POSSIBLE INFLUENCE OF PLEISTOCENE GLACIATION AND GAS-HYDRATE FORMATION ON GAS PRODUCTION FROM LITTLE OSAGE SHALE, SE KANSAS

The Little Osage Shale Member, Fort Scott Formation, Middle Pennsylvanian, southeastern Kansas, during the 19th and 20th centuries, produced dry gas and salt water from shallow, fractured reservoirs and presently is a source of "coal-bed" methane. The area lies in what was probably a prolonged permafrost zone during the Nebraskan and Kansan Glacial Stages. The fracturing of the Little Osage Shale reservoirs may have resulted in part from permafrost action during the glaciations, together with the melting intervals between, and subsequent to, the glacial stages.

The gas in the Little Osage Shale apparently is a mixture of thermogenic and biogenic types, resulting in part from gamma-ray bombardment of organic matter in the highly organic shale, as well as from microbial reduction of carbon dioxide. The gas may have been held in the gas-hydrate state during the glacial episodes, perhaps to depths of 500 m or more. Many of the Little Osage reservoirs lie at depths shallower than this. Alternate freezing and thawing of gas-hydrates in glacial and interglacial episiodes may have contributed to fracture porsity in the shale reservoirs.

If this model is correct, there are other possible examples in north-central and northeastern States and southern Ontario where shallow Paleozoic reservoirs may have been affected by permafrost condiutions. This report is intended to provide suggestions for further research, not as a finished product