Predicting Physical Properties of Fluid-Containing Rocks from Percolation Model Results

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0409279WangThe physics of displacement of water by an invading liquid or gas is an importantgeologic and engineering process. Examples include the migration of oil or gas intobrine-saturated rock or remediation of contaminated aquifers by injection of air. Thedistribution of the invading fluid can include intricate fingering due to the inherentrandomness of the pore structure and its influence on capillary forces. A successfulmethod to simulate the invading air is through a pore-scale, modified invasionpercolation model in which the rock's void space is represented by a statisticaldistribution of pore and throat sizes. Each pore is connected to several throats. Thethroat on the air-water interface that is invaded is the one at which the driving potentialsumming gravity, capillary, and viscous forces is greatest. The scientific goal of thisproject is to connect the distribution of the fluid phases obtained from the percolationmodel to predict the elastic and electrical properties of the bulk rock formation. Theinnovation proposed is to use a process-based quantification of fluid saturation at the porescale as the basis for predicting physical properties that are extremely sensitive to thefluid distribution. These predictions are important for inferring the fluid saturations fromgeophysical measurements. The working hypothesis is that the size distribution of thedefending water clusters is critical to the bulk elastic behavior. Small, isolated waterclusters behave in an elastically soft manner because the water is able to flow into nearbyair-filled voids. New laboratory measurements of elastic wave velocities duringevaporative drying are proposed. They and recent electrical resistivity measurementsduring evaporative drying conducted at Louisiana State University will be used tocalibrate and test the modeling process.Broader ImpactsThis research is expected have applications in exploring hydrocarbon reservoirs and inmonitoring remediation of contaminated aquifers. This research will provide key rocklaboratory measurements and modeling tools to simulate the displacement of water by airor gas and then predict the changes in geophysical properties. New data collected onchanges of elastic wave velocities during evaporative drying will be useful to otherresearchers testing their models. The research results will be disseminated throughpublications and oral presentations. The computer codes that will be developed as part ofthe research will be useful to researchers in industry and will be made available on theinternet.