7 Building a Static Model from Facies Mapping

A method frequently used for capturing heterogeneity in petroleum static models is facies mapping. Geological facies are assemblages of rocks, sediments or soils with a common origin and geologic history, which in this context would lead to similar hydrological behavior. For example, in a fluvial system, floodplain sediments would tend to have abundant fine-grained, layered muds, creating low hydraulic conductivity, and ratio of vertical to horizontal connectivity much less than one. Conversely, a gravel point bar deposit would have a high hydraulic conductivity with the ratio of vertical to hydraulic conductivity closer to unity. In facies mapping, each grid cell is assigned a facies code, which is then “mapped” to a corresponding set of hydraulic parameters (Figure 16).

Hydraulic conductivity properties from facies mapping
Figure 16 – Hydraulic conductivity properties from facies mapping (Brandenburg, 2020).

Of course, the facies are only known at the location of the boreholes; the rest must be assigned by some process. In the simplest scenario this is assigned based on the intuition of the modeler. However, many different but equally valid facies maps could be developed. This is the basis for more advanced geostatistical models that simultaneously honor both statistical constraints and geologic principles. Some of these models are very complex and represent the types of heterogeneity observed in carefully measured rock outcroppings and other geological studies at a much finer scale that the grid resolution of the flow model. Using this as the basis for a flow model requires a quantitative upscaling technique to make sure that the fine-scale flow properties are retained in the coarser grid.


Geologic Frameworks for Groundwater Flow Models Copyright © 2020 by J.P. Brandenburg. All Rights Reserved.