Geology Reference
In-Depth Information
Fig. 3.17.
Structure contour maps of a conical, dip-domain anticline.
a
Original map showing three
traverses where elevations have been extracted (
heavy EW lines
).
b
Map constructed by triangulating
points extracted from the three profiles in
a
3.6
Adding Information to the Data Base
Structure contour maps can be based on a significant amount of information in addi-
tion to the elevations on a single horizon. The shape of the contoured surface can be
controlled using the attitudes of bedding, data from multiple stratigraphic horizons,
and from pore-fluid behavior such as different groundwater levels or the presence or
absence of hydrocarbon traps as indicated by shows of oil and gas in wells. Finding the
structural trend and mapping based on trend are discussed in Chap. 5 and 6.
3.6.1
Bedding Attitude
If the bedding attitude is known from outcrop or dipmeter measurements (Fig. 3.18a),
it can be incorporated into the contouring. Attitudes at the well-bore or outcrop scale
can give insight into the shape of the surface but are subject to influence by small-scale
structures. The contours are not required to have the same dip everywhere on the map.
The contour spacing will change as the dip changes. Structure contours are perpen-
dicular to the bedding dip. The distance between the contours is given by Eq. 2.21. In
the example of Fig. 3.18, for a contour interval of 100 and dip of 25°, the spacing be-
tween the contours at map scale is 214, giving the structure contour map in the vicinity
of the control point shown in Fig. 3.18b.
If mapping is customarily done at a standard scale, then a map-spacing ruler
(Fig. 3.19) can be useful. A contour-spacing ruler shows the spacing between contours
for a variety of dips, given the map scale and the contour interval. It is constructed
using Eq. 2.21. The ruler is oriented perpendicular to the structure-contour (strike)
trend and the contour spacing for a given dip is easily plotted or the dip determined
from the contour spacing.
