Page 12 - Acquisition and Processing of Marine Seismic Data

1. INTRODUCTION 3

processing, and interpretation stages (Fig. 1.2). stacking, as well as subsequent migration
Data acquisition parameters generally strongly steps, etc.
affect the structure of the processing flows as On the other hand, even these primary pro-
well as the parameters of each processing step cesses strongly need some important prerequi-
in the flow. For instance, depths of the seismic sites. For instance, deconvolution requires a
streamer or gun array play the most important normal incidence stationary minimum phase
role in the frequency content of marine seismic wavelet, as well as a noise-free reflectivity
data. If a wider frequency band with relatively series. While an accurate stacking in 2D seismic
higher frequency content is required, then the data needs perfect hyperbolic reflection curves
streamer and/or gun array must be towed at on common depth point (CDP) gathers, 2D
shallower depths. This situation also controls poststack time migration algorithms need
the band-pass filter cut-off frequency values zero-offset sections consisting of only primary
during the processing steps later on. reflections generated by wave fields in-plane
Yılmaz (2001) defines the primary steps of the to the seismic survey. Today, stacking itself is
processing as (i) deconvolution, (ii) stacking, the most effective noise-suppression method
and (iii) migration (Fig. 1.2). Other processing that significantly removes both random and
steps can substantially be considered as contrib- coherent noise, such as multiple reflections.
utory methods used to prepare suitable inputs This process, however, produces a stack sec-
for these three major processing steps, to tion, but the oil and gas industry also needs
increase their efficiency. For instance, almost noise-free prestack seismic data in order to ana-
all of the preprocessing steps are used to prepare lyze amplitude versus offset (AVO) anomalies,
a noise-free input to deconvolution; velocity which may indicate possible hydrocarbon res-
analysis is needed to obtain velocities as input ervoirs. Likewise, seismic data as clean as pos-
to normal moveout (NMO) correction and then sible is also required for some other prestack

Seismic reflection work

Data Raw data Data Image Seismic
acquisition processing interpretation

Decon Stack Migration

QC
-1- -2- -3-
Selection of flow and data Selection of data processing Evaluation of the outputs of
processing steps most parameters that are most each processing step,
suitable for the input raw suitable for each processing removal of parameter
seismic data step selection issues

FIG. 1.2 Basic stages of a conventional seismic reflection project, consisting of data acquisition, processing and interpre-
tation, and primary steps of data processing along with the quality control (QC) recurrence in processing.