois

CARR, DAVID L., Consulting Geologist, Denver, CO, FABIAN O. IWERE, Sota Technologies, Englewood, CO, GEORGE W. PAUL, Advanced Resources International, Inc., Lakewood, CO, and YUSUF A. SHIKARI, Gas Research Institute, Chicago, IL

Stratigraphic heterogeneity has deleterious effects on reservoir performance in many Mount Simon (Cambrian sandstone) gas storage reservoirs in northern Illinois. The Mount Simon reservoir at Pontiac field (located 110 mi southwest of Chicago) was evaluated to determine the geologic factors influencing reservoir rock quality under a research effort sponsored by the Gas Research Institute (GRI). The primary objective of the GRI study is to examine the impact of shrinkage/re-expansion of aquifer gas storage reservoirs on gas deliverability.

Stratigraphic and petrophysical parameters were analyzed using well log and core data from 53 wells in Pontiac field. Chronostratigraphic units were defined by abruptly-based, blocky to upward-increasing gamma ray log patterns. A similar log response occurs in tidal deposits identified in core from nearby Lexington field; this model was adopted for the Pontiac field. Subtle log response variations suggest that the Pontiac-Mount Simon sandstone was deposited in a tide-dominated coastal zone where intermingling of low tidal flat and shallow-marine subtidal environments occurred. Subenvironments in this complex depositional system influence reservoir rock quality: best reservoir rock-tidal channel fill; fair to good reservoir rock-marine shoreface; shaly tight zones-tidal flats.

Since reservoir rock quality relates to depositional environments at Pontiac, evaluation of stratigraphic parameters can aid in the prediction of rock quality and the subsequent optimization of gas deliverability in other Mount Simon reservoirs.

AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)