The Art and Science of Contouring
Most significant petroleum exploration plays are accompanied by a series of contour maps representing the subsurface geology. Today, seismic maps are generally the foundation of a well recommendation or seismic-survey proposal. The following uses the discussions of Tucker (1988) and of Gadallah (1994) in giving a brief summary of contour mapping.
It is essential that the contour map convey to management the essential message. In the words of Tucker (1988, p. 741), “Here's the oil deposit!” We can interchange gas or mineral deposit for oil in that statement, depending on the play.
IMost of us are familiar with topographic maps that contain lines of constant elevation, known as elevation contours. The contours of a subsurface structural map for a given formation display the topography as it would appear if rocks above the formation were stripped away. Such contour maps display the dip of a formation, as well as any folding or faulting of the structure.
Maps can be constructed to display the depth of a formation from some datum level. The data for seismic contour maps are obtained by picking times or depths from seismic sections. Because the picks from the seismic section are the essential data for our map, they should be made with considerable care. Generally, the initial picks are made by using ties to well logs or formation tops. The times and depths are then picked through the seismic-data volume by correlating reflected arrivals from trace to trace.
It is worthwhile
Figures & Tables
Fundamentals of Geophysical Interpretation, SEG Geophysical Monograph Series No. 13, is a practical handbook for the petroleum geophysicist. Fundamental concepts are explained using heuristic descriptions of seismic modeling, deconvolution, depth migration, and tomography. Pitfalls in processing and contouring are described briefly. Applications include petroleum exploration of carbonate reefs, salt intrusions, and overthrust faults. The book includes past, present, and possible future developments in time-lapse seismology, borehole geophysics, multicomponent seismology, and integrated reservoir characterization.