Recognizing Sequences and Systems Tracts from Well Logs, Seismic Data, and Biostratigraphy: Examples from the Late Cenozoic of the Gulf of Mexico
Robert M. Mitchum, John B. Sangree, Peter R. Vail, Walter W. Wornardt, 1993. "Recognizing Sequences and Systems Tracts from Well Logs, Seismic Data, and Biostratigraphy: Examples from the Late Cenozoic of the Gulf of Mexico", Siliciclastic Sequence Stratigraphy: Recent Developments and Applications, Paul Weimer, Henry Posamentier
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Well information and biostratigraphy, along with seismic stratigraphy, offer an integrated sequence-stratigraphic interpretation for predicting reservoir, seal, and source rocks of petroleum. This approach is effective in thick, complex strata, such as the late Cenozoic deposits of the Gulf of Mexico Basin. This chapter offers well-log and seismic criteria for recognizing and characterizing depositional environments and siliciclastic rock types occurring in sequences and systems tracts of the Gulf of Mexico.
The general sequence-stratigraphic model consists of a depositional sequence with a lowstand systems tract consisting of basin floor fan, slope fan complex, and prograding complex; a transgressive systems tract; and a highstand systems tract. Each systems tract is deposited at a predictable position in an interpreted base level cycle caused by eustasy, and has recognizable signatures in well logs and seismic data. Reservoir sand distribution is characteristic for each systems tract. This eustatic cyclicity is superposed on the equally important tectonic and sediment-supply controls of a given basin. One depositional model for the Gulf of Mexico is a typical diapir-controlled subbasin bounded by a large contemporaneous expansion fault. The depositional environment is closely related to the history of subbasin development.
The sequence-stratigraphic approach is based upon the integration of four basic data sets, each of which is independent but incomplete within itself. These data sets include (1) well-log responses of deposits in each systems tract, (2) seismic facies of each systems tract determined from reflection termination and configuration patterns, (3) high-resolution biostratigraphic and paleobathymetric interpretation of wells penetrating the section, and (4) eustatic cycle charts with correlation of local biostratigraphy for dating physically recognized sequence boundaries and condensed sections.
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Applying depositional sequence stratigraphic concepts to the interpretation of siliciclastic depositional systems is becoming an increasingly important tool in petroleum geology. After a succession of breakthroughs during the 1970s and 1980s, sequence stratigraphic concepts now have entered a phase of intense application and documentation, especially with regard to successful implementation in the field of petroleum geology. Workers have applied these concepts to a variety of databases, ranging from outcrop to cores to electric logs and to multifold seismic data. Clearly, sequence stratigraphic concepts embody–not a rigid model or template–but rather a way of looking at geology. This volume has two purposes: to compile some recent applications of siliciclastic sequence stratigraphic concepts, and to present new studies focused on refining conceptual models. This memoir grew out of a 1991 symposium, "Variations in Depositional Systems Within a Sequence Stratigraphic Framework: Applications to Exploration," organized by the authors at the AAPG annual meeting at Dallas. Robert Loucks and Rick Sarg have edited a companion volume, also published by AAPG,“Entitled Carbonate Sequence Stratigraphy: New Developments and Applications.”