Abstract (Invited)

Nonlinear Models of Waves in Granulated Partially Wet Media

V.N.Nikolaevskiy (Institute of Earth Physics RAS, Moscow, Russia)

e-mail: victor@uipe-ras.scgis.ru

The problem of seismic waves in porous seams is extremely actual because of their action at residual oil at water flooding of reservoirs. The effect discovered recently means that relatively weak waves of low frequency can change stability of small drops in flows through porous space. For this, the wave energy has to transmit to much higher frequencies oscillations due to changes of wave modes and/or resonance effects. The simplest explanation is connected with solid friction at the grain contacts and crack edges emitting high frequency waves at any deformation of the material matrix. However, different models are developed in the frame of elastic . viscous theory. Really, wetting of pore space permits to add viscosity and the inertia of individual grains or a fluid, surrounding of gas bubbles, open the possibility for nonlinear models with internal oscillators. Their dynamics leads to internal resonance effects that select the special dominant frequencies and can create high frequency noise. As it is known, in saturated porous media there are two types of elastic P-waves and observed wavelets can belong to one of them. Their roles and effects are changing with gas saturation and depend also on the form of gas presence. If grains can rotate, the Cosserat mechanics will govern one more mode of oscillations (of very high frequency because the specified inertia moment has the order of square root of permeability). The interaction with seismic dispersion branch could lead to one more wave energy exchange. At last, the porous matrix as a multitude of solid particles in contact corresponds to very discrete net of loaded grains. The wave action changes the load distribution and this can be source of additional oscillations. The adequate mathematical models will be suggested and discussed.

Section : 6