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Practical Application Of Sequence Stratigraphy And Risk Analysis For Stratigraphic Trap Exploration.

Nakanishi, Takeshi

Doctor of Philosophy, 2002

University of Adelaide


This research outlines an evaluation procedure for stratigraphic trap exploration by employing sequence Stratigraphy, 3D seismic data visualization and quantitative risk analysis with case studies in an actual exploration basin.

Open-file Moorari and Pondrinie 3D seismic survey datasets chosen to test the procedure come from the Cooper-Eromanga Basin, onshore Australia, encompassing the Permian fluvio-lacustrine, Patchawarra, Epsilon, and Toolachee formations and the Jurassic fluvial, Poolowanna Formation. Employing an integration of sequence stratigraphic concepts applied to non-marine basins and advanced 3D seismic data visualization, eight stratigraphic trap prospects were extracted to be included in an exploration inventory.

In the Merrimelia 3D seismic survey dataset, the potential oil reservoir capacity of fluvial point bar sandstones in the Birkhead Formation was calculated (12.6 to 25.6 MMbbl in place), although the point bars were confirmed as water-wet and an effective stratigraphic trap was not included as prospect for the exploration inventory.

The geologic chance factors for and effective stratigraphic trap include the following within each depositional systems tract: reservoir, top-, lateral- and bottom seal. Additionally, the seal effectiveness of the adjacent depositional systems tracts and the appropriate spatial arrangement of these factors form part of the geologic chance factors. The confidence values for the existence of geologic chance factors were estimated according to sequence stratigraphic contexts, and multiplied to calculate the chance of geologic success of each prospect varying 4 to 34%. For probabilistic reserves estimation, geologically reasonable ranges were estimated for each reserves parameter employing Monte Carlo simulation to calculate the reserves distribution, ranging 3.9 to 21.2 bcf as mean values.

When a series of possible exploration portfolios, including single or multiple prospects from the prospect inventory are plotted in terms of the chance of geologic success vs. the mean value of the reserves estimate, an efficient frontier emerges. The portfolio candidates on the efficient exploration frontier were assessed with regard to expected net present value (ENPV) using a simple pre-tax cash flow model for the gas producing in the Cooper-Eromanga Basin. The results indicate that appropriate portfolios include multiple prospect exploration targeting the lowstand systems tract plays by single or multiple exploration wells.

Australian School of Petroleum



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