Method for improving crude oil recovery ratio in underground oil reservoir in later period of oil field oil recovery

Abstract

The invention provides a method for improving the crude oil recovery ratio in an underground oil reservoir in a later period of oil field oil recovery. The method comprises the following steps of: a, injecting an ultra-high-molecular polymer solution into an injection well subjected to polymer-activating agent binary compound flooding to be used as a pre-slug, wherein the injection quantity is 0.05 to 0.1 time of stratum void volume, the concentration of ultra-high-molecular polymers is 1800 to 2300mg / L, and the viscosity is greater than 80mPa.s; and b, compounding the ultra-high-molecular polymers with the concentration being 1800 to 2300mg / L and the viscosity being 50mPa.s or above and anionic-non-ionic surfactants with the concentration being 2000 to 5000mg / L and the interface tension being smaller than 5.0*10<-3>mN / m according to the weight part mixture ratio being (0.15 to 0.18): (0.2 to 0.5); uniformly stirring the mixture; and injecting the mixture into the injection well, wherein the injection volume is 0.1 to 0.3 time of the stratum void volume; and c, finally injecting an ultra-high-molecular polymer solution with the concentration being 800 to 1200mg / L and the viscosity being 20 to 30mPa.s into the injection well to be used as a substrate protective slug, wherein the injection volume is 0.05 to 0.1 time of the stratum void volume.

Description

Technical field: [0001] The invention relates to a technique for improving the recovery rate of crude oil in an underground oil reservoir in the later stage of oil recovery in an oil field. It is not only suitable for conventional oil reservoirs, but also for heterogeneous oil reservoirs and oil reservoirs after polymer flooding. The temperature of the oil reservoir is not higher than 90 ℃, salinity lower than 50000mg / l, calcium and magnesium ion concentration lower than 2000mg / l, crude oil viscosity lower than reservoir viscosity 200mPa.s, permeability 500×10 -3 μm 2 ~20000×10 -3 μm 2 . Background technique: [0002] With the continuous development of oil extraction, oil fields in many regions of the world have entered the stage of high water cut and ultra-high water cut in the later stage of development. In order to improve the recovery rate of old oil fields and increase the recoverable reserves, the following oil displacement methods mainly exist in the prior art: (1...

AI Technical Summary

Problems solved by technology

[0005] At present, the surfactants used for compound flooding in major oilfields in China are mostly complex systems formed by compounding different types of surfactants. The advantage of the compound system is that it is easy to achieve ultra-low interfacial tension, but it will cause the oil displacement agent to migrate underground. Chromatographic separation occurs in the medium, which affects the formation of ultra-low interfacial tension, thus affecting the oil washing efficiency