Geology Reference
In-Depth Information
correctly located formation top in another well, the apparent dip will be wrong, perhaps
even in the wrong direction (Fig. 10.2a). If the dip is determined from a core in a deviated
well (Fig. 10.2b) that is mistakenly thought to be vertical, then the inferred dip will be too
large. The apparent thicknesses are too large in both situations. A well that deviates up
dip will result in an apparent steepening of the dip between two wells and thicknesses (if
mistakenly corrected for dip) that will be too small (Fig. 10.2c).
10.2.2
Edge Effects
Both humans and computer-contouring algorithms appear to prefer contours that close
within the map area. In Fig. 10.3a, the triangulation algorithm has closed the contours
on southwest end of the anticline. Based on the available control, open contours to the
southwest (Fig. 10.3b) are equally valid and perhaps more geologically reasonable.
Fig. 10.3.
Is the closure real?
a
Anticline closed to the southwest in triangulated map from data in Fig. 3.5.
b
The same structure opened to the southwest (
heavy lines
), deleted contours
dashed
Fig. 10.4.
Edge effects on a map of the Sequatchie anticline. Control points are
solid squares
.
a
Map
from Fig. 3.23a.
b
Same map with region of no data
shaded
(diagonal lines)
