ABSTRACT
The areal seismic method has been developed over the last few years as a means of correctly imaging geological structure. However it was soon realized that many of the parameters which characterized hydrocarbon reservoirs could also be measured by the use of areal techniques. In the common-depth-point method (CDP) of collecting seismic reflection data the aim is to achieve a plane of seismic information in distance along the surface and in time into the geological section. The CDP stacking method is used to improve the signal-to-noise ratio, to remove multiples and it will give a representation of the subsurface particularly if the data are collected up-or-down dip. Thus the parameters characterizing a reservoir could be measured by a CDP line but the result would be information in only one dimension, along an up-or-down dip line through the reservoir.
Data can be collected in two-dimensions in space and one in time by a variety of techniques. The objective is to adequately sample the subsurface so that changes in various parameters can be mapped areally. Methods of data collection commonly used include the dragging of a cable along lines which are sufficiently close together and the shooting into lines of detectors which are at some angle to the lines of sources. Each seismic trace then represents a sampling of the subsurface. Variations in any measured parameter such as the amplitude, phase or power in the seismic signal or the velocity of propagation can be interpreted as an indication of changes in the physical properties of the rock matrix.
Having collected and processed what is essentially a cube of information a final problem remains: this is, display and interpretation. It is possible to display this information as a series of layers cut horizontally or vertically through the earth. This may be done on a television screen for video reproduction. The addition of an interactive computer system to the video presentation enables a three-dimensional interpretation of the cube to be made. The interpretation may then also be stored for video reproduction.
