PROCESSING OF SINGLE-CHANNEL, HIGH-RESOLUTION, SHALLOW SEISMIC REFLECTION DATA FOR IMAGING GAS CHARGED SEDIMENTS AND BURIED CHANNEL SYSTEM ON CENTRAL-WEST COAST OF INDIA

Abstract:

High-resolution, shallow-seismic reflection using sparker seismic source is one of the most popular offshore exploration methods for imaging sub-surface structures in near shore region. In the present study, high-resolution shallow-seismic reflection data were acquired using 300 Joule sparker energy source with multi-electrode spark array and single-channel streamer containing 16-hydrophones at a boat speed of about 4 knot. The data were recorded in SEG-Y format with record length of 500 ms, sampled at 40 µs. The problems in sparker seismic data are artefacts which primarily include (i) short-path multiples, (ii) long-path multiples, (iii) ghost reflections, (iv) secondary bubble effect, and (v) incoherent noise.

Short-path multiples, produced by reflectors at seabed/sub-seabed and sea surface, arrive at receiver immediately after the primary reflection, whereas, long-path multiples arrive later as a distinct event. Ghost reflections due to source and receiver arrangement below sea-surface produce a seismic wavelet, delay in time and reverse in polarity with respect to primary. Secondary bubbles (bubble effect) produced destructive interference that strongly attenuated amplitude of the signal, and produced frequency notching as demonstrated in power spectrum of raw seismic data. Incoherent noise present in seismic reflection data reduce the quality of the signal and can often lead to misinterpretation. Processing and analysis of seismic trace of the present study reveal that the artefact related to ghost reflections are not present in the data. However, short-path and long-paths multiples, secondary bubble effect and incoherent noise severely affected the quality of the seismic data.

This paper presents and discusses processing of high-resolution, single-channel seismic reflection data acquired between water depth 10 and 70 meter in near shore region of central-west coast of India. Our results show that quality of the processed data is highly improved and yield artefact free interpretable seismic sections. Based on the processed seismic data, several sub-surface features such as gas charged sediments, incised V-shaped valley, and late-Pleistocene to Holocene sedimentary strata are identified.