Petroleum Geology
Ohio's Source Rocks
Oil and natural gas form within organic-rich rocks that are buried and heated by natural geologic processes. These are referred to as source rocks and are typically organic-rich black shales, but they also can include coal beds which generate natural gas. Organic-rich shales form when organic matter, primarily in the form of algae living and dying in shallow seas, is deposited and buried with sediments on the seafloor. Over time, the sediment is compressed and undergoes chemical changes, resulting in consolidation of the sediments into rock. With deeper burial, the organic matter is heated and transformed into oil and natural gas. In Ohio, these rocks formed within the Appalachian Basin during the Paleozoic Era, which occurred from 541 to 252 million years ago. The source rocks in Ohio have been identified as the Point Pleasant Formation, the Olentangy and Ohio Shales, the Sunbury Shale, and Pennsylvanian-age coal beds.
Conventional oil and gas reservoirs typically are sandstones, limestones, and dolomites that trap oil and gas in pore spaces of the rock. Oil and natural gas are lighter than water and will migrate out of a source rock and buoyantly move upwards until they are trapped within the pores of a reservoir rock. A trap for oil and natural gas could include impermeable layers next to the permeable rocks or could be related to geologic structures, such as folds or faults in the rock units. In Ohio, oil and natural gas is produced from conventional reservoirs, such as the Rose Run sandstone, the Trenton Limestone, the “Clinton” sandstone, the Oriskany Sandstone, the Berea Sandstone, and Pennsylvanian-age sandstones.
Drilling Methods
Ohio has been commercially producing oil and natural gas continuously since 1860. For the first 150 years of oil and natural gas production in Ohio, companies drilled vertical wells to reach conventional reservoirs. Recently, new technologies have been applied to the production of oil and natural gas. Horizontal drilling into organic-rich black shales has opened up new opportunities for oil and natural gas production. Previously, oil and natural gas were explored by drilling into reservoir rocks. The current paradigm is to drill into the source rocks, such as a black shale; hydraulically fracture the shales to produce larger-scale permeability; and allow the oil, natural gas, and natural gas liquids to flow into the horizontal well bore. This methodology currently is being used in the exploration and production of oil, natural gas, and natural gas liquids of the Point Pleasant Formation of Ohio.
Digital Geophysical Logs
The ODNR Division of Geological Survey has released a major oil-and-gas dataset comprised of digital images of geophysical logs, some dating back to 1947, for more than 72,000 wells throughout the state. These logs are a fundamental dataset used by industry for oil-and-gas exploration, by government agencies for environmental restoration and remediation, and by academic institutions for research.
Geophysical logs for Ohio oil-and-gas wells are available in three media formats: raster image files in TIF format, Log ASCII Standard (LAS) files of geophysical log curves, and as paper printouts of scanned logs.
Raster Format
Raster-format digital logs simply are scanned images of the logs saved in TIF format. Features include:
- Use with software applications for automatic or semiautomatic creation of cross sections and other custom displays.
- Large file size—500 KB for a shallow well up to 80 MB for a deep well with color.
- Image quality depends on quality of original image (e.g., if paper copy of log is dark, washed out, or smudged, these same deficiencies will be evident in the digital image).
LAS Format
The LAS files of geophysical log curves are available for selected wells only. Some LAS files may show multiple curves including, but not limited to, resistivity, gamma ray, neutron, density, sonic, and others. Features include:
- Use with software applications for automatic or semiautomatic creation of cross sections and other custom displays.
- Can be used to calculate rock properties, such as porosity and lithology.
- Small file size.
Access to Geophysical Logs
Access to digital geophysical logs is provided through open data download or by purchasing the logs. Use the following materials to choose which digital logs you would like to acquire:
- List of available raster logs [15.0 MB .xls] – Updated 5/20/2022
- List of available LAS logs [179 Kb .xls] – Updated 7/15/2022
- List of log abbreviations [240 Kb .pdf]
- List of logging company abbreviations [240 Kb .pdf]
Open Data Download
Digital geophysical logs have been released through the ODNR Oil and Gas Well Interactive Map. Using the interactive map, locate the well of interest and left click on the well location. A pop-up will appear and show the basic attribute information for the well (see screen shot example). A hyperlink titled "Well Summary Report Link" will appear in the pop-up. Clicking on this link will take users to the Well Summary Report. At the bottom of this report are links to the scanned documents, including the digital geophysical logs in TIF and LAS format (if available).
Purchasing the Logs
Paper copies of the geophysical logs or large quantities of digital geophysical logs can be purchased from the Geologic Records Center.
Pricing Information:
- TIF files = $2.00 per log
- LAS files = $15.00 per file
- Paper files:
- $4.00 B&W / $5.00 color for entire well with Total Depth of <4,000 ft.
- $6.00 B&W / $10.00 color for entire well with Total Depth of 4,000‒6,000 ft.
- $8.00 B&W / $15.00 color for entire well with Total Depth of >6,000 ft.
Geophysical Log Index Files
Log Donations
The Division of Geological Survey actively seeks out and is happy to accept donations of geophysical logs to help build its archives. To donate geophysical logs, please contact the Geologic Records Center.
Additional Resources
Available Reports
Search for Division of Geological Survey reports and maps in our Publications Catalog. Or use the links below to search for publications held by one of our partners.
State Library of Ohio (Ohio Memory)
GIS and Database Resources
Wells reaching the base of the Cambrian Knox Dolomite in Ohio
Precambrian Structure Contours and Faults in Ohio
Underground Sources of Drinking Water (USDW)
Wells used to map the Trenton Limestone in northwestern Ohio
Wells that reach the top of the Knox Unconformity in Ohio
Miscellaneous support files for geologic records at the ODNR Division of Geological Survey