Microvisual Investigation of Foam Flow in Ideal Fractures: Role of Fracture Aperture and Surface Roughness

Abstract

AbstractFoam as a gas-mobility control agent is successful in enhanced oil recovery processes. An emerging application of foam is to aid surfactant solution delivery for EOR in heterogeneous porous media. In fractured reservoirs, foam acts as a blocking agent slowing and redirecting the transport of the aqueous phase in high transmissibility fractures. Foam aids the imbibition of foamer/surfactant solution into the matrix blocks so that remaining oil is drained. The design of such foam treatments for fractured media is an important factor for economic as well as recovery success. In this work we investigate the behavior of foam flow in fractures at various foam qualities and liquid and gas velocities. Laboratory experiments with different fracture replicates etched in silicon micromodels were used. Micromodels allow real time observations of flow behavior with a microscope and provide a fracture geometry that is easily replicated. A plain smooth fracture with different apertures (40 μm and 30 μm), a fracture with variable smooth apertures (either 20 μm or 40 μm) arranged in a checkerboard pattern and a constant-aperture fracture with a rough face were used to observe pre-generated foam in terms of texture, pressure drop and flow behavior. Mobility reduction factors for a wide range of foam qualities and flow rates were analyzed. Measured pressure drops increase linearly with an increase in foam quality up to 90%. At qualities greater than 90%, mobility reduction is only slightly reduced further. In general, mobility reduction factors (MRF) of 10-600 times were measured for low to high quality foams, respectively. Additionally video footage of foam at micro and macro scale is used to tie rheology to bubble shape and size. Study results are useful as input for upscaling of the rheology of foam fractures and for ultimate use in reservoir simulations to design effective chemical EOR treatments for fractured media.