A low permeability reservoir co 2 , n 2 hybrid flooding method

Abstract

The invention discloses a low-permeability reservoir CO2 and N2 mixed oil displacement method, and belongs to the technical field of oil field oil recovery. The method comprises the steps that a target block three-dimensional geologic model and a development well pattern model are utilized, the injection speed of CO2 and N2 is determined according to the rule that the spread ranges of CO2 and N2 intersect, and the well closing and opening time is determined after reservoir pressure reaches CO2 / crude oil minimum miscible pressure. The characteristic that CO2 on a reservoir longitudinal section is spread along the lower middle portion and N2 on the reservoir longitudinal section is spread along the upper middle portion, in combination with the horizontal reservoir development well pattern model, the spread range of gas in the longitudinal direction and horizontal direction is widened, it is avoided that injected gas overflows along cracks, and the effect of increasing the recovery degree of a producing well is achieved.

Description

technical field [0001] The present invention relates to a CO 2 , N 2 Oil displacement methods, especially involving CO in low permeability reservoirs 2 , N 2 The mixed oil flooding method belongs to the technical field of oil field recovery. Background technique [0002] Note CO 2 , N 2 Enhanced oil recovery has been applied industrially in oilfield development, in which CO 2 drive is the most widely used. Simple injection of CO 2 , N 2 Although they have their respective advantages, there are also many problems. [0003] CO 2 The main mechanism of flooding production increase is CO 2 After injected into the reservoir: ①It can be dissolved in crude oil to reduce the viscosity of crude oil; ②Extract light components in crude oil to form miscible flooding; ③Improve oil-water interfacial tension; ④Swell crude oil and maintain formation pressure, etc., while CO 2 The mechanism of flooding and production increase is mainly based on whether it is miscible and expanding...

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Problems solved by technology

[0004] CO 2 In the field application of flooding in low-permeability reservoirs, there are problems of small sweep range and slow increase of reservoir pressure

①Small affected area: CO 2 It is in a supercritical state under reservoir conditions, and the most significant change in supercritical density is a large change in density, while for shallow reservoirs (within 3000 meters) CO 2 Density below 0.5g / cm 3 , generally located in the middle and upper part of the reservoir; for deep reservoirs (above 3000 meters) CO 2 The density can be as high as 0.8g / cm 3 , which is close to the density of crude oil, generally located in the middle and lower part of the reservoir, however, most low-permeability reservoirs are deep reservoirs, CO 2 Unable to produce crude oil in the upper part of the reservoir; ②Slow increase of reservoir pressure: CO under high pressure 2 Both have high solubility in oil and water, and the CO injected into the formation 2 It exists in dissolved form, and the rate of increasing formation energy only through crude oil swelling is too slow, especially for reservoirs where the reservoir pressure is lower than the minimum miscible pressure, so that miscible flooding cannot be formed. Using increased formation pressure to achieve miscible flooding will waste a lot of CO 2 , increasing the production cost

[0005] N 2 The mechanism of increasing oil production is mainly to replenish formation energy quickly, mainly for huff and puff and low permeability and difficult water injection reservoirs, N 2 The main problems in the development are low oil displacement efficiency and small sweeping range

① Low oil displacement efficiency: due to N 2 Solubility in crude oil is very low, so the two are not easy to achieve miscibility under reservoir pressure, and the oil displacement efficiency is generally around 10%; ②The sweeping range is limited: N 2 It is a difficult-to-compress gas, and its density changes very little from normal pressure to conventional reservoir pressure, about 0.2g / cm 3 , so N 2 Mainly affects the upper part of the reservoir

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