Publications

Why is the horizontal, or lateral resolution of seismic data so limited? Sedimentary geology is, to a first approximation, one dimensional: it consists of approximately parallel horizontal layers with only gradual changes horizontally. This type of earth can be mapped with considerable precision by the seismic reflection method. But where horizontal changes in geology do occur, our usual seismic methods do not do very well at defining them: whether the changes are of a massive nature - such as on the flanks of a salt dome - or of a very subtle nature such as the boundary of a channel sand. These variations from "layer-cake" geology are precisely the features which trap hydrocarbons: faults, reefs, channels, etc. Only classic anticlinal traps with gently dipping flanks are close to layer-cake concepts, and most of those traps have already been drilled. As we look for smaller and smaller fields, we find we need better and better resolution of the lateral geological variations which trap oil and gas. This paper considers the factors which limit the resolution of lateral or horizontal geological variations by the seismic reflection method. Seismic interpreters use both unmigrated and migrated sections. The limitations of the two types of sections are different so they will be treated separately. Although it is well known that migration improves the lateral resolution of seismic data, about 60% of current shooting is still interpreted at least initially without migration.