Using 3D seismic data to map shallow-marine geohazards; a case study from the Santos Basin, Brazil

This paper documents a study that used high quality, conventionally processed, speculative 3D seismic data for two specific purposes: first, to identify and avoid any health, safety, security and environmental (HSSE) issues regarding the water bottom and, secondly, to avoid shallow (<1 s below the mud line) geohazards when drilling the wells. The study integrated existing legacy well data, new 3D data from the BM-S-52 concession and a targeted programme of water-bottom grab samples from the BM-S-52 concession, Santos Basin, offshore Brazil. Two aspects of the analysis are described: the first addresses the problem and solution adopted for characterizing the water-bottom environment in this area; the second addresses the interpretation of the data for shallow geohazards. The results of this case study have been accepted by the regulatory authorities as representing sufficient evidence of risk evaluation that no further dedicated site-survey data acquisition is required. This has led to savings in time and in costs which would otherwise have been expended on deep-water site-survey campaigns. Furthermore, the use of 3D seismic data for well-location planning brings benefits in improved imaging of the near-mud-line geology, full coverage over the whole concession, operational flexibility for changing well location and timely availability of data. The analysis workflow may also be applicable in other, similar deep-water areas.