Peter J. Eadington2
(1) CSIRO Petroleum Resources, North Ryde, Australia
(2) CSIRO Petroleum Resources, Sydney, Australia
In siliciclastic rocks, secondary oil migration that is dominated by gravity and capillary forces is confined by cyclic changes of displacement pressure in sand-shale sequences. An oil migration pathway will descend or climb within the carrier bed depending on the sedimentary facies and profile of displacement pressures.
An algorithm has been formulated to derive displacement pressure profiles for shaly sandstone. The displacement pressure is sensitive to sedimentary facies and depositional processes. A pore aperture parameter has been derived to determine displacement pressure in sandstone from common geophysical well logs.
The method involves the empirical estimation of permeability from well logs, and the derivation of a displacement pressure log for the target carrier bed interval. The oil migration confinement surfaces and associated oil migration pathways can be identified by comparing the displacement pressure log and the expected buoyancy pressure gradient for the migrating hydrocarbon. Evaluation of oil show data using the algorithm determines whether their spatial distribution within the carrier bed is indicative of secondary oil migration by gravity-capillary force dominated multiphase flow or by another process.
The algorithm has been applied to evaluate exploration wells in the Vulcan Sub-basin, in the NW Shelf of Australia. Preliminary results indicate that the method is effective in determining the confinement of oil migration. Potential and actual oil migration pathways have been determined using a suite of oil show data including well-site fluorescence, GOI™ (Grains containing Oil Inclusions) and solvent extracted hydrocarbons.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana