Faulting, High Resolution, Arkoma Basin
W.L. Chapman, G.L. Brown, D.W. Fair, 1983. "Faulting, High Resolution, Arkoma Basin", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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Figure 1 is a migrated high-frequency seismic section from the Arkoma Basin, Oklahoma. Figure 2 is an interpreted version of Figure 1, with two objective zones marked by arrows. The first zone, a shallow gas sand, exists at depth A (1,067 m, 3,500 ft) and the second zone, a faulted horizon, is at depth B (2,438 m, 8,000 ft). Figure 3 is the same high-frequency seismic section before seismic migration. The high frequency content in both Figure 1 and 3 gives excellent vertical resolution. However, the lateral resolution in Figure 3 is quite poor as evidenced by faults that are not easily detected. In contrast, the faults are readily identified in Figure 1. The difference between Figure 1 and Figure 3 illustrates quite dramatically how lateral resolution of seismic data may be greatly improved by seismic migration. Furthermore, this generalization applies not only to structurally complex areas but also to areas with seemingly monotonous "layer-cake" stratigraphy.
Frequency content at reflection A objective (Figure 2) is approximately 100 Hz with sufficient bandwidth to uniquely map the limits of the producing sand. Further interpretive work with inter active modeling supported gas sand thickness estimates from seismic data. Frequency content at the deeper horizon B is about 80 Hz. The 20 Hz of high-frequency loss between A and B objectives is apparently due to attenuation in the thick, dominantly shale section between these two seismic markers. This shale section is approximately 1,371 m (4,500 ft) thick. When coupled with migration frequency content at the deeper zone is certainly sufficient to accurately map faults as shown in Figure 2. The fault on the right exhibits about 35 msec or 53 m (175 ft) of vertical displacement.
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Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.