Simon Christopher Lang

A quantitative model for deposition of thin fluvial sand sheets

Sheetfloods are typically invoked as the mechanism responsible for the kilometre-scale transport of sand-sized sediment grains in shallow-gradient fluvial systems. This concept is based on the lateral extent of ancient thin, sheet sandstone deposits rather than on fluid dynamics, which has resulted in a loosely constrained model for sheetfloods. This study tested the conceptual mechanism by developing a depth-averaged, 2D computational fluid dynamics model. The model results compare well against observations from modern deposits at Lake Eyre to provide a quantitative, physically sound basis for sheetfloods that can be applied in ancient and modern settings to constrain otherwise qualitative interpretations.

Conducting comprehensive analyses of potential sites for geological CO2 storage

Publisher Summary This chapter illustrates that geological storage of CO2 may provide a solution to the problem of reducing anthropogenic emissions of greenhouse gases to the atmosphere. To accurately appraise a potential site in terms of its suitability for CO2 storage, a comprehensive workflow analyzing the detailed geological and geophysical characteristics of the site needs to be undertaken. In particular, potential sites need to be evaluated geologically in terms of their injectivity, containment, and capacity. Injectivity can be assessed by a review of the reservoir quality and by a detailed sequence stratigraphic model to estimate the likely flow-unit geometries and connectivity. Containment can be assessed via an analysis of the seal capacity (using MICP), and by assessing the possible migration pathways and trapping mechanisms from the structural geometry and stratigraphic architecture. In addition, integration of hydrodynamic analysis of formation water flow systems and geomechanical studies of fault stability and sustainable pore fluid pressures with the stratigraphic interpretation provide vital confirmation of the containment potential.

Quantitative sequence stratigraphy

Sequence stratigraphy based on wire-line logs, cores, and outcrops is entering its fourth decade of mainstream usage in industry and academia. The technique has proved to be an invaluable tool for improving stratigraphic analyses in both clastic and carbonate settings. Here we present a simple quantitative technique to support sequence stratigraphic interpretations in clastic shallow marine systems. The technique uses two pieces of data that are readily available from every subsurface field or outcrop study: (1) parasequence thickness (T) and (2) parasequence sandstone fraction (SF). The key assumptions are that parasequence thickness can be used as a proxy for accommodation at the time of deposition and parasequence sandstone fraction can be used as a proxy for sediment supply. This means that quantitative proxies for rates of accommodation development and sediment supply can be acquired from wire-line logs, cores, and outcrop data. Vertical trends in parasequence thickness divided by sandstone fraction (T/SF) approximate trends expected in systems tracts for changes in ratios of rate of accommodation development to rate of sediment supply. The technique, termed “TSF analysis,” can also be applied at lower-order sequence and composite sequence scales. It provides a quantitative and objective methodology for determining rank and order of sequence stratigraphic surfaces and units. Absolute T/SF values can be used to determine shoreline, stacked shoreline, and shelf-margin trajectories. Four case studies are presented, which demonstrate the robustness of the technique across a range of different data sets. Implications and potential future applications of TSF analyses are discussed.