Role of Geological Heterogeneity in Poroelastic Deformation of Geologic Medium due to Groundwater Extraction
Present research studied effect of vertical heterogeneity on poroelastic deformation of geologic medium and predicted land subsidence caused by groundwater extraction. One-dimensional numerical modeling of groundwater flow and sediment deformation was done by solving mass balance equations with Darcy’s flow mechanics for water-saturated poroelastic medium. Porosity and permeability of the medium were related using Kozeny-Carman equation. Simulations were conducted for an idealized 130 m thick geologic medium having a vertical sediment gradation ranging from coarse-grained sandstone at bottom to fine-grained siltstone (or mudstone) at top. A constant water production rate was assigned over a 50 m interval at the bottom. Simulations with heterogeneous sandstone/mudstone sequences were compared to homogenous sequences. The comparisons showed that deformation was higher for mudstone compared to sandstone due to less permeable and more compressible nature of mudstone. Another simulation was done using litho-stratigraphic section from the field site to calibrate model prediction with a field deformation data. Land subsidence prediction from the model showed a good match with deformation data from field measurements. Future research will be focused on studying deformation behavior of a poroelastic medium saturated with multiple fluids(water/methane).