Nano-structure of hydrolyzed polyacrylamide strengthened ultra stable nitrogen foam: Lab experiments and molecular dynamics simulation

Abstract

Foam flooding is an extremely effective method of enhanced oil recovery used to address uneven utilization in strongly heterogeneous reservoirs. However, conventional foam is not stable and is unevenly distributed in oil reservoirs during conventional foam flooding. Hydrolyzed polyacrylamide-strengthened nitrogen foam (HSNF) was therefore proposed to overcome the defects of conventional foam flooding. In this investigation, a comprehensive method was utilized to understand the mechanisms of HSNF with regard to its stability and distribution in reservoirs. In situ experimental characterization and molecular dynamics simulations were designed to examine the characteristics of HSNF. Foam stability was analyzed as a function of the viscosity of the liquid phase, adsorption, and pressure for HSNF and conventional foam. Parallel core flooding experiments were conducted to compare the oil recovery efficiencies of HSNF and conventional foam. Molecular dynamics simulations were utilized to examine the nanostructure of HSNF in brine. Foam stability tests demonstrated that foam stability was enhanced by increasing the viscosity and pressure of the liquid phase and reducing the adsorption capacity of the surfactant. HSNF increased the foam half-life by a factor of 1.67–27.1. The parallel core flooding experiments showed that HSNF effectively initiated flow in low-permeability cores to increase the mobilization of oil even when the permeability ratio was 14.86. However, conventional foam only achieved similar performance at a permeability ratio of less than 10.64. The molecular dynamics simulations revealed that the addition of hydrolyzed polyacrylamide improved the uniform distribution of the oil displacement agent in porous media, inhibited the diffusion of nitrogen in the foam system, and enhanced the interactions between the water phase and crude oil. This suggests that HSNF is a promising oil recovery agent for use in low-porosity, low-permeability, and strongly heterogeneous sandstone reservoirs.