The Woodford Shale formation of western and southern Oklahoma is hydrocarbon-rich shale that has served as the source rock for many Oklahoma oil and gas plays over the past century. Today, the Woodford Shale is an unconventional resource play similar in age and depositional environment to the prolific Barnett Shale to the south. Like the Barnett, the Woodford Shale contains a large amount of healed natural fractures, has very low permeability, and is amenable to production through hydraulic fracturing. Unlike the Barnett, the Woodford shale can also produce significant amounts of oil as well as gas. The characterization of natural fracture intensity and orientation has a direct impact on horizontal well orientation and completion strategies. In the study, we use volumetric seismic attributes to map the structural deformation of the Woodford Shale. Coherence allows us to map major faults that appear to have a wrench component, while curvature allows us to map more subtle folds and flexures within the Woodford and overlying Hunton Limestone formations. Analysis of the production data indicates that the best-producing wells correlate to zones associated with k2 most negative principal curvature (valley-shaped) anomalies. Furthermore, we find a strong correlation between lowimpedance lineaments with structural lineaments, strongly suggesting natural fracture-enhanced production.
Shale gas is one of the most promising unconventional resources for hydrocarbon exploration and production. Open fractures in shale provide critical porosity and permeability, while healed fractures can be opened for hydrocarbon flow through carefully-designed hydraulic fracturing programs. Recent technical and economic advancement in horizontal drilling techniques have made the Mississippian and Devonian Woodford Shale deposited over a large portion of the Midcontinent a significant hydrocarbon play. To date, the major use of 3D seismic data in the study of shale gas reservoir has focused on (1) mapping natural fractures (and karst) that can provide enhanced conduits for hydrocarbons (and in the Barnett shale for water from the underlying Ellenberger), and (2) mapping geo-mechanical brittleness and horizontal stress directions for effective hydraulic fracture stimulation. For effective fracability studies, core data and lab measurements of rock samples are critical, providing calibration of elastic parameters extracted from seismic data to identify fracture-prone zones (Goodway et al., 2006; 2007a). Direct measures of fractures include Amplitude vs. Azimuth (AVAZ) (Ruger, 1998; Goodway et al., 2007b), and azimuthal velocity anisotropy (Sicking et al., 2007; Roende et al., 2008; Jenner, 2001). Indirect methods of fracture prediction from post-stack data include geometric attributes such as coherence and curvature (Chopra et al., 2007; Blumentritt et al., 2006; Chopra et al., 2008). In this study, we applied a suite of post-stack seismic attributes to the Woodford Shale, and find that volumetric curvature-based attributes offer a very promising opportunity to delineate both large and small wavelength fracture lineaments.
Due to the recent advancements in geology, geophysics, and engineering, the Woodford Shale of the Midcontinent U.S.A. has become an important unconventional resource play. The area under the study is located in the Arkoma basin in southern Oklahoma (Figure 1).
