Geology Reference
In-Depth Information
Fig. 6.3.
Sections through the map in Fig. 6.2.
a
Normal section perpendicular to the fold crest.
b
Longitudinal section parallel to the fold crest.
c
Zig-zag or well-to-well cross section.
d
Oblique
3-D view of the structure showing the three cross sections
The effect of a curved section (Fig. 6.2) on the implied geometry of an elongate
dome is shown in Fig. 6.3. The correct geometry of the structure is shown by the nor-
mal section, a straight-line cross section perpendicular to the axial trace of the struc-
ture (Fig. 6.3a) and the longitudinal section (Fig. 6.3b) parallel to the crest of the struc-
ture. A line of section that is not straight, such as one that runs through an irregular
trend of wells or a seismic line that follows an irregular road, produces a false image
of the structure. The zig-zag section across the map (Fig. 6.3c) incorrectly shows the
anticline to have two local culminations instead of just one. This is a serious problem
if the cross section is used to locate hydrocarbon traps or to infer the deep structure
using the predictive section drawing techniques described in Sect. 6.4.
The first line of section across a structure chosen for interpretation should avoid
local structures, like tear faults, oblique to the main structural trend. Oblique struc-
tures introduce complexities into the main structure that are more easily interpreted
after the geometry of the rest of the structure has been determined. Returning to the
cylinder, now shown offset along a tear fault (Fig. 6.4), cross sections at a and c will
