Full Utilization Of Seismic Resolution - The Key To Deterministic Stratigraphic Interpretation From Marine Data
Authors: Nath Ashoke K. , Patch James R. 
Published: October 2008

Recently-developed technology has made meaningful quantitative Stratigraphic interpretation possible. The role of waveform, wavelet shape and duration is known to be vital in studies of reflection signal. The extraction and synthesis of these complex wavelets, generated by the various marine sources, leads to an understanding of the difficulties in the processing and interpretation of conventional marine data. The transformation of this complex wavelet to a simple response with zero phase response of short duration is an integral part of the recently developed technology "Wavelet Processing".

"Wavelet Processing" reduces the complexity of the seismic trace and allows direct correlation of seismic reflection response and the lithologic sequence. This improvement in resolution allows the use of direct and inverse modeling procedures in deterministic interpretation. Quantification of subsurface parameters, such as velocity, porosity and thickness, from seismic information are made possible.

Examples of the technology discussed demonstrate conclusively that the resolution of marine seismic data is the key to its use in stratigraphic interpretation. The utilization of knowledge of waveform duration and shape is vital in lithologic interpretation. Actual marine data cases and modeling examples are presented to support these conclusions.

INTRODUCTION

The re-discovery of the importance and use of amplitudes has been a landmark in the art of hydrocarbon exploration. The literature has been well documented with the amplitude related facets of direct and indirect indicators of hydrocarbons. Amplitude processing of seismic data provided the interpreter with another tool to recognize anomalies in the seismic section. However, exploration applications of stratigraphic nature, such as direct correlation of well log data with seismic data, thickness mapping from reflection amplitudes, etc., made requirements beyond the simple use of amplitudes. The obvious progression beyond amplitudes was a realization of the importance of waveform and the basic propagating wavelets.

This paper will address itself to show that:The knowledge of the propagating basic wavelet can be mathematically synthesized or extracted from recorded seismic data.The effects of this complex basic wavelet can be removed to produce a seismic section which is more representative of the existing acoustic interfaces and thus a closer representation of the subsurface lithology.The optimum resolution of seismic data can be achieved, thereby making subtle stratigraphic features easier to interpret.

WAVELET DETERMINATION

There are several methods of obtaining the knowledge of the basic seismic wavelet. These can be broadly classified into three categories:Extraction techniques assuming some known lithological sequence.Statistical approaches as exemplified by homomorphic methods and the autocorrelation of seismic traces over a long window.Wavelet synthesis which makes no lithological assumption but requires careful recording of the source signature and other related acquisition parameters.

Various aspects of these techniques have been discussed in the literature (Shugart and Barry, 19T5; Neidell et al, 19T5; Rives et al, 19T6, etc.), and we shall take a heuristic approach and comment on each one of them.