INTEGRATION OF SEQUENCE STRATIGRAPHY AND 3-D SEISMIC IMAGING IN LOW-ACCOMMODATION BASINS
B.A. HARDAGE, D.L. CARR, J.L. SIMMONS, JR., 1996. "INTEGRATION OF SEQUENCE STRATIGRAPHY AND 3-D SEISMIC IMAGING IN LOW-ACCOMMODATION BASINS", Stratigraphic Analysis Utilizing Advanced Geophysical, Wireline and Borehole Technology for Petroleum Exploration and Production, Jory A. Pacht, Robert E. Sheriff, Bob F. Perkins
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Pennsylvanian-age rocks in several areas of the Midcontinent of the United States were deposited in low-accommodation basinal settings, that is, in basinal areas where only modest vertical reliefs could accept the sediment influx. Many thin Pennsylvanian sequences in these low-accommodation environments exhibit severe lateral heterogeneity because they have been extensively reworked by repeated transgressions and regressions of a fluctuating sea. Consequently, the distinctive geometries of relic depositional features (such as meandering channels) tend to be distorted or even totally destroyed, as compared with how such geometries appear in high-accommodation basins where depositional topography, once buried, is rarely exposed to destructive processes. Our objectives are to show examples of 3-D seismic images of several depositional topographies in a moderate- to low-accommodation basin and to explain how these thin sequences can be identified in well control and interpreted in 3-D seismic data volumes.
One topographic feature that affected the areal continuity of many Pennsylvanian sequences in some Midcontinent basins will be shown to be a pock-marked surface that was created by numerous, irregularly spaced, and deep-rooted karst-collapse zones. In our study area of the Fort Worth Basin, we combined sequence stratigraphy with 3-D seismic imaging to document that many of these karst-collapse zones originate at deep Ellenburger levels and then extend vertically for a distance of 2,000 ft (600 m) or more into Pennsylvanian-age rocks. Across the basin during Pennsylvanian deposition, these collapsed zones created roughly circular depressions having diameters ranging from 1,000 ft (300 m) to 3,000 ft (900 m), and these depressions then became a dominant influence on the sediment distribution in the low-accommodation spaces of this basin.
Producing an accurate sequence-stratigraphic model from well logs is difficult in low-accommodation basins, because each sequence is thin and exhibits severe lateral facies changes. Interpreting these thin sequences in 3-D seismic images is particularly challenging. Both well-log-based sequence stratigraphy and 3-D seismic stratigraphy are further complicated when the depositional surface is continually disrupted by random karst collapse, such as documented in this study. Our data examples and interpretational techniques are described herein to assist people who have to evaluate hydrocarbon prospects involving thin, heterogeneous, low-accommodation sequences.