Iassonov P., M.S. Candidate. Department of Geological and Atmospheric Sciences, Iowa State University, 253 Science I, Ames, Iowa, 50011-3212.

Numerous observations and laboratory experiments show that low-frequency stress stimulation can significantly enhance mobilization and transport of non-aqueous phase liquids (NAPL) in porous media. However, the physical conditions and mechanisms governing the interaction between the stress (seismic) waves and multiphase flow in porous media are poorly understood, which holds back the development of reliable field techniques. Investigation of the fundamental principles and physical conditions governing the enhanced mobilization and transport of fluids in porous medium under the effect of low-frequency sonic waves is a necessary step to developing such techniques, which can be used in both ecological (e.g., enhanced remediation of contaminated groundwater) and industrial applications (increased efficiency of oil production).

There are several mechanisms thought to be responsible for the observed fluid-sound interaction. Among these mechanisms are the reduction in the effect of capillary forces due to the destruction of surface films adsorbed on pore boundaries, excitation of capillary-trapped oil blobs, coalescence of droplets due to the attraction (Bjerknes) forces induced by vibrations, or peristaltic transport known in physiology. Ultrasound may also reduce the viscosity of fluids due to the low shear stability of some polymeric liquids and due to its heating effect. The enhanced transport also occurs when sound interacts with a NAPL having nonlinear visco-elastic rheology.

The first stage of the project includes description and study of physical mechanisms responsible for accelerated percolation of fluids in presence of acoustic field (these mechanism may include the sound effect on capillary forces, coalescence of ganglia, induced migration of gas bubbles, visco-elastic effects et al.), and derivation of mathematical equations governing the percolation process. Completing of this stage requires extensive computations, primarily solving large systems of PDE. Effective tolls for solving such systems with easy manipulation of input parameters and management of the resulting data (visualization, comparison) would benefit the project by optimizing both quality and timeframe.

The second (prospective) stage of the project includes creation of the filed technique, that would involve development of highly efficient software applications for processing of geophysical data to provide optimal parameters for the application of the method (location(s) of the vibration sources, optimal pressure field in the oil reservoir etc.)

The problem is very complex, and even an investigation of a single factor presents a significant challenge. For example, several models for the peristaltic transport and capillary effects have been developed in the past 10 years, none of them still being able to reasonably explain field and laboratory observations.

The focus of current on-going work is the investigation of the effect of viscoelastic properties of fluids on the enhanced flow induced by vibrations. The solving of the problem is extremely complicated because of the complexity of wave phenomena in a porous media on a macroscopic level, as well as complicated geometry on a pore-scale level. There is also a lack of experimental data on viscoelastic properties of pore-filling fluids of interest. Our preliminary results include calculations for the simplified model of porous rock, giving the order of magnitude of the effect. Additional calculations were performed to estimate the required intensity of the sonic field to achieve significant effect.