RIASSUNTO
Abstract
Polymer augmented alkaline flooding (PAAF) is a relatively new EOR process, and its first version has been defined as injecting an alkaline slug chased by a polymer slug. During the early 1980's the second version of PAAF was introduced, being composed of a single slug of alkaline and polymer blended together, followed by a polymer slug.
A series of corefloods was conducted with alkaline solution, polymer solution, and a blend solution of alkaline and polymer in polymer solution, and a blend solution of alkaline and polymer in linear and radial Berea sandstone cores for studying the mechanisms of the second-version PAAF process. Sodium hydroxide was used as the alkaline agent, and the polymer was 30-percent hydrolyzed polyacrylamide. The efficiency of the second-version PAAF was compared with that of both alkaline flooding and polymer PAAF was compared with that of both alkaline flooding and polymer flooding alone.
Results showed that the synergistic effect of the second-version PAAF provides better efficiency than either alkaline or polymer alone for enhancing oil recovery. This chemical system of alkaline and polymer blended together yielded more oil recovery with increasing blend slug size.
Also, a phenomenon never before reported was observed. It is a visible residual oil saturation ring next to the region cleaned of oil adjacent to the injection sand face, and it was observed in both linear and radial cores after the application of the second version PAAF process. The size of this oil ring is similar to the size of the blend slug of alkaline and polymer.
Introduction
Since the early 1900's alkaline agents have been considered among chemicals to be added to floodwaters to remove oil from pore walls and to mobilize the mechanically entrapped oil globules or ganglia in porous media. The primary requirement for alkaline flooding application is that the crude oil must contain acidic components which will react favorably in an alkaline medium. The oil recovery mechanisms of alkaline flooding postulated to date are (1) in-situ surfactant generation (saponification) by neutralization, (2) reduction of the interfacial tension (IFT) at the oil-water interface, (3) wettability alteration, (4) emulsification with entrainment, (5) emulsification with entrapment, (6) emulsification with coalescence, (7) oil phase swelling, and (8) breaking out the rigid films. Also, alkali agent consumption due to reactions with reservoir fluids and rocks has been considered as the most important disadvantage.
There have been a number of alkaline flooding field trials with different base chemicals throughout the world. However, the recovery of additional oil has been less than 6 to 8 percent of the pore volume (PV), and generally around 1 to 2 percent of the pore volume (PV), and generally around 1 to 2 percent PV, mainly because of excessive alkaline consumption and percent PV, mainly because of excessive alkaline consumption and unfavorable mobility ratios resulting in poor sweep and displacement efficiencies.
Since the early 1960's polymers have been added to some floodwaters to accelerate the recovery of oil which would otherwise be produced after infinite water throughput during conventional waterflooding. Polymers are not able to displace trapped oil droplets and remove oil from the rock surface to decrease residual oil saturation.
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