Abstract: A Case Study of the Effects of Geological Heterogeneities in a Low Net-To-Gross Fluvial Reservoir

James D. Doyle, T. Jacobsen, A. Jones, D. Kjonsvik, W. England, C. Townsend

Understanding which heterogeneities most strongly influence reservoir performance for a given recovery process can focus data collection early in the life of a field and improve the reliability of reservoir simulation. The relative importance of sedimentary heterogeneities in influencing a waterflood in a low net-to-gross fluvial reservoir is compared to their relative influence on a gas flood in the same reservoir.

Using a combination of stochastic and deterministic modelling tools, geological models are developed with sedimentary architecture detailed in a four-level hierarchy ranging from sedimentary structures to the distribution of channel belts within floodplain deposits. At the lowest level, sedimentary structures are represented with an emphasis on the influence of cross stratification. Flow properties are then upscaled for each process, and the results are applied to the higher levels through the use of pseudo-relative permeabilities and capillary pressures. Experimental design is employed in separate screening studies for water and gas floods to efficiently examine the influence on recovery predictions of seventeen parameters describing sedimentary heterogeneities at different levels of the modelling hierarchy.

Results indicate that significant sedimentary heterogeneity parameters are distributed over the entire range of levels in the modelling hierarchy rather than being concentrated at the level of channel belts which has been the focus of much previous work for this type of reservoir. In a further evaluation, small-scale tectonic heterogeneities are applied stochastically to the reservoir models. The importance of sedimentary heterogeneities is then assessed in the presence of significant tectonic heterogeneity.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994