Method and apparatus for converting seismic traces to synthetic well logs

#This invention relates to seismic prospecting and more particularly to an improved method and apparatus for producing synthetic velocity logs.

#Well logs, that is records produced by lowering a logging tool into a well and recording the characteristics of the earth layer near the tool, have long been used as interpretive aids in exploration geophysics. Velocity logs, or impedance logs as they are sometimes known, are an aid in delineating the geology in the vicinity of the well, since they tend to identify sharp discontinuities between beds of different geologic structure.

#Much of exploration geophysics is based on the seismic process, and the utility of manipulating seismic data to create synthetic velocity logs has been appreciated. Much as an actual well log, it is desired to use the synthetic log as an aid in delineating the geology traversed by the seismic energy. However, due to the limitations of the seismic process, synthetic logs produced from seismic data heretofore have not been as useful as well logs in identifying rapid velocity changes or in delineating sharp discontinuities between subsurface bedding planes.

#Other objects and advantages will become apparent from the following detailed description when taken in conjunction with the drawings in which:

#FIG. 1 illustrates a portion of a conventional seismic trace suitable for processing in accordance with the present invention;

#FIG. 2 illustrates the seismic trace of FIG. 1 after processing in accordance with the present invention;

#While the invention will be described in connection with a preferred embodiment, there is no intent to limit it to that embodiment. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims.

#Turning now to the drawings, FIG. 1 illustrates a conventional seismic trace in wiggle trace format showing energy reflected from the subsurface in the seismic process. Due to the nature of the seismic process including the characteristics of the seismic source and the filtering of the seismic energy accomplished by the earth, the trace is rather severly band limited at both the low and high frequency ends of the spectrum. FIG. 1 also illustrates that the high frequency attenuation becomes more severe with increasing record time.

#By way of contrast, sonic logs taken in well bores retain a good deal of high frequency information content. Thus, as the logging tool traverses from one bedding plane to another, the log has sufficient frequency content to indicate the discontinuity between beds. As a result, sonic logs are useful along with other displays such as stacked lines in making geologic interpretations.