Abstract: Using Facies to Distribute Reservoir Properties: Hybrid Models of Fluvio-Deltaic Deposits in Prudhoe Bay Field, Alaska

James A. Lorsong, J.P. Bhattacharya, R. S. Tye

Traditionally, spatial distributions of porosity and permeability have been modeled by interpolating well data. In contrast, hybrid models use the spatial distribution of facies as a template for distributing reservoir properties. This results in more realistic distributions because facies define natural categories of properties, and their spatial distributions are more predictable.

Hybrid models were used to evaluate infill drilling benefits in fluvio-deltaic strata at Prudhoe Bay. Matching simulated flow to reservoir performance in the gravity drainage area required a detailed deterministic model. Facies association units, as determined from cores, well logs, and surveillance data, were mapped in 32 layers conforming to large shales that dominate recovery. Layer maps were then discretized into a fine grid. Reservoir properties were generated with variograms and substituted into the grid according to facies associations. Finally, properties were rescaled to a coarser grid for flow simulation.

In the waterflood area, quantifying effects of variable stratigraphy on sweep efficiency required a model in which multiple, equiprobable descriptions could be evaluated. Facies association units were modeled as rectangular objects stacked according to transition probabilities. Heuristics governed lateral relationships and overlap among objects at similar stratigraphic levels. Variations within facies associations were detailed in finely gridded object models in which properties were assigned by lithofacies. Properties rescaled from the fine-scale models were then substituted into a coarser flow simulation grid according to facies associations. Flow simulations of several facies arrangements indicated a range of waterflood recoveries.

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