Particle enhanced foam flow in porous media near the critical micelle concentration

Abstract

This thesis was performed in the framework of ErasmusMundus EU-INDIA scholarship programme. The main goal is to elucidate particle enhanced foam flow (surfactant water and nitrogen gas) in porous media near the critical micelle concentration. The thesis is divided in four parts: in the first part the modeling of foam flow is investigated, in the second part variables affecting the steady state pressure drop during foam flow are discussed, in the third part the stability of ash particles in the bulk dispersion is tested and in the final part, the effect of the particles on foam flow stability in porous media is experimentally studied. During the period of the study, the set ups for fluid flow and laser scattering of liquids are built and calibrated. We measured pressure drop histories before and after injection of ash particle dispersions with nitrogen gas (N2) across the measurement points in unconsolidated sand packs (1860 and 130 Darcy) and a Bentheimer sand stone core (3 Darcy). This was carried out for various surfactant concentrations (0.0375, 0.075 and 0.15 w/w%), for various gas and surfactant solution velocities (0.27-3.97 m/day), for two salinities (0, 0.5M NaCl) and for two pH values (6.5, 3.0). We used a mathematical formulation with a bubble population function by history matching the experiments. The two-phase flow model that leads to four equations, viz., a pressure equation, a water saturation equation, a bubble density equation and a surfactant transport-adsorption equation can describe the pressure drop during the foam flow experiments. Within the model, the rate of change of bubble density during the transient state can be equated to the bubble density generation function plus the terms accounting for the bubble transport, i.e., by convection and diffusion divided by the porosity saturation product. The effect of the variables (e.g. permeability) on the foam flow is studied by using symbolic regression. We applied a Monte Carlo method (Bootstrap) to calculate the parametric uncertainties. The data driven model obtained without prior knowledge of an underlying physical process can elucidate the general behavior and hierarchy of the variables affecting the steady state pressure drop. The statistical model gives the variable spaces for which more experiments are needed. The trends obtained from the subset of data cannot be derived from the complete data set purely on statistical grounds. To use ash particles in foamflow through porous media we measured their colloidal stability when surfactant is present or absent in the dispersion. We measured properties of dispersions, viz., zeta potential, sedimentation-coagulation behavior, light absorption and particle size for pH values ranging from3 to 11. For the optimal stability of an ash dispersion, we recommend an alkaline mediumwhen surfactant is absent and an acidic medium, when surfactant is present. An ash particle dispersion alone with nitrogen gas cannot generate foamin porous media. The flow of ash particles with foamin porous media (Bentheimer and sandpack) is related to the colloidal stability of the ash dispersion. We observed tiny change in the permeability of the porous media after foam flow experiments with ash particles.