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ABSTRACT: Reservoir Delineation Through Incremental Pay Thickness Model Correlations of Petrophysical and 3-D Seismic Data

D. B. Neff

Incremental pay thickness (IPT) seismic modeling can provide improved reservoir delineation through better correlation of petrophysical parameters to the three-dimensional (3-D) seismic data. Amplitude, isochron, and time structure maps created as part of a standard 3-D seismic interpretation on modern computer workstations often suggest variations in reservoir geometry, hydrocarbon distribution, and/or reservoir quality. Traditional modeling shows that multiple petrophysical and geological phenomena can cause similar seismic variations in amplitude, isochron, and time position. The IPT modeling technique addresses this problem by isolating individual parameters such as porosity, water saturation, shale content, and net-to-gross pay thickness so that uniqueness and nonuni ueness in the seismic waveform can be better understood.

Individual testing of petrophysical variables often shows both predictably systematic and unexpected changes in the seismic amplitudes. Amplitude variations due to changes in pay thickness can often be isolated from waveform differences caused by variations in porosity or sand-body geometry. This information allows for more accurate transformation of seismic data into reservoir pay maps such as net pay thickness, net porosity thickness, or hydrocarbon pore volume.

IPT modeling often shows that the relationship between a seismic attribute and pay thickness is nonlinear. Mathematical transforms based upon probability distribution patterns typically provide better reservoir estimates than those based on a more classic least squares fit regression trend. Also, IPT models give different seismic prediction reliability depending upon the pay parameter in question (i.e., gross pay thickness, net pay thickness, net porosity thickness, or hydrocarbon pore volume).

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990