Sand Injection Research Group | Phase 3
Research Assistants: Robert Waltham and Donald Christie
PhD Research Student: Gustavo Zvirtes
Detailed outcrop investigation is critical for accurate identification of key architectural characteristics unique to sandstone intrusions that are used to constrain pre-drill risks and identify potential reservoir targets. Accounting for the significance of undetected reservoir volume associated with sandstone intrusions is essential as they hold reserves and enhance reservoir connectivity. Outcrop analogue research of sand injection complexes remains integral.
Phase 3 focused on continued extensive and detailed analysis of outcrop analogues of sand injection complexes, integrated with core-scale description and interpretation, and forward seismic modelling of outcrop geology. Outcrop data acquisition was designed to support subsurface interpretation, at seismic and/or sub-seismic scale and based on challenges faced by SIRG members. Five linked themes were the focus of the project: 1) outcrop investigation, 2) 3D outcrop modelling and statistical analysis, 3) forward seismic modelling (of outcrop), 4) core description, and 5) micro-scale description and analysis.
1. Outcrop investigation and analysis
Fieldwork was continued and carried out on the PGIC and commenced on the adjacent Tumey Giant Injection Complex (TGIC). Extensive documentation was undertaken of external geometry, spatial distribution of sandstone intrusions and their internal structures, and similar features from depositional parent units.
(a) Detail of outcrop, Right Angle Canyon in PGIC; southern wing and part of southern inner sill are shown. (b) Geological interpretation of (a) showing the discordance of the sandstone intrusion and the jack-up of the overlying mudstone.
2. 3D outcrop modelling and statistical analysis
Outcrop analogues are routinely used to elucidate sandstone intrusion geometry, architecture, and spatial distribution. Accuracy of these data is critical to the development of “best possible” stochastic reservoir models, and ultimately dynamic simulation. 3D digital outcrop models (DOMs), created from lidar and aerial stereo-photogrammetric data, provide large (several km in width) and spatially accurate representations of outcrop. Methods to extract quantitative geometric data of sandstone intrusions from DOMs are employed that complement traditional fieldwork. All data are collated into a database and statistical analysis is undertaken to extract key metrics that may be used in subsurface evaluation and reservoir modelling and simulation.
3D digital outcrop model (DOM) of Right Angle Canyon outcrop in the PGIC. Width of view is approximately 2 km. DOM generated from an airborne 3D photogrammetric survey. Blue polylines illustrate interpreted dykes. Green polylines illustrate interpreted sills. Red polylines indicate top pick of a saucer-shaped intrusion, including wing-like and inner sill geometry.
4. Forward Seismic Modelling
Seismic interpretation of sandstone intrusions focuses on identifying discordant relationships and extracting “geobodies” when prioritising attractive reservoir targets for development wells. Typically, geobodies do not resemble sandstone intrusions. Our experiments using forward seismic modelling of seismic-scale sandstone intrusions aim to test and support seismic interpretation, and to optimise the value of outcrop data in subsurface interpretation. In subsurface studies where several styles of intrusion are inferred, geological templates of laterally extensive outcrop are excellent tools for constraining interpretation.
Synthetic seismic expression of Right Angle Canyon in the PGIC, using a zero-phase Ricker wavelet with a peak frequency of 30 Hz. The histogram shows the number of illumination vectors and the maximum dip angle of the reflections illuminated.
5. Micro-scale description and analysis
There is growing evidence that petrographic and granulometric characteristics are diagnostic of sandstone intrusions, and implicitly a product of the process of sand fluidisation and injection. Petrography and mineralogy become increasingly significant criteria when differentiation between sandstone intrusions and parent units is otherwise challenging, even when good outcrop or continuous core are available. Where the physical relationships between parent units and sandstone intrusions are limited, obscure or absent, petrographic and mineralogical characteristics may have lithostratigraphic significance. SIRG has developed, and continues to develop, methods to diagnostically identify sandstone intrusions, and thereby, gains insight into the process of sand injection. Granulometry has direct implications on grain sorting, pore-size distribution and thereby reservoir characteristics.