Seistec Seismic Profiles: A Tool to Differentiate Gas Signatures

Abstract

International audienceThe presence of gas is a common feature in many seismic sections. However, the origin of the gas is often difficult to determine. Recently acquired very high resolution seismic profiles using an IKB Seistec boomer provide useful insight to the understanding of the gas origins in a range of environmental settings including sea lochs and coastal lagoons. The gas features are described both from a qualitative point of view through their acoustic facies, and quantitatively through the associated seismic signal (polarisation, amplitude). Acoustic facies include acoustic turbidity, gas "curtains" and "blankets" as well as "white fringes" and "black shadows". All the features encountered have been related to specific gas nature generated by different sources (organic matter degradation in paleo-valley infillings, waste material effluent)

High-Resolution Acoustic Mapping of Gas Charged Sediments and Living Benthic Foraminifera Assemblages From the Ne Region of the Guanabara Bay (Rj, Brazil)

“…Following the classifications of Taylor (1992) and Baltzer et al (2005), it was possible to identify acoustic signatures of black shadow and acoustic blanket. Features related to percolation of gas as intra sedimentary plumes, turbidity pinnacle, and structures related to seepages to the water column, as acoustic plumes and pockmarks were also identified.…”

“…Depending on their seismic character, size and geometry, various descriptive features have been used for gas charged sediments, such as acoustic blanket, black shadow, plumes, curtain, and acoustic turbidity (Taylor, 1992;Yun et al, 1999;Garcia-Gil et al, 2002;Baltzer et al, 2005).…”

Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

“…The shallow gas features were defined in accordance with their shape and echo-character; in the shallow seismic high resolution record the works of GARCIA-GIL et al (2002), LEE et al (2005, BALTZER et al (2005), and TAYLOR (1992) among others were used as reference. The depth of the gas features was measured in milliseconds (ms) and the sound velocity used was 1500 m/s, so it is possible to estimate the depths of the features in meters.…”

“…Acoustic Plumes consisting of a series of parabolic high amplitude reflections occur frequently along the seismic line, typically every 100-200 meters (TAYLOR, 1992). Besides, Black Shadows (Figure 3), features that are different from gas curtains in that they permit the acoustic seabed to be reached, are present (BALTZER et al, 2005). Seepages were found in 2 profiles on dark blue lines in the south-central and north portions of Figure 3.…”

“…The formation of these gas structures results from their sedimentary environment, which may be due to recent sedimentation or human activity, among the evolutionary processes responsible for the characterization of the sedimentary deposition environment (GARCIA-GIL et al, 2002;BALTZER et al, 2005). The accumulation of these gases occurred in former geological periods (i.e., thousands of years before the present), due to the intense oxidization of organic matter in a sedimentary environment (GARCIA-GIL et al, 2002).…”