Deep coal seam carbon dioxide geological sequestration potential evaluation method for high-exploration-degree coal field

Abstract

The invention discloses a deep coal seam carbon dioxide geological sequestration potential evaluation method for a high-exploration-degree coal field, and relates to the technical field of deep coal seam carbon dioxide sequestration evaluation. The method comprises the following steps: firstly, on the basis of analyzing comprehensive geologic features of a coal loading area, determining a remaining coal seam reserve distribution rule; determining a coal-bearing stratum ground temperature and pressure gradient value, calculating a carbon dioxide sequestration critical depth, and determining a carbon dioxide geological sequestration main body depth; then preferably selecting a main area suitable for carbon dioxide sequestration; dividing carbon dioxide geological units according to construction conditions by taking a coal field as a unit; carbon dioxide geological unit division is carried out on each key block, and carbon dioxide sequestration amount calculation is carried out according to the units; and finally, optimizing the favorable area of the carbon dioxide sequestration unit by using an analytic hierarchy process-fuzzy evaluation method. According to the method, original coal field geological data are fully utilized, a large number of coal rock foundation geological parameters are easy to obtain, and a good theoretical basis is provided for subsequent realization of a regional dual-carbon target.

Description

Technical Field

[0001] The present invention relates to the technical field of deep coal seam carbon dioxide storage evaluation, and in particular to a method for evaluating the geological storage potential of carbon dioxide in deep coal seams of coal fields with a high degree of exploration. Background Art

[0002] CO2 geological storage is expected to become an effective method for carbon emission reduction. Deep unmineable coal seams are potential geological bodies for CO2 storage. CO2 injection into coal seams can displace the CH4 output of coal seams due to its competitive adsorption advantage and become a coalbed methane enhanced production method. Coalbed CO2 geological storage and CH4 enhanced mining (CO2-ECBM) technology integrates greenhouse gas emission reduction and new energy development, and is very promising. How to achieve CO2 injection into coal seams to reduce emissions, increase CH4 production and avoid catastrophic CO2 leakage is the main problem facing the academic community. Effectiveness, economy, long-term and safety are the main theoretical and technical issues facing CO2-ECBM, among which effectiveness is the basis and premise, and is also the focus of research in this field. The connotation of CO2-ECBM effectiveness is CO2 injectability, CO2 storage capacity and CH4 production capacity. Injectability is the core issue of the effectiveness of CO2 storage in coal seams. The injection of CO2 into coal seams will cause stress and strain effects on coal rock, which is manifested as volume expansion deformation and expansion stress of coal rock caused by the adsorption of CO2 into coal seams, which will reduce the permeability of coal reservoirs, the CO2 flow rate of injection wells, and the pressure transmission rate, which can directly lead to a decrease in the injectability of CO2 in coal seams. Deep coal seams (burial depth ≥ 800m) have higher geotemperature, reservoir pressure and geostress, and CO2 will exist in a supercritical state. For CO2-ECBM in deep coal seams, the stress and strain changes of coal rock caused by supercritical CO2 should be more significant, and the injectability of CO2 in deep coal seams is more prominent.

[0003] Based on this, a large number of scholars have taken coal reservoirs as the research object to explore the feasibility of CO2 geological storage. According to the research principles and differences in reservoir locations, it can be divided into CO2 geological storage in coal mine goaf areas and unmined coal seam areas (shallow unmined coal seam areas and deep unminable coal seam areas). Among them, the storage space in the coal mine goaf area is mainly the residual volume of rock voids in the caving zone and the fracture volume of the rock formation in the fracture zone plus the residual shaft and tunnel space. The sealing mechanism is relatively simple, and the sealing of the formation after CO2 injection becomes a difficulty that restricts this technology. In addition, the storage space in the unmined coal seam area is mainly the surface of the coal reservoir matrix. The displacement and replacement effect is the main mechanism that distinguishes it from the CO2 geological storage in the coal mine goaf area, and it is also one of the main factors restricting the CO2 storage effect. In the actual mining process of coal mines, due to the constraints of geological structure and other factors, a considerable amount of coal powder, coal blocks, coal pillars and goaf space coexist. While providing storage space for CO2, the adsorption mechanism can also enable CO2 to achieve the transformation from free state to adsorbed state. Whether the geological storage of CO2 in the goaf and unmined area of ​​the same structural unit is unified remains to be explored. In general, the current research on the evaluation system of different CO2 geological storage technologies in coal seam development areas is relatively independent, and has not formed a unified research whole, and the research theory in this field is not mature.

[0004] This shows that the prior art needs to be further improved. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the geological storage potential of carbon dioxide in deep coal seams of highly explored coalfields, which makes full use of the original coalfield geological data and easily obtains a large number of basic geological parameters of coal rocks, providing a good theoretical basis for the subsequent realization of regional dual carbon goals.

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

[0007] A method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a high-exploration coalfield comprises the following steps in sequence:

[0008] Step 1: Based on the analysis of the comprehensive geological characteristics of the coal-bearing area, clarify the distribution law of the remaining coal seam reserves;

[0009] Step 2: Further clarify the geothermal gradient and pressure gradient values ​​of coal-bearing strata, calculate the critical depth of carbon dioxide storage, and determine the main depth of carbon dioxide geological storage;

[0010] Step 3: Taking geological structure, coal-bearing sedimentary conditions and burial depth as the main factors, select the main areas suitable for CO2 storage in coal fields;

[0011] Step 4: Determine the main controlling factors in the main areas of carbon dioxide geological storage, and preliminarily analyze and summarize the influencing factors in the process of carbon dioxide geological storage mainly from the two aspects of coal reservoir characteristics and gas injection work system; Based on the sensitivity analysis of each influencing factor, determine the main controlling factors according to the principle of combining qualitative and quantitative evaluation, and analyze the effects of carbon dioxide geological storage under different schemes;

[0012] Step 5: Based on the results obtained in step 4 and step 3, the carbon dioxide geological storage units in the coalfield are divided according to the distribution law of the main controlling factors;

[0013] Step 6: Calculate the theoretical geological storage capacity and effective geological storage capacity of carbon dioxide in the coal-bearing area, and evaluate the geological storage potential of carbon dioxide in the main coal seams in the study area;

[0014] The amount of carbon dioxide geological storage in the coal-bearing area is calculated according to formula (1):

[0015] M t =A×H×ρ coal ×m (1);

[0016] In formula (1): M t is the theoretical geological storage capacity; A is the area of ​​CO2 geological storage; H is the thickness of the coal seam; ρ coal is the apparent density of coal rock; m is the unit storage capacity of CO2;

[0017] Step 7: Based on the carbon dioxide storage capacity of each unit and the physical properties of the coal reservoir, the hierarchical analysis-fuzzy comprehensive evaluation method is used to select the favorable areas for carbon dioxide geological storage.

[0018] In the above-mentioned method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield, in step one, on the basis of clarifying the distribution law of the remaining coal seam reserves, the basic geological characteristics, coal petrology characteristics, adsorption reservoir characteristics, reservoir physical properties characteristics and fluid characteristics of each coalfield are also clarified; wherein the basic geological characteristics include the tectonic environment of the reservoir, the reservoir distribution scale, and the roof and floor and hydrogeological characteristics related to the reservoir; the coal petrology characteristics include the coal rock type and metamorphic degree characteristics of the reservoir; the adsorption reservoir characteristics and reservoir physical properties characteristics include the gas content of the coal seam, the adsorption and desorption characteristics, and the pore and fracture distribution and permeability development status of the coal reservoir; the fluid characteristics include the characteristics and composition of gas and water and their physical properties.

[0019] In the above-mentioned method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield, in step 2, the temperature and pressure conditions of the corresponding coal seam burial depth are calculated based on the geothermal gradient value, pressure gradient value and burial depth data of the coal-bearing stratum. When the pressure is 7.38 MPa and the temperature is 31.1°C, it is taken as the critical point. If the temperature and pressure conditions corresponding to the coal-bearing stratum are ≥ the critical point, it means that the coal-bearing area is conducive to the geological storage of carbon dioxide; if the temperature and pressure conditions corresponding to the coal-bearing stratum are < the critical point, it means that the coal-bearing area is not conducive to the geological storage of carbon dioxide.

[0020] In the above-mentioned method for evaluating the carbon dioxide geological storage potential of deep coal seams in a coalfield with a high degree of exploration, when the geological structure is the main factor, the nature of the fault is first determined. If it is a normal fault, the area is a tensile fault, the coal seam roof and floor sealing is weak, and it is not suitable for carbon dioxide geological storage; if it is a reverse fault, the area is a compressive fault, the coal seam roof and floor sealing is strong, and it is suitable for carbon dioxide geological storage;

[0021] When the sedimentary coal-bearing conditions are the main factors, the lithology of the top and bottom plates of deep coal seams is judged. If it is a porous and dense rock layer such as mudstone or shale, the sealing property is strong; if it is a porous and loose rock layer such as sandstone, the sealing property is weak.

[0022] When burial depth is the main factor, the temperature and pressure conditions and critical point corresponding to the coal-bearing strata are used to determine whether the coal-bearing area is conducive to the geological storage of carbon dioxide.

[0023] The above-mentioned method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield, wherein the coal reservoir characteristics mainly include coal rank, organic microscopic components, permeability, physical and mechanical properties or water content, and the gas injection working system mainly includes the injection rate, injection pressure and injection time of carbon dioxide.

[0024] The above-mentioned method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield adopts a combination of COMET3 and Eclipse reservoir simulation software when conducting sensitivity analysis on various influencing factors; based on the existing geological conditions in the target area and the vertical well production data of ground development, the reservoir simulation software COMET3 is used to correct the reservoir parameters using the historical fitting method to achieve the maximum consistency with the actual geological conditions. On this basis, different engineering schemes are designed in accordance with the principle of statistical optimization from the two aspects of coal reservoir characteristics and working system, with the changes in coalbed methane production, carbon dioxide storage volume, and reservoir pressure under numerical simulation calculations as the main consideration indicators, and the sensitivity analysis of various influencing factors is gradually realized.

[0025] In the above-mentioned method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield, in step 6, the calculation of the unit storage capacity of CO2 m is shown in formula (2):

[0026] m=m a d+m v 0 +m s (2);

[0027] In formula (2): m ad is the CO2 adsorption storage capacity per unit mass of coal rock; m v0 is the static storage capacity of CO2 per unit mass of coal rock; m s is the amount of dissolved CO2 stored in the pore water of coal rock per unit mass;

[0028] The actual adsorption amount is obtained according to formula (3):

[0029]

[0030] In formula (3): m a is the actual adsorption amount, m e is the Gibbs adsorption capacity, ρ a is the density of the adsorbed phase, ρ(P,T) is the density of the free phase at temperature T and pressure P;

[0031] Further combined with formula (4), the theoretical geological storage capacity of carbon dioxide and the effective geological storage capacity of carbon dioxide in the coal-bearing area can be calculated;

[0032]

[0033] In formula (4): M is the molar mass of CO2; n ab (T,p) is the absolute CO2 adsorption storage capacity at a given temperature and pressure; φ is the porosity obtained by mercury injection or logging; S w is water saturation; p is pressure; Z is the CO2 compression factor at a certain temperature and pressure; ρ coal is the apparent density of coal rock; R is the molar gas constant, which is 8.314 Pa·m 3 ·mol -1 ·K -1 ; T is temperature; is the solubility of CO2 in pure water at a certain temperature and pressure.

[0034] The above-mentioned method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield has the following specific methods in step 7:

[0035] The factors affecting carbon dioxide geological storage are assigned values ​​and the weights of different factors are determined. The hierarchical analysis-simulation comprehensive evaluation method is used to compare the carbon dioxide storage effects among different units and determine the favorable areas for carbon dioxide geological storage.

[0036] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0037] (1) The present invention proposes a method for evaluating the potential of deep coal seams for carbon dioxide geological storage in coal fields with a high degree of exploration. First, based on the analysis of the comprehensive geological characteristics of the coal-bearing area, the distribution law of the remaining coal seam reserves is clarified; secondly, the geothermal and pressure gradient values ​​of the coal-bearing strata are clarified, the critical depth of carbon dioxide storage is calculated, and the main depth of carbon dioxide geological storage is determined; then, the main area suitable for carbon dioxide geological storage is selected by comprehensively considering factors such as geological structure, sedimentary coal-bearing conditions and burial depth; furthermore, the carbon dioxide geological unit is divided according to the structural conditions based on the coal field; at the same time, for each key block, the carbon dioxide geological unit is divided according to the burial depth conditions, and the carbon dioxide storage amount is calculated based on this unit. Finally, the hierarchical analysis-fuzzy evaluation method is comprehensively used to select the favorable area of ​​the carbon dioxide storage unit. The evaluation method of the present invention makes full use of the original coalfield geological data, and it is easy to obtain a large number of basic geological parameters of coal and rock, which creates a good data foundation for the deep coal seam carbon dioxide geological storage work and provides a good theoretical basis for the subsequent realization of the regional dual carbon goals.

[0038] (2) The evaluation method of the present invention forms a technical system for optimizing the evaluation of favorable areas for geological storage of carbon dioxide based on target coalbed methane. At the same time, it forms a simulation evaluation method and technology for geological storage of carbon dioxide in deep coal seams that comprehensively considers the geothermal field of deep coal seams, and establishes a set of calculation and evaluation technology for the geological storage of carbon dioxide based on the combination of numerical simulation and comprehensive fuzzy evaluation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below in conjunction with the accompanying drawings:

[0040] Figure 1 This is a flow chart of a method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a coal field with a high degree of exploration according to the present invention;

[0041] Figure 2 It is a coalfield division and structural outline map of the southwestern Shandong region in the embodiment of the present invention;

[0042] Figure 3 This is the map of No. 3 coal development area in southwestern Shandong;

[0043] Figure 4 This is the Juye coalfield carbon dioxide storage area division map;

[0044] Figure 5 This is a diagram for analyzing factors affecting carbon dioxide storage;

[0045] Figure 6 This is a schematic diagram of the vertical well numerical model;

[0046] Figure 7This is a schematic diagram of the vertical well group numerical model;

[0047] Figure 8 Determine the comparison chart for the weights of influencing factors based on the analytic hierarchy process;

[0048] Fig. 9 The demarcation map of Juye Coalfield Sealing Block 1 is to comprehensively consider the burial depth;

[0049] Fig.10 is the phase transition diagram of carbon dioxide;

[0050] Fig.11 This is the critical depth of CO2 geological storage in typical coal mines in southwestern Shandong;

[0051] Fig.12 Summary of CO2 storage parameters under different burial depths;

[0052] Fig.13 Summary of CO2 storage parameters for different storage units. DETAILED DESCRIPTION

[0053] The present invention proposes a method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a coalfield with a high degree of exploration. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0054] The COMET3 and Eclipse reservoir simulation software and operation methods described in the present invention can be implemented by those skilled in the art by referring to the existing technology, and will not be described in detail in this article.

[0055] like Figure 1 As shown, the present invention provides a method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a coalfield with a high degree of exploration, which comprises the following steps in sequence:

[0056] Step 1. On the basis of analyzing the comprehensive geological characteristics of the coal-bearing area, clarify the distribution law of the remaining coal seam reserves; on the basis of clarifying the distribution law of the remaining coal seam reserves, clarify the five major characteristics of each coalfield, namely, basic geological characteristics, coal petrology characteristics, adsorption reservoir characteristics, reservoir physical properties characteristics and fluid characteristics; among which, the basic geological characteristics include the tectonic environment where the reservoir is located, the reservoir distribution scale, and the roof and floor and hydrogeological characteristics related to the reservoir; the coal petrology characteristics include the coal rock type and metamorphic degree characteristics of the reservoir; the adsorption reservoir characteristics and reservoir physical properties characteristics include the gas content of the coal seam, adsorption and desorption characteristics, and the pore and fracture distribution and permeability development status of the coal reservoir; the fluid characteristics include the characteristics and composition of gas and water and their physical properties.

[0057] Step 2: Further clarify the geothermal gradient and pressure gradient values ​​of coal-bearing strata, calculate the critical depth of carbon dioxide storage, and determine the main depth of carbon dioxide geological storage; In step 2, relevant literature shows that supercritical carbon dioxide can maximize the effect of carbon dioxide geological storage, so clarifying the temperature and pressure conditions of supercritical carbon dioxide is the basis. At the same time, based on the coalfield geological exploration data, the geothermal gradient, pressure gradient and burial depth data of the target coal seams in each coalfield are statistically analyzed to calculate the temperature and pressure conditions of the corresponding coal seam burial depth.

[0058] According to the mechanism of CO2 geological storage, the supercritical state is the ideal state for achieving CO2 geological storage. The critical point is 7.38Mpa, 31.1℃. By comparing the temperature and pressure conditions corresponding to the coal seam with the critical point, it is determined whether the coal-bearing area is conducive to CO2 geological storage. The specific comparison method is as follows: Fig.10 As shown in the figure: if the temperature and pressure conditions corresponding to the coal seam are higher than the critical point, it means that the coal-bearing area is conducive to CO2 geological storage; if the temperature and pressure conditions corresponding to the coal seam are lower than the critical point, it means that the coal-bearing area is not conducive to CO2 geological storage.

[0059] Step 3: Taking geological structure, sedimentary coal-bearing conditions and burial depth as the main factors, select the main area suitable for carbon dioxide storage in coalfields; when the main factor is geological structure, first determine the nature of the fault. If it is a normal fault, the area is a tensile fault, the coal seam roof and floor sealing is weak, and it is not easy for carbon dioxide geological storage; if it is a reverse fault, the area is a compressive fault, the coal seam roof and floor sealing is strong, and it is suitable for carbon dioxide geological storage.

[0060] When the geological structure takes into account the sedimentary coal-bearing conditions, the rock properties of the top and bottom plates of the deep coal seams are judged. If they are porous and dense rock layers of mudstone or shale, the sealing property is relatively strong; if they are porous and loose rock layers of sandstone, the sealing property is relatively weak.

[0061] When the burial depth is taken into consideration in the geological structure, the temperature and pressure conditions and critical points corresponding to the coal-bearing strata are used to determine whether the coal-bearing area is conducive to the geological storage of carbon dioxide.

[0062] Step 4: Determine the main controlling factors in the main areas of carbon dioxide geological storage, and preliminarily analyze and summarize the influencing factors in the process of carbon dioxide geological storage mainly from the two aspects of coal reservoir characteristics and gas injection work system; based on the sensitivity analysis of each influencing factor, determine the main controlling factors according to the principle of combining qualitative and quantitative evaluation, and analyze the carbon dioxide geological storage effect under different schemes.

[0063] The characteristics of coal reservoirs mainly include coal rank, organic micro-components, permeability, physical and mechanical properties or water content, and the gas injection working system mainly includes the injection rate, injection pressure and injection time of carbon dioxide. This numerical simulation study was carried out in the form of a combination of COMET3 and Eclipse reservoir simulation software; based on the existing geological conditions in the target area and the vertical well production data of ground development, the professional coalbed methane reservoir simulation software COMET3 was used, and the historical fitting method was used to correct the reservoir parameters to achieve the maximum consistency with the actual geological conditions. On this basis, considering the characteristics of coal reservoirs and working systems, different engineering schemes were designed according to the principle of statistical optimization, with the changes in coalbed methane production, carbon dioxide storage volume and reservoir pressure under numerical simulation calculation as the main consideration indicators, and gradually realizing the sensitivity analysis of various influencing factors.

[0064] Step 5: Based on the results obtained in step 4 and step 3, divide the carbon dioxide geological storage units in the coalfield according to the distribution law of the main controlling factors.

[0065] Step 6: Calculate the theoretical geological storage capacity and effective geological storage capacity of carbon dioxide in the coal-bearing area, and evaluate the geological storage potential of carbon dioxide in the main coal seams in the study area;

[0066] The CO2 theory and effective geological storage capacity in coal-bearing areas are clarified, the CO2 geological storage potential of the main coal seams in the study area is evaluated based on the comprehensive geological conditions of the coal-bearing areas, the differences in the factors affecting CO2 geological storage are compared, and the relevant laws are explored.

[0067] On this basis, the CO2 storage capacity of key coalfield blocks is calculated, and the steps are as follows:

[0068] (1) Calculation method of CO2 geological storage in coal rock Based on the calculation method of coalbed methane geological resources, the CO2 geological storage per unit mass of coal rock is calculated, combined with the coal resources in the basin, to obtain the theoretical CO2 geological storage. The calculation method is as follows:

[0069] M t =A×H×ρ coal ×m (1);

[0070] Where: M t is the theoretical geological storage capacity, t; A is the area of ​​CO2 geological storage, m 2 ; H is the thickness of the coal seam, m; ρ coal is the apparent density of coal rock, g / cm 3 ; m is the unit storage capacity of CO2 (theoretical storage capacity of CO2 per gram of coal, mass), g.

[0071] (2) Generally speaking, the evaluated CO2 geological storage capacity per unit mass of coal rock is mainly composed of adsorption storage capacity, static storage capacity and dissolved storage capacity:

[0072] m=m ad +m v0 +m s (2);

[0073] Where: m ad is the CO2 adsorption storage capacity per unit mass of coal rock, g; m v0 is the static storage capacity of CO2 per unit mass of coal rock (free phase), g; m s is the amount of dissolved CO2 stored in the pore water of coal rock per unit mass, g.

[0074] (3) The CO2 adsorption storage capacity is accurately obtained through CO2 isothermal adsorption experiment. The Gibbs adsorption capacity is obtained in the experiment. There is a difference between the Gibbs adsorption capacity and the actual adsorption capacity ρ(P,T)*v a , the difference is defined as the Gibbs rejection. In order to obtain the actual adsorption amount, the formula is converted:

[0075]

[0076] Among them, m a is the actual adsorption amount, m e is the Gibbs adsorption capacity, ρ a is the density of the adsorbed phase, ρ(P,T) is the density of the free phase at temperature T and pressure P, and v a is the volume of the adsorbed phase.

[0077] (4) The adsorption storage capacity is obtained by the CO2 adsorption equation, the static storage capacity is obtained by the real gas state equation, and the dissolved storage capacity is obtained by the proposed solubility calculation equation. In summary, it can be converted into:

[0078]

[0079] Where: M is the molar mass of CO2, 44 g / mol; n ab (T,p) is the absolute adsorption storage capacity of CO2 at a given temperature and pressure, mmol / g; φ is the porosity obtained by mercury injection or logging, %. It should be noted that the pores are mainly large and medium pores. This is because if the total pore volume is used, the free phase part in the adsorbed and filled pores will be repeatedly calculated, increasing the evaluation error; S w is water saturation, %; p is pressure, MPa; Z is CO2 compression factor at a certain temperature and pressure; ρ coal is the apparent density of coal rock, g / cm 3 ; R is the molar gas constant, which is 8.314 Pa·m 3·mol -1 ·K -1 ; T is temperature, K; is the solubility of CO2 in pure water at a certain temperature and pressure, mmol / cm 3 .

[0080] Through the above calculations, the theoretical and effective geological storage capacity of CO2 in coal-bearing areas can be obtained, and the geological storage potential of CO2 in the main coal seams in the study area can be evaluated.

[0081] Step 7: Based on the carbon dioxide storage capacity of each unit and the physical properties of the coal reservoir, the hierarchical analysis-fuzzy comprehensive evaluation method is used to select the favorable areas for carbon dioxide geological storage.

[0082] In the above step 7, the factors affecting the geological storage of carbon dioxide are assigned values ​​from the three analysis aspects of structural conditions, coal seam conditions and social conditions, and the weights of different factors are determined. The hierarchical analysis-simulation comprehensive evaluation method is used to compare the carbon dioxide storage effects between different units and determine the favorable areas for the geological storage of carbon dioxide.

[0083] The present invention will be further described below in conjunction with specific embodiments.

[0084] Embodiment 1:

[0085] Taking the deep coal seams in southwestern Shandong as an example, the geological storage potential of carbon dioxide in deep coal seams of coal fields with high exploration degree is evaluated, which specifically includes the following steps:

[0086] Step 1: Analyze the comprehensive geological characteristics of the coal-bearing areas in southwestern Shandong, and on this basis, clarify the distribution pattern of the remaining coal seam reserves. Data show that there are 12 coal-bearing areas in southwestern Shandong, including Caoxian Coalfield, Danxian Coalfield, Juye Coalfield, Liangshan Coalfield, Ningwen Coalfield, Jining Coalfield, and Yanzhou Coalfield. Figure 2 shown. Figure 2 It shows that the fold structure in western Shandong is not well developed. Generally speaking, it mainly forms some monocline structures. The strata in western Shandong (west of Changyi-Dadian fault) are oriented from west to east from northeast and nearly east-west to northwest, and the inclination is also from northwest and north to northeast, with a gentle dip. Some open complex folds are developed in the southwest of Shandong, and these folds are incomplete due to the cutting of faults. The fault structure in western Shandong mainly includes four groups of faults: north-northeast, nearly east-west, nearly north-south and northwest. The north-northeast faults are mostly distributed on the east and west sides. The most influential ones are the Yishu fault zone on the east side and the Liaokao fault on the west side.

[0087] The main source rock strata of the Carboniferous-Permian System in western Shandong are three groups: Benxi Group, Taiyuan Group and Shanxi Group. The thickness of the Benxi Group is generally 30-50m, with an average of about 45m; it contains relatively stable thin coal seams and 1-3 coal lines. The thickness of the Taiyuan Group is generally 150-170m, containing 8-20 coal seams. There are more coal seams in southwestern Shandong and southern Shandong, 15-18 layers, and the total thickness of the coal seams is 2-4m. The coal seams are concentrated in the middle and lower parts of the Taiyuan Group. The thickness of the Shanxi Group is 60-120m, generally about 90m, containing 2-4 coal seams, generally with a total thickness of 4-8m, and the maximum thickness can reach about 12m. The thickness is 7-8m in the Wenning (Wenshang-Ningyang) area. In the coal-bearing areas in southwestern Shandong, the thickness of the coal seam reaches 11.5-18.0m, and the general thickness is 6-8m. The thickness is 10-14m in the Yutai-Tengxian area. The top and bottom of the Shanxi Formation coal seams are mostly in contact with or close to the sandstone layers, and the source-reservoir combination is relatively good. The coal seams are concentrated in the middle and lower parts of the Shanxi Formation. The best coal seam is the No. 3 coal seam of the Shanxi Formation, which is thick and stable. Therefore, the target coal seam for carbon dioxide storage is clearly No. 3 coal.

[0088] Step 2: Clarify the geothermal and pressure gradient values ​​of coal-bearing strata, calculate the critical depth of carbon dioxide storage, and determine the main depth of carbon dioxide geological storage. According to the coalfield geological exploration data, the geothermal gradient, pressure gradient and burial depth data of the target coal seams in each coalfield are statistically analyzed to calculate the temperature and pressure conditions of the corresponding coal seam burial depth. According to the CO2 geological storage mechanism, the supercritical state is the ideal state for achieving CO2 geological storage. The critical point is 7.38Mpa, 31.1℃. On this basis, the critical values ​​of CO2 geological storage in the main coal mines of each coalfield in southwestern Shandong were calculated. Fig.11 It shows that there are obvious differences in the critical values ​​of different coalfields, among which the critical depth of Juye coalfield is 664-1666m; the critical depth of Caoxian coalfield is approximately 772m. Based on the critical depth value and the occurrence characteristics of the three coals, the deep coal seam carbon dioxide geological storage unit of the three coals in southwestern Shandong was finally preliminarily determined, such as Figure 3 shown.

[0089] Figure 3 The results show that the favorable area for carbon dioxide geological storage in the deep coal seams of the Juye Coalfield No. 3 is the largest, mainly distributed in the western part of the coalfield; the favorable area for carbon dioxide geological storage in the Caoxian Coalfield is mainly concentrated in the southeast; the Jinxiang Coalfield is relatively small, and the favorable area for carbon dioxide geological storage is concentrated in the west; the favorable area for carbon dioxide geological storage in the Danxian Coalfield basically covers the entire coalfield.

[0090] Step three, comprehensively consider factors such as geological structure, sedimentary coal-bearing conditions and burial depth, and select the main areas suitable for CO2 storage. In terms of geological structure, first determine the nature of the fault. If it is a normal fault, the area is a tensile fault, the top and bottom plates of the coal seams are weakly sealed, and it is not easy to store carbon dioxide geologically; if it is a reverse fault, the area is a compressive fault, the top and bottom plates of the coal seams are strongly sealed, and it is suitable for carbon dioxide geological storage; in terms of sedimentary coal, determine the lithology of the top and bottom plates of the deep coal seams. If it is a porous and dense rock formation such as mudstone shale, the sealing property is strong; if it is a porous and loose rock formation such as sandstone, the sealing property is weak. In terms of burial depth, refer to step two to clarify the geothermal and pressure gradient values ​​of the coal-bearing strata, calculate the critical depth of carbon dioxide storage, and determine the main depth of carbon dioxide geological storage. Finally, determine the main areas suitable for CO2 storage, such as Figure 4 shown.

[0091] The regional division of CO2 storage is mainly based on the complexity of the structure under the condition of meeting the critical depth of CO2 storage. Taking Juye Coalfield as an example, four areas are divided in Juye Coalfield, the most northern complex structural area, the central undeveloped structural area, the southern simple structural area, and the eastern coal seam discontinuity area.

[0092] Step 4: Determine the main controlling factors of the potential for geological storage of carbon dioxide. Preliminary analysis and summary of the influencing factors in the process of CO2 geological storage from the two aspects of coal reservoir characteristics and gas injection work system; based on the sensitivity analysis of each influencing factor, determine the main controlling factors according to the principle of combining qualitative and quantitative evaluation, and analyze the effect of CO2 geological storage under different schemes. On the basis of a detailed analysis of the basic geological data in southwestern Shandong, based on the carbon dioxide storage mechanism and migration characteristics, the influencing factors of CO2 storage were determined: 9 influencing factors such as coal reservoir permeability, porosity, thickness, burial depth, gas content, bottom hole pressure, and well spacing, such as Figure 5 As shown. Based on the sensitivity analysis of various influencing factors by numerical simulation, the analytic hierarchy process (AHP) was first used to conduct a subjective analysis of each influencing factor, and then the weights obtained by the analytic hierarchy process were objectively corrected with the help of the entropy method. The main influencing factors affecting CO2 storage were finally determined by the subjective and objective comprehensive assignment method. Finally, combined with the actual basic geological conditions of the test area, the main influencing factors of CO2 displacement and storage in each test area were determined to determine the differences in the pilot tests between the two test areas.

[0093] Based on the clarification of influencing factors, vertical single well geological models and vertical well group geological models were constructed using Eclipse software to conduct numerical simulation research on carbon dioxide geological storage, such as Figure 6 and Figure 7 As shown in the figure. Figure 8As shown, it can be clearly seen that the well spacing has the highest weight, with a weight value of 1 / 4; the burial depth, permeability, bottom hole pressure, and injection rate are second; the porosity, fracture pressure, and thickness have the smallest weight. This study focuses on the impact of geological conditions on the carbon dioxide storage effect, so the burial depth is used as the main factor for subsequent zoning research.

[0094] Step 5: Based on the above, the CO2 geological storage units in the coalfield are divided according to the distribution law of the main controlling factors. The Juye coalfield block is divided into 4 CO2 storage areas according to the fault structure, and the CO2 storage capacity is calculated for each area. On this basis, the burial depth parameter is used to divide Block 1 into 15 storage units, such as Fig. 9 shown.

[0095] Step six, calculate the theoretical and effective geological storage capacity of CO2 under different storage units, and evaluate the geological storage potential of CO2 in the main coal seams in the study area. Based on the burial depth range of the No. 3 coal seam in Block 1, it is divided into 600, 700, 800, 900, 1000, 1100 and 1200m for the geological parameter selection of carbon dioxide. Taking into full consideration the temperature, pressure, porosity, apparent density, absolute adsorption capacity, water saturation, CO2 compression factor, solubility, molar mass, molar gas constant and other parameters at a specific burial depth, the storage capacity calculation formula (1) is used to calculate the theoretical unit storage capacity at a specific depth. The calculation results show that the theoretical unit storage capacity of 600-1200m is 1.97-2.02mmol / g. Fig.12 The summary of CO2 storage parameters under different burial depth conditions is shown. Fig.13 A summary of CO2 storage parameters for different storage units is shown.

[0096] In summary, the evaluation method of the present invention makes full use of the original coalfield geological data and is easy to obtain a large number of basic geological parameters of coal and rock, providing a good theoretical basis for the subsequent realization of the regional dual carbon goals.

[0097] Parts not described in the present invention can be implemented by referring to the existing technology.

[0098] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection claimed in the present application.

Claims

1. A method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield, characterized in that: The following steps are included in sequence: Step 1: Based on the analysis of the comprehensive geological characteristics of the coal-bearing area, clarify the distribution law of the remaining coal seam reserves; Step 2: Further clarify the geothermal gradient and pressure gradient values ​​of coal-bearing strata, calculate the critical depth of carbon dioxide storage, and determine the main depth of carbon dioxide geological storage; Step 3: Taking geological structure, coal-bearing sedimentary conditions and burial depth as the main factors, select the main areas suitable for CO2 storage in coal fields; Step 4: Determine the main controlling factors in the main areas of carbon dioxide geological storage, and preliminarily analyze and summarize the influencing factors in the process of carbon dioxide geological storage mainly from the two aspects of coal reservoir characteristics and gas injection work system; Based on the sensitivity analysis of each influencing factor, determine the main controlling factors according to the principle of combining qualitative and quantitative evaluation, and analyze the effects of carbon dioxide geological storage under different schemes; Step 5: Based on the results obtained in step 4 and step 3, the carbon dioxide geological storage units in the coalfield are divided according to the distribution law of the main controlling factors; Step 6: Calculate the theoretical geological storage capacity and effective geological storage capacity of carbon dioxide in the coal-bearing area, and evaluate the geological storage potential of carbon dioxide in the main coal seams in the study area; The amount of carbon dioxide geological storage in the coal-bearing area is calculated according to formula (1): M t =A×H×ρ coal ×m (1); In formula (1): M t is the theoretical geological storage capacity; A is the area of ​​CO2 geological storage; H is the thickness of the coal seam; ρ coal is the apparent density of coal rock; m is the unit storage capacity of CO2; Step 7: Based on the carbon dioxide storage capacity of each unit and the physical properties of the coal reservoir, the hierarchical analysis-fuzzy comprehensive evaluation method is used to select the favorable areas for carbon dioxide geological storage.

2. The method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield according to claim 1, characterized in that: In step one, on the basis of clarifying the distribution law of the remaining coal seam reserves, the basic geological characteristics, coal petrological characteristics, adsorption reservoir characteristics, reservoir physical properties and fluid characteristics of each coalfield are also clarified; wherein the basic geological characteristics include the tectonic environment of the reservoir, the reservoir distribution scale, and the roof and floor and hydrogeological characteristics related to the reservoir; the coal petrological characteristics include the coal rock type and metamorphic degree characteristics of the reservoir; the adsorption reservoir characteristics and reservoir physical properties include the gas content of the coal seam, adsorption and desorption characteristics, and the pore and fracture distribution and permeability development of the coal reservoir; the fluid characteristics include the characteristics and composition of gas and water and their physical properties.

3. The method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a coalfield with a high degree of exploration according to claim 1, characterized in that: In step 2, the temperature and pressure conditions of the corresponding coal seam burial depth are calculated based on the geothermal gradient value, pressure gradient value and burial depth data of the coal-bearing stratum. When the pressure is 7.38Mpa and the temperature is 31.1℃, it is taken as the critical point. If the temperature and pressure conditions corresponding to the coal-bearing stratum are ≥ the critical point, it means that the coal-bearing area is conducive to the geological storage of carbon dioxide; if the temperature and pressure conditions corresponding to the coal-bearing stratum are < the critical point, it means that the coal-bearing area is not conducive to the geological storage of carbon dioxide.

4. The method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield according to claim 3, characterized in that: When geological structure is the main factor, the nature of the fault is first determined. If it is a normal fault, the area is a tensile fault, the coal seam roof and floor sealing is weak, and it is not suitable for carbon dioxide geological storage; if it is a reverse fault, the area is a compressive fault, the coal seam roof and floor sealing is strong, and it is suitable for carbon dioxide geological storage; When the sedimentary coal-bearing conditions are the main factors, the lithology of the top and bottom plates of deep coal seams is judged. If it is a porous and dense rock layer, the sealing property is strong; if it is a porous and loose rock layer, the sealing property is weak. When burial depth is the main factor, the temperature and pressure conditions and critical point corresponding to the coal-bearing strata are used to determine whether the coal-bearing area is conducive to the geological storage of carbon dioxide.

5. The method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a coalfield with a high degree of exploration according to claim 1, characterized in that: The coal reservoir characteristics mainly include coal rank, organic microscopic components, permeability, physical and mechanical properties or water content, and the gas injection working system mainly includes carbon dioxide injection rate, carbon dioxide injection pressure and carbon dioxide injection time.

6. The method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a highly explored coalfield according to claim 5, characterized in that: When conducting sensitivity analysis on various influencing factors, a combination of COMET3 and Eclipse reservoir simulation software was used. Based on the existing geological conditions in the target area and the vertical well production data of ground development, the reservoir simulation software COMET3 was used to correct the reservoir parameters using the history fitting method to achieve the maximum consistency with the actual geological conditions. On this basis, considering the characteristics of the coal reservoir and the working system, different engineering schemes were designed according to the principle of statistical optimization, with the changes in coalbed methane production, carbon dioxide storage, and reservoir pressure under numerical simulation as the main considerations, and the sensitivity analysis of various influencing factors was gradually realized.

7. The method for evaluating the geological storage potential of carbon dioxide in deep coal seams of a coalfield with a high degree of exploration according to claim 1, characterized in that: In step 6, the calculation of CO2 storage unit m is shown in formula (2): m=m ad +m v0 +m s (2); In formula (2): m ad is the CO2 adsorption storage capacity per unit mass of coal rock; m v0 is the static storage capacity of CO2 per unit mass of coal rock; m s is the amount of dissolved CO2 stored in the pore water of coal rock per unit mass; The actual adsorption amount is obtained by formula (3): In formula (3): m a is the actual adsorption amount, m e is the Gibbs adsorption capacity, ρ a is the density of the adsorbed phase, ρ(P,T) is the density of the free phase at temperature T and pressure P; Further combined with formula (4), the theoretical geological storage capacity of carbon dioxide and the effective geological storage capacity of carbon dioxide in the coal-bearing area can be calculated; In formula (4): M is the molar mass of CO2; n ab (T, p) is the absolute CO2 adsorption storage capacity at a given temperature and pressure; φ is the porosity obtained by mercury injection or logging; S w is water saturation; p is pressure; Z is the CO2 compression factor at a certain temperature and pressure; ρ coal is the apparent density of coal rock; R is the molar gas constant, which is 8.314 Pa·m 3 ·mol -1 ·K -1 ; T is temperature; S CO2 is the solubility of CO2 in pure water at a certain temperature and pressure.

8. The method for evaluating the carbon dioxide geological storage potential of deep coal seams in a highly explored coalfield according to claim 1, characterized in that: The specific method in step seven is: assign values ​​to the influencing factors of carbon dioxide geological storage from three aspects: structural conditions, coal seam occurrence conditions and social conditions, and determine the weights of different factors; use hierarchical analysis-simulation comprehensive evaluation method to compare the carbon dioxide storage effects between different units and determine the favorable areas for carbon dioxide geological storage.

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