What are the pros and cons of adding an alkaline agent to the injected surfactant-polymer solution?
Short Answer:
Pros: Better overall performance
Cons: Potential complications
Long Answer:
Pros:
1. If the crude oil has the correct components, the alkaline agent can react with those components to develop in-situ surfactants. The in-situ surfactants developed will reduce or eliminate the amount of purchased surfactant required and, therefore, reduce purchased chemical cost.
2. Injected alkali will react with the reservoir rock to change its chemistry. This will 1) reduce adsorption of surfactant and polymer onto the rock surface, permitting the injected chemicals to contact a greater volume of the reservoir and 2) make the rock more water-wet, releasing oil from the rock.
3. When alkali is blended into a surfactant solution, it acts as a saline agent to cause the added surfactant to interact with the crude oil at surfactant's optimal salinity.
4. The elevated pH of an alkaline solution acts as a mild biocide, retarding bacterial growth in the injected solution and in the reservoir.
5. Elimination of divalent cations from the injected solution improves polymer stability and surfactant activity and permits higher temperature reservoirs to be chemically flooded.
6. Having alkali in the injected fluids removes divalent cations contained in reservoir water from mixing with the injected chemicals and, therefore, protects the polymer from thermal degradation.
7. If a water with H2S is used to dissolve chemicals, elevating the pH prevents polyacrylamide polymer oxidative degradation.
8. Since an alkaline agent acts as a saline agent, it reduces the volume of a polymer molecule and this permits the injected fluid to inject into smaller diameter pores. When this happens, a greater volume of the reservoir can be contacted by the injected fluid, facilitating higher recovery.
Cons:
1. Scale in the producing well can form due to the alkali mixing with produced water from different zones or from reaction by-products due to the alkali reacting with the reservoir rock.
2. Because alkali shrinks the size of the polyacyrlamide polymer in solution, a higher concentration of polymer is needed compared to that required for a solution with no alkali.
3. Alkaline agents are a hazardous material and must be handled with care when mixing.
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