Formation-scale migration pathways

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Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Critical elements of the petroleum system
Chapter Migration of petroleum
Author Martin D. Matthews
Link Web page
Store AAPG Store

Flow of an immiscible phase through a series of beds does not proceed uniformly but occurs preferentially through beds of higher permeability when possible. It is dependent on the capillary properties of individual beds, the proportion of higher- to lower-permeability beds, and spatial relationships of beds to the principal flow directions (bed-parallel and bed-perpendicular). These factors are similar to the factors reservoir engineers use to characterize reservoir heterogeneity. They are, however, more difficult to assess because of the uncertainty of the characteristics of low-permeability rocks. The knowledge base is currently undergoing rapid change.

Bed orientation control of flow

The effect of bedding geometry on permeability direction and magnitude is significant. The table below shows how bedding orientation controls flow of hydrocarbons during migration.

If bed orientation is… then the flow is…
parallel to the flow direction principally controlled by the most permeable units
perpendicular to the flow direction principally controlled by the least permeable units
randomly aligned to the flow direction not preferentially focused

Bed-parallel vs. bed-perpendicular flow

Figure 1 Difference in relative permeability at varying water saturations for bed-parallel vs. bed-perpendicular multiphase fluid flow in a wavy bedded rock. After Ringrose and Corbett.[1] Copyright: Geological Society.

The crosspiot in Figure 1 shows the difference in relative permeability at varying water saturations for bed-parallel vs. bed-perpendicular multiphase fluid flow in a wavy bedded rock. The water saturations need to be much lower in bed-perpendicular flow to achieve the same relative permeability. The flow within a bed is a function of the proportions of end-member lithologies, their permeability and capillary pressures, and the orientation of the beds to the direction of the flow.

See also

References

  1. Ringrose, S. P., and P. W. M. Corbett, 1994, Controls in two phase fluid flow in heterogeneous sandstones, geofluids, in Parnell, J., ed., Origin, Migration, and Evolutions of Fluids in Sedimentary Basins: Geological Society Special Publication no. 78, p. 141–150.

External links

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Formation-scale migration pathways
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