Chemical flooding methods hold particular attraction for recovering the "residual oil" left in the reservoir after waterflooding. This paper describes and compares the results for two promising methods, viz. micellar flooding and alkaline-surfactant-polymer (ASP) flooding processes. Both of these methods have been tested successfully in the field, notably micellar flooding.
Laboratory results are described for micellar floods in consolidated sandstone cores as well as in unconsolidated sand packs, including a two-dimensional model, equipped with horizontal or vertical wells. Floods were also carried out in unconsolidated cores using combinations of an alkali, surfactant and a polymer. Individual slugs were injected sequentially in some of the experiments, while the three components were mixed and injected as a single slug in other experiments. Oil recoveries in the two cases were similar.
Results for the two processes are compared and contrasted, showing that on the basis of oil volume recovered per unit mass of the chemical used, the two processes are similar, with micellar flooding having an edge. However, on the basis of total oil recovery micellar flooding is the superior process, with oil recoveries ranging from 50 to 80% of the oil left in the porous medium after a waterflood. Practical implications of the results are discussed.
Among chemical flooding methods, micellar flooding and alkaline-surfactant-polymer (ASP) flooding processes are particularly effective for recovering a large fraction of the conventional oil (25 °API, or higher) left in the reservoir after a waterflood - which could be as much as 60% of the original oil in place. Many field tests of the micellar flooding process and several of ASP have established the effectiveness of these methods for mobilizing waterflood residual oil.
The present laboratory study compares and contrasts the two processes, based on tertiary floods in sand packs and Berea sandstone cores.
A number of investigators have noted the use of an alkali for reducing the divalent ion content and increasing the negative charge of the rock with a view to reducing chemical loss1–2. Surkalo3 reported the alkaline-surfactant- polymer (ASP) process as an alternative to micellar flooding. Several field tests have also been reported.
Chemical flooding methods are based on improving the mobility ratio, i.e. making the mobility of the displacing flood less than or equal to the mobility of the displaced fluid, and increasing the capillary number, mainly by making the interfacial tension (IFT) between the displacing and the displaced phases as small as possible. Other effects are also present, such as formation of macro- and microemulsions, formation of precipitates, wettability changes, relative permeability shifts, etc. Macroemulsions may improve mobility ratio through drop entrainment and entrapment. At the same time, surfactant adsorption occurs on the rock surface. This is the principal limitation of most chemical flooding methods. The micellar and ASP processes address this problem somewhat differently. A brief description follows.
This process is a combination of the three processes, viz. alkaline, surfactant and polymer flooding, in that three slugs are used in a sequence.
