Advances in Fluid Dynamics of Subsurface Flow of Groundwater, Hydrocarbons, and CO2

Abstract:

In the past, the chemical methods of contaminant hydrogeology have dominated much of hydrogeological thinking. In their wake, understanding the physics of subsurface fluid flow and its application to practice and science seemingly has played a secondary role and it often has been replaced by numerical modelling only.

Building an understanding of the actual physics of subsurface flow beyond numerical modelling, however, is a confusing experience exposing one to conflicting statements from the sides of engineers, hydrogeologists, and, for a decade or more, by the followers of free convection and density-driven flow. Within the physics of subsurface flow a number of questions arise, such as:

• Is water really incompressible as assumed in engineering hydraulics?
• How does buoyancy work?
• Are underground buoyancy forces generally directed vertically upwards or downwards?
• What is the consequential difference between hydrostatic and hydrodynamic conditions?
• What are the force fields causing subsurface flow for water, hydrocarbons and CO₂?
• Is fluid flow really driven by pressure gradients as assumed in reservoir engineering?
• What is the effect of geothermal gradients on subsurface flow?
• Do convection cells and free convection exist on-shore?
• How does variable density flow work?
• Can today’s numerical codes adequately determine variable density flow?
• Does saltwater really sink to the bottom of geologic systems due to its higher density?
• Aquitards create confining conditions and thereby confine fluid movements to aquifers?
• Does more water flow in aquifers than aquitards?

 The presentation will shed light on the maze of conflicting statements issued within engineering hydraulics and groundwater dynamics. It will also present a field case and its numerical modelling of variable density flow at a major industrial landfill site.

The presentation will thereby foster the understanding of the correct physics involved and how this physics can be beneficially applied to practical cases regarding subsurface flow in general, hydrodynamic migration of contaminants, variable density flow, migration of hydrocarbons and CO₂, and to scientific processes in the present and within the geological past.