Abstract: Three-Dimensional Seismic Modeling and Seismic Facies Imaging
A set of 3-D rock-property models were generated for a lower Miocene shorezone system at Powderhorn field, Calhoun County, Texas. These models were based on detailed mapping of facies and rock-properties that involved 250 m of stratigraphic section over an area of 9 by 13 km. Examination of logs from 115 wells showed that fourteen sandy depositional units averaging 3-30 m in thickness were encased in 15 shale units. Effective porosity, P-wave velocity and bulk density were calculated from suites of wireline logs from five recent wells, and then expanded to older wells through regression with SP and resistivity logs.
Idealized 3-D seismic models were generated by convolving a Ricker wavelet with the primary reflection coefficient series from stacked 2-D P-wave velocity and impedance models. The analysis to these models revealed the potential and limitations of seismic facies imaging for a clastic depositional sequence. The idealized stratal slices show that to achieve the best imaging of depositional facies, seismic frequency should be tuned to the maximum sandstone thickness. Framework sand bodies surrounded by muddy deposits are better illustrated. The stratal resolution of seismic imagery depends not only on wavelet frequency, but also on the magnitude of geological interference.
The commonly used approach of peak picking on a workstation may not generate correct stratal slices because seismic events do not necessarily follow geological time lines. Our models show that peak picking often distorts reservoir facies images. In some cases, seismic events from sand bodies in different units may interfere, forming a new event. An event tying as many as six depositional units over 50 m has been observed. Phantom mapping between reference events produces truer stratal slices, and makes it possible to map detailed depositional history from 3-D seismic data.
Stratal slices from real 3-D seismic volumes in Gulf Coast Tertiary demonstrate that sequential, fairly high-resolution amplitude images of various depositional facies can be obtained from lower frequency seismic data. Depositional facies patterns on those stratal slices provide much desired high-frequency information that may not otherwise be recognized on vertical seismic sections.
AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana