Carbon dioxide "shallow storage deep burial" geological sequestration and safe disposal method

Abstract

The present application relates to a kind of carbon dioxide " shallow storage deep burying " geological storage and safe disposal method, for the development and utilization of the space of currently closed large-area coal mine underground goaf and deep strata, realize carbon dioxide " shallow storage deep burying ". Industrial waste gas CO2 is injected from ground high pressure into deep strata, realize the deep geological storage of carbon dioxide;A small amount of atmospheric state CO2 is injected into shallow goaf, and free state CH4 in the internal fracture space of goaf is moved towards the direction of extraction hole, and the mining efficiency of closed mine abandoned CH4 resources is improved;Through ground covering green plants, closed coal mining process strata collapse through fracture, and the CO2 diffused to the surface is absorbed and solidified.If CO2 leakage disaster occurs due to geological action stratum fracture, shallow goaf as emergency geological buffer storage or porous medium absorption body can prevent CO2 stored in deep strata from leaking to the ground quickly, causing suffocation and death of personnel, and provides valuable emergency disposal time for artificial plugging stratum fracture.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of geological carbon dioxide storage, and particularly relates to a method for carbon dioxide geological storage and safe disposal of "shallow storage and deep burial" of closed mines. BACKGROUND

[0002] In China, direct closure is generally used for resource-exhausted coal mines. On the one hand, the closure of coal mines will cause gas leakage in goaf. During the mining period of coal seams, a large number of mining-induced fissures are developed in the overburden strata of goaf, and some of the fissures may be connected to the ground. In addition, the pit closure process may not be completed, which may cause residual gas to leak to the ground through the shaft, through cracks or faults, and continuously release gas into the atmosphere for a long time, which not only increases the atmospheric CH4 emission, but also easily causes various suffocation, combustion, explosion and other disasters. On the other hand, the closure of mines will cause a series of ecological problems. Methane, as the second important greenhouse gas, has a global warming potential of 84 times and 28 times that of CO2 at the 20a level (short cycle) and 100a level (long cycle) respectively. If there is no timely environmental governance and land reclamation after a large number of coal mines are closed, it will aggravate soil erosion, cause soil infertility, rapid decline of biodiversity, and aggravate the greenhouse effect. About 20% of CH4 emissions in the world come from fossil fuel industries, and more than 1 / 3 of the total gas emission in China comes from coal mine gas, which is the main source of atmospheric CH4 emission. At present, the CO2 storage technology in coal mine goaf is still in the exploratory stage. The problems such as the sealing property of CO2 in the pressure state of coal mine goaf, the storage mode, the seepage law of CO2, the safety of CO2 storage, the plugging of CO2 escape channels and safety monitoring still need to be solved. The existing CO2 storage technology stores CO2 in the deep strata (salt water layer, basalt strata, etc.), and CO2 may leak to the surface after geological action, causing suffocation and death of personnel and greenhouse effect. SUMMARY

[0003] The present application aims to overcome the problems of traditional deep strata (salt water layer, basalt strata, etc.) CO2 storage, such as CO2 leakage to the surface after geological action, suffocation and death of personnel, and greenhouse effect, and proposes a method for carbon dioxide "shallow storage and deep burial" geological storage and safe disposal. The shallow goaf is used as an emergency geological buffer storage or porous medium absorption body for CO2 leakage in deep salt water layer storage, which effectively reduces the leakage risk of deep strata CO2 geological storage, and improves the extraction efficiency of CH4 in shallow goaf. The method is suitable for the space resource utilization of abandoned mine goaf and the safe geological storage of carbon dioxide.

[0004] The technical scheme of the present application is a carbon dioxide "shallow storage and deep burial" geological storage method: ① high-pressure CO2 injection is implemented in the deep stratum of a closed mine through a CO2 injection well to achieve geological storage; ② CO2 injection holes and CH4 extraction holes are arranged at different stratum positions in the shallow goaf to achieve replacement and driving of free-state CH4 in the goaf fissure space; and ③ the surface is covered with grass, the micro fissures formed during the mining period of the mine and penetrating to the ground are plugged, and a plant community is formed to achieve plant carbon fixation of the trace CO2 diffused to the ground in the shallow goaf due to capillary action and the like.

[0005] The deep stratum of the closed mine is generally selected to be a stratum with a depth greater than 2500 m, preferably a stable geological body such as a saline layer or basalt, and cannot have geological structure fissures such as faults.

[0006] The shallow goaf is generally selected to be a single goaf with a depth of 300-1500 m or a composite goaf formed by the mining of a coal seam group.

[0007] The CO2 is obtained by capturing industrial waste gas of major carbon emission enterprises such as thermal power plants and chemical plants.

[0008] The CO2 injection into the shallow goaf is stored in the pore space of the caving zone and fissure zone of the goaf in a normal pressure state to prevent the large-scale escape of CO2 in the goaf to the ground.

[0009] The distance between the CO2 injection holes and the CH4 extraction holes is 10-15 km.

[0010] The CO2 injection well is located at the intermediate position of the CO2 injection holes and the CH4 extraction holes, and the bottom of the well is located in the deep stratum with a depth greater than 2500 m, and is generally preferably a saline layer or a basalt stratum.

[0011] The CO2 injection holes and the CH4 extraction holes are arranged at different stratum heights in the shallow goaf, the CO2 injection hole release port is located in the caving zone of the original goaf coal seam floor, and the CH4 extraction hole port is located in the fissure zone of the original goaf coal seam roof. The density of CO2 is heavier than that of CH4 gas, and after being injected into the goaf, CO2 is first filled in the lower part of the goaf to drive CH4 to the fissure zone, and after standing, CO2 and CH4 gas are stratified, and gas extraction is performed when the CH4 concentration of the extraction hole reaches a certain value.

[0012] The ground plant community is preferably a plant with strong carbon fixation capacity and capable of adapting to local climate conditions, such as trees and shrubs, to achieve plant carbon fixation of the trace CO2 diffused to the ground in the shallow goaf.

[0013] When a geological disaster occurs in the storage area, CO2 leakage in the deep stratum first enters the shallow mine goaf as a buffer to avoid large-scale transient CO2 leakage.

[0014] A carbon dioxide "shallow storage deep burial" leakage emergency disposal method, when a fault is generated by an earthquake or other geological disasters, the CO2 stored in the deep pressure state migrates upward along the fault plane, and when it reaches the shallow goaf, it can be stored in the abandoned goaf porous medium to prevent leakage to the ground and cause suffocation and casualties, and ultimately realize the storage and absorption of CO2 through coal rock adsorption, coal-pore water-CO2 geochemical action, etc. This process can provide valuable emergency disposal time for ground personnel to block the fault fissure channel.

[0015] The present application has the following beneficial effects:

[0016] Compared with the traditional method of directly injecting carbon dioxide into the goaf or deep stratum for storage, the present application has the following significant improvements: ①The deep stratum and the shallow mine goaf are combined as a CO2 geological storage and storage carrier, which can effectively improve the safety. When an earthquake or other geological disasters occur in the storage area, seepage fissures are generated in the deep stratum, and CO2 leakage first enters the shallow mine goaf (porous medium buffer zone) instead of directly leaking into the surface atmosphere, effectively utilizing the mine goaf as a buffer to avoid CO2 transient large-scale leakage causing suffocation and other personal injury accidents. ②The injection of normal pressure CO2 into the shallow coal seam goaf can promote the desorption of adsorbed CH4 in the goaf and the displacement of free CH4 in the fissure space, realizing the redevelopment of abandoned resources in the mine, and reducing the greenhouse effect caused by CH4 escaping from the goaf. The CO2 release port is located at the lower part of the caving zone of the goaf, so that the normal CO2 displaces the free CH4 from the bottom and drives the CH4 towards the CH4 extraction hole, and the displacement is more sufficient. ③The carbon dioxide "shallow storage deep burial" realizes the effective utilization of the geological space of the abandoned mine, and the slow diffusion of CO2 from the shallow goaf to the surface promotes the growth speed of the surface green plants, which is beneficial to the ecological restoration and environmental improvement of the mine area. ④The CH4 is driven to the CH4 extraction hole, and when the CH4 concentration is greater than the threshold value, the CH4 is extracted, and when the CH4 concentration is less than the threshold value, the extraction is stopped, so that the CH4 extraction efficiency is higher, and the safety hazards and greenhouse effect caused by CH4 leakage are prevented. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Schematic diagram of carbon dioxide "shallow storage deep burial" geological storage and disposal method for single coal seam goaf

[0018] Figure 2 Schematic diagram of carbon dioxide "shallow storage deep burial" geological storage and disposal method for multiple coal seams (coal seam group) goaf

[0019] In the figure: 1—Collapse zone; 2—Fractured zone; 3—CO2 injection hole; 4—CO2 release hole; 5—Shallow goaf; 6—Goaf floor; 7—CH4 extraction hole; 8—CH4 extraction hole opening; 9—CO2 injection well; 10—Injection well bottom; 11—Deep strata; 12—Free CH4; 13—Grassland; 14—Microfracture; 15—Tree; 16—Shrub. Detailed Implementation

[0020] The invention will now be further described with reference to the accompanying drawings.

[0021] The present invention will be further described below, but this does not limit the invention to the scope of the described embodiments.

[0022] A method for geological sequestration and safe disposal of carbon dioxide using a "shallow storage, deep burial" approach, such as... Figure 1 , Figure 2 As shown: Based on the geological conditions of the closed mine, the distribution of the caving zone 1 and fracture zone 2 in the shallow goaf 5 of a single coal seam or multiple coal seams (coal seam group) is determined. A CO2 injection hole 3 is constructed at one end of the shallow goaf. The CO2 release hole 4 is located at the lower part of the caving zone 1 of the goaf 5, and should be as close as possible to the goaf floor 6. This arrangement ensures that the injected CO2 first fills the lower part of the caving zone, while simultaneously driving free CH4 upwards, which is more conducive to CH4 entering the fracture zone and achieving CH4 extraction. A CH4 extraction hole 7 is constructed 10-15 km away from the CO2 injection hole 3, with the extraction hole 8 located at the upper part of the fracture zone 2. A CO2 injection well 9 is constructed between the CO2 injection hole 3 and the CH4 extraction well 7. The bottom 10 of the CO2 injection well is located in a deep stratum 11 with a burial depth greater than 2500 m, generally preferably a saline aquifer or basalt stratum.

[0023] Industrial waste gas CO2 is injected in large quantities into the deep formation 11 through CO2 injection well 9 under high pressure to achieve effective CO2 sequestration. Here, high pressure refers to pressure greater than the formation pore pressure. Atmospheric CO2 is slowly injected into CO2 injection well 3 in the shallow goaf 5 to replace and drive away free CH4 (12) in the collapse zone 1 and fracture zone 2. The gas concentration in the CH4 extraction well 7 is sampled and monitored. The gas concentration can be monitored by conventional chromatographic sampling. Extraction is carried out when the CH4 concentration is greater than 30% and extraction is stopped when the CH4 concentration is less than 30%.

[0024] Finally, grassland 13 is covered on the surface to seal the micro-cracks 14 formed during mining that extend to the ground. At the same time, plants with strong carbon sequestration capacity and adaptability to local climate conditions, such as trees 15 and shrubs 16, are selected to achieve carbon sequestration of trace amounts of CO2 that diffuse to the surface from the shallow mined-out area due to capillary action.

[0025] The deep stratum is combined with the shallow mine goaf as a CO2 geological storage and storage carrier, which can effectively improve the safety. When a geological disaster such as an earthquake occurs in the storage area, seepage cracks are generated in the deep stratum, and CO2 leakage first enters the shallow mine goaf (porous medium buffer zone) rather than directly leaking into the surface atmosphere, which effectively utilizes the mine goaf as a buffer to avoid the CO2 transient large-scale leakage causing suffocation and other personal injury accidents.

[0026] The atmospheric CO2 injection into the shallow coal seam goaf can promote the desorption of the adsorbed CH4 in the goaf and the replacement of the free CH4 in the fissure space, realize the redevelopment of the abandoned mine resources, and reduce the greenhouse effect caused by the CH4 emission in the goaf. The CO2 release port is located at the lower position of the caving zone in the goaf, so that the normal CO2 replaces the free CH4 from the bottom and drives the CH4 to the CH4 extraction hole, and the replacement is more sufficient.

[0027] The carbon dioxide is "shallowly stored and deeply buried", which realizes the effective utilization of the abandoned mine geological space, and the slow diffusion of the CO2 in the shallow goaf to the surface promotes the growth speed of the surface green plants, which is beneficial to the ecological restoration and environmental improvement of the mine area. The CH4 is driven to the CH4 extraction hole, and when the CH4 concentration is greater than the threshold value, the extraction is carried out, and when the CH4 concentration is lower than the threshold value, the extraction is stopped, so that the CH4 extraction efficiency is higher, and the safety hidden danger and the greenhouse effect caused by the CH4 leakage are prevented.

[0028] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can modify the technical solutions described in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for geological sequestration and safe disposal of carbon dioxide by "shallow storage deep burial", characterized in that, Comprising the following steps ① High-pressure injection of CO2 into deep strata of a closed mine through a CO2 injection well to achieve geological storage, the deep strata of the closed mine being strata deeper than 2500 m, the deep strata being saltwater layers and basalt layers without faults; ②In different strata positions of shallow goaf, CO2 injection holes and CH4 extraction holes are arranged, CO2 is injected through CO2 injection holes, and CH4 is extracted through CH4 extraction holes 2， CO2 is stored in goaf fissure space in normal pressure state, and replaces and drives free state CH4, the shallow goaf is a single goaf with a buried depth of 300-1500 m or a composite goaf mined by coal seam group, CO2 injection holes and CH4 extraction holes are arranged at different strata heights of the shallow goaf, the CO2 injection hole release port is located in the caving zone of the original goaf coal seam floor, the CH4 extraction hole port is located in the fissure zone of the original goaf coal seam roof, the distance between the CO2 injection hole and the CH4 extraction hole is 10-15 km, the CO2 injection well is located at the middle position of the CO2 injection hole and the CH4 extraction hole, and the well bottom is located in a deep stratum with a buried depth greater than 2500 m; ③ The surface is covered with grass, the micro-fractures formed during mining that penetrate to the ground are plugged, and a plant community is formed, so that a small amount of CO2 diffused to the surface from the shallow goaf is fixed by plants; when a geological disaster occurs in the storage area, CO2 leakage from the deep strata first enters the shallow goaf of the mine as a buffer, so as to avoid large-scale transient CO2 leakage.

2. The method of geological sequestration and safe disposal of carbon dioxide "shallow storage deep burial" according to claim 1, characterized in that, Gas extraction is performed through a CH4 extraction hole when the concentration of CH4 reaches a threshold value.

3. The method of geological sequestration and safe disposal of carbon dioxide "shallow storage deep burial" according to claim 2, characterized in that, The threshold value is 30%.

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