Polyacrylamide, a water-soluble polymer, can improve oil recovery efficiency through a process known as enhanced oil recovery (EOR). There are several mechanisms by which polyacrylamide achieves this:

1. Viscosity Modification: Polyacrylamide can increase the viscosity of the water injected into oil reservoirs. This increased viscosity helps to improve the sweep efficiency by reducing the mobility of the injected water. The higher viscosity enables the injected water to displace oil more effectively, pushing it towards production wells and enhancing oil recovery.

2. Water Channeling Control: Polyacrylamide can control the permeability of the reservoir, particularly in highly permeable zones. By reducing the permeability of certain porous formations, polyacrylamide helps to divert the injected water flow away from the high-permeability channels (water fingers) and into the unswept areas of the reservoir. This way, it ensures more uniform and efficient displacement of oil.

3. Conformance Control: In some cases, oil reservoirs have heterogeneities or fractures that can cause water to bypass the targeted oil-bearing zones. Polyacrylamide can be injected to plug these high-permeability paths and divert the injected water into the desired areas. This technique is known as conformance control and helps improve overall oil recovery.

4. Clay Stabilization: Polyacrylamide can also act as a clay stabilizer. It prevents the swelling and migration of clays present in the reservoir, which could otherwise cause formation damage and reduce the permeability of the reservoir. By stabilizing the clay particles, polyacrylamide maintains the permeability of the reservoir and enhances oil recovery.

Overall, the addition of polyacrylamide as part of an EOR process helps to improve the mobility control of the injected water, reduce bypassing of oil, and maintain reservoir permeability. These factors contribute to increased oil recovery efficiency. It's worth noting that the effectiveness of polyacrylamide in enhancing oil recovery depends on various reservoir characteristics, such as reservoir type, oil properties, and injection strategies, which must be carefully considered during the planning and implementation of EOR projects