Polymer molecular morphology in alkali-surfactant-polymer (ASP) ternary composite system and its influence on rock pore structure

In this research, the molecular wire cluster size of alkali-surfactant-polymer (ASP) ternary system was measured by laser scattering method. The molecular morphology of the polymer in the ternary composite system was observed by scanning electron microscope. The effects of weak alkali ternary system on the pore structure of rocks were studied by mercury intrusion method and scanning electron microscope. The experimental results show that under the same conditions of alkali and surfactant concentration, with the increase of the relative molecular weight of the polymer, the molecular coil size Dh gradually increases. Under the same conditions of polymer relative molecular mass and surfactant concentration, the molecular coil size Dh gradually decreases with the increase of alkali concentration. In the strong alkali ternary system, the backbone of the polymer molecule is the thickest, showing a network structure, followed by the polymer solution, and the weak alkali ternary system is the thinnest, showing a branched chain structure. Different polymer concentrations have different degrees of entanglement between molecular chains. The higher the concentration, the higher the cohesive energy density between molecular chains and the stronger the entanglement. After alkali-surfactant-polymer (ASP) ternary system flooding, the average pore radius, the mean radius, and the median radius of the core all tend to increase gradually. The change of the average pore radius of the core after the strong alkaline water flooding is larger than that of the weak alkaline water flooding. Before ASP ternary system flooding, the rock particles are closely arranged and the pores are small and relatively uniform. However, after the ASP flooding, mottled bulges appeared, with obvious development of pores and movable debris attached to the rocks. Compared with weak alkali ASP flooding, the core pores become larger after strong alkali ASP flooding.