Takeshi Nakanishi1, Simon C. Lang2
(1) Adelaide University, Adelaide, Australia (2) University of Adelaide, Adelaide, Australia
The future for petroleum exploration in the predominantly non-marine Cooper-Eromanga Basin of onshore Australia, lies in the identification and appropriate risk assessment of stratigraphic traps. Using an integrated approach of sequence stratigraphy and 3D seismic data visualisation, a variety of stratigraphic trap prospects were identified in the Permian and the basal Jurassic successions.
The geologic chance factors for an effective stratigraphic trap include reservoir, top seal, lateral seal, bottom seal within each depositional systems tract, the seal effectiveness of the adjacent depositional systems tracts and the appropriate spatial arrangement of these factors. To assess the chance of geologic success, the confidence values for the existence of geologic chance factors were estimated according to the genetic-stratigraphic interval (e.g. lowstand, transgressive, highstand systems tracts). For probabilistic reserves estimation, geologically reasonable ranges were estimated for each parameter employing Monte Carlo simulation to calculate the reserves distribution.
When a series of possible exploration portfolios, including single or multiple prospects from a prospect inventory are plotted regarding the chance of geologic success vs. the mean value of the reserves estimate, an efficient exploration frontier emerges. The portfolio candidates on the efficient exploration frontier were assessed with regard to the expected net present value (ENPV) using a simple cash flow model. The results indicate that appropriate portfolios include multiple prospect exploration especially with lowstand systems tract plays using multiple exploration wells. The portfolio construction approach for stratigraphic trap exploration should be made consistent with conventional play types, to enable an assessment of all exploration opportunities.