Geoscience Reference
In-Depth Information
(a)
(b)
Map view
relay
Strike projection:
displacement profile
Fig. 3.19
(a) Schematic map to illustrate dip-azimuth calculation; (b) map view of relay ramp,
horizon, showing contours and dip arrows. The unfaulted part of the horizon dips
gently in a direction just west of north. Along the fault plane, provided the horizon
is picked there, it will exhibit strong dips in an easterly or north-easterly direction.
Most interpretation software provides the functionality to compute automatically the
magnitude and direction (azimuth) of the local dip of a picked horizon, provided that
it has been picked on every seismic trace, usually with an autotracker. Maps of these
attributes will highlight the faults. This is a much easier way to arrive at a first-pass fault
map than the time-consuming correlation of faults from one line to another in section
view. Just as importantly, it will bring to the interpreter's attention faults of small
apparent displacement that would probably not be recognised in section view but may
be significant baffles to fluid flow in the reservoir. Note that not all faults will be visible
on azimuth maps; if the fault happens to be parallel to the horizon contours locally, then
there will be no change in the azimuth of the dip at the fault, though the fault will be
obvious from its high dip values when a map of the magnitude of the dip is displayed. Dip
maps are an effective way to study the individual fault segments comprising composite
consist of closely spaced overlapping fault segments; displacement is transferred across
relay ramps between the terminations of the overlapping fault segments
(fig. 3.19(b)
)
.
Sometimes these ramps are cut by faults that connect the terminations of the two main
