The Application of Fourier Transform in the Interpretation of Subsurface Stratigraphy

Abstract

General seismic data interpretation involves direct fault and horizon mapping, sequence stratigraphy and seismic modeling to produce structural, stratigraphic and reservoir maps for the delineation, exploration and production of hydrocarbon in oil fields. The first two methods operate on stacked and migrated data, while the third is done without adequate calibration, inadequate display of final stacks, coarse processing and in time domain. Actual hydrocarbon entrapments are rarely detailed well enough to permit reliable location of wells from these studies alone owing to inherent noise. This paper presents the results of the application of time-frequency transform on 3D seismic data over an oil field in Niger Delta. The aim of the study was to develop a robust technique for mapping subtle stratigraphic units which are usually masked after normal data interpretation using spectral algorithm. The discrete Fourier transform applied in the interpretation of the 3D seismic data filters the field data recorded in time, and recovers lost sub-seismic geologic information content in frequency. The algorithm is based on fast Fourier transform technique and was developed within Matlab software. The results of the spectral decomposition yielded frequency maps (slices) at data sampling interval (4ms) over the reservoir window. The maps revealed sub-seismic faults, differences in lithology and better reservoir delimitation. The results gave enhanced structural disposition of the reservoir bed and more detailed indication of the variation of reservoir character with depth.

Keywords: Fourier transform, Spectral decomposition