Geophysical Exploration for Petroleum and Natural Gas

The fundamental digital processing techniques used to analyze seismic records taken in the exploration for petroleum and natural gas are described. These methods include the determination of the seismic velocity function for a prospect, static and dynamic corrections to the seismic traces, multiple coverage of a prospect and stacking, and deconvolution. The concept of minimum phase, or, what is the same thing, the concept of minimum delay, is defined and it is shown that a positive net down-going energy flow in a layered medium results in minimum-delay down-going wave motion. Seismic migration may be defined as the extrapolation of a wave field from a known boundary at the surface of the earth to an unknown boundary within the earth that depicts the geologic structure. The methods of maximum-convexity migration, and its equivalent, wavefront migration, as well as wave-equation migration, are given. Finally the statistical time-series model used in the method of the predictive deconvolution of seismic traces is presented, and it is shown that the method of predictive deconvolution is a valid method for removing either long-period or short-period reverberations even in the case of a nonminimum-delay source pulse.