Flow Unit Concept--Integrated Approach to Reservoir Description for Engineering Projects

W. J. Ebanks, Jr.

The successful application of secondary and tertiary oil recovery technology requires an accurate understanding of the internal architecture of the reservoir. Engineers have difficulty incorporating geological heterogeneity in their numerical models for simulating reservoir behavior. The concept of flow units has been developed to integrate geological and engineering data into a system for reservoir description.

A flow unit is a volume of the total reservoir rock within which geological and petrophysical properties that affect fluid flow are internally consistent and predictably different from properties of other rock volumes (i.e., flow units). Flow units are defined by geological properties, such as texture, mineralogy, sedimentary structures, bedding contacts, and the nature of permeability barriers, combined with quantitative petrophysical properties, such as porosity, permeability, capillarity, and fluid saturations. Studies in the subsurface and in surface outcrops have shown that flow units do not always coincide with geologic lithofacies.

The flow unit approach provides a means of uniquely subdividing reservoirs into volumes that approximate the architecture of a reservoir at a scale consistent with reservoir simulations. Thus, reservoir engineers can incorporate critical geological information into a reservoir simulation without greatly increasing the complexity of their models. This approach has advantages over more traditional methods of reservoir zonation whereby model layers are determined on the basis of vertical distributions of permeability and porosity from core analyses and wireline logs.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.