Oil recovery from subterranean spaces is initially accomplished by pumping or permitting the oil to flow to the surface of the earth through wells drilled into the oil-bearing stratum.
Oil can be recovered from such producing zones only if certain conditions exist—there must be adequate permeability or interconnected flow channels through the pore network of the oil-bearing stratums to permit the flow of fluids therethrough, and recovery efficiency (RE).
In the primary oil recovery stage, the RE is influenced by the natural energy or drive mechanisms present, such as water drive, gas cap drive, gravity, drainage, liquid expansion, and relative permeability of reservoir formation and combinations thereof within the formation, and this natural energy is utilized to recover petroleum. In this primary stage of oil recovery, the oil reservoir natural energy drives the oil through the pore network toward the producing wells and it is pumped out to the surface.
When natural energy source is depleted, or did not exist in the first place, some supplemental form of artificial energy must be added to continue RE. Waterflooding is a common system to push oil from one depleted well to another depleted well but does not displace oil with high efficiency since water and oil are immiscible and the interfacial tension between water and oil is quite high. Neither the properties nor the location of the remaining residual oil are adequately understood nor are the technologies to reach, mobilize and displace droplets of oil trapped in small capillaries in the reservoir adequately understood.
Accordingly, waterflooding has produced incremental oil recovery amounting to about additional 10 to 15% of the original oil in place (OOIP). Efforts have been made to utilize certain chemicals, mostly surfactants, to decrease the interfacial tension (IFT) between the water being injected and the reservoir oil, followed by research and study of imbibitions and capillary forces in order to displace the trapped oil in the underground formation and bring it to the surface. Such a technique is referred to as surfactant flooding.
However, problems have occurred with such waterflooding and have not been not solved by surfactant flooding, mainly bypass of fluids through the oil interphase structure wherein the oil phase breaks down to oil droplets due to changes in interfacial tension, imbibitions, and capillary forces between oil and water, with the oil droplets becoming trapped in the subterranean structure. Though chemicals flooding added RE, it does not solve the bypass (“fingering”) of fluids through the oil. No satisfactory stable displacement material or technique has been found to overcome the bypass of the fluid through the oil. The present discovery provides a process and a method which overcome that obstacle.
U.S. Pat. No. 4,811,791, U.S. patent application Ser. No. 07/322,601 and U.S. Pat. No. 5,244,574 are based on reducing interfacial tension (IFT) capillary forces, mainly between oil and water, to recover oil from different physical states (oil reservoir, oil spill on water, contaminates oil wells and surfaces). In the '601 application, soybean lecithin described in example 23 was dispersed as small unilamellar vesicles (SUV). It was discovered that using surfactant G23 on water broke up a continuous thin oil layer spread on top of water phase; into discrete oil droplets each of which is surrounded by monomolecular layer of phospholipids to enable recover oil spills on water.