Integrated Acoustic, Mineralogy, and Geomechanics Characterization of the Huron Shale, Southern West Virginia, USA

Abstract

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.

Evaluating the Effect of Natural Fractures on Production from Hydraulically Fractured Wells Using Discrete Fracture Network Models

“…The Mallory 145 well pad is one of these sites, and while the results should not be considered exemplary of unconventional reservoirs overall, they do provide significant insights into how an unconventional system may behave. Some aspects of the Mallory 145 experiment are described in Mulkern et al, 2010;Franquet et al, 2011;Moos et al, 2011;Geiser et al, 2012;Lacazette and Geiser, 2013; The Mallory 145 well site was developed by Pittsburgh-based EQT Corporation in Devonian shales and siltstones in southwestern West Virginia. The well pad has four vertically-stacked laterals from the Berea sandstone, Chagrin Shale, Lower Huron Siltstone and Lower Huron Shale.…”