Temperature and pressure simulation and phase state judgment algorithm for non-pure carbon dioxide burying, computer equipment and storage medium

Abstract

The invention discloses a temperature and pressure simulation and phase state judgment algorithm for non-pure carbon dioxide burying, computer equipment and a storage medium, and belongs to the technical field of carbon dioxide burying. The algorithm comprises the following steps: S1, constructing a temperature model and a pressure model of non-pure carbon dioxide burying in combination with a shaft structure; s2, the shaft is divided into calculation units according to needs; s3, calculating the temperature and pressure of non-pure carbon dioxide in each unit; and S4, comparing with the critical temperature and pressure of the non-pure carbon dioxide to obtain the phase state of the non-pure carbon dioxide in each unit. According to the temperature and pressure simulation and phase state judgment algorithm for non-pure carbon dioxide burying provided by the invention, the temperature and pressure of non-pure carbon dioxide fluids with different carbon dioxide contents and different impurity components in different depths in a shaft can be simulated, and then phase state judgment is carried out; long-term safe and stable injection of non-pure carbon dioxide fluid containing impurities can be guaranteed, the sealing safety is improved, and long-term effective sealing is achieved.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide burial technology, and relates to a temperature and pressure simulation and phase state algorithm for non-pure carbon dioxide burial, specifically a temperature and pressure simulation and phase state determination algorithm, computer equipment and storage medium for non-pure carbon dioxide burial. Background Technology

[0002] Carbon dioxide storage refers to the process of capturing carbon dioxide from the atmosphere and storing it underground using technological means. The wellbore, as the channel connecting the surface and the reservoir, is of great significance for studying the temperature, pressure, and phase state of carbon dioxide within it. During the flow of carbon dioxide within the wellbore, its temperature and pressure change to varying degrees with well depth, and these temperatures and pressures directly affect its phase state: carbon dioxide can reach a supercritical state at relatively low temperatures (304.2 K) and pressures (7.38 MPa). Supercritical carbon dioxide fluid exhibits characteristics of both gas and liquid, making it an ideal state for storage.

[0003] Current research on wellbore temperature and pressure during carbon dioxide burial mainly focuses on pure carbon dioxide, lacking research on impure carbon dioxide. However, the burial of impure carbon dioxide is gradually becoming a major focus for enterprises. Therefore, in order to ensure the safe and stable burial of carbon dioxide of different concentrations, further research is needed on the wellbore temperature, pressure, and phase state of impure carbon dioxide burial. Summary of the Invention

[0004] The purpose of this invention is to provide an algorithm, computer equipment, and storage medium for simulating temperature and pressure and determining phase state of non-pure carbon dioxide burial, in order to solve the current problem of lack of research on wellbore temperature, pressure, and phase state during non-pure carbon dioxide burial.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An algorithm for temperature and pressure simulation and phase determination of non-pure carbon dioxide burial includes the following steps:

[0007] S1. Combine the wellbore structure to construct temperature and pressure models for non-pure carbon dioxide burial;

[0008] S2. Divide the wellbore into calculation units as needed;

[0009] S3. Calculate the temperature and pressure of non-pure carbon dioxide in each unit;

[0010] S4. By comparing the critical temperature and pressure of non-pure carbon dioxide, the phase state of each unit of non-pure carbon dioxide can be obtained.

[0011] As a limitation, the pressure model is as follows:

[0012]

[0013] In the formula, dP is the pressure gradient of the well section; dz is the unit well section length; ρ is the density of the non-pure carbon dioxide fluid; g is the gravitational acceleration; θ is the wellbore inclination; f is the friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection casing; v is the flow velocity of the non-pure carbon dioxide fluid; r1 is the inner radius of the injection casing; and dv is the velocity gradient of the non-pure carbon dioxide fluid.

[0014] The temperature model is:

[0015]

[0016] In the formula, dT is the axial temperature gradient of the well section; dz is the unit well section length; W is the mass flow rate of the non-pure carbon dioxide fluid; C is the specific heat capacity of the non-pure carbon dioxide fluid; r1 is the inner radius of the injection casing; U is the overall heat transfer coefficient of the wellbore; T e η is the formation temperature; T is the temperature of the non-pure carbon dioxide fluid in the injection casing; η is the Joule-Thomson coefficient; dP is the pressure gradient of the well section; ρ is the density of the non-pure carbon dioxide fluid; f is the friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection casing; v is the flow velocity of the non-pure carbon dioxide fluid.

[0017] As a further definition, the overall heat transfer coefficient U of the wellbore includes the overall heat transfer coefficient U of the upper wellbore. u The overall heat transfer coefficient U in the middle section of the wellbore m and the overall heat transfer coefficient U of the lower wellbore l ;

[0018]

[0019]

[0020] In the formula, r1 is the inner radius of the injection sleeve; λ e r is the thermal conductivity of the formation. i r is the inner radius of the medium of the i-th order; i+1 λ is the outer radius of the medium of the i-th order; i r'7 is the thermal conductivity of the i-th sequence medium; r'5 is the outer radius of the middle layer cement sheath in the middle wellbore; r'6 is the outer radius of the inner layer cement sheath in the lower wellbore; h f The heat transfer coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve; α e t represents the formation thermal diffusivity; t represents the injection time of the non-pure carbon dioxide fluid.

[0021] As a further limitation, the formula for calculating the friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve is as follows:

[0022]

[0023] In the formula, R e Here, r1 is the inner radius of the injection sleeve, and ε is the roughness of the inner wall of the injection sleeve.

[0024] The present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-mentioned temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial.

[0025] The present invention also provides a computer-readable storage medium storing a computer program that executes the above-described temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial.

[0026] By adopting the above technical solution, the technical progress achieved by this invention compared with the prior art is as follows:

[0027] The temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial provided by this invention can simulate the temperature and pressure of non-pure carbon dioxide fluid with different carbon dioxide content and different impurity components at different depths in the wellbore, and then perform phase determination. This can ensure the long-term safe and stable injection of non-pure carbon dioxide fluid containing impurities, improve the safety of storage, and achieve long-term effective storage. Attached Figure Description

[0028] Figure 1 The flowchart shows the temperature and pressure simulation and phase state algorithm for non-pure carbon dioxide burial in the example.

[0029] Figure 2 This is a schematic diagram of the wellbore structure in the embodiment;

[0030] Figure 3 This is a graph showing the temperature variation of carbon dioxide and fluids with different contents of non-pure carbon dioxide as a function of well depth in the examples.

[0031] Figure 4 The graph shows the pressure variation of carbon dioxide and fluids with different contents of non-pure carbon dioxide as a function of well depth in the examples.

[0032] Figure 5 This is a graph showing the temperature variation with well depth for carbon dioxide and non-pure carbon dioxide fluids of different components in the examples;

[0033] Figure 6 The graph shows the pressure variation of carbon dioxide and non-pure carbon dioxide fluids with different components as a function of well depth in the examples. Detailed Implementation

[0034] The present invention will be further described in detail below through specific embodiments. It should be understood that the described embodiments are only for explaining the present invention and do not limit the present invention.

[0035] Example 1

[0036] This embodiment discloses a temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial, the flowchart of which is shown below. Figure 1 As shown, the specific steps include the following sequential steps:

[0037] S1. Construct temperature and pressure models for non-pure carbon dioxide burial based on the wellbore structure.

[0038] Wellbore structures for burying carbon dioxide are typically as follows: Figure 2 As shown, the wellbore consists of an upper, middle, and lower section. The number of cement sheath and casing layers differs in each section: For the upper section, the wellbore structure, from the inside out, includes injection casing, annular protection fluid, production casing, inner cement sheath, technical casing, middle cement sheath, surface casing, and outer cement sheath; for the middle section, the wellbore structure, from the inside out, includes injection casing, annular protection fluid, production casing, inner cement sheath, technical casing, and middle cement sheath; for the lower section, the wellbore structure, from the inside out, includes injection casing, annular protection fluid, production casing, and inner cement sheath.

[0039] For ease of explanation, assume that, apart from non-pure carbon dioxide fluid, other media in the upper wellbore (such as annular protective fluid, various casings, and cement sheaths) have an inner-outer position (i) on the wellbore cross-section, where i is an integer between 1 and 8. The inner and outer radii of the i-th rank medium are r and r', respectively. i and r i+1 The inner and outer surface temperatures of the medium at position i are T and T, respectively. i and T i+1 The thermal conductivity of the medium in the i-th order is λ. i For the middle and lower sections of the wellbore, because they are located in the outermost cement sheath (i.e., Figure 2 The outer radii of the middle and inner cement sheaths in the middle wellbore are not equal to the outer radii of the cement sheaths (i=4, 6) in the upper wellbore, and are respectively set as r'7 and r'5.

[0040] (1) Constructing a stress model

[0041] According to the law of conservation of mass and the principle of momentum balance of fluids, the following relationships exist between the parameters and variables:

[0042]

[0043] Therefore, the pressure model for this non-pure carbon dioxide burial is:

[0044]

[0045] In the formula: dP is the pressure gradient of the well section, Pa; dz is the length of the unit well section, m; ρ is the density of the non-pure carbon dioxide fluid, kg / m³. 3 g is the acceleration due to gravity (taken as 9.8), m / s². 2 θ is the wellbore inclination, °; ​​f is the friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection casing, dimensionless; v is the flow velocity of the non-pure carbon dioxide fluid, m / s; r1 is the inner radius of the injection casing, m; dv is the velocity gradient of the non-pure carbon dioxide fluid, m / s.

[0046] (2) Constructing a temperature model

[0047] Temperature variations in non-pure carbon dioxide fluid within the wellbore are typically influenced by multiple factors, including: heat changes resulting from convective heat transfer between the non-pure carbon dioxide fluid and the injection casing wall; heat changes generated by the non-pure carbon dioxide fluid absorbing frictional work; and heat changes generated by the Joule-Thomson reaction.

[0048] Taking a unit well section at any depth z in the wellbore as the research object, the heat Φ transferred between the wellbore and the formation is analyzed. a This can be expressed as:

[0049] Φ a =2πr1U(T e -T)

[0050] In the formula, r1 is the inner radius of the injection casing, in meters; U is the overall heat transfer coefficient of the wellbore (i.e., the comprehensive heat transfer capacity of the wellbore after considering it as a multi-layered solid-walled whole), in W / (m²). 2 ·K); T e T and T represent the formation temperature and the temperature of the non-pure carbon dioxide fluid injected into the casing, respectively, in K.

[0051] For this wellbore system, the energy conservation equation considering steady-state flow is:

[0052]

[0053] In the formula, dz is the unit well section length, in meters; ρ is the density of the non-pure carbon dioxide fluid, in kilograms per cubic meter. 3 v is the flow velocity of the non-pure carbon dioxide fluid, in m / s; e is the internal energy per unit mass of fluid, in m. 2 / s 2 P is the pressure of the non-pure carbon dioxide fluid, in Pa; g is the acceleration due to gravity (taken as 9.8), in m / s². 2 θ is the wellbore inclination, in degrees; Φ a Heat transferred between the wellbore and the formation, J / s; A pThe cross-sectional area of ​​the oil pipe is m. 2 .

[0054] Combining the mass conservation equation and the heat transfer equation, the energy equation can be simplified to:

[0055]

[0056] In the formula, dh is the enthalpy gradient of the non-pure carbon dioxide fluid in the well section, and m 2 / s 2 ; dz is the unit well section length, in meters; g is the gravitational acceleration (taken as 9.8), in meters per second. 2 θ is the wellbore inclination, °; ​​v is the flow velocity of the non-pure carbon dioxide fluid, m / s; dv is the velocity gradient of the well section, m / s; r1 is the inner radius of the injection casing, m; U is the overall heat transfer coefficient of the wellbore, W / (m³). 2 ·K); W is the mass flow rate of the fluid, kg / s; T e T and T represent the formation temperature and the temperature of the fluid injected into the casing, respectively, in K.

[0057] The enthalpy gradient equation can be expressed as:

[0058]

[0059] In the formula, dh is the enthalpy gradient of the non-pure carbon dioxide fluid in the well section, and m 2 / s 2 ; dz is the unit well section length, m; C is the specific heat capacity of the non-pure carbon dioxide fluid, dimensionless; dT is the axial temperature gradient of the well section, K; η is the Joule-Thomson coefficient, K / Pa; dP is the pressure gradient of the well section, Pa.

[0060] Combining the wellbore pressure drop equation, the flow and heat transfer model of non-pure carbon dioxide fluid in the wellbore can be obtained as follows:

[0061]

[0062] In the formula, dT is the axial temperature gradient of the well section, K; dz is the unit well section length, m; r1 is the inner radius of the injection casing, m; and U is the overall heat transfer coefficient of the wellbore, W / (m²). 2 ·K); W is the mass flow rate of the non-pure carbon dioxide fluid, kg / s; C is the specific heat capacity of the non-pure carbon dioxide fluid, dimensionless; T e T represents the formation temperature and the temperature of the non-pure carbon dioxide fluid injected into the casing, respectively, in K; η is the Joule-Thomson coefficient, in K / Pa; dP is the pressure gradient in the well section, in Pa; ρ is the density of the non-pure carbon dioxide fluid, in kg / m³. 3 f is the friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve, which is dimensionless; v is the flow velocity of the non-pure carbon dioxide fluid, in m / s.

[0063] It can be seen that, assuming other parameters remain stable, the temperature gradient of the non-pure carbon dioxide fluid inside the wellbore is mainly affected by the overall heat transfer coefficient U. Therefore, to obtain the temperature distribution of the non-pure carbon dioxide fluid in the wellbore, the overall heat transfer coefficient must first be determined.

[0064] The heat transfer coefficient reflects the efficiency of heat flow resulting from different heat transfer mechanisms. These mechanisms are related to the properties of the medium. When a non-pure carbon dioxide fluid flows in a wellbore, the radial heat transfer between the fluid and the injection casing, and between the injection casing and the formation, occurs via convection and conduction, respectively. The heat transfer coefficient varies in the upper, middle, and lower sections of the wellbore due to the different number of solid wall layers, requiring separate calculations.

[0065] First, consider the overall heat transfer coefficient U of the upper wellbore. u .

[0066] Assume the heat transfer coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve is h. f The heat transferred through thermal convection is:

[0067] Φ=2πr1h f (T1-T)dz

[0068] In the formula: r1 is the inner radius of the injection sleeve, in meters; h f dz is the heat transfer coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection casing, dimensionless; T1 is the temperature of the inner surface of the injection casing, K; T is the temperature of the non-pure carbon dioxide fluid in the injection casing, K; dz is the length per unit well section, m.

[0069] Based on the empirical correlations between the heat transfer coefficient and the Nusselt number, Reynolds number, and Prandtl number:

[0070]

[0071] In the formula: λ is the thermal conductivity of the non-pure carbon dioxide fluid, W / (m·K); N u R is the Nusselt number, dimensionless; r1 is the inner radius of the injection sleeve, in meters; R e It is a Reynolds number, dimensionless; P r ρ is the Prandtl number, dimensionless; v is the velocity of the impure carbon dioxide fluid, m / s; ρ is the density of the impure carbon dioxide fluid, kg / m³. 3 μ is the viscosity of the non-pure carbon dioxide fluid, Pa·s; c p Specific heat at constant pressure, J / (kg·K).

[0072] Assuming the annular protective fluid is in a relatively static state, the heat flow rate transferred between adjacent media between the production casing and the outer cement sheath via thermal conduction is:

[0073]

[0074] In the formula: λ i Let T be the thermal conductivity of the i-th order medium, W / (m·K); i Let T be the inner surface temperature of the i-th sequence medium, in K; i+1 dz is the outer surface temperature of the i-th sequence medium, in K; dz is the unit well section length, in m; r i Let r be the inner radius of the medium of the i-th order, m; i+1 Let be the outer radius of the i-th sequence medium, in m.

[0075] The heat transfer between the outer cement sheath and the formation is unsteady. Assuming the initial formation temperature changes linearly with formation depth, the heat flow between the outer cement sheath and the formation after the non-pure carbon dioxide fluid injection time reaches t is:

[0076]

[0077] In the formula: λ e T represents the thermal conductivity of the formation, in W / (m·K); e T9 is the formation temperature, K; T9 is the outer surface temperature of the 8th sequence medium, K; dz is the unit well section length, m; α e Let m be the thermal diffusivity of the formation. 2 / h; t is the injection time of the non-pure carbon dioxide fluid, h; r9 is the outer radius of the 8th sequence medium, m; a is the geothermal gradient (usually taken as 0.017 based on experience), K / m; b is the ground temperature, K.

[0078] The temperature expressions for different sections of the wellbore can be obtained from the temperature changes of the heat transfer system in the micro-segment of the wellbore:

[0079]

[0080] Therefore, we can conclude that:

[0081]

[0082] Thus, the overall heat transfer coefficient U of the upper wellbore can be obtained. u :

[0083]

[0084] Similarly, the overall heat transfer coefficients of the middle and lower sections of the wellbore can be obtained using the above derivation method:

[0085]

[0086] In the formula, r1 is the inner radius of the injection sleeve, in meters (m); λ e r is the thermal conductivity of the formation, W / (m·K); i Let r be the inner radius of the medium of the i-th order, m; i+1 Let λ be the outer radius of the medium of the i-th order, m; i r'7 is the thermal conductivity of the i-th sequence medium, W / (m·K); r'7 is the outer radius of the middle layer cement sheath in the middle wellbore, m; r'5 is the outer radius of the inner layer cement sheath in the lower wellbore, m; h f is the heat transfer coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve, and is dimensionless.

[0087] The friction coefficient f can be solved based on its relationship with the Reynolds number and the roughness of the inner wall of the injection casing, i.e.:

[0088]

[0089] In the formula: R e ε is the Reynolds number, dimensionless; r1 is the inner radius of the injection sleeve, m; ε is the roughness of the inner wall of the injection sleeve, μm.

[0090] S2. Divide the wellbore into calculation units as needed.

[0091] To improve calculation accuracy while reducing the amount of calculation, this embodiment divides the wellbore into calculation units of 1m for each well section.

[0092] S3. Calculate the temperature and pressure of the non-pure carbon dioxide in each unit.

[0093] In practical work, the relevant parameters of the wellbore structure and the basic parameters such as the injection parameters of non-pure carbon dioxide are shown in Table 1:

[0094] Table 1: Overview of Basic Parameters

[0095]

[0096]

[0097] In this embodiment, the non-pure carbon dioxide fluid is a mixture of carbon dioxide and nitrogen, wherein the molar fraction of nitrogen is 5%. Given the formation temperature as the initial wellbore temperature, and the density of the injected non-pure carbon dioxide fluid as the initial fluid density of the wellbore, the wellhead injection temperature, injection pressure, and injection velocity are used as the inlet temperature, pressure, and velocity of the wellbore in the first calculation unit.

[0098] (1) Calculate the temperature and pressure of the fluid at the outlet of the first unit using basic data.

[0099] The temperature and pressure at the inlet of the non-pure carbon dioxide fluid (i.e., the injection temperature and injection pressure in Table 1) were input into the NIST-SRD 23 database to obtain the relevant physical property parameters of the non-pure carbon dioxide fluid in the unit (including density, specific heat capacity, Joule-Thomson coefficient, thermal conductivity, and viscosity). The length of each calculation unit was taken as 1 m.

[0100] Substituting the inner diameter of the injection sleeve and the flow rate, density, and viscosity of the non-pure carbon dioxide fluid into the Reynolds number solution, the Reynolds number R of the fluid is obtained. e Furthermore, by determining the range of the Reynolds number, the friction coefficient f between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve is obtained by substituting the Reynolds number, the inner radius of the injection sleeve, and the roughness.

[0101] By incorporating the density, velocity, friction coefficient, gravitational acceleration, and wellbore inclination of the non-pure carbon dioxide fluid into the pressure model, the pressure gradient dP of the fluid in the first computational unit can be obtained.

[0102] Substitute the inner and outer radius of the casing, the thermal conductivity of the formation, the thermal conductivity of the medium, and the fluid heat transfer coefficient into the formula for calculating the total heat transfer coefficient to obtain the total heat transfer coefficient U of the wellbore in the first calculation unit.

[0103] Finally, by substituting the overall heat transfer coefficient, the inner radius of the injection casing, the mass flow rate, specific heat capacity, density, formation temperature, flow velocity, Joule-Thomson coefficient, the temperature of the non-pure carbon dioxide fluid in the injection casing (fluid temperature at the unit inlet), pressure gradient, and friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection casing into the temperature model, the temperature gradient dT of the first calculation unit wellbore can be obtained.

[0104] (2) Update the outlet temperature and pressure based on the average inlet and outlet temperatures and pressures.

[0105] Since the physical property parameters and other basic parameters substituted into the calculation of the temperature and pressure at the outlet of the first calculation unit in (1) are the values ​​at the inlet of the first calculation unit, while the physical property parameters of the non-pure carbon dioxide fluid in this calculation unit change with depth, the calculation results are inaccurate. Therefore, in order to improve the accuracy, it is necessary to further calculate and update the outlet temperature and pressure.

[0106] The average values ​​of the temperature and pressure at the inlet and outlet of the first calculation unit were taken and substituted into the NIST-SRD 23 database to obtain the physical property parameters of the non-pure carbon dioxide fluid. These parameters were then substituted back into the overall heat transfer coefficient calculation formula to update the overall heat transfer coefficient U of the wellbore in the first calculation unit. uThe temperature is then substituted into the temperature model to update the outlet temperature of the wellbore in the first calculation unit; and into the pressure model to update the outlet pressure of the wellbore in the first calculation unit.

[0107] Set the preset value to 0.00001, and repeatedly update the outlet temperature and pressure until the difference between the calculated results of the temperature and pressure of two adjacent outlets is less than the preset value. The calculation results can be considered to have converged, and the temperature and pressure of the current calculation unit outlet obtained by convergence can be used as the temperature and pressure of the next calculation unit inlet.

[0108] (3) Calculate the temperature and pressure of the non-pure carbon dioxide in each unit.

[0109] Based on (2), the temperature and pressure of the impure carbon dioxide in each calculation unit are calculated sequentially to obtain the temperature and pressure distribution of the impure carbon dioxide fluid in wellbores at different depths. The results are as follows: Figure 3 , Figure 4 As shown.

[0110] S4. By comparing the critical temperature and pressure of impure carbon dioxide, the phase state of each unit of impure carbon dioxide can be obtained.

[0111] By using the NIST-SRD 23 database to find that the critical temperature and pressure of the non-pure carbon dioxide fluid are 300.2 K and 8.144 MPa, respectively, the phase state of the non-pure carbon dioxide in the wellbore of the calculated unit can be obtained by comparing the calculated temperature and pressure of the non-pure carbon dioxide with the critical temperature and pressure.

[0112] Examples 2-4

[0113] This embodiment discloses a temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial with different impurity contents, including nitrogen impurities with molar fraction contents of 10%, 15% and 20%, respectively. The temperature and pressure simulation and phase determination of this non-pure carbon dioxide fluid are exactly the same as the operation steps in Embodiment 1.

[0114] The temperature and pressure distribution of this non-pure carbon dioxide fluid in wellbores at different depths are shown in the following figures. Figure 3 , Figure 4 As shown.

[0115] according to Figure 3 As shown, the temperature of carbon dioxide fluids of different purities in the wellbore generally increases with well depth. When the well depth does not exceed 2500 meters, the deviations of the temperature distribution curves are not significant, which means that adding nitrogen gas with a molar fraction of no more than 20% has little effect on the fluid temperature; when the depth exceeds 2500 meters, the fluid temperature at the same location in the wellbore will increase slightly with the increase of nitrogen content.

[0116] Simultaneously, by combining the supercritical temperature and pressure data of non-pure carbon dioxide fluids, the phase transitions of carbon dioxide fluids with different purities within the wellbore can be obtained: since the injection pressure at the wellhead is much higher than the supercritical pressure of each mixed fluid, the phase transitions of the mixed fluids within the wellbore are mainly affected by temperature. The phase transition points of each mixed fluid are marked with solid dots of different colors. Figure 3 As can be seen, when the nitrogen content is 20%, 15%, 10%, 5%, and 0%, the well depths at which the non-pure carbon dioxide fluid transitions from the liquid state to the supercritical state are 125 meters, 482 meters, 711 meters, 900 meters, and 1042 meters, respectively. This shows that the higher the nitrogen content, the closer the non-pure carbon dioxide fluid undergoes phase change in the wellbore to the wellhead. Furthermore, compared to pure carbon dioxide, the nitrogen-infused mixture undergoes phase change closer to the wellhead in the wellbore.

[0117] according to Figure 4 As shown, the pressure of carbon dioxide fluids of different purities in the wellbore generally increases with well depth. However, changes in nitrogen content cause significant deviations in the pressure curve of the fluid in the wellbore, indicating that the impurity content has a significant impact on the fluid pressure. For mixed fluids of different purities at the same well depth, the pressure decreases with increasing nitrogen content (i.e., decreasing carbon dioxide purity), and the pressure drop increases with increasing well depth.

[0118] Example 5

[0119] To further compare the effects of changes in different impurity gas sources on the temperature and pressure distribution and phase state of non-pure carbon dioxide fluid, this embodiment discloses temperature and pressure simulation and phase state determination algorithms for non-pure carbon dioxide burial with different components, including two impurities: nitrogen with a molar fraction of 10% and methane with a molar fraction of 10%, and compares their temperature and pressure with that of pure carbon dioxide fluid (100%) and carbon dioxide (80%) + nitrogen (20%) fluid.

[0120] The temperature and pressure simulation and phase determination of this non-pure carbon dioxide fluid are exactly the same as the operation steps in Example 1.

[0121] The temperature and pressure distribution of this non-pure carbon dioxide fluid in wellbores at different depths are shown in the following figures. Figure 5 , Figure 6 As shown.

[0122] Depend on Figure 5 It can be seen that, when the carbon dioxide purity is 80%, compared with pure carbon dioxide and carbon dioxide + nitrogen mixture, the temperature distribution curve of carbon dioxide + nitrogen + methane mixture in the wellbore is shifted downward. That is, at the same well depth, the temperature of the ternary component mixture is lower than that of the binary component mixture, and the closer to the bottom of the well, the more obvious the temperature deviation.

[0123] From the perspective of phase change, the well depth at which the mixed fluid of carbon dioxide, nitrogen and methane transitions from the liquid state to the supercritical state in the wellbore is 237 meters. This means that for non-pure carbon dioxide fluids with a purity of 80%, the phase transition location of the mixed fluid of carbon dioxide, nitrogen and methane is slightly deeper than that of the mixed fluid of carbon dioxide and nitrogen.

[0124] Depend on Figure 6 It can be seen that, when the carbon dioxide purity is 80%, compared with pure carbon dioxide and carbon dioxide + nitrogen mixture, the pressure distribution curve of carbon dioxide + nitrogen + methane mixture in the wellbore is shifted downward. That is, at the same well depth, the pressure of ternary component mixture is lower than that of binary component mixture, and the pressure deviation is more obvious closer to the bottom of the well.

[0125] Example 6

[0126] This embodiment provides a computer device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, to implement the above-mentioned temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial.

[0127] This memory is used to store non-transitory computer-readable instructions. Specifically, the memory may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may, for example, include random access memory (RAM) and / or cache memory. The non-volatile memory may, for example, include read-only memory (ROM), hard disk, flash memory, etc.

[0128] The processor may be a central processing unit (CPU) or other form of processing unit with data processing and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions. The processor is used to execute computer-readable instructions stored in the memory.

[0129] Those skilled in the art will understand that, in order to solve the technical problem of how to achieve a good user experience, this embodiment may also include well-known structures such as communication buses and interfaces, and these well-known structures should also be included within the protection scope of this disclosure.

[0130] For a detailed description of this embodiment, please refer to the corresponding descriptions in the foregoing embodiments, which will not be repeated here.

[0131] Example 7

[0132] This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial.

[0133] The computer-readable storage medium stores non-transitory computer-readable instructions thereon. When the non-transitory computer-readable instructions are executed by a processor, all or part of the steps of the methods of the foregoing embodiments are performed.

[0134] The aforementioned computer-readable storage media include, but are not limited to: optical storage media (e.g., CD-ROM and DVD), magneto-optical storage media (e.g., MO), magnetic storage media (e.g., magnetic tape or portable hard drive), media with built-in rewritable non-volatile memory (e.g., memory card), and media with built-in ROM (e.g., ROM cartridge).

Claims

1. An algorithm for temperature and pressure simulation and phase determination of non-pure carbon dioxide burial, characterized in that, Includes the following steps: S1. Combine the wellbore structure to construct temperature and pressure models for non-pure carbon dioxide burial; S2. Divide the wellbore into calculation units as needed; S3. Calculate the temperature and pressure of non-pure carbon dioxide in each unit; S4. By comparing the critical temperature and pressure of non-pure carbon dioxide, the phase state of each unit of non-pure carbon dioxide can be obtained.

2. The temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial according to claim 1, characterized in that, The pressure model is as follows: In the formula, dP is the pressure gradient of the well section; dz is the unit well section length; ρ is the density of the non-pure carbon dioxide fluid; g is the gravitational acceleration; and θ is the wellbore inclination. f is the friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve; v is the flow velocity of the non-pure carbon dioxide fluid; r1 is the inner radius of the injection sleeve; dv is the velocity gradient of the non-pure carbon dioxide fluid. The temperature model is: In the formula, dT is the axial temperature gradient of the well section; dz is the unit well section length; W is the mass flow rate of the non-pure carbon dioxide fluid; C is the specific heat capacity of the non-pure carbon dioxide fluid; r1 is the inner radius of the injection casing; and U is the overall heat transfer coefficient of the wellbore. T e η is the formation temperature; T is the temperature of the non-pure carbon dioxide fluid injected into the casing; η is the Joule-Thomson coefficient; dP is the pressure gradient of the well section; ρ is the density of the non-pure carbon dioxide fluid. f is the coefficient of friction between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve; v is the flow velocity of the non-pure carbon dioxide fluid.

3. The temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial according to claim 2, characterized in that, The overall heat transfer coefficient U of the wellbore includes the overall heat transfer coefficient U of the upper wellbore. u The overall heat transfer coefficient U in the middle section of the wellbore m and the overall heat transfer coefficient U of the lower wellbore l ; In the formula, r1 is the inner radius of the injection sleeve; λ e r is the thermal conductivity of the formation. i r is the inner radius of the medium of the i-th order; i+1 λ is the outer radius of the medium of the i-th order; i r′7 is the thermal conductivity of the i-th sequence medium; r′5 is the outer radius of the middle layer cement sheath in the middle wellbore; r′7 is the outer radius of the inner layer cement sheath in the lower wellbore; h f The heat transfer coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve; α e The thermal diffusivity of the formation; t represents the injection time of the non-pure carbon dioxide fluid.

4. The temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial according to claim 2 or 3, characterized in that, The formula for calculating the friction coefficient between the non-pure carbon dioxide fluid and the inner wall of the injection sleeve is as follows: In the formula, R e Here, r1 is the inner radius of the injection sleeve, and ε is the roughness of the inner wall of the injection sleeve.

5. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial as described in any one of claims 1-4.

6. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that executes the temperature and pressure simulation and phase determination algorithm for non-pure carbon dioxide burial as described in any one of claims 1-4.

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