The Ohio Geological Society

Rock Core Workshop

THURSDAY, May 21st, 2026

Lunch & Talk begin at 12:00 pm

Horace R. Collins Laboratory & Core Repository
3307 South Old State Rd.
Delaware, OH 43015

Lunch Provided for Registered Attendees
RSVP required

The Clinton Complexity—High-Resolution Mapping of

Reservoir Sandstones in Southeastern Ohio

Mindy Thomas, Ohio Geological Survey

Abstract: This talk will describe rock core and petrophysical testing of core from the Clinton Sandstone with examples of the core from the H.R. Collins Core Repository for your perusal!

As carbon capture, utilization, and storage (CCUS) continues to be of interest in legacy oil fields around the U.S.—particularly in Ohio’s Appalachian Basin—the Grimsby Sandstone, often referred to as the “Clinton Sandstone,” remains a viable CCUS candidate, both as a depleted reservoir and for enhanced oil recovery. Multiple Clinton fields in Ohio have recently been remapped and reexamined, as seen in the Midwest Regional Carbon Sequestration Partnership’s report (2020). However, the Gore Consolidated Oil Field (GCOF) of southeastern Ohio has received limited attention, primarily for economic considerations, leaving a gap in understanding its detailed geology. Since its discovery in 1907, James W. Castle has done the most work on Clinton Sandstone in the GCOF, which was published in 1998 and 2001. Sands identified by Castle in available cores were all interpreted as marine shoreface deposits, including shelf-bar complexes dominated by waves and tides before a returning transgression shifted the siliciclastic depositional environment back to a widespread carbonate factory.

From 2024–2025, this study reexamined and compared all available Clinton GCOF cores studied by Castle and stored at the Ohio Geological Survey core repository. Additional data for the cores were collected through the DOE’s National Energy Technology Laboratory, including XRF analyses and CT scans showing overlooked features such as marine ichnofossils, cementation variation, and subtle bedding. New, detailed core descriptions were completed along with facies descriptions and interpreted depositional environments.

This study then took the work a step further and utilized that core work, 117 digitized LAS well logs, and over 950 depth-registered raster geophysical logs in the GCOF to apply sequence stratigraphic principles to the Clinton Sandstone. Sequence boundaries and major/minor flooding surfaces were identified; in addition, shale/sand cutoffs were applied on gamma-ray logs to more accurately map sand-body morphologies at a high resolution in the field between stratigraphic surfaces. Net sand maps and cross sections generated for the GCOF—along with prior core work—showcase the incredible heterogeneity present in the Clinton reservoir, which is now reinterpreted as a potentially tidally influenced deltaic paleogeographic setting with associated depositional environments. Understanding the complex heterogeneity of the sand-body morphology presented is critical for assessing the viability of the Clinton GCOF as a future carbon storage unit.

Bio: Mindy Thomas is a geologist in the Energy Group at the Ohio Geological Survey, Ohio Department of Natural Resources, where her primary interests are in sedimentology/stratigraphy, subsurface mapping, and the energy/petroleum industry. Her current work projects entail the detailed core work and subsurface mapping of the Silurian Clinton Sandstone Formation for CCUS/EOR potential along with the USGS funded STATEMAP project addressing the diachronous boundary between the Devonian Columbus and Delaware Limestones. Both projects entail the use of abundant well-log data for mapping, field work, and core work, including utilizing the Geosurvey’s Geotek core scanner to collect density and gamma data on cores. Prior to her work in the division’s energy group, Mindy was originally hired to work as the Lake Erie geologist for the state, addressing many of the coastal erosion projects along the Lake Erie shore, and working on the periodic remapping of high areas of coastal erosion in Ohio. Before joining the Ohio Geological survey in 2021, Mindy worked for five years with Devon Energy out of Oklahoma City, doing both exploration and operations geology in the Powder River, Bighorn, and Anadarko Basins. Mindy graduated with her Master of Science in Geology from the University of Oregon working on Miocene-Pliocene deposits in the Sonoran Desert that recorded the arrival of the first through-going Colorado River. In addition, she received her Bachelor of Science from Miami University in Ohio, where her undergraduate research focused on field/lab work on Cretaceous sandstones in the Uinta Basin of Utah. In her spare time, Mindy enjoys spending time with her family, cake decorating, rock climbing, skiing, and embroidery.