Petrology and Depositional Environments of Sample Member (Mississippian): Redevelopment Target in Lawrence Field, Illinois

David P. Palmer, Mitchell K. Burk

Although the giant Lawrence field (400 million bbl oil recovered since the early 1900s) has been extensively waterflooded since the 1950s, opportunities for continued development are still being found. One ongoing redevelopment is in the Sample member of the Mississippian Ridenhower Formation in Sec. 17-20, T4N, R12W. During the 1950s waterflooding was initiated in the area with wells dually completed in the Sample and overlying Cypress Sandstone. Cypress average permeability is 10 times greater than the Sample's, so most of the injection went into the Cypress. Many wells were eventually plugged back to that zone. A well was recompleted in the Sample in 1987 with an initial production of 56 BOPD. Since then, 18 additional producers have been drilled.

Two cores and 40 modern well logs were used to develop a facies model of the Sample member. Cored lithologies include very fine-grained flaser-bedded shaly sandstone, fine-grained ripple-bedded sandstone, and fine to medium-grained cross-bedded sandstone. Small slump features and shale rip-up clasts occur at the base of the sandstone. Minor occurrences of bidirectional cross-bedding and reactivation surfaces were observed. No burrows were identified. The Sample Member is interpreted as a tidal-flat shoreline environment, with tidal channel, ebb tidal delta, and muddy tidal-flat facies present in core or inferred from well-log response. Correlation of SP logs with facies type permitted extrapolation of facies throughout the redevelopment area. A series of time-sequence facies distribut on maps identifies a tidal-flat shoreline environment prograding across a shallow carbonate shelf.

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