Reservoir Properties Inferred from Seismic Response in Areas with Minimal Log Control
J.D. Loren, J.T. Kulha, K.S. Renbarger, R.M. Sneider, 1991. "Reservoir Properties Inferred from Seismic Response in Areas with Minimal Log Control", The Integration of Geology, Geophysics, Petrophysics and Petroleum Engineering in Reservoir Delineation, Description and Management, Robert Sneider, Wulf Massell, Rob Mathis, Dennis Loren, Paul Wichmann
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The integration of regional petrophysical, geological, and geophysical data permits the detection of reservoir properties and the prediction of seismic response where log control is minimal. Because the necessary acoustic and density logs are frequently unavailable, incomplete or inaccurate, even in mature producing areas, forward modeling to create synthetic seismograms and amplitude versus offset (AVO) response is difficult. Synthetic acoustic and density logs can be created from commonly available resistivity logs and a uniquely derived sand fraction curve. Examination of drill cuttings, sidewall, and whole cores enhances the accuracy of the sand fraction curve, defines reservoir quality and delineates exploration opportunities. Rock, log, and calculated data are transformed into the time domain and integrated into the seismic data by means of the synthetic acoustic transit time.
The process algorithms are project-calibrated with a learning set of diversely representative high quality log data. After verifying algorithm calibration, the synthetic log generation process can then be applied regionally with confidence, even in older wells with “ancient” resistivity logs. The synthetic acoustic and density logs are the basis for models of variable lithology and fluid content, from which synthetic seismograms and AVO response are generated.
Comparison of modeled synthetic seismograms and AVO response to actual seismic data demonstrates a better agreement based upon synthetic acoustic and density logs as opposed to measured acoustic and density, constant density or Gardner’s general relationship. The models can be easily modified by varying pore fluids and bed thicknesses to find the range of amplitude changes and AVO effects that can be expected in the seismic data.