Deep coal seam CO2 storage potential calculation method based on coal seam geologic features

Abstract

The invention discloses a deep coal seam CO2 storage potential calculation method based on coal seam geological characteristics, and belongs to the technical field of CO2 geological storage. The method comprises the following steps: firstly, acquiring excess adsorption quantity of CO2 adsorbed by a coal seam under different time actions, and constructing an adsorption quantity calculation model under different time parameters by utilizing a relationship between the excess adsorption quantity and absolute adsorption quantity; then fitting porosity data under different adsorption times, and constructing a coal quality unit mass CO2 free quantity model; then, according to the CO2 solubility calculation model and the characteristic parameters of the target coal seam, a unit mass CO2 dissolved amount model is constructed; then, data of the relation between the migration distance of CO2 in the coal seam and time is taken, and a time-migration distance formula is fitted; and finally, establishing a unit mass coal sample supercritical CO2 storage capacity calculation model, and constructing a theoretical storage amount and actual storage amount equation of CO2 geological storage. By adopting the calculation method, a theoretical reference can be provided for shut-down coal mine CO2 sequestration development and utilization strategy research and sequestration address selection.

Description

Technical Field

[0001] The present invention relates to a method for calculating the CO2 storage potential of deep coal seams based on the geological characteristics of the coal seams, and belongs to the technical field of CO2 geological storage. Background Art

[0002] Evaluating the CO2 storage potential of deep coal seams is a key step in CO2 geological storage. By studying the effect of the interaction time between coal and supercritical CO2 on the pore structure of coal seams, we can effectively predict the CO2 storage potential of coal seams. The scientific and rational calculation method of storage potential directly affects the accuracy and effectiveness of the CO2 storage potential of deep coal seams.

[0003] CO2-ECBM technology, which injects CO2 into high-temperature, high-pressure coal seams, where it adsorbs and displaces CH4, not only increases CH4 production from coalbed methane but also allows the injected CO2 to be stored within the coal seam. This storage technology mitigates the adverse effects of the greenhouse effect and achieves the dual goals of CO2 geological storage and enhanced CH4 extraction. Although the technology has not yet reached a mature stage, several industrial trials have been conducted worldwide, initially demonstrating its feasibility and playing a crucial role in unlocking the potential of coal seams for storage.

[0004] Existing research on the interaction between coal and CO2 focuses on pressure, temperature, and coal rank, but little research has examined the impact of the interaction time between CO2 and coal on coal pore structure. Therefore, studying the interaction time between coal and supercritical CO2 is crucial and fundamental for implementing CO2-ECBM technology, assessing its impact on coal seam pore structure and its storage potential. Summary of the Invention

[0005] In order to overcome the problems in the background technology, the purpose of the present invention is to provide a method for calculating the CO2 storage potential of deep coal seams based on the geological characteristics of the coal seams, which can quantitatively calculate the CO2 geological storage amount under different CO2 adsorption times, and provide a scientific calculation method for evaluating the CO2 storage potential.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for calculating the CO2 storage potential of deep coal seams based on the geological characteristics of the coal seams includes the following steps:

[0008] (1) Based on the characteristics of deep coal seams, isothermal adsorption tests were conducted to obtain the excess adsorption capacity of coal samples at different CO2 adsorption time points, and the adsorption time-excess adsorption capacity formula was fitted. Then, based on the relationship between excess adsorption capacity and absolute adsorption capacity, a calculation model for CO2 adsorption capacity at different adsorption times was obtained;

[0009] (2) The porosity values ​​of coal samples reduced at different times by NMR testing are processed, and a calculation model for the free CO2 content per unit mass of coal samples is constructed based on the actual gas state equation and Maliot's law;

[0010] (3) The solubility of CO2 in formation water is obtained based on the CO2 solubility calculation model Then, a calculation model for dissolved CO2 per unit mass of coal sample was constructed;

[0011] (4) Obtain the relationship data of CO2 migration distance in coal seams at different times, and fit the time-coal seam CO2 migration distance formula and the time-maximum migration distance formula;

[0012] (5) A calculation model for the CO2 storage capacity per unit coal sample mass was established based on the existence form of CO2 in coal seams, and the theoretical storage capacity of CO2 geological storage was constructed considering the influence of time.

[0013] Preferably, the relationship between the excess adsorption capacity and the absolute adsorption capacity is:

[0014]

[0015] Among them, n a and n b Represent the excess adsorption capacity and absolute adsorption capacity, mmol / kg; ρ a and ρ g Represent the adsorption phase density and the bulk phase density, kg / m 3 .

[0016] Preferably, in step (2), the coal samples after being acted on by supercritical CO2 for different times are subjected to nuclear magnetic resonance testing, and the time-porosity formula is fitted based on the time-varying law of the porosity of the coal samples with different adsorption times according to the nuclear magnetic resonance T2 spectrum.

[0017] Preferably, in step (2), the calculation model of the free CO2 amount per unit mass of coal sample specifically includes:

[0018] S2-1: Based on the actual gas state equation and Maliot's law, the formula for the free CO2 content per unit mass of coal sample is obtained:

[0019] The actual gas state equation is:

[0020] PV = ZnRT (3);

[0021] Where P refers to the reservoir pressure, Pa; V refers to the gas volume, m 3 ; Z refers to the gas compressibility factor; n refers to the amount of gas substance, mol; R refers to the molar gas constant; T refers to the reservoir gas temperature, K.

[0022] According to the actual gas state equation, the amount of free CO2 in the coal seam can be obtained;

[0023]

[0024] where n free is the amount of free CO2 under standard conditions, cm 3 / g.

[0025] S2-2: Combined volume formula of target reservoir coal sample:

[0026]

[0027] Where V coal Refers to the volume of target reservoir coal sample, m 3 ;M coal Refers to the mass of the target reservoir coal sample, kg; Refers to the effective porosity occupied by free CO2, %; ρ coal Refers to the apparent density of coal, g / cm 3 .

[0028] S2-3: According to formulas (4) and (5), the amount of free CO2 per unit mass of coal sample under standard conditions can be obtained:

[0029]

[0030] Preferably, the CO2 solubility calculation model is:

[0031]

[0032] in m Na 、m K 、m Ca 、m Mg 、m Cl and are the solubilities of CO2, Na, K, Ca, Mg, Cl and SO4 in formation water, mol / kg; is the mole fraction of CO2 in the gas phase, dimensionless; is the fugacity coefficient of CO2, dimensionless; μ is the difference in standard chemical potential of CO2 in liquid and gas phases; δ1 is the binary interaction parameter between CO2 and Na; δ2 is the ternary interaction parameter between CO2, Na and Cl.

[0033] Preferably, the CO2 mole fraction in the gas phase is for:

[0034]

[0035] in Refers to the saturated vapor pressure of water, Pa.

[0036] The CO2 fugacity coefficient for:

[0037]

[0038] Among them, c1~c 15 is an empirical parameter.

[0039] Preferably, μ, δ1 and δ2 are calculated according to the following empirical formula:

[0040]

[0041] Where Par represents one of the three parameters μ, δ1 and δ2; a1-a 11 is an empirical parameter.

[0042] Preferably, the calculation model of dissolved CO2 per unit mass of coal sample is:

[0043]

[0044] where n s Refers to the dissolved CO2 storage volume per unit mass of coal sample, m 3 / kg; S W Refers to the average water saturation, %; is the average porosity of the reservoir, %; Refers to the solubility of CO2 in unit mass of coal sample, kg / m 3 ,

[0045] Preferably, the theoretical CO2 storage capacity calculation model per unit coal sample mass is:

[0046] M t =2πS 2 (t)×H×ρ coal ×n total (t) (15);

[0047] Among them, M t is the theoretical CO2 storage capacity, m 3 ;2πS 2 (t) is the geological storage area of ​​CO2 in coal seams, m 3 ;S 2 (t) is the CO2 migration distance at time t, m; H is the coal seam thickness, m; n total Indicates the total amount of CO2 stored in unit mass of coal, m 3 / g;n total =n ab +n free +n s, n ab is the amount of CO2 adsorbed per unit mass of coal, m 3 / g,n ab =2.24×10 -8 n b .

[0048] Beneficial effects of the present invention:

[0049] 1. In view of the fact that coal seams are heterogeneous rock formations, coal seam occurrence conditions are complex and changeable, and CO2-ECBM field projects involve too many variables, this paper proposes a new calculation method for evaluating the geological storage potential of coal seams. Based on the measurement and research of coal sample parameters such as coal seam pore structure distribution, porosity, and permeability, combined with quantitative models of adsorbed, free, and dissolved CO2, a multi-dimensional assessment of the CO2 storage potential of deep coal seams is achieved.

[0050] 2. The calculation method of the CO2 storage potential of deep coal seams based on the geological characteristics of coal seams described in the present invention introduces the time parameter for the first time, constructs dynamic models such as the adsorption amount-time calculation model, the porosity-time model, and the coal seam CO2 migration distance and time. Finally, a storage amount calculation model is constructed to reveal the change pattern of coal seam storage amount over time, and the evolution pattern of CO2 storage amount with adsorption time, which makes up for the deficiency of traditional methods that ignore the time effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a flow chart of the method for calculating the CO2 storage potential of deep coal seams based on the geological characteristics of the coal seams of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described in detail below with reference to an embodiment of the Yutianbao mining area in Chongqing, but the protection scope of the present invention is not limited thereto.

[0053] This paper addresses the issue of how the CO2 storage capacity of coal seams changes over time under the action of supercritical CO2. It proposes a method for calculating the CO2 storage potential of deep coal seams based on the geological characteristics of the coal seams. This method can quantitatively calculate the amount of CO2 geological storage under different CO2 adsorption times, providing a scientific calculation method for evaluating CO2 storage potential. It is worth noting that the solution requires simplification of simulations and calculations based on different needs. The following basic assumptions are proposed for the numerical simulation of gas migration patterns after CO2 injection into coal seams:

[0054] (1) The media used for sealing in the reservoir are all ideally uniform porous media and the anisotropy of the coal seam is ignored;

[0055] (2) The temperature must be kept constant throughout the entire process so that the flow of CO2 and CH4 in the coal seam is isothermal, and any thermal effects caused by gas adsorption and desorption must be ignored;

[0056] (3) The free gas in the coal seam is regulated by the ideal gas state equation;

[0057] (4) The adsorbed CO2 and CH4 in the coal seam are transported by diffusion in the pore system, following Fick's law; while the free CO2 and CH4 migrate by seepage, following Darcy's law;

[0058] (5) The permeability of the coal seam roof is not considered, the surrounding rock layers are assumed to have negligible permeability, and the presence of CH4 is ignored;

[0059] (6) Coal seams are mainly composed of CO2 and CH4. Without considering the influence of water, their adsorption and desorption behaviors follow the Langmuir equation;

[0060] (7) The deformation of the coal reservoir is elastic deformation with very small deformation.

[0061] Example 1

[0062] like Figure 1 As shown, a method for calculating the CO2 storage potential of deep coal seams based on the geological characteristics of the coal seams includes the following steps:

[0063] (1) Based on the characteristics of deep coal seams, isothermal adsorption tests were conducted to obtain the excess adsorption capacity of coal samples at different CO2 adsorption time points and fit the adsorption time-excess adsorption capacity formula. Then, based on the relationship between excess adsorption capacity and absolute adsorption capacity, a calculation model for CO2 adsorption capacity at different adsorption times was obtained, specifically including:

[0064] S1-1: Based on the pressure and temperature characteristics of the deep coal seams in Yutianbao, Chongqing, anthracite coal samples (coal samples were taken from the target study area to ensure that their geological conditions and mineral composition were consistent with the actual sealed coal seams) were subjected to isothermal adsorption tests to obtain excess adsorption capacity values. The coal samples were placed in a supercritical CO2 environment reactor to simulate the high temperature and high pressure conditions of deep coal seams (40°C, 8.1MPa). The pore structure and adsorption characteristics of the coal were changed through physical and chemical reactions such as adsorption, dissolution, and extraction between the supercritical CO2 and the coal seams. The treatment time was 1, 3, 7, 14, and 28 days, respectively. The excess adsorption capacity of the untreated coal samples and the coal samples treated for 1, 3, 7, 14, and 28 days was then fitted to obtain the time-excess adsorption capacity formula: n a =0.83+0.57ln(t a ); where n a is the excess adsorption capacity; t a is the supercritical CO2 treatment time.

[0065] The pressure and temperature characteristics of deep coal seams play a vital role in the excess adsorption amount. Here, the pressure and temperature characteristics of deep coal seams are to collect the real coal seam pressure and temperature. This embodiment takes Yutianbao Coal Mine as an example: 1. Pressure characteristics: According to the buried depth of the coal seam of Yutianbao Coal Mine (900-1000m), the experimental pressure is set to 8.1MPa, which matches the actual formation pressure (about 8.1MPa) to ensure that the physical state of supercritical CO2 (critical point: 7.38MPa, 31.04℃) is consistent with the deep coal seam. 2. Temperature characteristics: The experimental temperature is set to 40℃, which is consistent with the temperature of the deep coal seam (about 40℃) to avoid the interference of temperature differences on the adsorption behavior of coal samples.

[0066] S1-2: However, since the adsorption of CO2 by coal is not a monolayer adsorption, in the case of multilayer adsorption, the excess adsorption capacity obtained by the isothermal adsorption simulation experiment cannot fully reflect the absolute adsorption capacity of the coal sample. The absolute adsorption capacity is calculated using the relationship between the absolute adsorption capacity and the excess adsorption capacity:

[0067]

[0068] Among them, n a and n b Represent the excess adsorption capacity and absolute adsorption capacity, mmol / kg; ρ a and ρ g Represent the adsorption phase density and the bulk phase density, kg / m 3 According to the data, the main phase density of the coal seam in Yutianbao Coal Mine is 1340kg / m 3 , the density of adsorption phase is 1000kg / m 3 .

[0069] (2) The porosity values ​​of coal samples after treatment at different times are processed using nuclear magnetic resonance testing, and a calculation model for the free CO2 amount per unit mass of coal samples is constructed based on the actual gas state equation and Maliot's law, specifically including:

[0070] S2-1: Coal samples treated with supercritical CO2 for different periods of time were subjected to nuclear magnetic resonance (NMR) tests. The NMR T2 spectrum data were analyzed, and the porosity values ​​of the untreated coal samples and the coal samples treated for 1, 3, 7, 14, and 28 days were 2.05%, 3.52%, 4.83%, 5.25%, 5.30%, and 5.30%, respectively. The time-porosity formula was fitted based on the time-varying patterns of the coal samples treated for 1, 3, 7, 14, and 28 days:

[0071]

[0072] in, is the porosity of the coal sample, with a dimension of 1; t is the interaction time between supercritical CO2 and the coal sample, with a unit of day.

[0073] S2-2: Based on the actual gas state equation and Maliot's law, the formula for the free CO2 content per unit mass of coal sample is obtained, where the actual gas state equation is as follows:

[0074] PV = ZnRT (3);

[0075] Where P refers to the reservoir pressure, Pa; V refers to the gas volume, m 3 Z refers to the gas compressibility factor; n refers to the amount of gas, mol; R refers to the molar gas constant; T refers to the reservoir gas temperature, K. The gas compressibility factor Z of the Yutianbao coal seam under temperature and pressure is 0.32.

[0076] According to the actual gas state equation, the amount of free CO2 in the coal seam can be obtained;

[0077]

[0078] where n free is the amount of free CO2 under standard conditions, cm 3 / g;V coal Refers to the volume of target reservoir coal sample, m 3 ;.

[0079] S2-2: Combined volume formula of target reservoir coal sample:

[0080]

[0081] Where V coal Refers to the volume of target reservoir coal sample, m 3 ;M coal Refers to the mass of the target reservoir coal sample, kg; Refers to the effective porosity occupied by free CO2, %; ρ coal Refers to the apparent density of coal, g / cm 3 Yutianbao Coal Seam M coal is 2.7403×10 10 kg, ρ coal 1.34 g / cm 3 , About 0.0237200307%.

[0082] Under standard conditions, the calculation model of free CO2 per unit mass of coal sample is obtained:

[0083]

[0084] (3) The solubility of CO2 in formation water is obtained based on the CO2 solubility calculation model , and then build a calculation model for dissolved CO2 per unit mass of coal sample, including:

[0085] S3-1: Calculate the solubility of CO2 in formation water based on the CO2 solubility calculation model :

[0086]

[0087] in m Na 、m K 、m Ca 、 m Cl and are the solubilities of CO2, Na, K, Ca, Mg, Cl and SO4 in formation water, mol / kg respectively.

[0088] is the mole fraction of CO2 in the gas phase, dimensionless,

[0089]

[0090] Among them, P H2O Refers to the saturated vapor pressure of water, Pa;

[0091] is the fugacity coefficient of CO2, dimensionless;

[0092]

[0093] where c1-c 15 is an empirical parameter.

[0094] μ is the difference in standard chemical potential of CO2 in liquid and gas phases; δ1 is the binary interaction parameter between CO2 and Na; and δ2 is the ternary interaction parameter between CO2, Na, and Cl.

[0095] μ, δ1, and δ2 can be calculated according to the following empirical formulas:

[0096]

[0097] Where Par represents one of the three parameters μ, δ1 and δ2; a1-a 11 is an empirical parameter.

[0098] S3-2: Based on the characteristics of the coal seam to be evaluated, the solubility of CO2 in formation water calculated in combination with formula (7) Construct a calculation model for dissolved CO2 per unit mass of coal sample:

[0099]

[0100] where n sRefers to the dissolved CO2 storage volume per unit mass of coal sample, m 3 / kg; S W Refers to the average water saturation, %; is the average porosity of the reservoir, %; Refers to the solubility of CO2 in unit mass of coal sample, kg / m 3 ,

[0101] (4) Obtain the relationship data of CO2 migration distance in coal seams at different times, and fit the time-coal seam CO2 migration distance formula and the time-maximum migration distance formula, specifically:

[0102] Based on the geological parameters of the specific target reservoir, such as coal seam depth of 950m, reservoir temperature of 40℃, initial porosity of 0.09 and permeability of 5×10 -15 Gas injection parameters, such as the gas injection pressure of 14 MPa, were used to establish a thermal-fluid-solid coupling model using COMSOL Multiphysics software, and to establish the equation for the permeability of the coal matrix coal seam:

[0103]

[0104] Where k is the permeability; k0 is the initial permeability; φ0 is the initial porosity; ε V is the volume strain of the reservoir; α is the Biot coefficient; K s is the modulus of the object; Δε s is the total volume strain change; α s is the thermal expansion coefficient, K -1 ; ΔT is the temperature change, ΔP1 is the CH4 partial pressure change, MPa; ΔP2 is the CO2 partial pressure change, MPa;

[0105] Based on the above permeability equation, the permeability relationship equation at different times was statistically calculated. The CO gas pressure distribution and concentration distribution at different time points were simulated by the relationship between permeability and gas concentration. The partial differential control equation for the concentration change of a single gas component during the flow in the coal matrix and microcracks inside the low permeability coal seam is as follows:

[0106]

[0107] Where i = 1 or 2, subscript i = 1 indicates that the component is CH4, and subscript i = 2 indicates that the component is CO2; i represents the molar mass of gas i, kg / mol; C i Indicates the gas concentration in coal, mol / m 3 ρ c Indicates coal density, kg / m 3 ρ gaiIndicates the gas density, kg / m 3 ; b i represents the Langmuir pressure constant of gas i, MPa -1 ; V Li represents the Langmuir volume constant of gas i, m 3 / kg; R represents the universal gas constant, J / (mol·K); μ i represents the dynamic viscosity coefficient, Pa·s; D i represents the gas diffusion coefficient, m 2 / s;Q Si =±M i (C gfi -C gmi ) / τ i is the source or sink term of gas i, kg / (m3·s); C gfi and C gmi Represent the concentration of gas i in the coal matrix and coal microcracks, mol / m 3 ; τ i is the adsorption time of gas i on the coal matrix, s.

[0108] The maximum CO migration distance and saturation migration distance can be extracted from the CO gas pressure distribution and concentration distribution at different time points. Then, the time-distance data are fitted to obtain the time-saturation migration distance formula:

[0109] S=0.03t0+23.95(14);

[0110] S is the migration distance at saturation, m; t0 is the gas injection time, d.

[0111] Time-maximum migration distance formula:

[0112] S max =0.06t0+42.8(15);

[0113] There is a limit to the CO2 migration distance over time. The time-maximum migration distance formula can reflect the maximum impact range of CO2 that the reservoir can capture over time.

[0114] (5) A calculation model for CO2 storage capacity per unit coal sample mass is established based on the CO2 presence in coal seams, and the theoretical CO2 geological storage capacity is constructed by considering the time effect. Specifically, it includes:

[0115] S5-1: CO2 exists in coal seams in the form of free, adsorbed, and dissolved states. Considering the temporal variation factor, a formula for calculating the theoretical CO2 storage capacity per unit coal sample mass and the theoretical storage capacity of CO2 geological storage are constructed.

[0116] The calculation formula for the theoretical CO2 storage capacity per unit coal sample mass is:

[0117] M t =2πS 2 (t)×H×ρ coal ×n total (t) (16);

[0118] Among them, M t is the theoretical total CO2 storage capacity, m 3 ;2πS 2 (t) is the geological storage area of ​​CO2 in coal seams, m 2 ;S 2 (y) is the CO2 migration distance at time t, m; H is the coal seam thickness, m. 2 1.3×10 5 m 2 ; H is 5m; ρ coal 1.34 g / cm 3 .

[0119] n total =n ab +n free +n s (17);

[0120] where n total Indicates the total amount of CO2 stored in unit mass of coal, m 3 / g;n ab is the amount of CO2 adsorbed per unit mass of coal, m 3 / g,n ab =2.24×10 -8 n b . Yutianbao mining area reservoir n ab is 3.741×10 -5 m 3 / g;n free 8.5×10 -7 m 3 / g;n s 2.8×10 -8 m 3 / g; after calculation, we get M t 1.05×10 9 m 3 .

[0121] It is worth noting that in order to determine n totalThe total amount of CO2 stored in unit mass of coal should be calculated by using a coupled geological model to calculate the seepage of CO2 in the coal seam and obtain a gas pressure distribution map. At the same time, the distribution map should be observed to find the CO2 pressure stabilization point where the gas pressure and ground stress in the reservoir have reached equilibrium, indicating that the saturation state of CO2 geological storage has been reached at this time.

[0122] In order to verify the accuracy of the calculation results of the deep coal seam CO2 storage potential based on the geological characteristics of the coal seam in this invention.

[0123] The actual storage capacity of the coal seam is also related to the on-site injection time. In order to prevent CO2 leakage, CO2 geological storage is generally considered to be completed when CO2 is detected at the production wellhead and accounts for 2% of the produced gas, which is equivalent to the CH4 content. The actual storage capacity is then the CO2 injection capacity when CO2 gas is detected. The actual CO2 storage capacity formula is:

[0124] M0=M1+M2 (18);

[0125] Where M0 refers to the actual CO2 storage capacity, m 3 ; M1 refers to the CO2 injection volume in the interwell area, m 3 ; M2 refers to the remaining regional CO2 storage capacity, m 3 .

[0126] The calculated M0 is 1.05×10 9 m 3 The actual CO2 storage capacity M0 is 8.87×10 8 m 3 , the simulation is about 118.37% of the actual one.

[0127] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics, characterized by: The steps include: (1) Based on the characteristics of deep coal seams, isothermal adsorption tests were conducted to obtain the excess adsorption capacity of coal samples at different CO2 adsorption time points, and the adsorption time-excess adsorption capacity formula was fitted. Then, based on the relationship between excess adsorption capacity and absolute adsorption capacity, a calculation model for CO2 adsorption capacity at different adsorption times was obtained; (2) The porosity values ​​of coal samples reduced at different times by NMR testing are processed, and a calculation model for the free CO2 content per unit mass of coal samples is constructed based on the actual gas state equation and Maliot's law; (3) The solubility of CO2 in formation water is obtained based on the CO2 solubility calculation model Then, a calculation model for dissolved CO2 per unit mass of coal sample was constructed; (4) Obtain the relationship data of CO2 migration distance in coal seams at different times and fit the time-coal seam CO2 migration distance formula; (5) A calculation model for the CO2 storage capacity per unit coal sample mass was established based on the existence form of CO2 in coal seams, and the theoretical storage capacity of CO2 geological storage was constructed considering the influence of time.

2. The method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics according to claim 1 is characterized by: The relationship between the excess adsorption capacity and the absolute adsorption capacity is: Among them, n a and n b Represent the excess adsorption capacity and absolute adsorption capacity, mmol / kg; ρ a and ρ g Represent the adsorption phase density and the bulk phase density, kg / m 3 .

3. The method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics according to claim 1 is characterized by: In the step (2), the coal samples after being subjected to supercritical CO2 for different times are subjected to nuclear magnetic resonance testing, and the time-porosity formula is fitted based on the time-varying law of the porosity of the coal samples with different adsorption times according to the nuclear magnetic resonance T2 spectrum.

4. The method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics according to claim 1 is characterized by: In step (2), the calculation model of the free CO2 amount per unit mass of coal sample specifically includes: S2-1: Based on the actual gas state equation and Maliot's law, the formula for the free CO2 content per unit mass of coal sample is obtained. The actual gas state equation is: PV = ZnRT (3); Where P refers to the reservoir pressure, Pa; V refers to the gas volume, m 3 ; Z refers to the gas compressibility factor; n refers to the amount of gas substance, mol; R refers to the molar gas constant; T refers to the reservoir gas temperature, K; According to the actual gas state equation, the amount of free CO2 in the coal seam can be obtained; where n free is the amount of free CO2 under standard conditions, cm 3 / g; S2-2: Combined volume formula of target reservoir coal sample: Where V coal Refers to the volume of target reservoir coal sample, m 3 ;M coal Refers to the mass of the target reservoir coal sample, kg; Refers to the effective porosity occupied by free CO2, %; ρ coal Refers to the apparent density of coal, g / cm 3 ; The amount of free CO2 per unit mass of coal sample under standard conditions is obtained:

5. The method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics according to claim 1 is characterized by: The CO2 solubility calculation model is: in m Na 、m K 、m Ca 、m Mg 、m Cl and are the solubilities of CO2, Na, K, Ca, Mg, Cl and SO4 in formation water, mol / kg; is the mole fraction of CO2 in the gas phase, dimensionless; is the fugacity coefficient of CO2, dimensionless; μ is the difference in standard chemical potential of CO2 in liquid and gas phases; δ1 is the binary interaction parameter between CO2 and Na; δ2 is the ternary interaction parameter between CO2, Na and Cl.

6. The method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics according to claim 5 is characterized by: The CO2 mole fraction in the gas phase for: in Refers to the saturated vapor pressure of water, Pa; Indicates the pressure of CO2 in the reservoir, Pa. The CO2 fugacity coefficient for: (9)； where c1-c 15 is an empirical parameter; T is the reservoir gas temperature; The μ, δ1 and δ2 are calculated according to the following empirical formula: Where Par represents one of the three parameters μ, δ1 and δ2; a1-a 11 is an empirical parameter.

7. The method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics according to claim 1 is characterized by: The calculation model of dissolved CO2 per unit mass of coal sample is: where n s Refers to the dissolved CO2 storage volume per unit mass of coal sample, m 3 / kg; S W Refers to the average water saturation, %; is the average reservoir porosity, %; Refers to the solubility of CO2 in unit mass of coal sample, kg / m 3 , 8. The method for calculating the CO2 storage potential of deep coal seams based on coal seam geological characteristics according to claim 1 is characterized by: The theoretical CO2 storage capacity calculation model per unit coal sample mass is: M t =2πS 2 (t)×H×ρ coal ×n total (t)(15); Among them, M t is the theoretical CO2 storage capacity, m 3 ;2πS 2 (t) is the geological storage area of ​​CO2 in coal seams, m 3 ;S 2 (t) is the CO2 migration distance at time t, m; H is the coal seam thickness, m; n total Indicates the total amount of CO2 stored in unit mass of coal, m 3 / g; n total =n ab +n free +n s (16); n ab is the amount of CO2 adsorbed per unit mass of coal, m 3 / g,n ab =2.24×10 -8 n b .

Images