Monitoring the Spanish gas fields in the R�a de Vigo (1991?2001)

Abstract

The Ria de Vigo is located on the NW coast of Spain, and includes gassy areas studied in several high-resolution seismic surveys between 1991 and 2001. The position of the acoustic blankings and gas seepages has been monitored vertically and spatially in the surveyed area. Also, a 253-cm-long vibrocore was recovered in a gas field in the inner part of the ria. The predominant facies of the core is dark mud with small bioclastic fragments and a very strong H2S smell. The repeated surveys of this ria show that these shallow gas fields have been active in the last decade and were active in the past (buried collapse structures). Available direct gas analyses show that methane is one of the components of the gas in the ria. Thus, bacterial degradation of organic matter in shallow sediments is considered the most likely source for the gas in the Ria de Vigo.