Investigating the role of structural and stratigraphic heterogeneities in regionally extensive mudstones in controlling vertical and lateral fluid migration in sedimentary basins
In sedimentary basins mudstones and shales, which are often termed sealing lithologies, are critical in controlling vertical and lateral fluid migration pathways. These sealing lithologies can be regionally extensive and can be centimeters to hundreds of meters thick. The burial, compaction, and deformation history of sealing lithologies are determined by the physical properties of the sediment, along with the stress regime and pore fluid pressure (cf. Maltman, 1994). Understanding the breaching of these seals, sometimes referred to as seal bypass (Cartwright et al., 2007) is key to containing possible escape pathways to the seabed. Alongside the vertical leakage through the propagation of hydraulic fractures, it has been shown (e.g., Streit & Hillis, 2004) that rising fluid pressure can induce fault slip, temporarily increasing the permeability in the fault zone allows for vertical migration. Understanding the dominant flow pathways and the redistribution of fluid pressures through time is to understand at what point fluid pressures could create fault permeability that could lead to vertical escape. Improving our understanding of the vertical and lateral flow (including cross-flow at fault juxtapositions) within sedimentary basins is important in understanding the distribution of pore fluid pressures,
Using 2-D and 3-D seismic reflection data, integrated with well data from the North West Shelf of Australia, this project will investigate the controls of fluid flow pathways from the scale of individual faults (10’s meters), up to the regional (100’s kilometers). These interpretations will be used to constrain both 2-D and 3-D numerical models to which investigate the timing of episodic changes in fluid flow pressure. Changes in modeled fluid pressures will be used in turn for evaluating the likelihood of fault slip. The key aims of the project will be to investigate:
1) Constrain the structural and stratigraphic structural and stratigraphic heterogeneities in sealing lithologies;
2) Constrain pathways and mechanisms for increasing pore pressure prior to vertical leakage at, or close to structural discontinues, including investigating the transient changes in pore pressures before, during, and after vertical leakage;
3) Investigate the likelihood of changes in pore fluid pressure resulting in fault slip at different depths and pressures within the basin;
4) Consider the implications of vertically connected seal bypass systems for the storage of CO2 in geological sequestration projects.