Seismic attribute driven integrated characterization of the Woodford Shale in west-central Oklahoma

Abstract

The organic-rich, silty Woodford Shale in west-central Oklahoma is a prolific resource play producing gas and liquid hydrocarbons. We calibrated seismic attributes and prestack inversion using well logs and core information within a seismic geomorphologic framework to define the overall basin architecture, major stratigraphic changes, and related variations in lithologies. Core measurements of elastic moduli and total organic content (TOC) indicated that the Woodford Shale can be broken into three elastic petrotypes important to well completion and hydrocarbon enrichment. Upscaling these measurements facilitates regional mapping of petrotypes from prestack seismic inversion of surface data. Seismic attributes highlight rugged topography of the basin floor of the Paleo Woodford Sea, which controls the lateral and vertical distribution of different lithofacies containing variable quantity of TOC as well as quartz, which controls brittleness. Depressions on the basin floor contain TOC-lean cherty lithofacies alternating with TOC-rich lithofacies, resulting in brittle-ductile rock couplets. In contrast, basin floor highs are characterized by overall TOC-rich ductile lithofacies. Seismic attributes illuminate complex post-Woodford tectonic deformation. The Woodford Shale is known to be naturally fractured on outcrop. Image log analysis in other shale plays showed a good correlation between such tectonic features and natural fractures. These features need to be correlated with well trajectories and production data to determine which hypothesized "fracture sets," if any, improve well performance.

Seismic modeling evaluation of fault illumination in the Woodford Shale

“…Similar features were observed by Gupta (2012) and Guo et al (2010) in the Woodford Shale overlying the Hunton Limestone reflectors. While seismic amplitudes adjacent to large faults are often inaccurate due to limited migration aperatures and inaccurate velocities, the faults in their survey often exhibited offsets less than ¼ wavelength.…”

“…In this paper, we generate, process, image, and invert a suite of prestack seismic models to determine whether the anomalies are seismic artifact or geologic feature of interest. Guo et al (2010), working on a Woodford survey in the Arkoma Basin and Gupta (2012), working on a Woodford Figure 1. Horizon slices along the top Woodford through (a) k 2 -most negative principal structural curvature, (b) acoustic impedance, and (c) most-negative curvature (a 2 nd derivative) of the acoustic impedance volumes.…”

Analysis of a Pull-Apart Basin and Its Associated Fractures in the Woodford Shale, Central Oklahoma

“…The Woodford Shale was deposited in the palaeo-Oklahoma Basin, central USA during sea-level transgression (Figure 1) [8] dip (<2˚) towards southwest and the palaeo-shoreline is in the northeast [11].…”

Seismic attributes and the road ahead

“…Layering is also critical, with favorable interbedding of brittle and ductile layers leading to better completion (Stephens et al, 2011). While engineers are quite comfortable with geomechanical estimates, in both the Woodford and Barnett Shales there is a depositional imprint, with higher TOC and higher concentration of radiolarians (forming brittle chert) in the deeper parts of the basins and less on the shelf (Gupta et al, 2013). These locally deeper parts of the basin have their own seismic stratigraphic expression, such that one can "infer" areas that may be more productive using "softer" attributes like spectral components that are sensitive to vertical variability.…”