ABSTRACT: Hydrocarbon Production from Shallow Marine Sandstones in the Mississippian Cypress Formation at Lawrence Field, Illinois

WHITAKER, S. T., R. D. COLE, and J. P. GRUBE, Illinois State Geological Survey, Champaign, IL

Sandstones in the Mississippian Cypress Formation are some of the most prolific hydrocarbon producers in the Illinois basin. Most of the sandstones are fine-grained, well sorted, mature quartzarenites that commonly have been classified as deltaic in origin. Due in part to an oversimplification of the geologic model, drilling and recovery practices may not effectively drain these reservoirs.

Sedimentological analysis of 24 cores from the Cypress at Lawrence field, and extensive geophysical log analysis, has delineated sand body trends consistent with deposition in coastal to near-shore, shallow marine settings. Depositional facies include bioturbated tidal flat sequences, offshore bar and tidal or interbar channels, and subtidal ripple-laminated to climbing ripple-laminated sheet sandstones.

Core analyses indicate that depositional environment and diagenetic alteration of the Cypress sandstones are key factors that affect the degree of reservoir heterogeneity at Lawrence field. Tightly cemented calcareous intervals of various thicknesses within the mature sandstones, and shale intervals which occur as fissile to non-fissile beds, can act as barriers to fluid flow and affect recovery efficiency. The type and degree of heterogeneity within the reservoirs must be determined in order to accurately predict recovery methods that will optimize recovery.

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