Design and Implementation of an Intermediate-Scale Test to Study the Effects of Soil Heterogeneity on Methane Gas Migration

Understanding the soil gas migration in unsaturated/partially saturated soil is vital in several timely problems that include carbon loading to the atmosphere from the bio-geochemical activity and leakage of gases resulting from subsurface activities, hydraulic fracturing, and geologic storage of carbon. This study describes the design and implementation of an intermediate-scale experimental setup to study soil gas migration that is affected by subsurface activity, such as geologic heterogeneity and spatial and temporal variability of soil water content. A 3D intermediate-scale laboratory test tank was packed with sandy soils, and tests were conducted under both homogeneous and heterogeneous packing configurations for comparison. A high spatial resolution distributed network of sensors was installed in the tank. After first saturating the tank, the water was allowed to drain to create static water distribution. The gas was injected at the bottom of the tank at a constant rate of 0.01 l/min. The data from the distributed sensor network allowed us to demonstrate how the spatial variability of the soil moisture controlled by the heterogeneity affects the gas migration pathways through the soil profile and the gas loading to the atmosphere. These types of accurate datasets generated under highly controlled laboratory conditions will be helpful for testing models before field application.