High-Resolution Marine Data and Interpretation

Abstract

ABSTRACT Study of selective seismic and geologic data in a portion of the offshore Gulf of Mexico indicates that with proper application of geoseismic techniques on broadband seismic data, the hydrocarbon potential of an area may be assessed and specific reservoirs quantified. Various techniques, such as wavelet processing of seismic data, petrophysical analysis of well log data, and calibration methodology are essential to establishing the technical framework for further analysis of stratigraphic and structural traps. Enhancement and special treatment of these data by various new proprietary techniques, used with sound geologic concepts, permit a more reliable qualitative as well as quantitative interpretation of reservoirs and potential reservoirs. The geologic meaning of seismic amplitudes and their measurements are important to not only explorationists, but to exploitation geologists and reservoir engineers as well. Experience gained in areas (fields) of known production can lead to expansion of confidence limits into wildcat areas where there is little or no control. Although the example demonstrated is in the Tertiary clastic section of the Gulf of Mexico, concepts and techniques employed are applicable in any geological environment, so long as physical principals permit. INTRODUCTION In recent years, the use of broadband seismic data and amplitude measurements are receiving increasing attention of geologists, exploitation engineers and geophysicists because of the need to quantify net thickness for seismically thin units. This new interest has brought about a new interrelation of the three disciplines, and with this new interrelationship, techniques permit a more reliable qualitative as well as quantitative interpretation of reservoirs and potential reservoirs. Through seismic processing, the primary objective is to reduce the recorded seismic signal to the filtered reflectivity series produced by the earth's stratigraphic subsurface. The complex time series, as recorded, contains the following elements:The basic seismic wavelet convolved with the reflectivity series of the earth.Coherent noise which includes multiple events, diffractions, wave spreading, etc.Random noise from instruments and earth filtering. Careful field gathering, combined with common-depth-point stacking procedures, can appreciably decrease the contribution by the noise components. Frequency filtering and predictive deconvolution further attenuate these effects. However, traditional processing techniques have had limitations in resolution due to the constructive and destructive interference which results from the complex components and appreciable time length of the "basic wavelet". The complex shape of the basic wavelet is derived from:Source signature.Source ghost.Receiver ghost.Instrument phase distortion.Cable and geophone phase distortion. Traditionally, deconvolution has been used as the processing procedure to shorten the wavelet and thus decrease the complexity of the seismic trace. However, the results of deconvolution are unpredictable and variable.