Chris Dyt

SEDSIM IN HYDROCARBON EXPLORATION

Since 1994 SEDSIM has been applied to hydrocarbon exploration and production problems in Australia under contract to various oil companies, including Woodside Petroleum Ltd., Mobil Exploration & Producing Australia Pty, Ltd., Texaco Inc., and Shell Development Australia Pty, Ltd. The NW Shelf of Australia is an active, frontier, hydrocarbon exploration area. From the Middle Jurassic to the Tertiary the sedimentation was predominantly siliciclastic on a variable bathymetry that generally was subsiding thermally but subject to local higher amplitude tectonic movement. The paleotopography is determined relatively easily from adequate seismic coverage, and the sediment supply was dominated by large rivers with channels that are active today. Combined stratigraphic/structural plays have been proven along the shelf and the future challenge is to identify potential stratigraphic plays which have little or no seismic expression. Stratigraphic forward modeling can contribute to the development of play concepts in such circumstances. Two case studies from the Neocomian (Barrow and Browse), one from the Aptian (Yampi Shelf), and one from the Oxfordian (Kendrew) are given.

3D modelling of flexural isostatic deformation

Modelling of the isostatic loading of the earths crust in three dimensions is a difficult problem due to the length scales involved, the lack of scalability of the underlying equations and the slow convergence of the solution under conventional techniques. In this paper, a new method to solve the three-dimensional (3D) flexure equation has been developed. The long-standing challenge in numerically modelling flexural isostasy at large scale and high rigidity is addressed. The program is capable of modelling both local and regional isostatic compensation. Compared with other schemes, the isostatic model presented here is more robust and computationally efficient.

COMPUTER MODELLING OF THE OXFORDIAN DEPOSITIONAL SYSTEMS IN THE KENDREW TROUGH, DAMPIER SUB-BASIN

A 3D depositional modelling program, SEDSIM, was used to model the various depositional systems operating in the Kendrew Trough, Dampier Sub-basin during a two million year period of the Oxfordian. The simulation covers an area of 40 km by 100 km, from the Goodwyn Field in the southwest to the Lambert Field in the northeast, covering the Rankin Trend, Kendrew Trough, Madeleine Trend and part of the Lewis Trough. The simulation started from the Jurassic main unconformity (156.7 Ma) forward to 154.7 Ma using a spatial resolution of 1 km and a time step of 5 ka. The 3D model from the simulation quantitatively mimics the interaction of the palaeogeographic setting, sediment supply, sea level fluctuations, tectonic movement and palaeo-oceanographic setting in three dimensions, to simulate the spatial and temporal distribution of sedimentary facies. The model identified five Oxfordian leads within the Kendrew Trough, including two major slope and basin-floor fan systems, a shelfal-shoreface system, a deltaic system, and a submarine channel system. The study has shown that 3D depositional models produced by SEDSIM are not only able to depict the spatial and temporal distribution of depositional systems on a basin scale, but are also capable of making useful contributions to the understanding of play fairway and lead development.

Multigrain seabed sediment transport modelling for the south-west Australian Shelf

With increasing concerns about climate change and sea-level rise, there is a need for a comprehensive under- standing of the sedimentary processes involved in the erosion, transport and deposition of sediment on the continental shelf. In the present paper, long-term and large-scale seabed morphological changes on the south-west Australian con- tinental shelf were investigated by a comprehensive sediment transport model, Sedsim. The investigated area covers the continental shelf and abyssal basins of the south-western region. The regional seabed is sensitive to environmental forces and sediment supply, and most terrigenous sediment carried down by major rivers is trapped in inland lakes or estuaries. Only a small fraction of fine-grain sediment reaches the continental shelf. The simulation has also confirmed that the Leeuwin Current and high-energy waves play the most important roles in regional long-term seabed evolution. Although the numerical implementation only approximates some forcing and responses, it represents a significant step forward in understanding the nature of potential long-term seabed change as a response to possible climate change scenarios. The 50-year forecast on the seabed morphological changes provides a reference for the management of coastal and offshore resources, as well as infrastructure, in a sustainable way.

Modelling Coastline Change of the Darss-Zingst Peninsula with Sedsim

Coastlines do not change because of sea level variation alone. Instead, the changes are the result of a complex interaction between climate and geologically controlled processes. Especially on a local scale, sedimentary dynamics play an important role. Even with a rising sea level, concurrent sediment accumulation may prevent coastline retreat. On the other hand, erosion may accelerate marine transgressions remarkably. The southern coast of the Baltic Sea is an impressive example for the impact of erosion, transport, and accumulation of sediments to coastline change during the Holocene. Since the end of the Littorina transgression the coastline morphology has been shaped here mainly by longshore sediment transport controlled by the geological situation and glacioisostatic influence. The longshore sediment transport is driven by wind and consequently waves shaping young Holocene structures like the Darss-Zingst peninsula. In order to model these processes, Sedsim (SEDimentary Basin SIMulation), a stratigraphic forward modelling software, has been applied for the Darss-Zingst peninsula on a centennial time scale. In Sedsim, the sedimentary dynamics are modelled by an approximation to the Navier–Stokes equation. Using high-resolution digital elevation data, information about the local wave characteristics, geology, estimates of sea level rise, and experimental scenarios for the development of the Darss-Zingst peninsula through the coming 840 years are presented. The results of the experiments show possible implications to the area of investigation and may serve as a basis for decision makers in coastal zone management.

Aeolian Sediment Transport Integration in General Stratigraphic Forward Modeling

A large number of numerical models have been developed to simulate the physical processes involved in saltation, and, recently to investigate the interaction between soil vegetation cover and aeolian transport. These models are generally constrained to saltation of monodisperse particles while natural saltation occurs over mixed soils. We present a three-dimensional numerical model of steady-state saltation that can simulate aeolian erosion, transport and deposition for unvegetated mixed soils. Our model simulates the motion of saltating particles using a cellular automata algorithm. A simple set of rules is used and takes into account an erosion formula, a transport model, a wind exposition function, and an avalanching process. The model is coupled to the stratigraphic forward model Sedsim that accounts for a larger number of geological processes. The numerical model predicts a wide range of typical dune shapes, which have qualitative correspondence to real systems. The model reproduces the internal structure and composition of the resulting aeolian deposits. It shows the complex formation of dune systems with cross-bedding strata development, bounding surfaces overlaid by fine sediment and inverse grading deposits. We aim to use it to simulate the complex interactions between different sediment transport processes and their resulting geological morphologies.