Oil displacement system and oil displacement method for medium permeability oil reservoirs

Abstract

The invention provides an oil displacement system for medium permeability oil reservoirs. The oil displacement system includes an association polymer with a molecular weight of 182.3-3521 ten thousands, and in terms of mole percent, the association polymer is obtained by polymerization of acrylamide, 0.12%-9.2% of a hydrophobic monomer and 0-16.08% of a functional monomer. In the oil displacement system, the association polymer concentration is 400-3500mg / L. Compared with the prior art, a small amount of the hydrophobic monomer and functional monomer are introduced to a polymer molecular chain to obtain the association polymer, the association polymer can associate into a reversible spatial network structure with certain strength, thus greatly improving the system viscosity, and establishing a high resistance coefficient and high residual resistance factor, and because of the introduction of the functional monomer and increase of the spatial network structure strength, the system can have good temperature resistance and salt tolerance, shear resistance and aging stability, has a better effect of improving oil-water mobility ratio on medium permeability oil reservoirs, and improves the injected water sweep efficiency, thus better improving the recovery ratio of medium permeability oil reservoirs.

Description

Technical field [0001] The invention belongs to the technical field of petroleum exploitation, and in particular relates to an oil displacement system and an oil displacement method for medium permeability reservoirs. Background technique [0002] Old oil fields at home and abroad have entered the late stage of development. After long-term water flooding development, the water cut of medium permeability reservoirs has risen rapidly, with water cuts as high as 80%. If the existing water injection technology is used for development, it is quite difficult to improve the recovery factor. , The economic benefits of oil field development are poor, and there is an urgent need to develop new oil development technologies to enable the effective development of unused reserves, thereby greatly improving the recovery rate of old oil fields and the utilization rate of proven oil and gas resources to meet the needs of the national economy Development and national oil security needs. In view o...

AI Technical Summary

Problems solved by technology

Natural polymers are limited by seasons and regions and have high cost, relatively poor thermal and biological stability, and are prone to degradation, so their application in high-temperature and high-salt reservoirs is limited; the most widely used synthetic polymers are polymers. Although acrylamide can increase the viscosity of the aqueous solution to a certain extent, it is easy to break the long molecular chain due to the strong shearing action of the blast hole during the construction process; it is easily affected by the formation environment (temperature, salinity, etc.), and there are the following problems : 1) When applied under the condition of high temperature and high salinity, the hydrolysis of polyacrylamide is serious when the temperature is high; 2) when the formation temperature exceeds 75°C, as the formation temperature rises, the formation of hydrolyzed polyacrylamide precipitation accelerates; 3 ) High temperature and high salt can easily cause hydrolyzed polyacrylamide to precipitate from the aqueous solution, and the higher the degree of hydrolysis, the more significant this phenomenon is; 4) The viscosity of the solution is very sensitive to temperature and salinity, and the retained viscosity of the solution is very high in a high temperature and high salt environment. Low

Therefore, the application of polyacrylamide in slightly harsh reservoir conditions is greatly limited

In order to obtain higher viscosity of polyacrylamide, the polymer concentration and molecular weight must be increased, and the cost will increase significantly

Due to the single adjustable parameters that determine the size of its molecular coils, the matching with reservoir pore throats is poor, and the established resistance coefficient and residual resistance coefficient are small, which cannot effectively expand the swept volume and seal the dominant channel of water flooding

When surfactants and alkalis are added to form a binary (ternary) system, the viscosity and elasticity of polyacrylamide and most surfactants and alkalis will be reduced to varying degrees, and the fluidity control ability will be reduced (creating a negative synergistic effect) )

Ordinary polyacrylamide can only adjust the molecular weight and degree of hydrolysis and the adjustment range is limited. In view of the above problems, it is difficult to further overcome the above problems on the basis of its existing molecular structure.

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