Reconnaissance 3-D Seismic as a Modern Exploration Tool

Abstract

TCPL has recently carried out ‘reconnaissance or exploration’ 3-D surveys, in three different blocks, each designed to solve a different type of problem. In each case a considerable improvement in data quality and the resulting structural/stratigraphic interpretation was achieved. The Kupe South structure is a wrench-induced feature cross-cut by numerous small-medium faults. Stratigraphic changes across the prospect produce a variable quality seismic event at the top reservoir level. The Pataka Prospect comprises a narrow horst block trend within the Oakura fault zone, offshore New Plymouth. Accurate determination of potential reserves required a reliable interpretation of the fault configuration, and the amount of displacement of the reservoir horizon by the critical faults. The Waitara Prospect is affected by a ‘no-data’ zone possibly associated with volcanics in the near surface. It was necessary to define the extent and nature of the no-data zone and to calculate the effect of the interpreted volcanics on the time structure map. Prior to the surveys we modelled the effects of such critical parameters as sail-line separation, final interpolation spacing and the dimensions of the 3-D grids using existing 2-D data. Good results were obtained with a wider line spacing than is strictly required for true 3-D. Whilst the Reconnaissance 3-D method has not removed all of the difficulties with interpretation, a considerable improvement was obtained in data quality and ease of interpretation.