3D SEISMIC INTERPRETATION AND NONMARINE DEPOSITIONAL PROCESSES AT THE GORGON GAS FIELD, NW SHELF, AUSTRALIA
BARBARA J. RADOVICH, BURNET OLIVEROS, 1996. "3D SEISMIC INTERPRETATION AND NONMARINE DEPOSITIONAL PROCESSES AT THE GORGON GAS FIELD, NW SHELF, AUSTRALIA", Stratigraphic Analysis Utilizing Advanced Geophysical, Wireline and Borehole Technology for Petroleum Exploration and Production, Jory A. Pacht, Robert E. Sheriff, Bob F. Perkins
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As part of the ongoing assessment of the Gorgon gas field on the North West Shelf of Australia, Texaco conducted a detailed sequence stratigraphic study of the 3D seismic data and well logs in the gas-bearing sands of the Triassic, nonmarine Mungaroo Formation. This field is on a series of tilted horst blocks in the northern Carnarvon Basin and is being appraised by a partnership of Texaco, Shell, Chevron, and Ampolex. The data reveal a nonmarine sequence stratigraphic architecture made up of a series of stacked fluvial sequences dominated by the processes of incision and aggradation. Wireline log shapes show blocky gamma ray shapes with sharp bases followed by fining-upward patterns. The ‘base’ of each sand is a sequence boundary, and log correlation indicates incision into older units at this boundary. The sequence boundary is the time-correlatable horizon on the 3D seismic interpretation workstation and allows proper delineation of each pay sand amplitude. The seismic data show that truncation of seismic reflections from beneath each sequence boundary is a major part of the interpretation of the seismic data. Amplitude extractions, guided by the sequence boundary, reveal high amplitude lineaments and low amplitude areas that can be interpreted to represent the plan-view pattern of sandy lithofacies within a time-correlative unit. Amplitude maps are also overprinted by the constructive and destructive interference effect on the seismic amplitudes caused by younger sequences incising too deeply from above. Instantaneous frequency of the seismic data is used to adjust lowered seismic amplitudes that result from thicknesses that exceed tuning. After adjustment, ‘sweet spots’ on the maps are more accurately represented. Understanding these processes allows the sequence stratigrapher and quantitative geophysicisl to produce a more geologically insightful interpretation and calibration of the 3D seismic geometries and amplitudes.