Northside: Petrophysical Evaluation of Shales for Well Completion Decisions in Resource Plays

Shales are complex and heterogeneous but their petrophysical properties can be assessed with the proper tools and methods.  New logging technology such as elemental spectroscopy, nuclear magnetic resonance, and cross dipole acoustic logging provides the necessary detail to characterize shales.  Interpretations from these logs provide the operator with explanations for post-fracture well performance.  They also can predict future performance by identifying lithofacies in the shale which are preferential for completion and horizontal drilling. 

Wireline logs provide the means for estimating geomechanical properties and reservoir quality. New pulsed-neutron technology measures total organic carbon (TOC) directly.  The static rock mechanical properties of gas shales are determined by a micromechanical model that simulates triaxial core deformation from logging data. The micromechanical shale model is constructed from the TOC and mineralogy characterization along with the acoustic properties and NMR porosity.

Case studies of wells logged in the Barnett, Woodford, and Haynesville are presented.  In one case from the Haynesville the identification of siliceous content using geochemical logs helped the operator to explain a 100% difference in gas production between two wells.  The results were further confirmed by the detection of fractures using new near wellbore imaging techniques that incorporate multi-component shear wave analysis.  The identification of open gas-filled fractures in the Haynesville from wireline logs is one of the most valuable tools for deciding perforation staging and horizontal drilling locations.

When the ideal logging suite is not available in every well, petrophysical methods can be used to extract some of the relevant rock properties from conventional logging data.  These methods allow the operator to extend the advanced models developed in the vertical pilot hole to lateral wells.