1 Overview

A model of subsurface geology is needed before simulating groundwater flow. The petroleum industry has had better defined procedures for geologic modeling than the groundwater industry, so the Ground Water Project provides this book to review the basic process of subsurface modeling including techniques from both a groundwater and petroleum perspective. Given the commercial interests of the petroleum industry, attention is focused on accurately simulating the volume, flow and extraction of fluids from the subsurface. The techniques described in this book, in particular the concepts of net thickness (the thickness of coarser-grained strata that support fluid flow)  versus gross thickness (the total vertical thickness between bounding units), are not only important to petroleum production, but also relevant to simulating groundwater fluxes, which can be of interest to water resource modelers who are estimating storage volume in aquifers.

Numerical models constructed to simulate contaminant fate and transport require more detailed delineation of geology. For such applications, the distribution of heterogeneous geological properties is needed because contaminants follow preferential paths through connected high hydraulic conductivity zones and many fate and transport processes depend on the interchange of fluids with differing chemistry between zones of differing hydraulic conductivity.

Modeling techniques presented here pertain only to clastic aquifers, which are composed of sediments or sedimentary rocks derived from mechanical weathering, basically some combination of gravel, sand, silt, and clay. These may be unconsolidated (loosely packed, uncemented grains) or consolidated (tightly packed, cemented grains). These techniques do not apply to fractured bedrock, karst, or other aquifers where secondary porosity is the dominant flow pathway.

The groundwater software Visual MODFLOW FLEX from Waterloo Hydrogeologic is used in this book. It is a software program that facilitates groundwater flow modeling with the most commonly used  groundwater flow simulation tool: the USGS MODFLOW code. It also has the advantage of sharing some ancestry with Schlumberger’s Petrel software, an oil and gas industry standard for subsurface geologic modeling. The RockWorks geologic modeling software is also used in this book. It is used to generate a distribution of geologic materials that can be assigned hydraulic properties which are then converted into values for a groundwater modeling grid such as one defined by MODFLOW.


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