阅读说明：本技术 一种气田井口天然气脱碳与co2回注提高采收率的方法 (method for improving recovery ratio by decarbonization of natural gas at gas field wellhead and CO2 reinjection ) 是由 王秀林 宋鹏飞 侯建国 李又武 单彤文 张丹 赵思思 姚辉超 穆祥宇 张瑜 侯海 于 2019-09-04 设计创作，主要内容包括：本发明公开了一种气田井口天然气脱碳与CO_2回注提高采收率的方法。所述方法包括如下步骤：采用天然气制氢方法,将来自于气田井口的天然气处理得到提纯后的CO_2和H_2；将所述CO_2回注至气田用于提高天然气采收率；CO_2经压缩机增压后回注至所述气田；该方法尤其适用于高压、高空速的工况。本发明方法直接在天然气气田坑口实现天然气脱碳制氢,尤其适用于高压和高空速工况,不必大幅降低气田天然气压力,减少能量损失；且坑口脱出的二氧化碳回注至天然气气田用于提高采收率。(The invention discloses a method for improving recovery ratio by decarbonization of natural gas at a gas field wellhead and reinjection of CO 2. The method comprises the following steps: the method for preparing hydrogen from natural gas is adopted, and the natural gas from a gas field wellhead is treated to obtain purified CO2 and H2; reinjecting the CO2 to a gas field for enhanced natural gas recovery; CO2 is pressurized by a compressor and then is reinjected to the gas field; the method is especially suitable for the working conditions of high pressure and high airspeed. The method directly realizes the hydrogen production by decarbonization of the natural gas at the pithead of the natural gas field, is particularly suitable for working conditions of high pressure and high airspeed, does not need to greatly reduce the pressure of the natural gas in the gas field, and reduces energy loss; and the carbon dioxide removed from the pithead is reinjected to the natural gas field for improving the recovery ratio.)

1. A method for improving natural gas recovery rate by CO2 reinjection at a gas field well head comprises the following steps:

the method for preparing hydrogen from natural gas is adopted, and the natural gas from a gas field wellhead is treated to obtain purified CO2 and H2;

Reinjecting the CO2 to a gas field for enhanced natural gas recovery;

The method is particularly suitable for the working conditions of high pressure and high airspeed.

2. the method of claim 1, wherein: the method further comprises the step of adding oxygen or air to the natural gas.

3. The method according to claim 1 or 2, characterized in that: and the CO2 is pressurized by a compressor and then is injected back to the gas field.

4. The method according to any one of claims 1-3, wherein: the method for producing hydrogen from natural gas comprises the following steps of:

Methane reforming decarbonization reaction, CO shift reaction, low-temperature methanol washing and pressure swing adsorption;

Washing with methanol at low temperature to obtain purified CO 2;

And obtaining purified H2 through pressure swing adsorption.

5. The method of claim 4, wherein: and pressurizing purge gas generated by the pressure swing adsorption and mixing the purge gas with the natural gas.

6. The method according to claim 4 or 5, characterized in that: and the heat generated by a heat exchanger arranged between the methane reforming decarburization reaction and the CO shift reaction is used for producing steam.

7. the method according to any one of claims 1-3, wherein: the method for producing hydrogen from natural gas comprises the following steps of:

Methane reforming decarburization reaction, CO shift reaction and low-temperature methanol washing;

And washing with methanol at low temperature to obtain purified CO 2.

8. The method of claim 7, wherein: and heat exchange treatment is carried out before the methane reforming decarburization reaction, between the methane reforming decarburization reaction and the CO shift reaction and between the CO shift reaction and the low-temperature methanol washing.

9. The method according to any one of claims 1-3, wherein: the method for producing hydrogen from natural gas comprises the following steps of:

methane reforming decarbonization reaction, CO shift reaction, pressure swing adsorption and/or membrane separation.

10. The method according to any one of claims 4-9, wherein: before the methane reforming decarbonization reaction, the method for preparing hydrogen from natural gas further comprises the step of carrying out desulfurization treatment on the natural gas.

Technical Field

The invention relates to a method for improving natural gas recovery efficiency by CO2 reinjection at a well head of a gas field, belonging to the field of natural gas recovery.

background

CO2 enhanced reservoir recovery is one of the fast evolving enhanced recovery technologies in recent years. Years of research and practice prove that the CO2 is injected into shale gas, coal bed gas and conventional natural gas reservoirs to effectively improve the natural gas recovery ratio (EGR) by utilizing the difference of adsorptivity of CO2 and CH4, so that the natural gas recovery ratio is improved, the economic benefit is increased, an important way of integration of CO2 gas capture, sequestration and application (CCUS) is realized, and the method is a win-win way of increasing energy and protecting the environment. Indeed, CO2 enhanced recovery is one of the best options for achieving CCUS in terms of stability of CO2 sequestration, scale of utilization, value of utilization creation, and the like.

Taking coal bed gas as an example, injecting CO2 can increase the total cleat pressure of the coal bed and locally reduce the partial pressure of methane in cleats, thereby improving the desorption speed and the diffusion speed; the structural characteristics of the carbon dioxide molecules determine that the adsorption effect of the carbon dioxide molecules on the coal matrix is greater than that of the methane molecules, the carbon dioxide molecules and the methane molecules have a competitive effect on the adsorption of the coal matrix, and more methane is desorbed from the coal matrix through the competitive adsorption displacement effect.

However, a large amount of CO2 resources are not possible near the oil and gas field, and the problem of the source and price of CO2 must be solved for large-scale application. The CO2 is collected from cities, power plants, chemical plants and the like and transported to oil and gas fields, long-distance CO2 pipelines or compression tank trucks are generally required to be paved for transportation, the transportation cost is high, and the economic efficiency and the engineering technical feasibility of CO2 for improving the recovery ratio are influenced. It is therefore desirable to provide a method for enhanced natural gas recovery by CO2 reinjection at the gas field wellhead.

Disclosure of Invention

the invention aims to provide a method for improving the recovery ratio of natural gas by reinjecting CO2 at a well head of a gas field, which can remove carbon in the natural gas into high-purity CO2 at the well head of the gas field, convert the carbon into high-purity H2, output the H2 as a market product, and reinjecting CO2 to the gas field at the well head to improve the recovery ratio. The method of the invention can not only reduce the price of CO2 and omit the transportation of large-scale CO2, but also directly supply high-purity hydrogen to the market and provide hydrogen resources for hydrogenation stations.

the method for improving the natural gas recovery rate by CO2 reinjection at the well head of the gas field comprises the following steps:

The method for preparing hydrogen from natural gas is adopted, and the natural gas from a gas field wellhead is treated to obtain purified CO2 and H2;

Reinjecting the CO2 to a gas field for enhanced natural gas recovery;

The method is suitable for the working conditions of high pressure (0.5-20 MPa) and high airspeed (2000-20000 h < -1 >).

the method further comprises the step of adding oxygen or air into the natural gas, wherein the oxygen or air is used for increasing the temperature of the methane decarburization reaction, and the adding amount of the oxygen or air is 0-30% of the natural gas.

in the above method, the CO2 is pressurized by a compressor and then injected back into the field for enhanced natural gas recovery (EGR).

In the above method, one scheme of the method for producing hydrogen from natural gas is as follows: comprises the following steps which are carried out in sequence:

Methane reforming decarbonization reaction, CO shift reaction, low-temperature methanol washing and pressure swing adsorption;

Washing with methanol at low temperature to obtain purified CO 2;

And obtaining purified H2 through pressure swing adsorption.

In the method of the invention, the methane reforming decarbonization reaction can be carried out under the conventional conditions, wherein CH4, C2H6, C3H8, C4H10 and C5+ in natural gas undergo a reforming reaction with steam.

In the method, the CO shift reaction can be carried out under conventional conditions and can be divided into a high-temperature CO shift reaction and a low-temperature CO shift reaction which are carried out in sequence, and through the reaction, CO and water vapor react under a catalyst to generate CO2 and H2 and release a large amount of heat.

In the method, the low-temperature methanol washing can be carried out under conventional conditions and is used for removing sulfur, nitrogen and carbon dioxide, and CO2 with the purity of more than 80% is obtained from the top of a CO2 product through working procedures of a CO2 desorption tower, a flash tank and the like in a working section.

in the process of the present invention, the pressure swing adsorption may be carried out under conventional conditions for producing high purity H2; and the purge gas (containing a certain concentration of CH4) generated by the pressure swing adsorption is mixed with the natural gas after being pressurized.

in the method, the heat generated by the heat exchanger arranged between the methane reforming decarburization reaction and the CO shift reaction is used for producing steam, the steam can be generated by a steam drum, one part of the steam is used as a reaction raw material, and the other part of the steam is output as a byproduct.

In the above method, another scheme of the method for producing hydrogen from natural gas is as follows: comprises the following steps which are carried out in sequence:

Methane reforming decarburization reaction, CO shift reaction and low-temperature methanol washing;

Washing with methanol at low temperature to obtain purified CO 2;

and heat exchange treatment is carried out before the methane reforming decarburization reaction, between the methane reforming decarburization reaction and the CO shift reaction and between the CO shift reaction and the low-temperature methanol washing.

In the above method, another scheme of the method for producing hydrogen from natural gas is as follows: comprises the following steps which are carried out in sequence:

methane reforming decarbonization reaction, CO shift reaction, pressure swing adsorption and/or membrane separation.

in the above method, before the methane reforming decarbonization reaction, the method for producing hydrogen from natural gas further comprises a step of desulfurizing the natural gas to remove a small amount of H2S which may be contained in the natural gas.

The invention has the following advantages:

(1) The natural gas decarburization hydrogen production is directly realized at the pithead of the natural gas field, and the method is particularly suitable for working conditions of high pressure and high airspeed, so that the natural gas pressure of the gas field does not need to be greatly reduced, and the energy loss is reduced;

(2) Injecting the carbon dioxide removed from the pithead back to the natural gas field for improving the recovery ratio;

(3) The pressure adaptation range of the pressure regulator for the natural gas field is wide and ranges from 0.5MPa to 20 MPa;

(4) The reaction heat absorption and release characteristics are fully utilized, and the heat balance design is realized;

(5) Adding high purity oxygen to increase natural gas reforming temperature and methane conversion efficiency;

(6) Obtaining a high-purity hydrogen product;

(7) the purity of the separated carbon dioxide is high, the cost of the carbon dioxide can be greatly reduced, and the whole carbon emission is reduced.

Drawings

FIG. 1 is a schematic diagram of a first process flow of decarbonization and CO2 reinjection for enhanced recovery of natural gas from a wellhead of a gas field.

FIG. 2 is a schematic diagram of the second process flow of decarbonization of natural gas from the wellhead of the gas field and CO2 reinjection for improving the recovery ratio.

FIG. 3 is a schematic diagram of the process flow of decarbonization of natural gas at the wellhead of the gas field and CO2 reinjection for improving the recovery ratio.

FIG. 4 is a schematic diagram of the process for decarbonizing natural gas at the wellhead of the gas field and reinjecting CO2 to improve the recovery ratio.

FIG. 5 is a schematic diagram of a fifth process flow of decarbonization of natural gas from a wellhead of a gas field and CO2 reinjection for enhanced recovery of oil according to the present invention.

The respective labels in FIG. 1 are as follows:

1 deep desulfurization reactor, 2, gas-gas mixer, 3, reforming reactor, 4 high-temperature CO shift reactor, 5 low-temperature CO shift reactor, 6 low-temperature methanol washing, 7 pressure swing adsorption unit (PSA), 8 purge gas circulating compressor, 9CO2 compressor, 10, steam drum, 11 membrane separation, G1 natural gas raw material gas, G2 hydrogen, G3 CO2, G4 air or oxygen, and W1 boiler water.

Detailed Description

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.