Lessons Learned from the Floyd Shale Play

The Black Warrior Basin’s Floyd shale has long been considered a potential shale gas play. It is a source rock responsible for conventional oil and gas production from Mississippian and Pennsylvanian age sands, as well as being the stratigraphic equivalent of the successful shale gas plays in the Barnett Shale (Fort Worth Basin) and the Fayetteville Shale (Arkoma Basin). There are areas within the basin where the Floyd shale is thick enough (up to 200 ft), has a high enough organic matter content (2.0-7.0 % TOC), and has reached a high enough thermal maturity (vitrinite reflectance >1.30 % Ro) to pass the initial screening for a shale gas opportunity. But tests of the interval with both vertical and horizontal wells have yet to produce gas volumes approaching commercial quantities.

To determine what is limiting the deliverability of gas from the Floyd Shale, the source rock and reservoir properties were characterized. With respect to kerogen type, organic matter content, thermal maturity, bulk mineralogy, porosity, and permeability, the Floyd compares favorably with successful shale gas plays. Analysis of core and cuttings samples indicates there is gas charge, and the monitoring of the well completion process indicated that fractures were opened during reservoir stimulation. So why did the Floyd shale fail to produce?

Detailed analysis of core including geochemical testing, porosity and permeability measurement, capillary suction time and Birnell hardness testing, and detailed mineralogical and depositional fabric studies suggest potential fluid sensitivity and/or proppant embedment issues contribute to the lack of production. Other possible contributing factors include formation pressure, wettability, and “seal” issues.

These results are a reminder that a gas shale is not just the source but also the reservoir, and it demonstrates the importance of integrating all data, including reservoir rock properties, when evaluating source rocks as potential shale gas plays.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California