Ian D. Bryant¹, Oswaldo Viloria¹, J. Gary Peters², Dennis R. Swagger²
(1) Schlumberger-Doll Research, Ridgefield, CT
(2) Team Energy, Bridgeport, IL

Abstract: Integrated geological and petrophysical evaluation of the Mansfield Sandstone, Illinois basin to optimize secondary recovery from mature fields

We have fully cored the Pennsylvanian age Mansfield Sandstone in the Ashworth lease, Indiana, and have recorded a full suite of logs in two wells. The logs and core indicated average porosity of 17% and permeabilities to over 100 mD. The core revealed the reservoir to be sandstone with thinly interbedded shales. On the basis of tidal bundles, trace fossils in the core and mapping of well log signatures, we interpreted the sand to have been deposited as a tidal channel or bar.

Traditional wireline logs are unable to resolve the individual thin shale laminae that form important barriers to charge and drainage of the reservoir. Thin clusters of tidal clay drapes effectively isolate from charging the thin sands at the top and bottom of the pay zone. Formation tester pressures in one well indicate these thin shales can likewise create pressure compartments within the pay zone that appears homogenous on traditional logging suites.

Evaluation of multiple depths of invasion measured by an induction tool enables us to compute in-situ estimates of residual oil saturation, connate water saturation and producible oil. These parameters are critical to assessing economic viability and designing waterfloods to increase recovery from the many mature fields in the basin that produce from Pennsylvanian sandstone reservoirs.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana