Workflows for Sweet Spots Identification in Shale Plays Using Seismic Inversion and Well Logs

Worldwide interest in shale plays has rapidly increased in recently years, thanks to the combination of horizontal drilling and hydraulic fracturing. Shale formations act as both the source and the reservoir for the natural gas and usually exhibit anisotropic properties at larger scale. Geological and petropysical studies found that the right combination of thickness, TOC (total organic carbon), maturity, porosity, high gas-in-place and fracability are important for shale plays sweet spots identification. Usually integration of the petrophysical well logs and geological core analysis can easily help to calculate these important elements around the borehole. For example, the Passey equation (Passey, 1990) can be used to estimate TOC, and dipole sonic data can be utilized to optimize the hydraulic fracturing and to measure the formation anisotropic parameters (Horne et al., 2012). Anisotropy plays a key role in the shale gas sweet spots evaluation. Seismic data, especially the wide-azimuth seismic angle gathers, offer valuable information for this shale sweet spots identification. However, special technologies and workflows are required to infer the meaningful properties, such as TOC, anisotropic epsilon and delta parameters, and in-situ stress, from the seismic data and then calibrated with both borehole data and geological understandings. Four major categories will be studied in the paper: 1) petrophysical model for shale gas evaluation; 2) seismic anisotropic inversion to simultaneously estimate the anisotropic epsilon, delta and gamma ( in addition to compressional velocity (Vp), shear velocity (Vs) and density; 3) seismic TOC inversion; 4) geomechanical properties calculation and interpretation.