Abstract

During the year 2000, Conoco Indonesia Inc. Ltd. (CII) acquired and processed a large regional 3D survey, covering 2500 square kilometers of the Gabus Sub-Basin, West Natuna, offshore Indonesia. In addition to re-assessing the previously drilled structural highs and associated, hydrocarbon discoveries, the main potential for prospect generation within the area is anticipated to be stratigraphic plays within complex fluvial and marginal lacustrine deposits.

Because the basic structural configuration of the area is relatively well understood from previous 2D seismic data and the major highs have been drilled (although not optimally), interpretation of the 3D data has focused primarily on stratigraphy rather than structure. To optimize stratigraphic information the interpretation has utilized available software to analyze the 3D data as a volume rather than the traditional methodology of interpreting a 3D volume as a series of 2D lines. To perform this type of interpretation, over a large area and within a limited time frame, a workflow combining suitable interpretation software within CII has been used to perform 3D horizon picking, seismic attribute analysis and visualization. Facies maps have been generated and correlated to major sequence tracts allowing a series of geological time slices to be reconstructed for the Basin.

The workflow involved undertaking an initial data assessment and structural interpretation using visualization and standard 3D seismic interpretation software. This was followed by interpretation of regionally consistent surfaces using a fast and accurate auto-picking tool, based on trace shape similarity to propagate horizons omni-directionally. The auto-picker also allowed the horizon to be viewed in amplitude, real time during the interpretation, which contributed significantly to producing a robust interpretation in the complex environments of deposition. The regional surfaces were used to slice through the 3D seismic volume and produce a series of geological time slices and attribute maps.

The interpretation of diagnostic seismic facies for prospective sequences has identified new prospectivity within the area. Source rock distribution has been re-interpreted based on seismic facies and the regional hydrocarbon charge model up-dated accordingly. This is expected to move the area into a mature phase of exploration during which stratigraphic prospects will be targeted and existing, currently un-commercial, discoveries re-assessed.