The Fast Lab

We analyze the displacement of a viscous fluid by a miscible more viscous one in heterogeneous porous media. We performed lattice Bhatnagar–Gross–Krook simulations, which were previously successfully applied to the study of the dispersion of a passive tracer in a stochastic heterogeneous porous medium. In the present situation, the flow is stable (no viscous fingering) and leads to an overall Gaussian dispersion, the coefficient of which decreases as the viscosity ratio increases. The results are in reasonable agreement with the stochastic approach of Welty and Gelhar.

It is well known that particle aggregation can occur in a non-Newtonian (polymeric) fluid during sedimentation but this effect has not yet been documented in a quant. way.We present an exptl. study of the behavior of a few non-Brownian particles settling along their line of centers in a weakly elastic and strongly shear-thinning fluid at low Reynolds numbersInstantaneous velocities of the settling particles have been measured in three polymeric fluids that present different rheol. properties.According to previous works, the behavior of the two particles reveals the existence of a critical initial separation distance under which the particles form a chained doublet.At small separation distances we show that both particles experience an effective constant viscosity but of lower value for the second particle.Particle interactions are successfully described by analogy with the classical approach in a Newtonian creeping flow.Our anal. allows a quant. prediction of the particle positions with time.We also demonstrate that the critical distance for particle aggregation is linked to the fluid relaxation characterized by transient shear viscosity measurements.The same approach shows a good agreement in the more complex case of three particles that will be detailed in part 2 of this work.