Abstract

The Caney Shale is one of several unconventional energy reservoirs in the southern Midcontinent. It is comprised largely of organic-rich shale with subordinate interbeds of siltstone, sandy siltstone, and limestone in the upper part of the formation. Shale is presumed to be the hydrocarbon source rock and contains minute organic particles from which the hydrocarbons are generated. The shale also functions as a reservoir since gas is both stored within natural fractures and sorbed on organic molecules. Hydrocarbons are also stored within the siliciclastics and limestone. Importantly, the non-shale reservoir interbeds enhance lateral hydrocarbon movement within the formation because they locally have intergranular and/or matrix porosity and permeability. These hydrocarbon-transmitting beds vary in thickness from a few feet to over 20 ft and can be laterally persistent for miles. Thus, the Caney has ready-made lateral conduits that slowly drain hydrocarbons from the encapsulating shale. In southern Oklahoma, the Caney Shale has a total organic carbon (TOC) content of ~2-8% which is generally less than in the Woodford Shale but is more than sufficient to produce gas and oil.

In Oklahoma, oil and gas production from the Caney Shale through June 2005 is attributable to about 18 wells in the Arkoma and Ardmore Basins. Cumulative production is at least 1 billion cubic ft (BCF) gas and 17 thousand barrels oil (17 MBO). The best wells have cumulative production of 100 to over 300 million cubic ft gas (MMCFG) each. Rapid declines within a 2-year period are attributed to natural fracturing whereas slow declines over several years are normal for the reservoir. To date, all producing wells are completed in vertical holes.

The Caney Shale is a formal subsurface formation name and is largely equivalent to the Fayetteville Shale which crops out in the Ozark Uplift of northeast Oklahoma. Stratigraphically, it is roughly equivalent to the Barnett Shale of north Texas but is probably much different in composition. At the outcrop, the Caney lacks significant fracturing that characterizes cherty zones of the Woodford and Barnett Shales.

At the surface, the Caney appears to be a fissile, gray to dark gray shale that weathers into papery layers that are not generally calcareous. Locally, the Caney has limy beds, phosphate nodules and limy concretions. The nodules are not believed to be the principal source of the abnormally high gamma-ray radiation as detected from subsurface well logs.