Natural gas migration path identification method and system

Abstract

The invention discloses a natural gas migration path identification method and system, and belongs to the technical field of oil and gas geology and exploration evaluation, and the method comprises the steps: taking the fractionation of carbon isotope in the natural gas migration process as a research object, and coupling a diffusion effect and an adsorption effect to construct a migration fractionation model; selecting a calibration well, and fitting measured data of the carbon isotope concentration value of the calibration well to determine optimal parameters of the migration and fractionation model; in the actual identification process, carbon isotope concentration value measured data of different well positions are input and substituted into the migration fractionation model to calculate the natural gas migration distances of the different well positions; and comparing the natural gas migration distances of different well positions, and inferring the migration direction and the migration path of the natural gas from the starting place in combination with the regional structure and the well position. According to the method, a carbon isotope migration and fractionation model is utilized to invert a natural gas migration distance and a migration path, and is used for constructing a reservoir forming mode.

Description

Technical Field

[0001] This application relates to the fields of oil and gas geology and exploration evaluation technology, and in particular to a method and system for identifying natural gas migration paths. Background Technology

[0002] Natural gas accumulation is controlled by multiple stages, including hydrocarbon generation, reservoir formation, caprock formation, and migration. Among these, migration paths and accumulation models are crucial aspects of oil and gas geological evaluation, directly impacting resource exploration deployment and reserve prediction. Existing natural gas migration studies primarily rely on structural interpretation, fluid inclusions, and reservoir distribution characteristics, which have the following limitations: conventional structural interpretation often fails to accurately characterize the specific migration paths of natural gas, resulting in unclear migration routes; current determinations of natural gas migration distances and paths largely depend on seismic attributes or analogical studies, lacking physically parameter-driven computational models and quantitative tools; and the inability to quantitatively calculate migration paths makes it difficult to directly link quantitative migration calculations with the accumulation process, affecting the construction of accumulation models and the accuracy of predictions. Summary of the Invention

[0003] This application aims to provide a method and system for identifying natural gas migration paths by using a carbon isotope migration fractionation model to invert the migration distance and path of natural gas, and to construct a reservoir formation model.

[0004] To achieve the above objectives, the technical solution of this application is as follows: A method for identifying natural gas migration paths, comprising: Taking the fractionation of carbon isotopes in the natural gas migration process as the research object, a migration fractionation model was constructed by coupling diffusion and adsorption effects; Select calibration wells and fit the measured carbon isotope concentration values ​​of the calibration wells to determine the optimal parameters of the transport fractionation model; In the actual identification process, the measured carbon isotope concentration values ​​of different well locations are input and substituted into the migration fractionation model to calculate the migration distance of natural gas at different well locations; By comparing the natural gas migration distances at different well locations and combining the regional geological structure and well location, the migration direction and path of natural gas from its origin can be inferred.

[0005] Optionally, after comparing the natural gas migration distances at different well locations and combining regional geological structures and well locations to infer the migration direction and path of natural gas from its origin, the method further includes: combining the migration path with the gas reservoir distribution characteristics to construct a natural gas reservoir formation model.

[0006] Optionally, a transport and fractionation model can be constructed by coupling diffusion and adsorption, including: establishing a carbon isotope diffusion model and a carbon isotope adsorption model, and coupling the carbon isotope diffusion model and the carbon isotope adsorption model to construct a transport and fractionation model.

[0007] Optionally, establishing a carbon isotope diffusion model includes: combining the error function with the one-dimensional Fick's second law to obtain a carbon isotope diffusion model.

[0008] Optionally, establishing a carbon isotope adsorption model includes: simplifying the adsorption amount by combining the Langmuir adsorption model to obtain a carbon isotope adsorption model.

[0009] Optional, optimal parameters for a deterministic transport fractionation model include: maximum fractionation amplitude, adsorption compensation term, and adsorption compensation characteristic distance.

[0010] Optionally, during the actual identification process, the measured carbon isotope concentration values ​​of different well locations are input and substituted into the migration fractionation model to calculate the natural gas migration distance of different well locations. This includes: when the origin of natural gas in the gas field to be identified is known, the migration time and effective diffusion coefficient are set according to geological events, and the measured carbon isotope concentration values ​​of different well locations are input into the calibrated migration fractionation model to calculate the natural gas migration distance of different well locations.

[0011] Optionally, after constructing a natural gas accumulation model by combining migration paths with gas reservoir distribution characteristics, the method may also include: providing a quantitative interpretation of complex migration processes based on the natural gas accumulation model.

[0012] Optionally, a quantitative explanation of complex migration processes can be provided based on natural gas accumulation models, including: Based on the differences in isotopic fractionation during different transport processes, it can be determined whether it is gas chimney or lateral transport.

[0013] A natural gas migration path identification system includes: one or more processors; and a storage device for storing one or more programs that, when executed by the one or more processors, cause the one or more processors to implement the natural gas migration path identification method as described above, and to identify natural gas migration paths according to the natural gas migration path identification method.

[0014] The natural gas migration path identification method and system proposed in this application are the first to use a carbon isotope migration fractionation model to calculate the natural gas migration distance, thereby quantifying the natural gas migration distance and path. At the same time, the mechanism of the carbon isotope migration fractionation process is analyzed, taking into account diffusion and adsorption, and the physical significance is clear. The natural gas migration path identification method can provide an intuitive diagram of the natural gas migration path and accumulation model, which helps guide exploration deployment. It is not only applicable to a single gas field, but can also be extended to the study of natural gas migration in other basins.

[0015] To make the above-mentioned features and advantages of the application more apparent and understandable, specific embodiments are provided below, and detailed descriptions are given in conjunction with the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a flowchart of the natural gas migration path identification method proposed in this application.

[0017] Figure 2 The parameter calibration curves for the transport fractionation model are shown.

[0018] Figure 3 This is a graph showing the relationship between carbon isotope concentration and migration distance at different well locations in the Lingshui LS36-1 gas field.

[0019] Figure 4 This is a schematic diagram of the horizontal migration direction and path from the Shenhai No. 1 L17-2 gas field to the Lingshui LS36-1 gas field.

[0020] Figure 5 This is a schematic diagram of the natural gas accumulation model of the Lingshui LS36-1 gas field. Detailed Implementation

[0021] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] In one embodiment of this application, please refer to Figure 1 , Figure 1 This is a flowchart of the natural gas migration path identification method proposed in this application. The natural gas migration path identification method proposed in this application includes: Step S1: Taking the fractionation of carbon isotopes in the natural gas migration process as the research object, a migration fractionation model is constructed by coupling diffusion and adsorption.

[0023] Step S2: Select calibration wells and fit the measured carbon isotope concentration values ​​of the calibration wells to determine the optimal parameters of the migration fractionation model.

[0024] Step S3: In the actual identification process, input the measured carbon isotope concentration values ​​of different well locations, and substitute them into the migration fractionation model to calculate the natural gas migration distance of different well locations.

[0025] Step S4: Compare the natural gas migration distances at different well locations, and infer the migration direction and path of natural gas from its origin by combining regional geological structures and well locations.

[0026] Step S5: Combine migration paths with gas reservoir distribution characteristics to construct a natural gas accumulation model.

[0027] The natural gas migration path identification method proposed in this application is the first to use a carbon isotope migration fractionation model to calculate the natural gas migration distance, thereby quantifying the natural gas migration distance and path. At the same time, it conducts a mechanism analysis of the carbon isotope migration fractionation process, considering diffusion and adsorption, and the physical significance is clear. The natural gas migration path identification method can provide an intuitive diagram of the natural gas migration path and accumulation model, which helps guide exploration deployment. It is not only applicable to a single gas field, but can also be extended to the study of natural gas migration in other basins.

[0028] In step S1, please refer to Figure 1 In step S1, the fractionation of carbon isotopes during natural gas migration is studied, and a migration fractionation model is constructed by coupling diffusion and adsorption.

[0029] As an example, a transport and fractionation model is constructed by coupling diffusion and adsorption, including: establishing a carbon isotope diffusion model and a carbon isotope adsorption model, and coupling the carbon isotope diffusion model and the carbon isotope adsorption model to construct a transport and fractionation model.

[0030] As an example, establishing a carbon isotope diffusion model includes: combining an error function with Fick's second law to obtain the carbon isotope diffusion model. Establishing a carbon isotope adsorption model includes: simplifying the adsorption amount using the Langmuir adsorption model to obtain the carbon isotope adsorption model.

[0031] Specifically, according to Wiefich's second law, diffusion describes the change in the concentration gradient of isotopes with distance. Wiefich's second law states as follows: Where C represents the concentration value; x Indicates the distance moved; t Indicates the transport time; D Let represent the effective diffusion coefficient. Solving this partial differential equation yields an analytical solution to Wiefich's second law, expressed as follows: in, Represents the residual error function; This indicates the initial concentration value.

[0032] Furthermore, for carbon isotopes, isotopic fractionation during natural gas migration causes changes in carbon isotope concentration with diffusion. Combining the error function and one-Vickers' second law, a carbon isotope diffusion model is obtained, as follows: in, Indicates the transport distance as x The migration time is t Carbon isotope concentration values ​​at time; This represents the initial carbon isotope concentration value; A Indicates the maximum fractionation range; Represents the error function. .

[0033] As an example, the adsorption process is represented by the Langmuir adsorption model, which describes the retention effect of gas in a porous medium. Since the adsorption amount is pressure-dependent, the exponential decay relationship of pressure with transport distance is expressed as follows: in, Indicates the transport distance as x The pressure of time; Indicates the initial pressure; L This represents the adsorption compensation characteristic distance.

[0034] Furthermore, combining the Langmuir adsorption model and considering the effect of pressure on the adsorption amount, the change in adsorption amount with pressure is obtained as follows: in, Indicates the transport distance as x The amount of adsorption at that time; This represents the volume of adsorbed gas under standard conditions when the adsorbent is completely covered by a single layer. This represents the equilibrium partial pressure of the adsorbate in the gas phase.

[0035] Furthermore, for carbon isotopes, the adsorption capacity is simplified using the Langmuir adsorption model to obtain the carbon isotope adsorption model, as follows: in, B This represents the adsorption compensation term. .

[0036] As an example, a transport and fractionation model is constructed by coupling diffusion and adsorption, including: coupling a carbon isotope diffusion model with a carbon isotope adsorption model to construct a transport and fractionation model, as shown below: .

[0037] In step S2, please refer to Figure 1 In step S2, a calibration well is selected, and the measured carbon isotope concentration values ​​of the calibration well are fitted to determine the optimal parameters of the transport fractionation model.

[0038] As an example, wells with relatively clear initial underground migration direction and migration path of natural gas are selected as calibration wells. The measured carbon isotope concentration values ​​of the natural gas origin of the calibration well and the migration distance from the natural gas origin of the calibration well to the calibration well are obtained. The measured carbon isotope concentration values ​​of the calibration well at the current time are also measured.

[0039] As an example, the measured carbon isotope concentration values ​​at the natural gas origin of the calibration well are used as the initial carbon isotope concentration values.

[0040] As an example, multiple calibration wells were selected to fit the measured carbon isotope concentration values ​​of the calibration wells to determine the optimal parameters of the migration fractionation model.

[0041] As an example, the optimal parameters for the transport fractionation model that need to be determined include: maximum fractionation amplitude. A Adsorption compensation item B and adsorption compensation characteristic distance L .

[0042] As an example, before determining the optimal parameters of the migration fractionation model using measured carbon isotope concentration data from calibration wells, the process also includes: setting migration time based on geological events. t and effective diffusion coefficient D .

[0043] In one embodiment of this application, the geological medium along the migration path of the calibration well is tight sandstone, and the migration time is set according to the geological events of the calibration well. t For 1 million years, the effective diffusion coefficient D Common values ​​for dense sandstone .

[0044] Furthermore, the measured carbon isotope concentration values ​​of the calibration well, the migration distance from the natural gas origin of the calibration well to the calibration well, the initial carbon isotope concentration values, the set migration time and diffusion coefficient are substituted into the migration fractionation model to determine the optimal parameters of the migration fractionation model and complete the calibration of the migration fractionation model.

[0045] In one embodiment of this application, the maximum fractionation range is determined. A The adsorption compensation term is 31.21‰. B The adsorption compensation characteristic distance is 50.00‰. L It is 61359m.

[0046] In step S3, please refer to Figure 1 In step S3 of the process, during the actual identification process, the measured carbon isotope concentration values ​​of different well locations are input and substituted into the migration fractionation model to calculate the natural gas migration distance of different well locations.

[0047] As an example, in the actual identification process, measured carbon isotope concentration values ​​at different well locations are input and substituted into the migration fractionation model to calculate the natural gas migration distance at different well locations. This includes: when the origin of natural gas in the gas field to be identified is known, to determine the specific migration path of natural gas at different well locations in the gas field to be identified, the migration time is set according to geological events. t and effective diffusion coefficient D Input the measured carbon isotope concentration values ​​at different well locations into the calibrated migration fractionation model; that is, the carbon isotope concentration values ​​after migration. Calculate the migration distance of natural gas at different well locations. x .

[0048] In one embodiment of this application, taking the Lingshui LS36-1 gas field in the Beibu Gulf Basin of the South China Sea as an example, the measured data of carbon isotope concentration values ​​at different well locations in the Lingshui LS36-1 gas field are collected, as shown in Table 1.

[0049] Table 1. Measured carbon isotope concentration data at different well locations in the Lingshui LS36-1 gas field. Furthermore, given that the natural gas origin of the Lingshui LS36-1 gas field is the L17-2b well site of the Shenhai No. 1 L17-2 gas field, the initial carbon isotope concentration values ​​were obtained. The value is -37.2‰. Taking the LS36-1d well location as an example, the migration time is set according to geological events. t and effective diffusion coefficient D Input the measured carbon isotope concentration values ​​of the LS36-1d well site into the calibrated migration fractionation model, and calculate the natural gas migration distance at the LS36-1d well site. x As shown in Table 2; the parameter calibration curves of the transport fractionation model are shown in Table 2. Figure 2 As shown.

[0050] Table 2. Relevant parameters of the migration and fractionation model from well L17-2b to well LS36-1d. Furthermore, the migration distance of natural gas at other well locations in the Lingshui LS36-1 gas field was calculated. x Please see Figure 3 , Figure 3 The graph shows the relationship between carbon isotope concentration and migration distance at different well locations in the Lingshui LS36-1 gas field, as shown in the figure. Figure 3 The figure shows the relationship between carbon isotope concentration values ​​and migration distance at different well locations in the Lingshui LS36-1 gas field.

[0051] In step S4, please refer to Figure 1In step S4, the migration distance of natural gas at different well locations is compared, and the migration direction and path of natural gas from the origin are inferred by combining regional geological structure and well location.

[0052] As an example, based on the relationship curves between carbon isotope concentration values ​​and migration distances at different well locations in the Lingshui LS36-1 gas field, a planar distribution trend is constructed by comparing the migration distances at different well locations. Furthermore, combining regional geological structures and well location, the planar migration direction and path of natural gas are inferred from well locations in ascending order of displacement distance. The planar migration direction and path of natural gas extend from well locations with smaller displacement distances to well locations with larger displacement distances. Please refer to [link / reference]. Figure 4 , Figure 4 This diagram illustrates the planar migration direction and path from the Shenhai No. 1 L17-2 gas field to the Lingshui LS36-1 gas field. Based on the planar distribution trend of the migration distance, it can be inferred that natural gas migrated southeast from the Shenhai No. 1 L17-2 gas field to the western block of the Lingshui LS36-1 gas field, then southwest to the central block of the Lingshui LS36-1 gas field, and finally northwest to the eastern block of the Lingshui LS36-1 gas field, accumulating in the western, central, and eastern blocks of the Lingshui LS36-1 gas field.

[0053] In step S5, please refer to Figure 1 The S5 step combines the migration path with the gas reservoir distribution characteristics to construct a natural gas reservoir formation model.

[0054] For example, please refer to Figure 5 , Figure 5 This is a schematic diagram of the natural gas accumulation model in the Lingshui LS36-1 gas field, as shown below. Figure 5 As shown, after obtaining the planar migration direction and path of natural gas, i.e. the planar distribution law of natural gas, the gas reservoir distribution characteristics under the geological conditions under the planar distribution law can be obtained.

[0055] Specifically, combining the planar gas reservoir distribution characteristics under the geological conditions of this planar distribution pattern, the planar distribution trend of the migration path is matched with the planar gas reservoir distribution characteristics; further, combining the vertical gas reservoir distribution characteristics under the vertical stratigraphic layering pattern of the gas reservoir under this planar distribution pattern, a natural gas accumulation model is constructed: the Shenhai-1 L17-2 gas field is the starting point, natural gas is laterally diverted along the boundary of the central canyon, and accumulates in the western block of the Lingshui LS36-1 gas field; when the natural gas from the Shenhai-1 L17-2 gas field migrates along the boundary of the central canyon... When it moves to the top of the biogas gas window, it merges with the natural gas generated inside the biogas gas window, completing secondary enrichment. The mixed natural gas enters the fracture network of the gas chimney and migrates vertically along the fractures. Because the fractures inside the gas chimney penetrate the interlayer, the sealing effect of the interlayer fails, and the natural gas eventually accumulates and adjusts to form a reservoir at the top of the gas chimney, that is, in the middle block of the Lingshui LS36-1 gas field. Finally, because the natural gas pressure at the top of the gas chimney is higher than that on the east side, a lateral pressure difference is formed, driving the natural gas to adjust laterally to the east, accumulating and forming a reservoir in the eastern block of the Lingshui LS36-1 gas field.

[0056] As an example, after constructing a natural gas accumulation model by combining migration paths with gas reservoir distribution characteristics, it also includes: providing a quantitative explanation of complex migration processes, such as gas chimney transport and lateral migration, based on the natural gas accumulation model.

[0057] As an example, a quantitative explanation of complex migration processes based on natural gas accumulation models includes: Since the isotopic fractionation of gas chimney migration is significantly greater than that of transverse sand body transport, the difference in isotopic fractionation between different migration processes can be used to determine whether it is gas chimney or transverse migration.

[0058] This application also provides a natural gas migration path identification system, the natural gas migration path identification system comprising: one or more processors; and a storage device for storing one or more programs that, when executed by the one or more processors, cause the one or more processors to implement the natural gas migration path identification method as described above, and to identify natural gas migration paths according to the natural gas migration path identification method.

[0059] The natural gas migration path identification method and system proposed in this application are the first to use a carbon isotope migration fractionation model to calculate the natural gas migration distance, thereby quantifying the natural gas migration distance and path. At the same time, the mechanism of the carbon isotope migration fractionation process is analyzed, taking into account diffusion and adsorption, and the physical significance is clear. The natural gas migration path identification method can provide an intuitive diagram of the natural gas migration path and accumulation model, which helps guide exploration deployment. It is not only applicable to a single gas field, but can also be extended to the study of natural gas migration in other basins.

[0060] Although this application has been disclosed above with reference to embodiments, it is not intended to limit this application. Anyone skilled in the art may make some modifications and refinements without departing from the spirit and scope of this application. Therefore, the scope of protection of this application shall be determined by the appended claims.

Claims

1. A method for identifying natural gas migration paths, characterized in that, include, Taking the fractionation of carbon isotopes in the natural gas migration process as the research object, a migration fractionation model was constructed by coupling diffusion and adsorption effects; Select calibration wells and fit the measured carbon isotope concentration values ​​of the calibration wells to determine the optimal parameters of the transport fractionation model; In the actual identification process, the measured carbon isotope concentration values ​​of different well locations are input and substituted into the migration fractionation model to calculate the migration distance of natural gas at different well locations; By comparing the natural gas migration distances at different well locations and combining the regional geological structure and well location, the migration direction and path of natural gas from its origin can be inferred.

2. The natural gas migration path identification method as described in claim 1, characterized in that, After comparing the natural gas migration distances at different well locations and combining regional geological structures and well locations to infer the migration direction and path of natural gas from its origin, the process also includes: combining the migration path with the gas reservoir distribution characteristics to construct a natural gas reservoir formation model.

3. The natural gas migration path identification method as described in claim 1, characterized in that, The transport and fractionation model is constructed by coupling diffusion and adsorption effects, including: establishing a carbon isotope diffusion model and a carbon isotope adsorption model, and coupling the carbon isotope diffusion model and the carbon isotope adsorption model to construct a transport and fractionation model.

4. The natural gas migration path identification method as described in claim 3, characterized in that, The carbon isotope diffusion model is established by combining the error function with the one-dimensional Fick's second law.

5. The natural gas migration path identification method as described in claim 3, characterized in that, The carbon isotope adsorption model was established by simplifying the adsorption amount using the Langmuir adsorption model.

6. The natural gas migration path identification method as described in claim 1, characterized in that, The optimal parameters of the determined transport fractionation model include: maximum fractionation amplitude, adsorption compensation term, and adsorption compensation characteristic distance.

7. The natural gas migration path identification method as described in claim 6, characterized in that, In the actual identification process, the measured carbon isotope concentration values ​​of different well locations are input and substituted into the migration fractionation model to calculate the natural gas migration distance of different well locations. This includes: when the origin of natural gas in the gas field to be identified is known, the migration time and effective diffusion coefficient are set according to geological events, and the measured carbon isotope concentration values ​​of different well locations are input into the calibrated migration fractionation model to calculate the natural gas migration distance of different well locations.

8. The natural gas migration path identification method as described in claim 2, characterized in that, After constructing a natural gas accumulation model by combining migration paths with gas reservoir distribution characteristics, the process also includes: providing a quantitative interpretation of complex migration processes based on the natural gas accumulation model.

9. The natural gas migration path identification method as described in claim 8, characterized in that, Quantitative explanations of complex migration processes based on natural gas accumulation models include: Based on the differences in isotopic fractionation during different transport processes, it can be determined whether it is gas chimney or lateral transport.

10. A natural gas migration path identification system, characterized in that, include: One or more processors; A storage device for storing one or more programs that, when executed by one or more processors, cause the one or more processors to implement the natural gas migration path identification method as described in any one of claims 1-9, and to identify natural gas migration paths according to the natural gas migration path identification method.

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