CASE HISTORY 4: Seismic Modeling of Fault-Related Folds
Peter F. Morse, Guy W. Purnell, Donald A. Medwedeff, 1991. "Seismic Modeling of Fault-Related Folds", Seismic Modeling of Geologic Structures: Applications to Exploration Problems, Stuart W. Fagin
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We present examples from a class of geologic models for compressional tectonic regimes along with their corresponding seismic expressions on unmigrated and migrated seismic profiles. The geologic models are based upon fault-related fold theory (Suppe 1983, 1985). For most of our seismic examples, we use modeling and migration programs based on the acoustic wave equation. Such wave-equation techniques, while not as computationally fast, often handle complex models more realistically than geometric raytracing and provide output better suited for subsequent data processing.
Synthetic 2-D zero-offset sections, computed using the wave-equation exploding-reflector approach, lead to (1) recognition of patterns associated with different fault-related folds, and (2) prediction of some of the difficulties in working with unmigrated and migrated seismic sections. Synthetic multioffset shot records, generated using the 2-D acoustic wave equation, demonstrate difficulties in imaging beneath fault-propagation folds using the conventional CMP method. A synthetic 3-D zero-offset survey across a 3-D fault-bend fold demonstrates that conventional 2-D seismic lines acquired in the fault-slip direction are insufficient for correct structural imaging and interpretation; hence, 3-D data acquisition and processing are necessary.
Finally, we examine a case history from Lost Hills field, San Joaquin Valley, California. This study demonstrates that geologically plausible interpretations consistent with both well and seismic data can be generated by iterating between geologic interpretations and synthetic zero-offset sections.