Sequence Stratigraphy of the Woodford Shale and Application to Drilling and Production

Roger Slatt
University of Oklahoma

The Woodford Shale in Oklahoma commonly is subdivided into Lower, Middle, and Upper members. Yet, based upon lithologic variability determined from core and/or well logs, the members can be further subdivided, particularly the productive Middle member. Subdivision is readily accomplished within the context of sequence stratigraphy (Slatt and Rodriguez, 2012): the Woodford comprises a 2nd order depositional sequence comprised of several 3rd (and most likely 4th) order (para)sequences. These intervals are verified by a combination of well and core descriptions, and more recently, by palynology (Molinares, in prep.). Such parasequences are correlative and map-pable for considerable distances using well logs and 3D seismic (when calibrated with logs) (Amorocho, 2012).

Sequence stratigraphic intervals and their rock properties can be related to geomechanical (as well as geochemical) properties. Ge-omechanical characterization has led to development of the concept of brittle-ductile couplets,that can be correlated and mapped (Slatt and Abousleiman, 2011). Brittle strata tend to be enriched in bio-genic quartz and/or carbonate material and ductile strata tend to be enriched in clays and organic matter.

Because depositional sequences and parasequences occur at a vari-ety of geologic time scales, brittle-ductile couplets also occur at a variety of stratigraphic scales. Thus, there is a natural, predictable link between sequence stratigraphy and geomechanics. The recogni-tion of such couplets can better target landing zones for horizontal drilling and artificial fracturing.

References:

Amorocho, J.D., 2012, Sequence stratigraphy and seismic interpretation of the Upper Devonian-lower Mississippian Woodford Shale in the Cherokee Platform; a characterization approach for unconventional resources, M.S. thesis, University of Oklahoma, 109p.

Molinares, C. E., in progress, Stratigraphy and palynomorphs composition of the Woodford Shale in the Wyche Farm shale pit, Pontotoc County, Oklahoma.

Slatt, R.M. and Y. Abousleiman, 2011, Merging sequence stratigra-phy and geomechanics for unconventional gas shales, The Leading Edge, March, 2011,p. 274-282.

Slatt, R.M. and N.D. Rodriguez, 2012, Comparative sequence strati-graphy and organic geochemistry of gas shales: commonality or coin-cidence: J. Natural Gas Sci. and Engn., doc:10.1016/j.jngse.2012.01.008.

AAPG Search and Discovery Article #90184 © AAPG Woodford Shale Forum, Oklahoma City, Oklahoma, April 11, 2013