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Abstract
In order to determine the matching relationship of polymer molecular weight and reservoir permeability in ASP (alkaline/surfactant/polymer) flooding, a number of core flooding experiments with different polymer molecular weights are performed. Two types of curves for the relationship between the pressure difference and the injection pore volume multiples are obtained. One describes the characteristics of the core plugging; the other describes the characteristics of the injection well. The relationship between the polymer molecular cyclotron radius and the pore throat radius used to describe the relationship between the polymer molecular weight and the core permeability. The results indicate that when the ratio of the pore throat radius (rh) to the polymer molecular cyclotron radius (rp) is greater than 7, the injection of ASP system with a variety of molecular weights will not be blocked; on contrary, when the ratio is less than 7, the core will be blocked. The range of water permeability of the core is determined by the value of the polymer molecular weight. The ratio between the pore throat radius (rh) to the polymer molecular cyclotron radius (rp) for the ASP system is greater than that of polymer system (rh/rp = 5). A scanning electron microscope (SEM) is used to compare the morphology of polymer molecules in polymer solution and ASP solution, and shows that the dimension of polymer molecular coils in ASP solution is smaller than that in polymer solution, which is caused by the double effect of alkali and surfactant.
Highlights
About 7000 billion barrels of oil still remain in reservoirs after conventional recovery methods [1].This value is the target of enhanced oil recovery (EOR) techniques
When the molecular weight of the polymer is too low, the need for the amount of polymer increases to satisfy the requirement for viscosity
Cao et al, conducted experimental research on permeability limits of polymer flooding in low permeability oil layers. He used the relationship between molecular radius of gyration and pore radius to represent the relationship of the polymer molecular weight and the core permeability
Summary
About 7000 billion barrels of oil still remain in reservoirs after conventional recovery methods [1].This value is the target of enhanced oil recovery (EOR) techniques. Before conducting ASP technology in the field it is a vital task to study the relationship between the molecular weight and the polymer concentration and the permeability of reservoir [8]. Cao et al, conducted experimental research on permeability limits of polymer flooding in low permeability oil layers He used the relationship between molecular radius of gyration and pore radius to represent the relationship of the polymer molecular weight and the core permeability. Luo et al, studied the relationship between polymer molecular size and pore size for conglomerate reservoirs and found the conglomerate reservoir with water permeability more than 55 × 10−3 μm could not be blocked by polymers with molecular weight less than 3.57 × 107 [12]. No literature reported such a relationship for ASP flooding
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