Research for the Enhanced Oil Recovery Mechanism of Heavy Oil After Composite Huff and Puff Assisted by Edge-Bottom Water Displacement

In the late stage of exploiting heavy oil reservoirs with edge-bottom water, we are faced with problems such as high crude oil viscosity, channeling of bottom water, and rapid rise in water cut. To clarify the synergistic effect of N₂, CO₂, N₂ foam, and viscosity reducer in water control and oil increase, and solve the problem of edge-bottom water rushing into production wells, one-dimensional sand-pack huff and puff experiments were carried out. First, the N₂ foam huff and puff experiment evaluated the effect of N₂ foam on controlling bottom water. Then the viscosity reducer-assisted CO₂ huff and puff experiment analyzed the synergistic viscosity reduction ability between the two to mobilize the remaining heavy oil. Next, the N₂ foam–viscosity reducer–CO₂ huff and puff experiment clarified the synergistic effect between the three. Finally, the N₂ foam–viscosity reducer–CO₂–N₂ huff and puff experiment solved the problem of insufficient reservoir energy based on synergistic precipitation and oil increase. Experimental results show that N₂ foam–viscosity reducer–CO₂–N₂ huff and puff is the optimal water control and oil increase solution. This solution can significantly reduce water production and increase oil production. In the one-dimensional sand-pack experiment, this technical solution reduced the water content by 68% and increased the recovery rate by 16.09%. The research results provide a reference for the development of exploitation technology schemes for similar edge-bottom water heavy oil reservoirs after entering high water cut.