Seismic modeling and interpretation of porosity in the upper St. George group (Ordovician) Carbonates, Port au Port Peninsula, western Newfoundland

Hulburt, Sean Corey (2012) Seismic modeling and interpretation of porosity in the upper St. George group (Ordovician) Carbonates, Port au Port Peninsula, western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The geophysical and lithological heterogeneous nature of the Ordovician St. George Group Carbonates complicates the exploration process on the West coast of Newfoundland. Preferential hydrothermal dolomitization, uplift along the St. George Unconformity, and multiphase structural deformation are responsible for reservoir development in the Upper St. George Group. The ability to map porosity in a heterogeneous dolomitized reservoir such as the Upper St. George Group, prior to drilling, on 2-D seismic data is particularly advantageous for cost effective exploration. Porosity alters the acoustic response of seismic data and a synthetic seismogram study is designed to reveal the effect of porosity on waveform. Block porosity models are designed by statistical analysis in reservoir intervals known from well log data in the Upper St. George Group. The block models are representations of petrophysical changes in bulk density and sonic interval transit time caused by increasing porosity. Since the synthetic seismic trace is a product of the two petrophysical parameters, bulk density and sonic interval transit time, attributes displaying changes fromporosity can be recorded and used as proxies for finding porosity related attribute changes on 2- D seismicdata. Four well data sets on the Port au Port Peninsula (Port au Port -1, Long Range A-09, St. George's Bay A-36, and Long Point M-16) are used in generating models for this study. Synthetic seismograms are designed from block models at 0, 5, 10, and 15% porosity at 20, 40 and 80Hz Ricker wavelets. Multiple Ricker wavelets are implemented to determine which frequency best reveals porosity effects on the synthetics. Complex trace attributes (Instantaneous phase, instantaneous frequency, and reflection strength) are analyzed on each modeled synthetic seismogram. Ultimately, this process creates a predictive tool for mapping porosity in the vicinity of a well in 2-D seismic sections by matching attributes from models to attributes from the real seismic data.

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