Gas accumulations revealed by high-resolution seismics in the Patos Lagoon, southern Brazil.

WESCHENFELDER, J.; CORRÊA, I.; AYUP-ZOUAIN, R.; ALIOTTA, S.; PEREIRA, C.; DE VASCONCELLOS, V.

Vigo, España.

Conferencia; VIII International Conference on gas in marine sedimens.; 2005

Universidade de Vigo, Dpto. Xeociencias Mariñas e Ordenación do Territorio

A high resolution seismic survey was conducted in the Patos Lagoon, southern Brazil, aboard of the research vessel LARUS of the Fundação Universidade do Rio Grande. Around 400 km of seismic profiles were collected using a 3.5 kHz frequency device, which provided a rather good penetration depth and resolution of the acoustic signal. Acoustic anomalies detected in the form of anomalous seismic responses reveal that gassy sediments are common in several areas of the Patos Lagoon. The gas within the sediments leads to a widespread acoustic masking in some sectors of the records, hiding the sedimentary structure below the gas-charged horizons. In the zones where the gas does not appear to be present, acoustic windows allow a good resolution of the seismic records. ‘Acoustic turbidity’ is a common anomaly, associated with other acoustic phenomena like ‘gas brightening’ and ‘acoustic blanking’. Based on the characteristic of the acoustic anomalies it was possible to recognize sectors with ‘pocket gas’ and sectors with ‘acoustic turbid zones". As indicated by the seismic records, the main gas accumulations occur in areas of former topographic lows. Some of these topographic lows can be linked to former river courses that have dissected the coastal plain of the state of Rio Grande do Sul during the regressive events of the Upper Quaternary. The sedimentary filling of these incised channel and valley systems is linked to sedimentary processes of subsequent transgressive events. The source of the shallow gas in the coastal plain of Rio Grande do Sul is related to evolutionary processes that formed and structured a complex system of channels, lagoons and barriers during the multiple regressive and transgressive events of the Quaternary period.ARUS of the Fundação Universidade do Rio Grande. Around 400 km of seismic profiles were collected using a 3.5 kHz frequency device, which provided a rather good penetration depth and resolution of the acoustic signal. Acoustic anomalies detected in the form of anomalous seismic responses reveal that gassy sediments are common in several areas of the Patos Lagoon. The gas within the sediments leads to a widespread acoustic masking in some sectors of the records, hiding the sedimentary structure below the gas-charged horizons. In the zones where the gas does not appear to be present, acoustic windows allow a good resolution of the seismic records. ‘Acoustic turbidity’ is a common anomaly, associated with other acoustic phenomena like ‘gas brightening’ and ‘acoustic blanking’. Based on the characteristic of the acoustic anomalies it was possible to recognize sectors with ‘pocket gas’ and sectors with ‘acoustic turbid zones". As indicated by the seismic records, the main gas accumulations occur in areas of former topographic lows. Some of these topographic lows can be linked to former river courses that have dissected the coastal plain of the state of Rio Grande do Sul during the regressive events of the Upper Quaternary. The sedimentary filling of these incised channel and valley systems is linked to sedimentary processes of subsequent transgressive events. The source of the shallow gas in the coastal plain of Rio Grande do Sul is related to evolutionary processes that formed and structured a complex system of channels, lagoons and barriers during the multiple regressive and transgressive events of the Quaternary period.