ALKALINE FLOODING OF LOW ACID NUMBER CRUDE OIL

Alkaline flooding is the earliest chemical flooding method reported. Its usage
was in the beginning limited to reservoirs with high acid numbers because of the
assumption that recovery is due to in situ surfactant that is formed from alkali-acidic
components reactions. Alkaline flooding while succeeded in increasing microscopic
sweep did not reduce the mobility ratio. Consequently, the macroscopic sweep was
not improved. Later work proved that improvement in recovery was not dependent
on high acid number. This work aims to relate the increase in recovery by alkaline
flooding due to end-points relative permeability changes and formation of 1FT
reducing components that do not depend on acids.
Dulang crude, Waxy crude and Sodium Hydroxide as the alkaline solution
were tested. Removals of acids from the crudes were effected by adding 2-
Ethylimidazole in Ethanol with the crudes. The extracted and un-extracted crudes
were used in alkaline flooding using Berea sandstone cores with initial water
flooding; End-points relative permeability changes and incremental recoveries from
alkaline flooding were measured from the displacement tests for comparisons. Core
properties after displacements were also inspected for any effective porosity and
permeability alterations. Effluents from the displacement test were tested for alcohol
formation which was expected to be a major Interfacial Tension (1FT) reducing
component.
Synthetically mixed crude oil (n-Heptanes/ Butanol/ Oleic Acid) were tested
with alkaline solution to identity component which affected the 1FT the most.
Emulsion stability test was also conducted using Dulang crude with alkaline solution
to quantity the Interfacial Viscosity (IFV) which could play a major role in
improving the volumetric efficiency.
Incremental recoveries from alkaline flooding for un-extracted crude were
around 7- 10% whereas for the extracted crude 5-6% incremental. End-points
relative permeability to the displacing fluid, Krw' was reduced to around 30 - 50%
in alkaline flooding compared to water flooding in all the displacement tests, thus
leads to a lower Mobility Ratio of 0.5 - 0. 7 in the case for alkaline flooding. pH
detection of more than 0.5 indicates a high possibility of alcohol formation from the
effluents of the displacement runs. Effective permeability of the core sample prior to flooding increased after the displacement test with an increase of around 0.2 - 13%
increment from all cases.
From all the synthetic crude mixture, Butanol as one of the type of alcohol,
lead to the greatest 1FT reduction of 0.14 Dynes/em at 5% wt concentration. This
confirmed that even if very small amount of alcohol was formed, it can lead to a very
low 1FT. From emulsion stability test, at 2 % wt concentration of alkaline, the
emulsion formed was the most stable giving the longest time for separation of around
33 minutes. This explained the stability of emulsion droplets formed in alkaline
flooding which improved the volumetric efficiency thus leading to a higher oil
recovery.
Alkaline flooding still offers a cheap alternative to other interfacial tension
(1FT) reducing chemical process. Well defined relationships between the recovery
improvements to key mechanisms in alkali flooding can be valuable in designing
flooding processes using alkali as part of alkali polymer or alkali-surfactant-polymer
flooding.