--> Computer Methods Used for Delineating and Unfolding Structure Horizons, by Curtis P. Henderson; #91024 (1989)

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Computer Methods Used for Delineating and Unfolding Structure Horizons

Curtis P. Henderson

The application of computer mapping software has increased the ability of the geologist in modeling multiple horizons. By following procedures and using the relationships that exist between structure horizons, the geologist can create conformable structure, isochore, and isopach maps, and then can use these to unfold the structure.

With the use of the computer, an isochore map is easy to create and is one of the basic tools used to make conformable structural horizons. After the top horizon is modeled and a grid is created, the gross interval (isochore) is determined by subtracting the height of each data point of the deeper horizon from the grid at the same X and Y value of the data point. The thickness value can be gridded creating the isochore grid model. The isochore grid can then be subtracted from the first structural grid resulting in a grid of the deeper structure.

Isochore maps are best used for doing volume determinations but lack the stratigraphic definition that isopach maps yield. Isopach maps are generated by applying the formula of stratigraphic thickness equals vertical thickness, multiplied by the cosine of the dip of the structure. To observe the actual isopach, the structural shape must be removed. The procedure can be executed by moving the structural grid locations from their respective positions along dip. The amount that the grid nodes are moved is based on the steepness of the dip angle, so that the length along the structure horizon is equal to the square root of [(x1-x2)2 + (y1-y2)2 + (z1-z2)2] where x, y, and z are the values at ne grid node and x1, y1, and z1 are the values of the adjacent grid node. The resulting lengths between each node are then summed first in a north-south direction and then in an east-west direction. Stratigraphic conformable horizons are built by combining the isopach maps onto one layer. This process of stacking the horizons and viewing them in cross section aids in revealing the geological history.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.