The influence of fault permeability on single-phase fluid flow near fault-sand intersections: Results from steady-state high-resolution models of pressure-driven fluid flow
- Cornell Univ., Ithaca, NY (United States)
- Australian National Univ., Canberra (Australia)
By integrating numerical analysis with field information, we have developed realistic cross-sectional models of faulted sand-shale sequences at 3 km or greater depth to investigate how fluid-flow patterns vary with fault permeability. Simulated (isotropic) permeability ranges for shale were 10{sup {minus}19} to 10{sup {minus}17} m{sup 2} (porosity {phi} = 10-35%) and for sand were 10{sup {minus}14} to 10{sup {minus}12} m{sup 2} ({phi} = 20-25%). Fault permeability ranged between 10{sup {minus}21} to 10{sup {minus}1} m{sup 2} among four models. Our results were obtained with a novel multigrid finite-element technique allowing the rapid solution of fluid flow on very fine meshes that represent thin faults and interlayered sand-shale strata with their correct aspect ratios (up to {ge}800:1) and incorporate permeability contrasts with the country rock of up to ten orders of magnitude. Pressure-driven flows have been calculated for boundary pressures, simulating a transition from hydrostatic to 0.8 lithostatic with increasing depth. The four high-resolution models show that fault permeability and juxtaposition relationships across the fault control hydrodynamic fluid-flow patterns. The greater the difference between the permeability of the fault and that of the undeformed country rock, the more the flow patterns differ from those predicted by a simple geometrical analysis of sand-juxtaposition relationships across the fault, assuming that flow occurs only across overlapping sands. In our small-scale models and in another idealized basin-scale model of pressure-driven fluid flow, the direction of flow in faulted sand units can be reversed by changing the fault permeability changed with time.
- OSTI ID:
- 415005
- Journal Information:
- AAPG Bulletin, Vol. 80, Issue 11; Other Information: PBD: Nov 1996
- Country of Publication:
- United States
- Language:
- English
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