Fifty years of case histories

Abstract

Fifty years of case histories naturally reflect different and ever‐changing technology, but the underlying theme remains unchanged: to show that careful surface measurements can reveal physical properties of the subsurface. Finding a salt dome with a torsion balance in the 1920s and defining reservoir properties with shear waves in the 1980s involve different techniques, but in both the physical properties of the rocks are interpreted from geophysical measurements to solve geologic problems. Most early case histories attempted to establish the validity of geophysical tools; an example would be attempting to show the usefulness of refraction fan shooting by comparing its results with drill hole information. Later tools would in turn be compared with established tools. Reflection seismic interpretations were compared with torsion balance and refraction fan shooting results. As the science of geophysics became more accepted, case histories focused on more detailed aspects of technology and on discovery of subtle traps. Early papers dwelt at length on the application of geophysics to large features and on comparison of results with drill information. Later case histories continued to use geologic information to test geophysical interpretation, but they emphasized the subtle and hidden aspects rather than the obvious. The most recent case histories seldom deal with large structures. Instead they demonstrate the source wavelet required to resolve a stratigraphic trap or the effect that changing the reservoir fluid has on the reflection character so that hydrocarbons can be identified, or inferred, directly from the seismic data. Geophysical exploration has evolved and case histories reflect that evolution.

Modeling GPR data to interpret porosity and DNAPL saturations for calibration of a 3-D multiphase flow simulation

“…This type of dialogue also led to the aspiration for a more robust GPR data interpretation, available through existing geophysical technology. A cursory review of the vast literature on the use of seismic data to delineate oil fields suggests alternate methods (Kettle 1985;Horvath 1985). One preferred method to produce the desired GPR data set for porosity and saturation interpretation consists of: 1) carefully processing the data to remove the variable near-field effects on the starting pulse; 2) correcting for variable lateral positioning, timing, and gain; and 3) migrating the data in a manner that best preserves variations in geology within the final waveforms.…”