Calibration of Seismic Attributes for Reservoir Characterization ...

BACKGROUNDThe Stratton field is located in South Texas approximately 30 miles southwest of Corpus Christi(Figure 1) in Kleberg and Nueces counties. The 2 square-mile migrated 3-D seismic volume,containing 100 inlines and 200 crosslines spaced at 55 feet intervals, sampled at 2 ms in time,has been provided by the Texas Bureau of Economic Geology (Hardage et al, 1994) togetherwith data from 21 well logs and one Vertical Seismic Profile (VSP). The data were acquiredusing an 8-120 Hz Vibroseis sweep. Like many gas fields with a long production history, the logsuites vary greatly among the wells. The wells were drilled from the 1950’s to the early 1990’sand generally were logged with gamma, resistivity, and neutron logs. Since sonic logs are notavailable for any wells in the field, we rely on a checkshot derived from the VSP. There are nolog data available for the nonproducing shallow channel region investigated here. We havereceived limited production data provided by the operator Collins & Ware.The major producing formations are the nonmarine fluvial Upper Vicksburg and Middle Frioformations (Figure 2). The Upper and Middle Frio contain nonmarine channels; the Lower Friohas been described as a coastal plain, and the Upper Vicksburg Formation is thought to be deltaicin origin. The Frio formation is comprised of thin-bedded sandstones and mudstones as thin as10 ft. A series of growth faults in the Vicksburg terminate at an unconformity at the base of theFrio. The horizons and growth faults are identified on a seismic section in Figure 3.In this study, we analyzed a shallow non-productive horizon containing an apparent channel, anda deeper productive horizon just above the Frio-Vicksburg unconformity.Figure 1 Location of the Stratton Field (adaptedfrom Hardage 1995).Figure 2 Stratigraphic sequence of the OligoceneAnnual Technical Progress Report Michigan Technological University DE-AC26-98BC15135October, 2001 Page 14