Visualization of Foam Migration Characteristics and Displacement Mechanism in Heterogeneous Cores

Foam can improve the sweep efficiency and increase the oil displacement efficiency, which plays an important role in the oil exploitation of heterogeneous reservoirs. The ordinary core flooding experiments can not reflect the transport characteristics of foam inside the porous. While, experimental research on the foam displacement mechanism is mainly carried out by using a microfluidic visualization model, which is quite different from the actual reservoir conditions. In this study, a new method to visually study the displacement mechanism of foam in a heterogeneous core was established. MR(magnetic resonance) images and T2 (transverse relaxation time) spectrum were obtained for a heterogeneous core during foam injection. The corresponding relationships between the relaxation time region and the fluid signal in the large/medium/small pores of the core were established and then used to describe the migration characteristics of foam in pores of different sizes. The effects of the foam parameters on the apparent viscosity of the foam and the sweep efficiency in high- and low-permeability layers were studied. The results showed that injection rates, gas-liquid ratios, and surfactant concentrations, could obviously influence the ability of foam to block the large pores and enhance the sweep efficiency in the medium and small pores. The injection parameters affected the apparent viscosity of the foam and the water saturation in each layer of heterogeneous core. It was demonstrated that the method could be used to screen the injection parameters of foam and evaluate the adaptability of the foam types in heterogeneous cores.