Exploiting Visualization Technology For Geophysical Interpretation
Authors: James H.E. , Lupin S.P. , Sperruzza T.D. 
Published: October 2008

Visualization technology allows the interpreter to view geophysical data through a single 3D view transform. Traditionally the interpreter has been forced to view data in 2D and then build a mental 3D image. Interpreters have become adept at this task, however the direct viewing of data in 3D lets the interpreter view data in their original coordinate space and effort can be transferred from visualizing the data to visualizing changes in the data over time, a difficult task with traditional displays.

Many exploration blunders have been associated with incorrect TVD correction of deviated wells or errors in reconciling seismic and well datums. With 3D displays it is possible to show log curves, tops and synthetics along borehole paths.

Visualization technology shows horizon and fault surfaces as lit surfaces. These surfaces are directly comprehended by the brain without any conscious effort. It is not usually necessary to subsample the data when using this display technique.

Visualization technology also supports transparency. Closely spaced transparent surfaces will enhance common features and features that cross between surfaces maybe detected. Transparency may be used more conventionally in displays that show multiple horizons and faults.

Visualization technology can be used to display more information informs that are easier to understand than conventional contour maps.

INTRODUCTION

Most of the data that geophysicists and geologists work with are either implicitly three dimensional or exist in three dimensional space. The two common spaces are the 3D space of the earth where (x,y,z) coordinates are measured in distance or the 3D space of reflection seismology where (x,y) coordinates are measured in distance and the z coordinate measures two-way reflection time. Traditional methods of interpretation have relied on 2D cross sections of the data and plan view maps. Modem computer graphics allow us to explore our data in 3D space.

PROJECTIONS

To see our 3D data on a 2D computer screen it is necessary to project the data from 3D to 2D. There are many ways to do this. One common projection is the "perspective projection", this is the scheme often used in representational art where objects at a distance appear smaller than nearer objects. This projection creates a similar visual effect to photographs and the human visual system, so it is the projection of choice for realism. Another common projection is the "cabinet projection". This projection is a parallel projection where size does not diminish with distance from the viewer, but lines parallel to the viewing direction are foreshortened by one half. Schematics of these two projections are shown in Figure 1. The Cabinet projection is sufficiently realistic to fool the viewer into believing that the scene is in perspective, but allows the viewer to compare the sizes of features at different distances. We tend to use this projection when surfaces are rendered translucently.

To project data recorded in two-way reflection time we typically choose an arbitrary velocity of 10,000 ft/sec or 3,000 meters/sec to convert two-way times to distances. Slower velocities maybe used to achieve some vertical exaggeration.