Chapter 4: Seismic Delineation of Thin Sandstone Reservoirs in a Shale-Rich Sequence Using Instantaneous Frequency and Reflection Amplitude Attributes from 3-D Data, Texas Gulf Coast

A combination of seismic trace attributes including instantaneous frequency and reflection amplitude was successfully used to seismically delineate gas-prone reservoir facies consisting of thin, discontinuous sandstone reservoirs in a shale-rich stratigraphic sequence. This type of reservoir section poses special problems for seismic interpretation due to a high degree of lateral and vertical variation in the ratio of net sandstone to gross interval thickness. Individual sandstone reservoirs are also below the limit of seismic bed resolution, further complicating the evaluation. Instantaneous frequency maps were used directly to map the areal distribution of reservoir-prone intervals. The addition of calibrated average amplitude maps provided the ability to discriminate between homogenous shale-rich sections and relatively homogenous sandstone-rich sections characterized by amalgamated siltstones and sandstones. The lithofacies prediction model developed using this integrated geological, petrophysical, and seismic interpretation technique was confirmed by the results of two new wells which penetrated the target interval described in this study. Instantaneous frequency maps with overlays of amplitude and time structure contours successfully identified stratigraphic intervals favorable for gas accumulation and trapping.