A method for studying similarity criteria for heavy oil reservoirs

Abstract

The application discloses a kind of heavy oil reservoir similarity criterion research methods, comprising: the numerical model of heavy oil steam compound huff and puff is established;The physical and mathematical model of the heavy oil steam compound huff and puff is established;Similarity criterion number derivation and screening;The parameter inversion of the key similarity criterion number after screening is carried out.The application uses the numerical model of heavy oil steam compound huff and puff to compare and analyze the exploitation mechanism, and clearly improves the effect of heavy oil steam compound huff and puff EOR, and based on numerical means, the key similarity criterion number with greater sensitivity of heavy oil steam compound huff and puff model is screened and determined, and the experimental parameters are designed according to the similarity criterion conversion ratio, which provides guidance for better design and heavy oil steam compound huff and puff experiment, and can be used to improve the development effect of heavy oil reservoir in the later stage of high cycle huff and puff, and slow down the recovery factor decline rate.

Description

Technical Field

[0001] This invention relates to the field of heavy oil steam combined huff and puff optimization technology, specifically a method for studying similarity criteria of heavy oil reservoirs. Background Technology

[0002] Heavy oil is crude oil with high asphaltene and gum content and high viscosity. Because its viscosity is greatly affected by temperature, an increase of 8-9°C can reduce it by half. The main development methods for heavy oil reservoirs include waterflooding, steam injection, steam drive, SAGD (Super Aquatic Energy Depletion), and reservoir burning. Steam injection is the most widely used method in my country. In a certain Shengli oilfield, over 96% of the production comes from steam injection; however, most steam injection wells have now entered a high-cycle injection phase, with cycle production and oil-gas ratio declining with each cycle, leading to increasingly poor oilfield profitability. Using CO2 combined injection can increase formation elastic energy and has achieved good results in field implementation.

[0003] Heavy oil steam combined huff and puff is a technology that switches from steam huff and puff to CO2 combined huff and puff at the end of the steam huff and puff process, or vice versa. Currently, the research methods for heavy oil steam combined huff and puff extraction technology in the oil extraction field are still imperfect and require further clarification. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the technical problem solved by this invention is that the current research methods for heavy oil steam combined huff and puff extraction technology are not perfect, and there is a lack of research on similarity criteria for heavy oil steam combined huff and puff extraction. At present, the development effect of heavy oil reservoirs in the later stage of high cycle huff and puff is poor, and the recovery rate deceleration rate is high.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for studying similarity criteria of heavy oil reservoirs, comprising:

[0008] Establish a numerical model for heavy oil vapor combined huff and puff;

[0009] Establish the physical and mathematical model of the heavy oil vapor composite huff and puff;

[0010] Derivation and selection of similarity criterion numbers;

[0011] The key similarity criteria numbers after screening are used for parameter inversion.

[0012] As a preferred embodiment of the heavy oil reservoir similarity criterion research method described in this invention, the establishment of the heavy oil steam combined huff and puff numerical model includes:

[0013] Establish geological and reservoir numerical simulation models;

[0014] Optimization and fitting of the parameters of the geological and reservoir numerical simulation model;

[0015] Optimize the injection and production parameters of the geological and reservoir numerical simulation model;

[0016] Determine the throughput round combination.

[0017] As a preferred embodiment of the heavy oil reservoir similarity criterion research method described in this invention, the establishment of the heavy oil steam combined huff and puff physical-mathematical model includes:

[0018] The relationship between the changes in the state parameters of a unit at a certain instant during the heavy oil steam injection process is determined, and a similarity model is established through mathematical equations;

[0019] The boundary conditions and initial conditions of the entire heavy oil vapor combined huff and puff and injection process are quantitatively characterized.

[0020] As a preferred embodiment of the heavy oil reservoir similarity criterion research method described in this invention, the initial conditions are:

[0021] Temperature field, pressure field, and oil saturation field during CO2 injection at the end of steam huff and puff;

[0022] CO2 concentration field, pressure field, and oil saturation field during the final stage of CO2 combined huff and puff steam injection.

[0023] As a preferred embodiment of the heavy oil reservoir similarity criterion research method described in this invention, the boundary conditions include the fluid not flowing through the caprock and the side boundaries of the well network being closed boundaries;

[0024] The fluid does not flow through the cap layer, which can be expressed as:

[0025]

[0026] Where K is the reservoir permeability, K ra Let μ be the relative permeability of phase a. a Let P be the viscosity of phase a. a For phase a pressure, ρ a Let α be the density of phase a, g be the gravitational acceleration, Z be the Z-direction of the unit cell, H be the height in the Z-direction, o be the oil phase, g be the gas phase, and w be the water phase.

[0027] The closed boundary can be represented as:

[0028]

[0029] Where r is the cylindrical radius of the element, R e The radius of the well network.

[0030] As a preferred embodiment of the heavy oil reservoir similarity criterion research method described in this invention, the derivation and selection of the similarity criterion number includes:

[0031] The similarity criterion number of the physical-mathematical model of heavy oil vapor combined huff and puff is derived by using the integral analogy method.

[0032] The completeness of the number of similarity criteria is tested using Buckingham's theorem, and all the number of similarity criteria is tested and completed using dimensional analysis.

[0033] The derived similarity criteria are initially screened.

[0034] As a preferred embodiment of the heavy oil reservoir similarity criterion research method described in this invention, the principle of the preliminary screening is as follows:

[0035] The principle of independent repetition;

[0036] The existence of multiple criteria leads to contradictory relationships;

[0037] This can be satisfied by default and does not require separate simulation.

[0038] As a preferred embodiment of the method for studying similarity criteria of heavy oil reservoirs according to the present invention, the method includes: performing a final selection on the number of similarity criteria after preliminary screening, wherein the final selection includes:

[0039] Define and assign values ​​to the distortion coefficient ω. i The degree of change in the similarity criterion number is characterized as follows:

[0040]

[0041] Where m is the original model and p is the modified model;

[0042] Based on the given distortion coefficient ω i =1%, deriving the slightly changed similarity criterion number from the unchanged similarity criterion number;

[0043] Based on the similarity criterion number after the slight change, the target parameter is determined by numerical simulation.

[0044] Establish sensitivity factor α i The calculation equation, with only the i-th similarity criterion number changing slightly, expresses the degree of change of the target parameter in the numerical simulation results as follows:

[0045]

[0046] in, S represents the degree of change of the target parameter. i Let S be the cumulative oil production after slight changes in the similarity criterion, and let S be the cumulative oil production when the similarity criterion remains unchanged.

[0047] Based on the magnitude of the similarity criterion number sensitivity factor, the key similarity criterion number that affects the combined huff and puff effect of heavy oil vapor is selected.

[0048] As a preferred embodiment of the method for studying similarity criteria of heavy oil reservoirs described in this invention, the key similarity criteria are: pressure, steam dryness, time, permeability, and injection intensity.

[0049] As a preferred embodiment of the heavy oil reservoir similarity criterion research method described in this invention, the parameter inversion includes:

[0050] Experimental parameters were constructed by converting proportional relationships based on the number of key similarity criteria.

[0051] Experiments were conducted on the aforementioned experimental parameters to obtain the mechanism by which combined throughput enhances oil recovery.

[0052] The beneficial effects of this invention are as follows: This invention utilizes a numerical model of heavy oil steam combined huff and puff to conduct comparative analysis of the extraction mechanism, clarifying the effect of heavy oil steam combined huff and puff on improving oil recovery. Based on numerical methods, it screens and determines the number of key similarity criteria with high sensitivity of the heavy oil steam combined huff and puff model, and designs experimental parameters according to the conversion ratio of similarity criteria. This provides guidance for better designing and conducting heavy oil steam combined huff and puff experiments, which can be used to improve the development effect of heavy oil reservoirs in the later stage of high-cycle huff and puff, and slow down the rate of decline in recovery. Attached Figure Description

[0053] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0054] Figure 1 A flowchart illustrating a method for studying similarity criteria in heavy oil reservoirs, as provided in one embodiment of the present invention;

[0055] Figure 2 A three-dimensional numerical model diagram of heavy oil composite huff and puff in a method for studying similarity criteria of heavy oil reservoirs provided in an embodiment of the present invention;

[0056] Figure 3The temperature field of the combined CO2 injection and injection at the end of the steam injection phase is provided in an embodiment of the present invention for a method of studying similarity criteria for heavy oil reservoirs.

[0057] Figure 4 This invention provides a method for studying similarity criteria for heavy oil reservoirs, including the combined steam huff and puff and CO2 injection pressure field at the end of the steam huff and puff phase.

[0058] Figure 5 This invention provides a method for studying similarity criteria in heavy oil reservoirs, which involves a saturation field during the final stage of steam huff and puffing followed by CO2 injection.

[0059] Figure 6 This invention provides another saturation field in a method for studying similarity criteria for heavy oil reservoirs, specifically in the final stage of steam huff and puff followed by CO2 injection and huff and puff.

[0060] Figure 7 This invention provides a method for studying similarity criteria in heavy oil reservoirs, including a CO2 concentration field in a combined CO2 huff and puff transfer steam huff and puff process.

[0061] Figure 8 This invention provides a method for studying similarity criteria of heavy oil reservoirs, which includes a CO2 composite huff and puff transfer steam huff and puff saturation field. Implementation

[0062] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0063] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0064] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0065] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0066] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0067] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0068] Example 1

[0069] Reference Figure 1-8 As an embodiment of the present invention, a method for studying similarity criteria of heavy oil reservoirs is provided, comprising:

[0070] S1: Establish a numerical model for heavy oil steam combined huff and puff, see attached... Figure 2 ;

[0071] Furthermore, the establishment of the numerical model for heavy oil vapor combined huff and puff includes:

[0072] Establish geological and reservoir numerical simulation models;

[0073] It should be noted that precise and detailed comparative studies of reservoirs and detailed descriptions of oil reservoirs provide a reliable basis for geological modeling. The numerical simulation model of oil reservoirs is established by simulating sand layers, reservoir characteristics, basic rock properties, and dividing planar grids to create an initial reservoir model.

[0074] Optimization and fitting of the parameters of the geological and reservoir numerical simulation model;

[0075] It should be noted that the reservoir working regime and adjustable parameter range are determined, the fitting results are analyzed by benchmarking historical data fitting indices, and the reservoir numerical simulation model is corrected based on the fitting results to determine a reservoir numerical simulation model that meets the field reservoir conditions.

[0076] Optimize the injection and production parameters of the geological and reservoir numerical simulation model;

[0077] It should be noted that the three-field (oil saturation, reservoir pressure, and reservoir temperature) distribution characteristics of the late-stage simulation model of heavy oil steam injection were studied, and injection and production parameters such as steam injection dryness, steam injection intensity, steam injection temperature, and production pressure were optimized to determine the optimal parameters that are consistent with the field conditions.

[0078] Determine the throughput round combination.

[0079] It should be noted that, based on the optimal parameters determined after fitting, throughput simulations of different throughput combinations were conducted, and the optimal combination was determined with the degree of harvest as the criterion.

[0080] S2: Establish the physical and mathematical model of the heavy oil vapor composite huff and puff;

[0081] Furthermore, the establishment of the physical and mathematical model for heavy oil vapor combined huff and puff includes:

[0082] The relationship between the changes in the state parameters of a unit at a certain instant during the heavy oil steam injection process is determined, and a similarity model is established through mathematical equations;

[0083] It should be noted that the state parameters include parameters such as mass and motion within the reservoir. A similarity criterion mathematical model is established for a reservoir unit based on the mass equation (continuity equation), motion equation (Darcy equation), energy equation, and saturation equation.

[0084] The boundary and initial conditions of the entire heavy oil vapor combined huff and puff and injection process are quantitatively characterized, as can be seen in the appendix. Figure 3-8 .

[0085] Specifically, the initial conditions are:

[0086] Temperature field, pressure field, and oil saturation field during CO2 injection at the end of steam huff and puff;

[0087] CO2 concentration field, pressure field, and oil saturation field during the final stage of CO2 combined huff and puff steam injection.

[0088] Specifically, the boundary conditions include the fluid not flowing through the caprock and the side boundaries of the well network being closed boundaries;

[0089] The fluid does not flow through the cap layer, which can be expressed as:

[0090]

[0091] Where K is the reservoir permeability, K ra Let μ be the relative permeability of phase a. a Let P be the viscosity of phase a.a For phase a pressure, ρ a Let α be the density of phase a, g be the gravitational acceleration, Z be the Z-direction of the unit cell, H be the height in the Z-direction, o be the oil phase, g be the gas phase, and w be the water phase.

[0092] The closed boundary can be represented as:

[0093]

[0094] Where r is the cylindrical radius of the element, R e The radius of the well network.

[0095] S3: Derivation and selection of similarity criterion numbers;

[0096] Furthermore, the derivation and selection of the similarity criterion number includes:

[0097] The similarity criterion number of the physical-mathematical model of heavy oil vapor combined huff and puff is derived by using the integral analogy method.

[0098] It should be noted that, according to the first similarity theorem, the ratio of any corresponding terms should be equal, and this is derived using the integral analogy method.

[0099] The completeness of the number of similarity criteria is tested using Buckingham's theorem, and all the number of similarity criteria is tested and completed using dimensional analysis.

[0100] The derived similarity criteria are initially screened.

[0101] Specifically, the principles of the preliminary screening are as follows:

[0102] The principle of independent repetition;

[0103] It should be noted that the principle of independent repetition means that the number of similarity criteria can be represented by a linear combination or linear transformation of several other similarity criteria. Since it is repetitive with respect to itself, repetition means non-independence. Removing the repetitive similarity criteria makes them independent.

[0104] The existence of multiple criteria leads to contradictory relationships;

[0105] It should be noted that some derived similarity criterion numbers may imply different physical correspondences, that is, they do not have a form that represents a unique physical parameter, so that each similarity criterion number represents the unique physical parameter it contains.

[0106] This can be satisfied by default and does not require separate simulation.

[0107] It should be noted that the saturation of oil and water vapor under the experimental conditions can be assumed to be satisfied, and is satisfied according to the 1:1 ratio.

[0108] It should be noted that the above preliminary screening process, which involves screening each of the many derived similarity criteria, is tedious. By seeking the commonalities and differences among the similarity criteria, the screening workload is simplified and time is saved.

[0109] Furthermore, a final selection is performed on the number of similarity criteria after the initial screening, the final selection including:

[0110] Define and assign values ​​to the distortion coefficient ω. i The degree of change in the similarity criterion number is characterized as follows:

[0111]

[0112] Where m is the original model and p is the modified model;

[0113] Based on the given distortion coefficient ω i =1%, deriving the slightly changed similarity criterion number from the unchanged similarity criterion number;

[0114] Based on the similarity criterion number after the slight change, the target parameter is determined by numerical simulation.

[0115] Establish sensitivity factor α i The calculation equation, with only the i-th similarity criterion number changing slightly, expresses the degree of change of the target parameter in the numerical simulation results as follows:

[0116]

[0117] in, S represents the degree of change of the target parameter. i Let S be the cumulative oil production after slight changes in the similarity criterion, and let S be the cumulative oil production when the similarity criterion remains unchanged.

[0118] Based on the magnitude of the similarity criterion number sensitivity factor, the key similarity criterion number that affects the combined huff and puff effect of heavy oil vapor is selected.

[0119] Specifically, the key similarity criteria are: pressure, steam dryness, time, permeability, and injection intensity.

[0120] S4: Perform parameter inversion on the number of key similarity criteria after screening.

[0121] Furthermore, the parameter inversion includes:

[0122] Experimental parameters were constructed by converting proportional relationships based on the number of key similarity criteria.

[0123] It should be noted that the conversion ratio is determined based on the actual situation.

[0124] Experiments were conducted on the aforementioned experimental parameters to obtain the mechanism by which combined throughput enhances oil recovery.

[0125] Specifically, based on the simulation of formation energy storage and release using multiple sand-filled pipes with different radii, this study investigates the variation patterns of fluid production, oil production, and gas production, as well as the temperature field, pressure field, and sweep radius of the heavy oil steam / CO2 combined huff and puff method under different pressures and conditions, in order to obtain the mechanism of combined huff and puff to enhance oil recovery.

[0126] Example 2

[0127] Reference Figure 1-8 As an embodiment of the present invention, a specific application of the method for studying similarity criteria of heavy oil reservoirs is provided:

[0128] S1: Establish a numerical model for heavy oil vapor combined huff and puff;

[0129] Furthermore, the establishment of the numerical model for heavy oil vapor combined huff and puff includes:

[0130] Establish geological and reservoir numerical simulation models;

[0131] When applying the method, a detailed analysis of the geological features, crude oil properties and other reservoir characteristics of the target block is performed. The number of grid steps is set, and a series of parameters such as permeability and reservoir porosity are set according to the field data to establish a numerical model of heavy oil vapor composite huff and puff.

[0132] Optimization and fitting of the parameters of the geological and reservoir numerical simulation model;

[0133] When applying the model, the working system and adjustable parameter range of the simulation model are formulated by analogy with the actual reservoir production situation. The results are analyzed by comparing the fitting index with historical data to obtain a reservoir numerical simulation model that meets the reservoir conditions.

[0134] Optimize the injection and production parameters of the geological and reservoir numerical simulation model;

[0135] It should be noted that the three-field (oil saturation, reservoir pressure, and reservoir temperature) distribution characteristics of the late-stage simulation model of heavy oil steam injection were studied, and injection and production parameters such as steam injection dryness, steam injection intensity, steam injection temperature, and production pressure were optimized to determine the optimal parameters that are consistent with the field conditions.

[0136] Determine the throughput round combination.

[0137] It should be noted that, based on the optimal parameters determined after fitting, throughput simulations of different throughput combinations were conducted, and the optimal combination was determined with the degree of harvest as the criterion.

[0138] S2: Establish the physical and mathematical model of the heavy oil vapor composite huff and puff;

[0139] Furthermore, the establishment of the physical and mathematical model for heavy oil vapor combined huff and puff includes:

[0140] The relationship between the changes in the state parameters of a unit at a certain instant during the heavy oil steam injection process is determined, and a similarity model is established through mathematical equations;

[0141] In application, mathematical models are established based on changes in mass, motion, saturation, etc., including but not limited to:

[0142] The mass equation (inflow minus outflow equals change)

[0143]

[0144] Equations of motion (Darcy's equations)

[0145]

[0146] Saturation equation

[0147] S o +S g +S W =1

[0148] In the formula, r represents the radius of the element, θ represents the angle of the element, z represents the thickness of the element, and ρ represents the radius of the element. a (a = o, g, w) represents the three-phase density of oil, gas, and water, u a (a = o, g, w) represents the flow velocities of each phase, q a (a = o, g, w) represents the injection mass, φ represents the reservoir porosity, and S a (a = o, g, w) represents the three-phase saturation of oil, gas, and water, μ a (a = o, g, w) represents the viscosity of the three phases of oil, gas, and water, P a (a = o, g, w) represents the three-phase pressure of oil, gas, and water, K. a (a = o, g, w) represents the three-phase permeability of oil, gas, and water, K ra (a = o, g, w) represents the relative permeability of the three phases of oil, gas, and water.

[0149] The boundary conditions and initial conditions of the entire heavy oil vapor combined huff and puff and injection process are quantitatively characterized.

[0150] Specifically, the initial conditions are:

[0151] Temperature field, pressure field, and oil saturation field during CO2 injection at the end of steam huff and puff;

[0152] CO2 concentration field, pressure field, and oil saturation field during the final stage of CO2 combined huff and puff steam injection.

[0153] During application, the injected high-temperature steam can reach 350℃. The reservoir temperature at the end of the heavy oil steam combined huff and puff process is higher than the original formation temperature. This higher temperature environment provides a significant advantage for the next stage of CO2 extraction, enhancing crude oil fluidity during CO2 combined cold extraction. This mechanism can be quantitatively characterized as follows:

[0154] T = T0 + Rk T

[0155] In the formula, T0 is the temperature around the injection wellbore, R is the distance from the horizontal wellbore, and k T This represents the temperature gradient.

[0156] Furthermore, under the superposition of the thermal recovery system and the residual cold-extraction viscosity-reducing system, the range of crude oil that can be dissolved and viscous by CO2 combined huff and puff is further expanded. The initial concentration conditions of CO2 combined huff and puff, i.e. the CO2 concentration field at this time, can be expressed as:

[0157] α=α0+k α R

[0158] In the formula, α0 is the CO2 concentration around the wellbore, and k α This represents a concentration gradient.

[0159] Furthermore, the initial pressure conditions during steam injection, i.e. the pressure field state at the end of CO2 combined injection, can be expressed as:

[0160] P = P0 + k p R

[0161] In the formula, P0 is the pressure around the wellbore, and k P This represents the pressure gradient.

[0162] Specifically, the boundary conditions include the fluid not flowing through the caprock and the side boundaries of the well network being closed boundaries;

[0163] The fluid does not flow through the cap layer, which can be expressed as:

[0164]

[0165] Where K is the reservoir permeability, K ra Let μ be the relative permeability of phase a. a Let Pa be the viscosity of phase a, Pa be the pressure of phase a, and ρ be the viscosity of phase a. a Let α be the density of phase a, g be the gravitational acceleration, Z be the Z-direction of the unit cell, H be the height in the Z-direction, o be the oil phase, g be the gas phase, and w be the water phase.

[0166] The closed boundary can be represented as:

[0167]

[0168] Where r is the cylindrical radius of the element, R e The radius of the well network.

[0169] S3: Derivation and selection of similarity criterion numbers;

[0170] Furthermore, the derivation and selection of the similarity criterion number includes:

[0171] The similarity criterion number of the physical-mathematical model of heavy oil vapor combined huff and puff is derived by using the integral analogy method.

[0172] It should be noted that similar phenomena have the same governing equations. Therefore, according to the first theorem of similarity, the ratio of any corresponding terms should be equal. This can be derived using the integral analogy method.

[0173] The completeness of the number of similarity criteria is tested using Buckingham's theorem, and all the number of similarity criteria is tested and completed using dimensional analysis.

[0174] The derived similarity criteria are initially screened.

[0175] Specifically, the principles of the preliminary screening are as follows:

[0176] The principle of independent repetition;

[0177] The existence of multiple criteria leads to contradictory relationships;

[0178] This can be satisfied by default and does not require separate simulation.

[0179] It should be noted that the above preliminary screening process, which involves screening each of the many derived similarity criteria, is tedious. By seeking the commonalities and differences among the similarity criteria, the screening workload is simplified and time is saved.

[0180] Furthermore, a final selection is performed on the number of similarity criteria after the initial screening, the final selection including:

[0181] Define and assign values ​​to the distortion coefficient ω. i The degree of change in the similarity criterion number is characterized as follows:

[0182]

[0183] Where m is the original model and p is the modified model;

[0184] Based on the given distortion coefficient ω i =1%, deriving the slightly changed similarity criterion number from the unchanged similarity criterion number;

[0185] Based on the similarity criterion number after the slight change, the target parameter is determined by numerical simulation.

[0186] Establish sensitivity factor αi The calculation equation, with only the i-th similarity criterion slightly changed, shows the degree of change of the target parameter in the numerical simulation results, expressed as follows:

[0187]

[0188] in, S represents the degree of change of the target parameter. i Let S be the cumulative oil production after slight changes in the similarity criterion, and let S be the cumulative oil production when the similarity criterion remains unchanged.

[0189] Based on the numerical model established by S1, the number of similarity criteria to be finally screened is simulated to determine the target parameters and further determine the size of the sensitivity factors. The size of the sensitivity factors of the similarity criteria is shown in Table 1.

[0190] Table 1. Basic Information on Sensitive Factors for Similarity Criteria

[0191]

[0192] Based on the magnitude of the similarity criterion number sensitivity factor, the key similarity criterion number that affects the combined huff and puff effect of heavy oil vapor is selected.

[0193] Specifically, the key similarity criteria are: pressure, steam dryness, time, permeability, and injection intensity.

[0194] S4: Perform parameter inversion on the number of key similarity criteria after screening.

[0195] Furthermore, the parameter inversion includes:

[0196] Experimental parameters were constructed by converting proportional relationships based on the number of key similarity criteria.

[0197] Specifically, reservoir parameters are converted into experimental parameters through similarity criteria conversion ratios. This process takes into account the actual situation and the proportional conversion relationship of similarity criteria numbers, converting dryness, pressure, time, injection rate, and permeability into experimental parameters.

[0198] Experiments were conducted on the aforementioned experimental parameters to obtain the mechanism by which combined throughput enhances oil recovery.

[0199] Specifically, this invention utilizes multiple sand-filled pipes of varying radii to simulate formation energy release, investigating the variations in fluid production, oil production, and gas production, as well as temperature, pressure, and sweep radius of heavy oil steam / CO2 combined huff and puff wells under different pressures and conditions. This aims to uncover the mechanism by which combined huff and puff enhances oil recovery. Based on a reservoir numerical simulation method using heavy oil steam combined huff and puff technology, this invention compares different huff and puff combinations, using a daily time step and the same operating regime. A 12-cycle simulation is conducted using equivalent seepage, and the simulation results are analyzed to determine that the optimal combination for the large-cycle "hot-cold-cold" pattern is the best. The residual temperature during the steam huff and puff stage is a key factor ensuring the effectiveness of cold production huff and puff development. The injection of combined cold production significantly increases formation elastic energy, improving the subsequent oil production rate and production cycle of hot production. Based on the established numerical model, considering the similarity conditions satisfied by the model and prototype, such as geometric similarity, kinematic similarity, and dynamic similarity, and taking into account both steam huff and puff and CO2 combined huff and puff, it is considered as a system. Geometric similarity, kinematic similarity, and dynamic similarity are considered, and the initial state during huff and puff alternation is quantitatively characterized. Finally, a similarity criterion for the heavy oil steam combined huff and puff model is established. Using a combination of integral analogy and dimensional analysis, 35 similarity criterion numbers for the entire system are derived, and 17 similarity criterion numbers are obtained based on the selection principle. By defining the sensitivity factor and distortion coefficient of the similarity criterion numbers, and using numerical simulation software with a given distortion coefficient of 1%, the changed similarity criterion numbers are calculated. Then, the magnitude of the sensitivity factor is determined according to the sensitivity factor formula, thereby obtaining the sensitivity factor for each similarity criterion number. Finally, the five similarity criterion numbers with larger sensitivity factors are obtained. Based on the similarity ratio conversion relationship, they are converted into specific experimental parameters, and experiments are designed and conducted.

[0200] Heavy oil steam combined huff and puff experiments show that, with an injection temperature of 350℃, steam dryness of 80%, and an injection rate of 10 ml / min, the recovery rate of heavy oil steam combined huff and puff is significantly improved compared to steam huff and puff, with an estimated recovery increase of approximately 13.03 cm under laboratory conditions and a maximum recovery rate of 13.12%. This huff and puff extraction technology can provide guidance for the study of heavy oil reservoir development.

[0201] Example 3

[0202] To verify the effectiveness of the techniques used in this method, a comparative experiment was conducted to confirm the actual effectiveness of the method.

[0203] This invention addresses the heavy oil steam / CO2 combined huff and puff process, considering the changes in the mass (injection and outflow), motion state (Darcy equation), and energy of the oil, gas, and water phases. It also takes into account constraints (boundary conditions and initial conditions) to represent the completeness of the entire heavy oil steam / CO2 combined huff and puff reservoir development process. A key feature of this approach is the use of numerical simulation to accurately determine the temperature, pressure, and oil saturation fields during the initial conditions of steam huff and puff to CO2 or CO2 to steam huff and puff. This mathematical approach forms a complete similarity criterion system, laying a solid foundation for maximizing the simulation of the actual on-site development process. As shown in Table 2, the combined huff and puff process achieves nearly one percentage point higher recovery compared to traditional steam huff and puff.

[0204] Table 2: Comparison of Heavy Oil Steam Huff and Puff and Combined Huff and Puff

[0205]

[0206] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for studying similarity criteria in heavy oil reservoirs, characterized in that, include: Establish a numerical model for heavy oil vapor combined huff and puff; A physical and mathematical model for the heavy oil vapor combined huff and puff is established; wherein, the physical and mathematical model quantifies and characterizes the boundary conditions of the entire heavy oil vapor combined huff and puff and injection process; The boundary conditions include the fluid not flowing through the caprock and the side boundaries of the well network being closed boundaries; The fluid does not flow through the cap layer, which is indicated as follows: Where K is the reservoir permeability, K ra Let μ be the relative permeability of phase a. a Let P be the viscosity of phase a. a For phase a pressure, ρ a Let α be the density of phase a, g be the gravitational acceleration, Z be the Z-direction of the unit cell, H be the height in the Z-direction, o be the oil phase, g be the gas phase, and w be the water phase. The closed boundary is represented as: Where r is the radius of the unit column coordinates, and Re is the radius of the well pattern; Derivation and selection of similarity criterion numbers; The key similarity criteria numbers after screening are used for parameter inversion.

2. The method for studying similarity criteria for heavy oil reservoirs as described in claim 1, characterized in that: The establishment of the numerical model for heavy oil vapor combined huff and puff includes: Establish geological and reservoir numerical simulation models; Optimization and fitting of the parameters of the geological and reservoir numerical simulation model; Optimize the injection and production parameters of the geological and reservoir numerical simulation model; Determine the throughput round combination.

3. The method for studying similarity criteria for heavy oil reservoirs as described in claim 1 or 2, characterized in that: The establishment of the physical and mathematical model for heavy oil steam combined huff and puff includes: Determine the relationship between the changes in state parameters of a unit at a certain instant during the heavy oil steam / CO2 injection process, and establish a similar model through mathematical equations; The boundary and initial conditions of the entire heavy oil vapor combined huff and puff and injection process are quantitatively characterized.

4. The method for studying similarity criteria for heavy oil reservoirs as described in claim 3, characterized in that: The initial conditions are: Temperature field, pressure field, and oil saturation field during CO2 injection at the end of steam huff and puff; CO2 concentration field, pressure field, and oil saturation field during the final stage of CO2 combined huff and puff steam injection.

5. The method for studying similarity criteria for heavy oil reservoirs as described in claim 4, characterized in that: The derivation and selection of the similarity criterion number includes: The similarity criterion number of the physical-mathematical model of heavy oil vapor combined huff and puff is derived by using the integral analogy method. The completeness of the number of similarity criteria is tested using Buckingham's theorem, and all the number of similarity criteria is tested and completed using dimensional analysis. The derived similarity criteria are initially screened.

6. The method for studying similarity criteria for heavy oil reservoirs as described in claim 5, characterized in that: The principles of the preliminary screening are as follows: The principle of independent repetition; The existence of multiple criteria leads to contradictory relationships; The default condition is met, and no separate simulation is required.

7. The method for studying similarity criteria for heavy oil reservoirs as described in claim 6, characterized in that: The number of similarity criteria after the initial screening is then used for final selection, which includes: Define and assign values ​​to the distortion coefficient ω. i The degree of change in the similarity criterion number is characterized as follows: Where m is the original model and p is the modified model; Based on the given distortion coefficient ω i =1%, deriving the slightly changed similarity criterion number from the unchanged similarity criterion number; Based on the similarity criterion number after the slight change, the target parameter is determined by numerical simulation. Establish sensitivity factor α i The calculation equation, with only the i-th similarity criterion slightly changed, shows the degree of change of the target parameter in the numerical simulation results, expressed as follows: in, S represents the degree of change of the target parameter. i Let S be the cumulative oil production after slight changes in the similarity criterion, and let S be the cumulative oil production when the similarity criterion remains unchanged. Based on the magnitude of the sensitivity factor of the similarity criterion number, the key similarity criterion number that has a greater impact on the combined huff and puff effect of heavy oil vapor is selected.

8. The method for studying similarity criteria for heavy oil reservoirs as described in claim 7, characterized in that: The key similarity criteria are: pressure, steam dryness, time, permeability, and injection intensity.

9. The method for studying similarity criteria for heavy oil reservoirs as described in claim 8, characterized in that: The parameter inversion includes: Experimental parameters were constructed by converting proportional relationships based on the number of key similarity criteria. Experiments were conducted on the aforementioned experimental parameters to obtain the mechanism by which combined throughput enhances oil recovery.

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