The physics of displacement of water by an invading liquid or gas is an important geologic and engineering process. Examples include the migration of oil or gas into brine-saturated rock or remediation of contaminated aquifers by injection of air. The distribution of the invading fluid can include intricate fingering due to the inherent randomness of the pore structure and its influence on capillary forces. A successful method to simulate the invading air is through a pore-scale, modified invasion percolation model in which the rock's void space is represented by a statistical distribution of pore and throat sizes. Each pore is connected to several throats. The throat on the air-water interface that is invaded is the one at which the driving potential summing gravity, capillary, and viscous forces is greatest. The scientific goal of this project is to connect the distribution of the fluid phases obtained from the percolation model to predict the elastic and electrical properties of the bulk rock formation. The innovation proposed is to use a process-based quantification of fluid saturation at the pore scale as the basis for predicting physical properties that are extremely sensitive to the fluid distribution. These predictions are important for inferring the fluid saturations from geophysical measurements. The working hypothesis is that the size distribution of the defending water clusters is critical to the bulk elastic behavior. Small, isolated water clusters behave in an elastically soft manner because the water is able to flow into nearby air-filled voids. New laboratory measurements of elastic wave velocities during evaporative drying are proposed. They and recent electrical resistivity measurements during evaporative drying conducted at Louisiana State University will be used to calibrate and test the modeling process. Broader Impacts This research is expected have applications in exploring hydrocarbon reservoirs and in monitoring remediation of contaminated aquifers. This research will provide key rock laboratory measurements and modeling tools to simulate the displacement of water by air or gas and then predict the changes in geophysical properties. New data collected on changes of elastic wave velocities during evaporative drying will be useful to other researchers testing their models. The research results will be disseminated through publications and oral presentations. The computer codes that will be developed as part of the research will be useful to researchers in industry and will be made available on the internet.
