Shales are one of the most heterogeneous and complex natural materials found. Recent spike in the activities in shale gas and oil plays has been possible through horizontal drilling and hydraulic fracturing, which requires better understanding of mechanical properties. Complexities associated with elastic properties of shale are amplified with presence of wide range of organic fraction present in them. There is a need to understand the mechanical properties of organics and their associated impact on bulk mechanical properties. Scanning Electron Microscopy with focused ion beam milling and nano-indentation have been employed to calculate mechanical properties of kerogen at the submicron level in Woodford shale samples of different maturities. A displacement of 500 nm was applied to investigate mechanical properties of kerogen and force in the range of 400–500 mN was applied to measure average mechanical properties of shale. Young’s modulus of kerogen was found to be linked to localized porosity as well as maturity. Kerogen in different samples with vitrinite reflectance range of 0.5–6.36 % and almost no porosity showed Young’s moduli in the range of 6–15 GPa, whereas, kerogen with significant porosity showed values as low as 1.9–2.2 GPa. Young’s modulus measured by nanoindentation on small shale samples (~ 5–10 mm) was found to be in good agreement with dynamic modulus measured on core plugs (~cm). Young’s modulus is most sensitive to the Total Organic Carbon present. Increase in organics is found to qualitatively reduce both Young’s modulus and hardness. Measurement of elastic properties of shale is significant for optimizing hydraulic fracture design, for well stability study and better seismic velocity prediction in shale. This technique requires small sample dimension, on the order of millimeters, for experiment and thus eliminates the requirement of larger, centimenter, size samples. This is particularly significant for shale as they are mechanically and chemically unstable which makes retrieval of larger core samples challenging.

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.

Woodford Shale exhibits complex geophysical features (e.g., sub-seismic fractures) that are critical for gas exploration. Seismic attributes are effective tools in characterizing the patterns of discontinuities within shale reservoirs. In this study, we characterize a fault/fractures system within Woodford shale by integrating seismic attributes analyses and lab experiment modeling for better interpretation of this system.

Seismic analysis plays a very important role in the characterization of shale gas reservoirs. Several seismic attributes including curvature and coherence attributes are commonly used to highlight discontinuities (Marfurt, 2010). But very often, the complexity of the discontinuity pattern is not clearly seen in these attributes. At the same time, studying the discontinuity patterns along with stratigraphic changes can also provide important clues for shale gas exploration. For the current study, we analyzed the Woodford Shale in the Anadarko basin (Figure 1) with the aid of some newly developed geometric attributes including reflector convergence and reflector rotation along with some common attributes including coherence, curvature and coherent energy.