Applying 3D Seismic Technology to Better Understand the Mechanical Variability of the Lower Barnett Shale in the Northern Fort Worth Basin
Pioneer Natural Resources
Pioneer Natural Resources has acquired wide azimuth 3D seismic data and modern petrophysical log suites in the Barnett Shale “Combo Play” of the northern Fort Worth basin (northern Wise and southern Montague counties). Mechanical properties including Young’s Modulus and Poisson’s Ratio and Lame’s coefficients Lambda and Mu were calculated from carefully edited p and s wave velocities and density values measured in over 20 pilot wells across the study area. This data compared favorably with measurements made in the cored intervals of two of the wells and indicated that the mechanical properties of the Lower Barnett vary both vertically and areally at a frequency that makes accurate prediction almost impossible from the existing well data base. In an attempt to provide greater predictability, the pilot wells were carefully tied in the time domain to the final migrated 3D volumes and a neural net type of post-stack seismic inversion was run on each 3D survey. Each inversion utilized multiple seismic processing derivatives as inputs to form predictive relationships between the seismic and a chosen mechanical property from the pilot wells. In this way, 3D volumes of the various mechanical properties were generated. Detailed examination of these volumes indicated that, although there was some loss of vertical resolution from the original logs, the seismic did a good job in tracking lateral variations within gross intervals of the Lower Barnett.
Further characterization of the Lower Barnett has been achieved using horizon based attributes, calculated from detailed interpretation of the high quality 3D seismic data, to predict fractures in the targeted interval. Comparing the seismic predicted fracture orientation and density with fracture calculations from high-resolution resistivity and micro-seismic data acquired in a test horizontal well program, a surprising relationship was observed that appears to challenge the existing dogma on the preferred horizontal well orientation in the play area. Applying this approach has helped Pioneer Natural Resources better orientate horizontal wells to take advantage of local variations in fracture density and strike and where warranted, drill leases whose surface footprints do not conform to the standard NW-SE elongation and maximize the company’s access to the resource.
AAPG Search and Discovery Article #90164©2013 AAPG Southwest Section Meeting, Fredericksburg, Texas, April 6-10, 2013