| A positive correlation between earthquakes and changes in oil production from wells, observed in the late 1950s, resulted in the first attempt to use the energy of seismic waves to improve oil recovery. Recently, low-frequency stress wave pulsing has been receiving increasing attention as a means for the removal of nonaqueous liquids from groundwater aquifers. Little is known, however, about the partitioning of vibrational energy between subsurface fluids and the rock/soil matrix, which hinders advances in developing seismic wave stimulation as a reliable field technique for hydrocarbon recovery and environmental remediation. Although a number of laboratory investigations have been performed, they were limited in their ability to provide meaningful results without knowing beforehand what conditions are optimal and what level of outcome can be achieved in the field. This study represents the first step in developing a rational theory to explain mechanisms governing the interactions between stress (seismic) waves and multiphase flows in porous media under a pressure-pulsing boundary condition. The goal is to provide a fundamental physical basis for effective use of seismic wave stimulation.; In modeling multiphase flows in porous media, a critical issue is the proper mathematical description of the interactions among the constituents. Numerous studies of subsurface multiphase flows have made contributions toward developing constitutive relationships needed for representing these interactions, but inertial coupling between the different phases has not been taken into consideration in current hydrological models. In the present study, the acceleration vectors of fluids relative to the solid phase were treated as independent variables to construct constitutive equations. To assure that the second law of thermodynamics is not violated, it was demonstrated that the functional dependence of the Helmholtz free energy for each phase in the entropy inequality was not altered by the inclusion of relative acceleration vectors as independent constitutive variables. The resulting momentum balance equations governing immiscible two-phase flows in deformable porous media then account for the reaction of fluids to an acceleration of the solid matrix.; A mathematical model was proposed to quantify the impact of elastic wave excitation on a fluid-containing porous medium by formulating a boundary value problem for a core sample packed with unconsolidated sand permeated by water, a simpler system than current laboratory experiments investigating seismic stimulation. (Abstract shortened by UMI.)... |
