Map View Subsalt AVO Modeling
LINDSAY, RICHARD O., DAVID R. MUERDTER, CHARLES M. SKIDMORE, AND DAVIS W. RATCLIFF
3-D PreStack
Depth
Migration
(3-D PreSDM) has demonstrably opened the Gulf of
Mexico Subsalt Trend by producing clear and well defined images of the pre-salt
geologic section. Amplitude and AVO anomalies have subsequently mapped and by
drilling, proven to be associated with hydrocarbons. Yet to date, these
associations are qualitative at best. Insight into the understanding of subsalt
amplitude and AVO anomalies is gained by the combination of 3-D raytracing, 3-D
pore pressure prediction and map-domain AVO modeling. 3-D raytracing through the
3-D PreSDM velocity volume into the pre-salt section reveals a richness of
incidence angles on subsalt horizons. The magnitude and richness of distribution
of these angles was not anticipated from simple salt layer models. From this
insight alone one must anticipate AVO anomalies in the subsalt section.
Collected from raytracing are volumes of incidence angles at perspective subsalt
horizons. Extracted at prospective horizons, these angles are combined with
spatially varying shale cap-rock and reservoir rock properties (caused by
variations i pore pressure) to create seismic amplitude and AVO model maps.
Multiple solutions are created while varying the reservoir pore fluids. Revealed
is insight into decoupling the raypath distortion and pore pressure effects from
reservoir pore fluid effects.