Gravity assisted composite gas displacement method

Abstract

The invention provides a gravity assisted composite gas displacement method. According to the method, a first displacement gas is injected into a high position of a structure, and a second displacement gas is injected into a middle position of the structure, wherein the density of the second displacement gas is higher than that of the first displacement gas; the second displacement gas forms a miscible zone between the first displacement gas and crude oil; the miscible zone performs miscible displacement on the crude oil under driving of the first displacement gas. Based on the gravity override principle, the composite gas displacement method has the advantages that vertically downward stable displacement is realized through gas cap energy formed by override of the first displacement gas with lower density, gas channeling is delayed, so that the gas injection sweep efficiency is increased, the miscible pressure of an oil reservoir is reduced by the second displacement gas, miscible displacement is realized, the oil displacing efficiency of gas is increased, and the ultimate recovery ratio of the crude oil is increased remarkably.

Description

technical field [0001] The invention relates to the technical field of oil exploitation, in particular to a gravity-assisted composite gas drive method. Background technique [0002] At present, the average oil recovery rate is between 30% and 60%, and the industry usually uses the injection of displacement medium to enhance the recovery rate. According to the difference in displacement media and displacement methods, the current displacement technologies for enhanced oil recovery are divided into four categories, as follows: chemical flooding (including polymer flooding, surfactant flooding, alkali flooding and chemical composite flooding) ); gas flooding (divided into gas miscible flooding and gas immiscible flooding, the commonly used displacement medium gas mainly includes CO 2 , N 2 , hydrocarbon gas, flue gas, etc.); thermal flooding; microbial flooding. [0003] Since deep and ultra-deep sandstone reservoirs have high temperature (greater than 90°C), high salinity ...

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Problems solved by technology

[0004] However, in the actual mining process, CO with many advantages 2 Flooding also has many disadvantages, for example: CO 2 Flooding reduces coal seam permeability because CO 2 Displace CH 4 After that, the coal will expand in volume and cause a decrease in permeability; CO 2 Flooding requires a large amount

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