Cleats in Coals of Eastern Oklahoma

S. A. Friedman
Geologist/Retired, Oklahoma Geological Survey

Cleat orientation and frequency in coal beds are important because of their relationship to coalbed methane (CBM) production. Face cleat orientation (strike) is the primary factor determining fluid flow direction and thus permeability in bituminous coal beds.

The orientation of face and butt cleats, the dominant vertical fractures in Oklahoma Desmoinesian coals, were mapped at some 500 locations by Friedman (1971–95), Hemish (1978–98), and Iannacchione and Puglio (1979) in 27 bituminous coals in 17 eastern Oklahoma counties.

Face cleats strike north-northwestwards in most of the Oklahoma part of the Arkoma Basin and in the northeast Oklahoma shelf. This trend in both areas is normal to the axes of major anticlines, synclines, and faults in eastern Oklahoma. However, in 3 counties in the Basin the major structures trend northeastward, north-northeastward, or eastward, and face cleats are normal to these trends. Facecleat frequency is a minimum of 2 per inch in the shelf and a maximum of 12 per inch in the Basin.

In parts of the Basin, lateral CBM wells appear to have yielded the greatest rate of production. Most of these wells have lateral trends almost normal to the average orientation of the face cleats. Vertical wells in the Basin appear to produce CBM at a greater rate than those in the shelf.

Therefore, knowledge of face cleat orientation and frequency in bituminous coal beds must be applied during drilling to maximize CBM production in Oklahoma and probably in other states.

AAPG Search and Discovery Article #90903©2001 AAPG Mid-Continent Meeting, Amarillo, Texas