Integrated Method for PAYTHICK Calibration in Plio-Pleistocene Slope Sediments, Offshore Texas, Gulf of Mexico

HANNA, ROBERT W., DAVID J. REYNOLDS,* JACK P. HORKOWITZ, and WILLIAM G. DILLON, BP Exploration, Houston, TX

Quantified estimates of net hydrocarbon pay thickness are computed from seismic amplitude amomalies through integration of petrophysical and seismic studies using the program PAYTHICK This technique is currently used in production and appraisal projects with well control and is now being applied to exploration plays far removed from wells.

PAYTHICK is based on the time and amplitude (time-amp) response of a wedge model of hydrocarbon filled sand encased in shale. Input consists of two tracked, time-amp events for the top and base of the anomaly, velocities for the model and sand shale, and calibration constants for the model time-amp response. Keys to exploration use of this technique are normalization of amplitude information to a background (or nonanomalous) reflectivity and knowledge of trend petrophysical properties. Event amplitudes are normalized to a background RMS amplitude level of 1.0 using an interactive event-orient algorithm. The background well RMS amplitude is computed from the average filtered reflectivity of ten wells. Petrophysical trends established for the Texas Gulf of Mexico Plio-Pleistocene slope rovide equations of acoustic impedance and velocity in shales and fluid-substituted sands (using Gassmann). The seismic wavelet's character is stabilized by postmigration processing to correct the phase and enhance the bandwidth.

Combination of this calibration data for specific prospects uses petrophysical equations, seismic wavelet character, and the RMS well calibration to derive model amplitudes for PAYTHICK A comprehensive single-line display of the PAYTHICK analysis shows tracked seismic data, together with graphs of anomaly attributes and net pay thickness. Lateral variations in net pay thickness can be observed on this display and used together with average net pay thickness for the entire anomaly to evaluate 2-D exploration prospects. Tests on six drilled anomalies showed the net pay footage within the expected thickness range. This integrated technique allows seismic data to directly drive consistent exploration reserve volume calculations far removed from well control.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)