Unconventional shale gas reservoirs are economically viable hydrocarbon prospects, and their development has rapidly increased in North America. These reservoirs must be routinely drilled horizontally and hydraulically fracture stimulated to maximize production rates. Identification of the different chemostratigraphic units or lithofacies that make up these reservoirs is crucial for devising completion strategies because some lithofacies are more favorable to gas recovery due to their organic content and geomechanical characteristics.Lithofacies are indicative of eustatic changes during deposition and are typical geo-markers related to the preservation and amount of accumulated Total Organic Carbon (TOC) for a given basin. Gas content is related to TOC and varies according to lithofacies. Based on the mineralogical and TOC content, some lithofacies are favorable for gas production (e.g., siliceous lithofacies) and the geomechanical properties of these lithofacies often possess low fracture gradients that are conducive to forming extensive fracture fairways for recovery of gas. Other lithofacies can be fracture barriers and zones of fracture propagation attenuation (e.g., carbonate lithofacies).A shale gas facies expert system was developed with the goal of chemostratigraphically characterizing different shale plays and utilizing an integrated petrophysical reservoir evaluation approach to identify optimal completion intervals. This system can aid operators design selective completion strategies, which can potentially reduce fracturing expenses and optimize well productivity. The expert system incorporates a combination of density, neutron, acoustic, nuclear magnetic resonance and geochemical logging measurements. This system first characterizes the lithofacies based on their geochemical makeup and then flags the most favorable and unfavorable zones using a simple "stop-light" approach based on the petrophysical and geomechanical properties.

Exploitation of unconventional shale gas reservoirs depends on successful hydraulic fracturing and horizontal drilling. Mineralogy, organic matter content, acoustic anisotropy, and in-situ stress all play an important role for well completion design. As part of a comprehensive site study of the Upper Devonian Huron shale, borehole acoustic and mineralogy logging data, in addition to conventional logs, were acquired in a vertical well prior to hydraulic fracturing and microseismic monitoring of a series of laterals drilled from the same location. The acoustic data was processed for compressional wave, cross-dipole shear, Stoneley-derived horizontal shear, radial velocity variations, and borehole Stoneley reflectivity indicators. The cross-dipole anisotropy and the near-well radial slowness variations provided information about intrinsic anisotropy and stress sensitivity to determine the source of dipole-mode anisotropy. Significant transverse acoustic anisotropy was detected and used to obtain vertical and horizontal dynamic elastic properties. The mineralogy and petrophysical analysis were used to generate a micromechanical constitutive model to reproduce numerically the laboratory stress-strain behavior of the rock, from which quasi-static mechanical properties were determined. These were calibrated against triaxial tests on core samples from an offset well, and the vertical and horizontal static elastic rock properties were used to estimate the vertical variation of the horizontal stress. The resulting stress profile, along with accurate mineralogy and petrophysical analysis, provides important information to select the best vertical locations of lateral wells and to identify natural fracture barriers.

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