Reliable initial reservoir estimates can be made for a prospect without the benefit of reservoir engineering information. This is done by combining petrophysical data such as sonic, gamma-ray, density, and resistivity logs with inverted seismic profiles and geologic models.
To delineate and appraise the reservoir volume adequately with seismic data, the reduction, processing, and display must be subject to strict quality control. The wavelet must be converted to zero phase, contracted and centered on the reflection coefficient that corresponds to the target beds. The useful spectrum of the data must be as broad as possible to define the geologic boundaries properly. There must be a good estimate of the amplitude spectrum of the wavelet and a successful deconvolution to remove effects of the source signature. Noise maintenance or reduction must precede inversion of seismic data to pseudo-sonic logs. The lowfrequency gap in seismic records must be restored deterministically by the use of a geologic model with interval velocities specified. Time-variant processes should be minimized or avoided. A reliable calibration of absolute transit times must be obtained given that the inversion algorithm was stable and satisfied all assumptions involved in its use. Finally, results must be displayed or printed out so that data manipulations can be reviewed critically.
Having achieved a rigid quality control, explorationists should now feel comfortable with initial reservoir estimates based on these data sets. Financial planning and forecasting can then proceed on a more secure basis earlier in the exploration and development of a prospect.