Nanoparticle-Stabilized Foams for High-Temperature, High-Salinity Oil Reservoirs

Abstract

Abstract The goal of this work is to develop foams stabilized by a combination of nanoparticles and surfactants for high-temperature, high-salinity reservoirs. Two types of silica nanoparticles (LNP1, LNP2) with different grafted low molecular weight ligands/polymers were used. First, aqueous stability tests of these formulations were performed at high-temperature (80 °C) and high-salinity conditions (8 wt% NaCl and 2 wt% CaCl2). The screened nanoparticles were used in combination with a surfactant. Second, bulk foam tests were performed to evaluate their foaming performance in bulk. Finally, oil displacement experiments were conducted in an in-house, custom-built 2D sand pack with flow visualization. The sand pack had two layers of silica sand — top layer with 40-70 mesh and bottom layer with 100-120 mesh, which resulted in a permeability contrast of 6:1. Water flood with subsequent foam flood was performed. The grafting of low-molecular-weight polymers/ligands on silica nanoparticle surfaces resulted in steric stabilization under high-temperature and high-salinity conditions. In the oil displacement experiments in the layered sand packs, the water flood recoveries were low (~33% OOIP) due to channeling in the top high-permeability region, leaving the bottom low-permeability region completely unswept. Foam flooding with just the surfactant leads to a drastic improvement in sweep efficiency. It resulted in an incremental oil recovery as high as 43.3% OOIP. Different cross-flow behaviors were observed during foam flooding. Significant cross-flow of oil from low-permeability region to high-permeability region was observed for the case of surfactant. Conversely, the LNP2-surfactant blend resulted in no crossflow from the low permeability layer with complete blocking of the high-permeability region due to the formation of in-situ emulsion. Such selective plugging of high-perm channels via nanoparticles with optimum surface coating has significant potential in recovering oil from heterogeneous reservoirs.