InSAR measurement and modeling of ground deformation caused by salt water injection in West Texas

As a byproduct of oil and gas production, the wastewater (mostly salt water) 'flowback fluid', is injected into disposal wells. The injection depth should be as deep as possible, otherwise, the harmful wastewater will pollute the groundwater. Fluid injection into the reservoir can increase fluid pressure and decrease effective stress, finally causing surface uplift. Surface uplift found in Ken Regan field, west Texas, is likely caused by salt water injection in a disposal well. Interferometric synthetic aperture radar (InSAR), which is an effective tool for measuring ground deformation caused by injection and withdrawal of fluid, is used to detect this uplift. Multi-temporal ALOS PALSAR data were acquired for time-series InSAR analysis. InSAR results show that the cumulative uplift between January 2007 to March 2011 is about 12 cm. Total injection volume during the time period is up to 8×10⁴ m³. The time series deformation is correlated with the accumulated injection volume, and the high correlation implies the cause of the uplift is wastewater injection. Inverse elastic model and forward pore-elastic model are applied to simulate this deformation. We use Mogi model as the elastic model to roughly estimate the location, volume, and depth of the injection. Monte Carlo method is applied to optimize those parameters to get the best fits of the time series deformation maps. Defmod, a finite element analysis package for modeling crustal deformation, is used to build a pore-elastic model. Rock parameters of different strata such as Young's modulus, Poisson's ratio, and permeability are considered. Given these pre-known parameters and hydrocarbon-related information, we can simulate the ground uplift in a spatio-temporal domain. The pore-elastic model can also help narrow the range of the rock parameters using InSAR derived deformation. Our analysis will provide valuable information about how the ground surface and subsurface reacts to the increased stress from wastewater injection and the hydrogeological characteristics of the oilfield.