Improvements in the resolution of seismic data discovered a New Basin in the Gulf of Carpentaria

Abstract

The Gulf of Carpentaria is a sparsely explored shallow water frontier area and was covered by very poor quality seismic data up to 1973. During 1980 to 1982, five oil companies acquired 48-fold and 24-fold seismic data which established a regional grid. The quality of those data is good above the Base Mesozoic Unconformity that forms the base of the Carpentaria Basin, but poor below it. A strong seismic event, which is associated with that unconformity, masks any reflections from deeper horizons and only horizons above it can be interpreted with confidence. The major processing problem encountered was severe multiples associated with the strong seismic event from that unconformity. A dry hole drilled in 1984 discouraged additional exploration until 1989, when Phoenix Resources acquired several km of 60-fold seismic data in the northeastern part of the Gulf. The 1989 survey used 120 groups and 3000 m cable while the 1980 surveys had used 96 groups and 2400 m cable. The significant features in processing of 1989 data by Phoenix were velocity analysis at 1 km intervals, compared to 5 km intervals for the 1980 data, application of multiple attenuation filter before stacking and F-K filter after stacking and migration. Seven 1980 lines were reprocessed by Phoenix in 1989, with velocity analysis at 2 km intervals, application of velocity filter and F-K demult before and after velocity analysis, before stacking, and dip filter after stacking and migration. The 1989 seismic data and the reprocessed 1980 data show reasonably good reflections from deeper events below the Base Mesozoic Unconformity. The interpretation of the deeper events on these sections indicates the presence of a thick sedimentary sequence below the unconformity, defining a new basin. This basin has been named the Bamaga Basin and is a potential petroleum province.