Fault Seal, Migration and Accumulation: An Integrated Approach

Stephen Dee¹, Dan Carruthers², Brett Freeman¹, and Graham Yielding^3
1 Badley Geoscience Ltd, Lincolnshire, United Kingdom
² The Permedia Research Group Inc, Ottawa, ON
³ Badley Geoscience Ltd, N/A, United Kingdom

Fault bounded traps in siciliclastic rocks depend on capillary seal to retain hydrocarbons. Estimates of fault zone properties such as SGR (shale gouge ratio) or CSP (clay smear potential) can be used, in turn, to estimate threshold capillary entry pressure. Modelling of fill spill and reservoir filling history then depends on the effectiveness of that calibration. In this paper we use capillary-based migration modelling to test the sensitivities in the calibrations between fault-zone property and capillary entry pressure. Petroleum migration occurs at geological timescales and solving petroleum flow trajectories and emplacement patterns can be accomplished with modified invasion percolation techniques. These algorithms honour the salient controls on petroleum flow while having the advantage of low computation times. Speed of processing encourages risk analysis by facilitating rapid evaluation of multiple scenarios for the same geometric configuration, leading to an assessment of the uncertainties involved in fault seal analysis. The migration model is defined as a dense, regular, 2D or 3D grid of properties. Faults are introduced directly into the model by their capillary properties at the appropriate grid cell. Petroleum fluids are introduced at pre-specified locations and are free to move according to the balance of the local water pressures, petroleum buoyancies and resistive capillary pressures. We discuss a set of tightly constrained examples that demonstrate the heterogeneity of fault-flow behaviour; for example a single fault may be conductive or transmissive, horizontally or vertically at different locations on its surface. We also examine the migration paths in terms of the importance or stair-stepping versus vertical conductive flow.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005