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The primary reservoir units of the PNG Highlands include shoreface and incised-valley estuarine sandstone deposits within the Late Jurassic and Early Cretaceous Imburu and Toro Sandstone formations. Regional understanding of both the depositional environments in which these sands were deposited and their extent, is key to building accurate field-scale geological models. In the absence of good quality seismic data, this study uses various input data from 100–150 wells spread along 300 km of the fold belt to predict reservoir presence and quality. Data types include: core sedimentological interpretation, core analysis, well tops, and well logs to predict reservoir presence and quality. True Stratigraphic Thickness maps, Neural-Network based lithofacies logs, and normalised GR logs have subsequently been generated and used to produce a Regional 3D Petrel volume from which properties can be fed directly into field-scale models. Markov Chain, GR cut-offs, and Neural-Network based analysis on normalized GR have all been tested as a means to generate depositional facies for each reservoir unit. The result shows laterally and vertically extensive shoreface and incised-valley deposits that continue for 10's to 100's of kilometres along the fold belt. Numerous offset wells, and wells positioned off structure, help control the proximal-to-distal relationships and show an overall onshoreto-offshore trend from SW to NE with two main sediment inputs coming from the SE and the NW. Shorter range variability in the model is introduced by populating the depositional facies with lithofacies. Each lithofacies has been assessed in terms of rock quality using both qualitative and quantitative datasets including: routine core analysis, petrology, AFTA, and vitrinite reflectance data to populate the model with meaningful porosity and permeability values. Results show that the impact of burial history and rock composition is subtle but significant and gives insight as to the role the post-depositional history has played on the present regional properties distribution. The collective result of this study shows a consistent and common interpretation of the reservoir stratigraphy and properties between all of the PNG Highland Fields. |
