Seismic-Attribute Characterization of the Eagle Ford Shale, Dimmit County, South Texas

Recent exploration within the Eagle Ford Shale in the Maverick Basin has focused primarily on identifying faults and fracture networks that may provide flow paths for in situ hydrocarbons. However, not all fracture zones are located in hydrocarbon sweet spots. In this study, we integrated seismic attributes and acoustic impedance with wireline logs to determine hydrocarbon sweet spots by predicting total organic content (TOC) distribution within the Eagle Ford Shale in Dimmit County. We computed TOC from wireline logs and then used seismic attributes to predict TOC at every seismic-trace location within the seismic survey. In addition, we examined the distribution of high-resistivity zones using the deep induction log (ILD) to identify possible hydrocarbon concentration within the shale.

Results show that within the Eagle Ford, NE-SW-trending lenticular intervals occur with relatively higher acoustic impedance, similar to those of the overlying Austin Chalk. These intervals contain lenticular bodies that are likely to be carbonate intervals, which show up on impedance slices as streaks. Faults within the Eagle Ford trend NE-SW, have throws ranging from approximately 3 to 30 m (~10-100 ft), and occur within and along these lenticular bodies. Therefore, the streaks could be more brittle than those of the surrounding shale matrix. The lenticular bodies are associated with TOC values that are lower than those in the surrounding shale matrix. Lateral discontinuities observed in the TOC distribution are due not only to faulting but also to the presence of carbonate streaks within the Eagle Ford shale. The north part of the survey, in which there are numerous faults, contains lower TOC values than does the less-faulted south part. The relationship between quality factor (Q), one of the key seismic attributes used in the inversion process, and both TOC and resistivity is nonlinear. The high-resistivity intervals are located mostly within the Upper Eagle Ford and are above the horizon that separates the Upper from the Lower Eagle Ford Shale.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California