Enhanced recovery of a viscous oil with a novel surfactant

Steam-based recovery methods are usually employed to recover heavy and viscous oils, but they are not efficient in deep and thin oil reservoirs. Chemical flooding is studied here to improve recovery of a viscous oil (about 300 cp at the reservoir temperature of 70 degrees C) from a thin, high permeability, unconsolidated reservoir. A large number of novel short-hydrophobe based surfactants were designed and synthesized. As these surfactants do not require expensive aliphatic alcohols for their synthesis, they are likely to be less costly than conventional anionic surfactants. Only phenol hydrophobe-based non-ionic surfactants with varying number of propylene oxide (PO) and ethylene oxide (EO) groups are discussed in this paper. These surfactant molecules were investigated for their aqueous stability, interfacial tensions (IFT) with a viscous crude oil, and oil recovery from sandpack or sandstone cores. Surfactant phase behavior experiments with viscous crude oil showed low IFT (not ultralow) for single surfactant systems. A chemical formulation using only a single surfactant (Phenol-7PO-15EO) was chosen for corefloods in sandpacks and sandstone cores. Water flood recovered about half of the original oil and reduced the oil saturation to about 48% in the high permeability sandpacks. The tertiary surfactant polymer flood with Phenol-7PO-15EO increased the cumulative recovery to 99% for sandpacks. The oil recovery was insensitive to injection brine salinity in the range studied. As the permeability decreased, the tertiary oil recovery decreased. Surfactant-polymer formulations with this surfactant can be recommended for high permeability sandstone reservoirs with viscous oils, but not for sub-Darcy sandstones.