Oil displacement system and method for low permeability reservoir

Abstract

The invention provides an oil displacement system for a low permeability reservoir. The oil displacement system comprises an associative polymer having molecular weight of 1014000 to 9975000. The associative polymer comprises, by mole, acrylamide, 0.09-10.2% of a hydrophobic monomer and 0-15.4% of a functional monomer. In the oil displacement system, a concentration of the associative polymer is in a range of 200 to 3500 mg/L. Compared with the prior art, a small amount of the hydrophobic monomer and functional monomer are introduced into the polymer molecular chain so that the associative polymer is obtained and the hydrophobic groups are combined into a space network structure in the aqueous solution so that the viscosity of the system is greatly improved, a high resistance coefficient is built and a high residual resistance coefficient is built. Through introduction of the functional monomer into the space network structure, the system has good resistance to a temperature, a salt and shearing and good aging stability, improves an oil-water mobility ratio of low permeability reservoir, improves injection water wave and efficiency and improves the recovery of low permeability reservoir.

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 low-permeability reservoirs. Background technique [0002] With the development of petroleum exploration and development, the proportion of low-permeability oilfields in newly proven reserves is increasing. Low-permeability oil reservoirs account for more than half of the oil and gas fields discovered in my country, and their production capacity construction accounts for more than 70% of the total. Low-permeability oil and gas fields have become the main battlefield for oil and gas development and construction. Due to the small size of pore throats and fractures in low-permeability reservoirs, prominent capillary phenomenon, and high resistance to oil and gas flow, it is difficult to develop and low recovery. Therefore, how to better develop them is an inevitable trend of current research. ....

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Problems solved by technology

The molecular weight of natural polymers is not easy to control, and after decomposition, it is easy to generate a large number of residues to block the formation, which is not suitable for the use of low-permeability reservoirs, and it is subject to seasonal and regional restrictions and high cost. The thermal stability and biological stability are relatively poor, and it is easy to occur Therefore, its application in high-temperature and high-salt oil reservoirs is limited; polyacrylamide, as a mature synthetic polymer, can increase the viscosity of aqueous solution to a certain extent, but it is easy to be damaged due to the strong shearing action of blast holes during construction. Break the long molecular chain, resulting in the irreversible loss of the viscosity of the displacement fluid; it is easily affected by the formation environment (temperature, salinity), and there are the following problems: 1) When it is applied under the condition of high temperature and high salinity, when the temperature is high The hydrolysis of polyacrylamide is severe; 2) When the formation temperature exceeds 75°C, as the formation temperature rises, the precipitation of hydrolyzed polyacrylamide accelerates; 3) High temperature and high salt easily cause hydrolyzed polyacrylamide to precipitate from the aqueous solution and hydrolyze 4) The viscosity of the solution is very sensitive to temperature and salinity, and the retention viscosity of the solution is very low in a high-temperature and high-salt environment

Therefore, the application of poly

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