Analysing Seismic Attributes

Abstract

Attributes are properties of reflected seismic wave signals and are analyzed to reveal geologic information they carry, concealed in the images. The attributes are essentially the kernel properties of a seismic wave, i.e., the instantaneous amplitude, phase and frequency and polarity and can be called the primary attributes. Later with advent of high resolution 3D seismic volume data, several advanced and powerful attribute techniques, such as geometric attributes have evolved. Amplitude-based attributes are the most convenient to predict reliable rock-fluid parameters, and in some cases they act as direct hydrocarbon indicators. The thin-bed related ‘tuning thickness’ phenomenon, complex trace analysis, sweetness and spectral decomposition techniques used widely for identifying and characterizing thick and thin oil and gas sands are commonly included in primary attributes. The geometric attributes which are important and are used extensively are derived from 3D seismic volume include the coherence, curvature and dip and azimuth attributes. These primary and the geometric attributes are discussed with their geological significance and applications in reservoir engineering and reservoir management. ‘Ant tracking’ an intelligent technique for mapping fractures in reservoirs is also outlined.

Display of attributes such as composite frames of multi-attributes, overlays with suitable color blending play important role in visualization and interpretation of subtle reservoir characters and are included with illustrations. Limitations of attributes and their analyses are stressed.