The Woodford Shale covers virtually the entire state of Oklahoma and is far more complex then other Devonian black shales found in North America. This complexity is especially evident in southern Oklahoma where the Woodford consists of alternating bands of chert-like amorphous silica and silica-rich shale. These chert-like silica bands can vary from seven inches (17.8 cm) thick, separated by one or two inches (25 to 51 cm) of shale, to one inch (25 cm) of silica for every two feet (0.61 m) or more of shale.
The area’s complex structural geology and mineralogy have broad implications, affecting drilling and completion design, production practices and ultimately well productivity. In particular, they can have a major impact on horizontal drilling, slowing penetration rates and quickly destroying bits.
Woodford Shale production in Oklahoma began in the 1930s. The first horizontal wells were not drilled until 2004-2005 as gas prices increased and completion techniques improved. Currently, almost 2,000 wells are in production with approximately 475 of them vertical and more than 1,500 of them horizontal.