Particle detachment from the rock during suspension transport in porous media was widely observed in laboratory corefloods and for flows in natural reservoirs. A new mathematical model for detachment of particles is based on mechanical equilibrium of a particle positioned on the internal cake or matrix surface in the pore space. The torque balance of drag, electrostatic, lifting and gravity forces, acting on the particle from the matrix and the moving fluid, is considered. The torque balance determines maximum retention concentration during the particle capture. The particle torque equilibrium is determined by the dimensionless ratio between the drag and normal forces acting on the particle. The maximum retention function of the dimensionless ratio (dislodging number) closes system of governing equations for colloid transport with particle release. One-dimensional problem of coreflooding by suspension accounting for limited particle retention, controlled by the torque sum, allows for exact solution under the assumptions of constant filtration coefficient and porosity. The explicit formulae permit the calculation of the model parameters (maximum retention concentration, filtration and formation damage coefficients) from the history of the pressure drop across the core during suspension injection. The values for maximum retention concentration, as obtained from two coreflood tests, have been matched with those calculated by the torque balance on the micro scale.

Using Kaluza-Klein theory we study the quantum mechanics of a scalar particle in the background of a magnetic cosmic string and in the background of a chiral cosmic string. We show that the wave functions, the phase shifts, and scattering amplitudes associated with the particle depend on the global features of those spacetimes. These dependences represent gravitational analogues of the well-known Aharonov-Bohm effect. In addition, we discuss the Landau levels in the presence of a cosmic string in the framework of Kaluza-Klein theory. ͓S0556-2821͑99͒03610-3͔

Flow of suspensions in porous media with particle capture and detachment under alternate flow rates is discussed. The mathematical model contains the maximum retention concentration function of flow velocity that governs the particle release and is used instead of equation for particle detachment kinetics from the classical filtration model. An analytical model for suspension injection with alternate rates was derived, and a coreflood by suspension with alternate rates was carried out. The modelling and laboratory data are in a good agreement, which validates the modified particle detachment model with the maximum retention function.

Using Kaluza-Klein theory we study the quantum mechanics of a scalar particle in the background of a chiral cosmic string and of a magnetic cosmic string. We show that the wave functions and the energy spectra associated with the particle depend on the global features of those space-times. These dependences represent the analogs of the well-known Aharonov-Bohm effect. This effect appears as the sum of two contributions, one of gravitational origin and the other of electromagnetic origin. * E-mail: valdir@fisica.ufpb.br 253 Mod. Phys. Lett. A 2000.15:253-258. Downloaded from www.worldscientific.com by FLINDERS UNIVERSITY LIBRARY on 02/06/15. For personal use only.

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