Predictive Stratigraphic Forward Modelling of the Ceduna Sub-Basin; Application to Fault Sealing

Abstract

Stratigraphic Forward Modelling is a sedimentary process simulation that recreates the way that stratigraphic successions develop and are preserved. It reproduces numerically the physical processes that eroded, transported, deposited and modified the sediments over variable time periods. In a forward modelling approach, data are not used as the anchor points for facies interpolation or extrapolation, but to test and validate the results of the simulation. Stratigraphic forward modelling is an iterative approach, where input parameters have to be modified until the results are validated by actual data. The goal of this model has been to predict potential sedimentary composition of the Ceduna sub-basin, in particular to model potential constituents of the fringes of the Ceduna Delta, which are as much as several hundreds of kilometres from the nearest well control. Regional 2D interpretation provided initial screening to refine the regional stratigraphic and structural frameworks, while the interpretation of the Trim 3D survey was used to produce a static geological model focused on investigating fault sealing potential in the Tiger and Hammerhead supersequences. Stratigraphic forward modelling, matching output sedimentology predominantly to the Gnarlyknots-1A and Potoroo-1 wells was utilised to create a shale volume. In turn this stratigraphy was combined with depth converted structural model created from the seismic interpretation of the Trim 3D creating a geocellular model to test potential scenarios in which the faults would be sealing or leaking with regard to across fault flow. The results of the modelling do not conclusively predict sealing or leaking with respect to across fault flow. In fact the four cases modelled lie directly across the field of phyllosilicate framework fault rocks which are associated with the sealing to leaking transition in fault zone membrane sealing potential with shale gouge ratios in the range of 10–40%. The sandiest case predicts some, though very little sealing to across fault flow, while the shaliest case predicts mostly sealing. The probable scenario is thought to be one of the in between cases at which stage sealing to across fault flow exhibits a high sensitivity to the modelled lithologies.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015