Effects of air injection on flow through porous media: Observations and analyses of laboratory‐scale processes

Abstract

[1] The effects of air injection on flow through porous media were explored in a series of 1-m and 2-m laboratory flow cells. Our motivation was to examine air barriers as an alternative to hydraulic barriers to inhibit saline intrusion in coastal areas. Steady flow conditions were created in homogeneous and heterogeneous unconsolidated sand systems. Dry air was injected at progressively higher flow rates through a well in the center of each flow cell. Discharge and NaClÀtracer breakthrough data were measured at the outflow reservoir of each cell. In addition, a dye tracer was used to visualize the flow patterns. In all cases, air injection was found to produce stable, low-conductivity barriers that reduced discharge by an order of magnitude or more. Effective hydraulic conductivity values determined from discharge and hydraulic head data showed exponential declines with increased air-injection rates in all cases. Numerical simulation was used to quantify hydraulic conductivity and effective porosity values in the saturated and aerated regions created by air injection, and to study advective flow behavior. Pore-filling cement formed in the air-injection region and was analyzed to determine its composition, mass, and volume. Approximately 60% of the cement consisted of soluble minerals, and 40% was less soluble carbonates. Evaporation and increase in solution pH due to stripping of CO 2 by the injected air were responsible for creating the cement. The cement occupied <10% of the pore space in the sand-cement aggregate. Both the air and mineral pore-fillings dissolved when air injection ceased, indicating that both barriers are temporary. These results serve as a preliminary proof of concept that air-injection barriers might effectively inhibit undesired subsurface flow, such as saline intrusion or contaminated groundwater.

Entrapped air effects on dipole flow test in sand tank experiments: Hydraulic conductivity and head distribution

“…However, processes at this scale are very important for numerous applications, including in situ remediation (Fry et al, 1996), interpretation of pumping tests in unconfined aquifers (e.g., Moench, 1997), protection of coastal aquifers from saline intrusion (Dror et al, 2004), etc. Recently, Vogel et al (2000), Silliman et al (2002), Dunn and Silliman (2003), and Dror et al (2004), indicated an urgent need for experimental studies that assess K in the nearsaturation conditions. Zlotnik and Zurbuchen (1998) proposed to explore the potential of DFTs to detect entrapped air near the water table.…”

The Local Geometry of Gas Injection into Saturated Homogeneous Porous Media

“…The injection of gases below the water table in sedimentary aquifer materials, or sparging, is a method commonly employed to reduce contamination with volatile compounds (e.g., Reddy et al, 1999;Lazik et al, 2002;Reddy and Tekola, 2004), and has been proposed as a method to emplace trapped gas to promote biological processes and to reduce permeability (e.g., Fry et al, 1997;Dror et al, 2004). There have been several very useful articles devoted to observational study of the geometry of gas invasion in sandy materials in homogeneous materials (e.g., Clayton, 1998;Elder and Benson, 1999;Roosevelt and Corapcioglu, 1998).…”

In‐Well Degassing Issues for Measurements of Dissolved Gases in Groundwater

“…The measurement and sampling of dissolved gases in shallow groundwater, which can be acquired from the atmosphere (e.g., Christiansen 1944; Ryan et al 2000), subsurface biogeochemical reactions (e.g., Reynolds et al 1992), and even human introduction (e.g., Dror et al 2004), are important for a variety of reasons. These include use in groundwater age‐dating (e.g., Aeschbach‐Hertig et al 1999) and flow path tracing (e.g., Wilson and Mackay 1996) and for monitoring biogeochemical reactions occurring in the subsurface (as discussed by Ryan et al 2000), such as denitrification (e.g., Blicher‐Mathiesen et al 1998), natural attenuation processes for petroleum hydrocarbon plumes (e.g., Amos et al 2005), or iron wall treatment of organic compounds (Zhang and Gillham 2005), for examples.…”