Changes

==Seismic interpretation of faults==

==Seismic interpretation of faults==

The seismic data set is interpreted primarily using vertical time sections. These are displays that show a series of vertical seismic traces displayed side by side ([[:file:M91Ch6FG47.JPG|Figure 1]]). The peaks or the troughs are filled in with black shading or color. Continuous reflections stand out as an overlapping array of peaks or troughs. These create patterns on a seismic section that give a representation of the geological structure in the subsurface. The seismic interpreter will look for discontinuities in the seismic reflections likely to represent faulting. Various techniques can help in picking faults. The interpretation can be cross checked against attribute maps showing changes in seismic dip (magnitude of the time gradient), azimuth (direction of maximum dip), or abrupt changes in amplitude.<ref name=Dalleyetal_1989>Dalley, R. M., E. E. A. Gevers, G. M. Stampli, D. J. Davies, C. N. Gastaldi, P. R. Ruijetnberg, and G. J. D. Vermeer, 1989, Dip and azimuth displays for 3-D seismic interpretation: First Break, v. 7, p. 86–95.</ref> <ref name=Hesthammerandfossen_1997>Hesthammer, J., and H. Fossen, 1997, Seismic attribute analysis in structural interpretation of the Gullfaks field, northern North Sea: Petroleum Geoscience, v. 3, no. 1, p. 13–26.</ref> Another method is to use semblance data to detect edges in the data (see [[Lithofacies maps]]).

The seismic data set is interpreted primarily using vertical time sections. These are displays that show a series of vertical seismic traces displayed side by side ([[:file:M91Ch6FG47.JPG|Figure 1]]). The peaks or the troughs are filled in with black shading or color. Continuous reflections stand out as an overlapping array of peaks or troughs. These create patterns on a seismic section that give a representation of the geological structure in the subsurface. The seismic interpreter will look for discontinuities in the seismic reflections likely to represent faulting. Various techniques can help in picking faults. The interpretation can be cross checked against attribute maps showing changes in seismic dip (magnitude of the time gradient), [[azimuth]] (direction of maximum dip), or abrupt changes in amplitude.<ref name=Dalleyetal_1989>Dalley, R. M., E. E. A. Gevers, G. M. Stampli, D. J. Davies, C. N. Gastaldi, P. R. Ruijetnberg, and G. J. D. Vermeer, 1989, Dip and azimuth displays for 3-D seismic interpretation: First Break, v. 7, p. 86–95.</ref> <ref name=Hesthammerandfossen_1997>Hesthammer, J., and H. Fossen, 1997, Seismic attribute analysis in structural interpretation of the Gullfaks field, northern North Sea: Petroleum Geoscience, v. 3, no. 1, p. 13–26.</ref> Another method is to use semblance data to detect edges in the data (see [[Lithofacies maps]]).

==Structural core logging==

==Structural core logging==

==Fault detection methods==

==Fault detection methods==

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M91Ch13FG80.JPG|{{figure number|2}}Dipmeter or image data can be used to pick likely fault planes in wells. Changes in dip amplitude or azimuth can indicate that a fault is present. Drag patterns may also be seen on the dip data above and below the fault intersection in a well (from Schlumberger<ref name=Schlumberger_1981>Schlumberger, 1981, Dipmeter interpretation, volume 1—Fundamentals: New York, Schlumberger, 61 p.</ref>). Courtesy of Schlumberger.

M91Ch13FG80.JPG|{{figure number|2}}Dipmeter or image data can be used to pick likely fault planes in wells. Changes in dip amplitude or [[azimuth]] can indicate that a fault is present. Drag patterns may also be seen on the dip data above and below the fault intersection in a well (from Schlumberger<ref name=Schlumberger_1981>Schlumberger, 1981, Dipmeter interpretation, volume 1—Fundamentals: New York, Schlumberger, 61 p.</ref>). Courtesy of Schlumberger.

M91Ch13FG81.JPG|{{figure number|3}}The stratigraphy in a well penetrating a normal fault will be incomplete due to fault cutout.

M91Ch13FG81.JPG|{{figure number|3}}The stratigraphy in a well penetrating a normal fault will be incomplete due to fault cutout.

M91Ch13FG82.JPG|{{figure number|4}}Repeated sections can be seen in a vertical well drilled through a reverse fault or with a highly deviated well penetrating a normal fault.

M91Ch13FG82.JPG|{{figure number|4}}Repeated sections can be seen in a vertical well drilled through a reverse fault or with a highly deviated well penetrating a normal fault.