A method, device and equipment for determining fire-flooding air injection pressure of high-viscosity oil reservoir

Abstract

The application discloses a method, device and equipment for determining air injection pressure of high-viscosity oil reservoirs in fire flooding. The method comprises the following steps: obtaining additional air injection resistance and starting pressure gradients of different fire flooding combustion zones; and then determining the air injection pressure of the target oil reservoir in the fire flooding after steam stimulation and preheating according to the obtained additional air injection resistance and starting pressure gradients of different fire flooding combustion zones. Through the above method, the air injection pressure of the target oil reservoir in the fire flooding after steam stimulation and preheating is accurately calculated, the formation preheating parameters of the high-viscosity oil reservoir are successfully optimized, the best fire flooding time and air injection pressure of the high-viscosity oil reservoir are effectively determined, stable high-temperature fire flooding is realized, and the blank of the air injection pressure calculation method of the high-temperature fire flooding of the high-viscosity oil reservoir is filled.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, and in particular to a method, apparatus and equipment for determining the air injection pressure of fire-driven oil reservoirs. Background Technology

[0002] Fire flooding technology involves continuously injecting air into the formation through a gas injection well and igniting the oil layer to achieve intra-layer combustion. The heat generated by the in-situ combustion of heavy components heats the oil layer, causing the crude oil to crack, decrease viscosity, and flow, thereby driving the formation crude oil towards the production well. It has a comprehensive oil displacement effect, combining steam flooding, hot water flooding, and flue gas flooding. Currently, it has been industrially applied in extra-heavy oil reservoirs with crude oil viscosity below 25,000 mPa·s in the later stages of steam injection development, becoming a replacement technology for significantly improving oil recovery after steam injection in heavy oil reservoirs. During the industrial promotion of fire flooding, in some heavy oil areas, the formation crude oil viscosity exceeds 25,000 mPa·s, reaching as high as 80,000 mPa·s or more. Direct conversion to fire flooding development presents problems such as high air injection pressure, large displacement resistance, difficulty in gas injection ignition, and inability to maintain stable combustion at the fire front. The main reason is that a highly saturated "oil wall" (such as...) forms at the displacement front during fire flooding. Figure 1 As shown in the diagram, the higher the crude oil viscosity, the greater the displacement resistance of the "oil wall," and the corresponding increase in gas injection pressure. This leads to a decrease in gas injection rate, inability to maintain stable combustion in the formation, and in severe cases, formation flameout. While replacing the compressor with a higher-pressure equipment and high-pressure injection pipeline can solve this problem, it also presents issues such as slow fire line advance, high air-to-oil ratio, and large equipment investment, making it economically unfeasible. Therefore, fire flooding technology is generally applied to ordinary heavy oil reservoirs with lower viscosity abroad.

[0003] Currently, the strategy for dealing with high air injection pressure in high-viscosity oil areas during fire flooding is to first conduct steam injection and huff-and-puff production simultaneously on both injection and production wells. After the viscosity of the crude oil between wells decreases, a test injection of gas is performed. If the injection pressure can be kept stable, fire flooding can proceed; otherwise, new steam preheating is implemented. This method has the following two problems: First, excessive steam injection can create large steam channeling channels between injection and production wells. After switching to fire flooding, the combustion front will rush along these channels, causing fire. Second, if the steam injection volume is small, hydraulic connectivity is not formed between injection and production wells. However, after crude oil is extracted from the near-wellbore area, certain cavities are formed. The test injection of air is generally short, and the injected gas can be stored in these cavities, resulting in low and relatively stable injection pressure at the wellhead. This can lead to misjudgment, resulting in the lack of flue gas migration channels after switching to fire flooding, causing the air injection pressure to rise continuously, leading to a decrease in injection rate and the inability of the formation to maintain stable combustion.

[0004] For heavy oil, the seepage pattern within the reservoir is non-Darcy flow with an initial pressure gradient. Heavy oil only begins to flow when the driving pressure gradient exceeds its initial pressure gradient (i.e., the initial pressure gradient). Simultaneously, heavy oil exhibits highly sensitive viscosity-temperature characteristics; its viscosity decreases rapidly with increasing temperature. When the inflection point temperature is exceeded (generally 50-70℃ for extra-heavy oils, varying significantly among different oil types), the seepage pattern conforms to Darcy flow. The literature "Experimental Study on Initial Pressure Gradient of Heavy Oil Reservoirs" (Xinjiang Petroleum Geology, April 2012), "Experimental Study on Initial Pressure Gradient of Nonlinear Seepage in Heavy Oil" (Petroleum Drilling and Production Technology, May 2016), and the Chinese patent "Prediction Method and System for Pressure Distribution of Vertical Well Thermal Recovery in Low-Permeability Heavy Oil Reservoirs" (ZL201610264206.4) disclose methods for determining pressure gradients and initial pressures in heavy oil reservoirs. These methods can be used to calculate parameters such as starting pressure and drainage radius for purely physical displacement processes such as steam injection and steam drive in heavy oil reservoirs. However, for fire drive, the extraction process involves complex physicochemical processes such as combustion (oxidation) of crude oil and air, crude oil upgrading, steam / hot water drive, and flue gas drive. The fluid seepage process in the formation is also quite complex. Currently, there is no method to determine the air injection pressure that takes into account the complex displacement process of fire drive when implementing fire drive in high viscosity reservoirs. Summary of the Invention

[0005] The purpose of this invention is to address the problems of high direct air injection pressure and lack of quantitative guidance for steam injection preheating in high-viscosity oil reservoirs during fire flooding. Based on the fire flooding mechanism, combined with the characteristics of combustion zone migration and displacement, viscosity-temperature variation law, and rheological properties of heavy oil, calculation formulas for the starting pressure gradient and air injection pressure of different zones are established. A method, device, and equipment for determining the air injection pressure in high-viscosity oil reservoir fire flooding are proposed to guide the optimization of formation preheating parameters, determine the optimal timing for switching to fire flooding, and determine the optimal air injection pressure. This achieves stable high-temperature fire flooding displacement and fills the gap in the calculation method of high-temperature fire flooding air injection pressure in high-viscosity oil reservoirs.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A method for determining the air injection pressure in a high-viscosity oil reservoir during fire flooding, the method comprising:

[0008] Obtain additional gas injection resistance and start-up pressure gradients for different fire-driven combustion zones;

[0009] Based on the additional gas injection resistance and the starting pressure gradient of the different fire-driven combustion zones, the fire-driven air injection pressure of the target reservoir after steam huff and puff preheating is determined.

[0010] As a further improvement of the present invention, the air injection pressure for fire-driven oil reservoir after steam huff and puff preheating is determined based on the additional air injection resistance and the starting pressure gradient of different fire-driven combustion zones, and is obtained by the following formula:

[0011]

[0012] In the formula, P is the air pressure injected during fire driving; G i The starting pressure gradients represent different fire-driven combustion zones. G1 is the starting pressure gradient of the already burned zone, G2 is the starting pressure gradient of the high-temperature zone (>200℃), G3 is the starting pressure gradient of the zone where condensate, modified oil, and high-temperature flue gas act together, G4 is the starting pressure gradient of the combustion flue gas zone, and G5 is the starting pressure gradient of the original remaining oil zone. i The widths of different fire-driven combustion zones are defined as follows: l1 is the width of the already burned zone; l2 is the width of the high-temperature zone (>200℃); l3 is the width of the zone where condensate, modified oil, and high-temperature flue gas interact; l4 is the width of the zone where combustion flue gas interacts; and l5 is the width of the original remaining oil zone. f This is to increase the resistance to gas injection.

[0013] As a further improvement of the present invention, G1≈0; G2≈0;

[0014] Wherein, K3 is the reservoir permeability in the zone where condensate, modified oil, and high-temperature flue gas interact, K4 is the reservoir permeability in the zone where combustion flue gas interacts, and K5 is the reservoir permeability in the original remaining oil zone; μ3 is the crude oil viscosity in the zone where condensate, modified oil, and high-temperature flue gas interact, μ4 is the crude oil viscosity in the zone where combustion flue gas interacts, and μ5 is the crude oil viscosity in the original remaining oil zone; A and B are coefficients;

[0015] l1 = 0.03t ~ 0.05t; where t is the number of days of reservoir combustion after ignition; l2 = 7; l3 = 10; l4 = 30; l5 is the remaining width obtained by subtracting the sum of the widths of the four regions l1, l2, l3, and l4 from the distance between the injection well and the production well; P f =1.

[0016] As a further improvement of the present invention, the method further includes:

[0017] The determined fire-driven air injection pressure is compared and analyzed with the actual injection pressure of the air injection equipment;

[0018] If the determined fire-driven air injection pressure is less than or equal to the actual injection pressure of the air injection device, then the air injection and ignition are performed directly at the fire-driven air injection pressure.

[0019] If the determined fire-driven air injection pressure is greater than the actual injection pressure of the air injection equipment, then a second round of steam huff and puff preheating is performed on the target reservoir, and the second fire-driven air injection pressure is re-determined. This process continues until the target reservoir is preheated for the nth round of steam huff and puff, and the determined nth fire-driven air injection pressure is less than or equal to the actual injection pressure of the air injection equipment. In this case, the air injection and ignition are performed at the nth fire-driven air injection pressure.

[0020] As a further improvement of the present invention, the high-temperature zone >200°C includes: a combustion zone, a coking zone, and a steam zone;

[0021] The zone where condensate, modified oil, and high-temperature flue gas interact includes: a high-temperature condensate zone, an oil wall, and a first-part residual oil zone;

[0022] The combustion flue gas action zone is the second part of the remaining oil zone.

[0023] The present invention also provides a device for determining the air injection pressure in fire-flooding of high-viscosity oil reservoirs, the device comprising:

[0024] The acquisition unit is used to acquire the additional gas injection resistance and the starting pressure gradient of different fire-driven combustion zones;

[0025] The determining unit is used to determine the fire-driven air injection pressure of the target reservoir after steam injection preheating, based on the additional air injection resistance and the starting pressure gradient of the different fire-driven combustion zones.

[0026] As a further improvement of the present invention, the determining unit determines the fire-driven air injection pressure of the target reservoir after steam injection preheating based on the additional air injection resistance and the starting pressure gradient of the different fire-driven combustion zones, and obtains it through the following formula:

[0027]

[0028] In the formula, P is the air pressure injected during fire driving; G i The starting pressure gradients represent different fire-driven combustion zones. G1 is the starting pressure gradient of the already burned zone, G2 is the starting pressure gradient of the high-temperature zone (>200℃), G3 is the starting pressure gradient of the zone where condensate, modified oil, and high-temperature flue gas act together, G4 is the starting pressure gradient of the combustion flue gas zone, and G5 is the starting pressure gradient of the original remaining oil zone. i The widths of different fire-driven combustion zones are defined as follows: l1 is the width of the already burned zone; l2 is the width of the high-temperature zone (>200℃); l3 is the width of the zone where condensate, modified oil, and high-temperature flue gas interact; l4 is the width of the zone where combustion flue gas interacts; and l5 is the width of the original remaining oil zone. f This is to increase the resistance to gas injection.

[0029] As a further improvement of the present invention, G1≈0; G2≈0;

[0030] Wherein, K3 is the reservoir permeability in the zone where condensate, modified oil, and high-temperature flue gas interact, K4 is the reservoir permeability in the zone where combustion flue gas interacts, and K5 is the reservoir permeability in the original remaining oil zone; μ3 is the crude oil viscosity in the zone where condensate, modified oil, and high-temperature flue gas interact, μ4 is the crude oil viscosity in the zone where combustion flue gas interacts, and μ5 is the crude oil viscosity in the original remaining oil zone; A and B are coefficients;

[0031] l1 = 3t ~ 5t; where t is the number of days of reservoir combustion after ignition; l2 = 7; l3 = 10; l4 = 30; l5 is the remaining width obtained by subtracting the sum of the widths of the four regions l1, l2, l3, and l4 from the distance between the injection well and the production well; P f =1.

[0032] As a further improvement of the present invention, the device further includes:

[0033] The analysis unit is used to compare and analyze the determined fire-driven air injection pressure with the actual injection pressure of the air injection equipment.

[0034] If the determined fire-driven air injection pressure is less than or equal to the actual injection pressure of the air injection device, then the air injection and ignition are performed directly at the fire-driven air injection pressure.

[0035] If the determined fire-driven air injection pressure is greater than the actual injection pressure of the air injection equipment, then a second round of steam huff and puff preheating is performed on the target reservoir, and the second fire-driven air injection pressure is re-determined. This process continues until the target reservoir is preheated for the nth round of steam huff and puff, and the determined nth fire-driven air injection pressure is less than or equal to the actual injection pressure of the air injection equipment. In this case, the air injection and ignition are performed at the nth fire-driven air injection pressure.

[0036] This invention also provides a device for determining the air injection pressure in fire-flooding of high-viscosity oil reservoirs, the device comprising a processor and a memory; wherein,

[0037] The memory is used to store machine-executable instructions;

[0038] The processor is configured to read and execute machine-executable instructions stored in the memory to implement any of the aforementioned methods for determining the air injection pressure in high-viscosity oil reservoirs.

[0039] The beneficial effects of this invention are:

[0040] The present invention provides a method, apparatus, and equipment for determining the air injection pressure for high-viscosity reservoir fire-driven operations. By acquiring the additional injection resistance and the starting pressure gradient of different fire-driven combustion zones, and based on these acquired factors, the air injection pressure for fire-driven operations in the target reservoir after steam huff and puff preheating is accurately calculated. This method successfully guides the optimization of formation preheating parameters in high-viscosity reservoirs, effectively determines the optimal timing for transitioning to fire-driven operations and the optimal air injection pressure, achieves stable high-temperature fire-driven displacement, and fills the gap in methods for calculating the air injection pressure for high-temperature fire-driven operations in high-viscosity reservoirs.

[0041] This invention establishes regional starting pressure gradients based on the migration characteristics of the combustion zone in the seepage channel between injection and production wells during the fire-flooding process in high-viscosity oil reservoirs, as well as the range of action of oil displacement and viscosity reduction mechanisms such as high-temperature combustion, crude oil upgrading, and flue gas scavenging. It also provides a method for calculating the air injection pressure during fire-flooding in high-viscosity oil reservoirs. This invention solves the current problems of excessive steam injection in high-viscosity oil reservoirs causing fire spread and insufficient steam preheating leading to a continuous increase in air injection pressure and the inability of the formation to maintain stable combustion.

[0042] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0043] Figure 1 This is a distribution diagram of the fire-driven combustion zone pattern and its migration characteristics according to the present invention.

[0044] Figure 2 This is a flowchart of the method for determining the air injection pressure in high-viscosity oil reservoir fire flooding according to the present invention;

[0045] Figure 3 This is a schematic diagram of the device for determining the air injection pressure in high-viscosity oil reservoir fire flooding according to the present invention. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] This invention proposes a method for determining the air injection pressure during fire flooding in high-viscosity oil reservoirs, such as... Figure 2As shown, this method is mainly based on the fire-driven oil displacement mechanism, combined with the migration and displacement characteristics of the combustion zone, the viscosity-temperature variation law, and the rheological properties of heavy oil. First, indoor experimental methods are used to determine the starting pressure gradient of the target reservoir under different viscosity conditions. Then, combined with the viscosity-temperature curve of the target reservoir, the crude oil viscosity under different temperature field distributions between injection and production wells is determined. Next, based on the combined viscosity reduction effect and displacement characteristics at different locations in the fire-driven combustion zone, the starting pressure gradient of different zones is determined. The minimum starting pressure is calculated segment by segment, and finally, the air injection pressure between injection and production wells is obtained. The specific content of the invention is as follows:

[0048] (1) Determine the starting pressure gradient G of the target reservoir under different viscosity conditions:

[0049] The starting pressure gradient G of the target reservoir under different viscosity conditions was determined through indoor experiments. Its general expression is: In the formula, G is the starting pressure gradient, in MPa / m; K is the reservoir permeability, in mD; μ is the crude oil viscosity of the region under formation conditions, in mPa·S; and A and B are coefficients.

[0050] (2) A steam huff and puff preheating was carried out on the target reservoir. The viscosity-temperature curve of the target reservoir was measured by indoor experiments. The temperature field and crude oil viscosity field distribution between injection and production wells after steam huff and puff preheating of high viscosity reservoir were calculated, thereby determining the crude oil viscosity of the target reservoir under different temperature field distribution conditions.

[0051] (3) Divide the fire-driven combustion zone of the target reservoir after steam injection preheating, and calculate the starting pressure gradient and zone width of each fire-driven combustion zone after partitioning.

[0052] according to Figure 1 The distribution and migration characteristics of the combustion zone in the fire-driven flooding system are shown in the diagram. Combined with multiple displacement effects such as temperature, crude oil upgrading, steam / hot water flooding, and flue gas flooding, the combustion zone is divided into five regions:

[0053] ① Burned Zone: In this zone, the crude oil saturation is basically 0, and the rock pores are basically filled with air. Therefore, the starting pressure gradient in this zone can be approximated as zero, i.e., G1≈0. The width l1 of this zone is 0 at the moment of ignition. After ignition, it can be calculated based on the fire line advancing 3-5cm per day; that is, l1=0.03t~0.05t, in meters; where t is the number of days of oil reservoir combustion after ignition.

[0054] ② High-temperature zone > 200℃: This zone includes the combustion zone (firewall), coking zone and steam zone. Due to the high temperature and low oil saturation, heavy oil in this zone is a Newtonian fluid that conforms to Darcy flow. The fluid is mainly in the gas phase. Therefore, the starting pressure gradient G2 in this zone is approximately 0. In addition, according to the indoor physical model experiment and the similarity criterion, the width l2 of this zone generally does not exceed 7m.

[0055] ③ Zone of combined action of condensate, modified oil, and high-temperature flue gas: This zone includes a high-temperature condensate zone, an oil wall, and a portion of the remaining oil zone. Based on experimental and field test results, unlike the "overall migration and continuous displacement" model of high-saturation oil walls formed by fire flooding of low-viscosity ordinary heavy oil, the oil walls formed by fire flooding of high-viscosity reservoirs mainly migrate within seepage channels formed by preheating with steam injection. The modified crude oil content and water content are higher in this zone. Furthermore, the displacement characteristic involves the high-temperature condensate from the modified crude oil and the combustion flue gas forming a mixed fluid that strips and mixes the high-viscosity heavy oil in the channels. This results in crude oil emulsification and viscosity reduction, forming foam-carrying oil and emulsion slip effects, thus lowering the crude oil viscosity. The viscosity reduction rate in this zone can reach over 60%. Combined with the starting pressure gradient G of the target reservoir under different viscosity conditions determined through indoor experiments, the average starting pressure gradient in this zone is: In the formula, K3 is the reservoir permeability of the region, in mD; μ3 is the crude oil viscosity before fire flooding in the region, in mPa·s; A and B are coefficients. Furthermore, based on indoor physical model experiments (calculated according to similarity criteria) and numerical model studies, the average width l3 of the region is 10 m.

[0056] ④ Combustion flue gas action zone: This area mainly consists of remaining oil fields. The reservoir temperature is low, the crude oil viscosity is high, and the displacement resistance is significant. For high-viscosity reservoirs, the gas-liquid mixture from upstream can only be successfully extracted from production wells if a seepage channel exists. This area is primarily characterized by the viscosity-reducing and displacement effects of nitrogen and carbon dioxide in the flue gas, with an average viscosity reduction rate exceeding 25%. Therefore, the average starting pressure gradient in this area is... In the formula, K4 is the reservoir permeability of the region, in mD; μ4 is the crude oil viscosity before fire flooding in the region, in mPa·s; A and B are coefficients. Furthermore, based on indoor physical model experiments (calculated according to similarity criteria) and numerical model studies, the average width l4 of the region is 30 m.

[0057] ⑤ Original Remaining Oil Zone: This area is the part of the remaining oil zone closest to the production well and furthest from the burned zone. It is largely unaffected by fire flooding. The main displacement effect is that the mixed fluid in the seepage channel flows to the bottom of the production well and is extracted due to the pressure difference between injection and production. The average starting pressure gradient in this area is... In the formula, K5 is the reservoir permeability of the region, in mD; μ5 is the crude oil viscosity before fire flooding in the region, in mPa·s; A and B are coefficients. Furthermore, the width l5 of the region is the distance between the injection well and the production well minus the sum of the widths of the first four regions.

[0058] (4) Calculate the air injection pressure for fire-driven high-viscosity oil reservoirs.

[0059] The air pressure for fire-driven injection can be calculated using the following formula: Where: P is the air injection pressure of the injection well, in MPa; G i With l i These correspond to the starting pressure gradient and region width of each combustion zone in the fire-driven combustion system. G1 is the starting pressure gradient of the already burned zone, G2 is the starting pressure gradient of the high-temperature zone (>200℃), G3 is the starting pressure gradient of the zone where condensate, modified oil, and high-temperature flue gas act together, G4 is the starting pressure gradient of the combustion flue gas zone, and G5 is the starting pressure gradient of the original remaining oil zone. l1 is the region width of the already burned zone, l2 is the region width of the high-temperature zone (>200℃), l3 is the region width of the zone where condensate, modified oil, and high-temperature flue gas act together, l4 is the region width of the combustion flue gas zone, and l5 is the region width of the original remaining oil zone. f To account for the additional gas injection resistance caused by the coking zone and the movement resistance of the oil wall, the empirical value is generally 1 MPa.

[0060] (5) Compare the calculated fire-driven air injection pressure P with the actual injection pressure of the air injection equipment to determine whether the calculated fire-driven air injection pressure P can be directly used to inject air into the target reservoir.

[0061] If the calculated fire-driven air injection pressure P is less than or equal to the actual injection pressure of the air injection equipment, then the air injection and ignition will be carried out directly at the fire-driven air injection pressure P.

[0062] If the calculated air injection pressure P for fire-driven oil recovery is greater than the actual injection pressure of the air injection equipment, a second round of steam huff and puff preheating is required for the target reservoir. The second air injection pressure is then recalculated using the aforementioned method. This process continues until the nth round of steam huff and puff preheating is completed, at which point the calculated nth air injection pressure is less than or equal to the actual injection pressure of the air injection equipment. In this case, the nth air injection pressure is used for gas injection and ignition of the target reservoir. This ensures stable combustion in the formation, enabling successful exploitation of high-viscosity oil reservoirs.

[0063] This invention also provides a device for determining the air injection pressure in fire-flooding of high-viscosity oil reservoirs, such as... Figure 3As shown, the device includes an acquisition unit for acquiring additional gas injection resistance and the starting pressure gradient of different fire-driven combustion zones, and a determination unit for determining the fire-driven air injection pressure of the target reservoir after steam huff and puff preheating based on the acquired additional gas injection resistance and the starting pressure gradient of different fire-driven combustion zones. Sometimes the device may also include an analysis unit for comparing and analyzing the determined fire-driven air injection pressure with the actual injection pressure of the air injection equipment.

[0064] The present invention also provides an apparatus for determining the air injection pressure of fire flooding in high-viscosity oil reservoirs. The apparatus includes a processor and a memory; wherein the memory is used to store machine-executable instructions; and the processor is used to read and execute the machine-executable instructions stored in the memory to implement the aforementioned method for determining the air injection pressure of fire flooding in high-viscosity oil reservoirs.

[0065] The following examples illustrate the effectiveness of the method for determining the air injection pressure in high-viscosity oil reservoirs provided by this invention:

[0066] Example 1

[0067] A fire flooding operation is planned for a high-viscosity oil block. The oil reservoir is buried at a depth of 550m, with an original formation temperature of 23℃. Under formation conditions, the crude oil viscosity is 63000mPa·S and the average permeability is 850mD. A reverse five-point fire flooding well pattern will be adopted, namely one central gas injection ignition well and four production wells. The distance between the gas injection ignition well and the production wells is 70m.

[0068] Using this invention, the starting pressure gradient of the target reservoir under different viscosity conditions was first determined through indoor experiments: If direct gas injection and ignition is attempted, a compressor unit with a rated pressure of 8MPa will be used for on-site testing, but gas injection will fail. Based on the calculation of the starting pressure gradient, the required gas injection pressure is at least 46.79MPa. Such a high injection pressure requires a large investment in gas injection equipment and high-pressure pipelines, which is clearly not economically worthwhile.

[0069] To reduce the viscosity of crude oil in the reservoir, steam preheating is carried out simultaneously in the injection and production wells to form a seepage channel between them. Specifically, 3000t of steam is injected into each well, followed by well shut-in and recovery. When the production-injection ratio reaches 1.1 (i.e., 3000t of steam is injected and 3300t of liquid is produced), the air injection pressure is analyzed to determine if the conditions for switching to fire-driven operation are met. The temperature field and crude oil viscosity field distribution between the injection and production wells after steam preheating are calculated using numerical simulation software. Since steam preheating is carried out simultaneously in the injection and production wells, the temperature is lower and the viscosity is higher in areas farther from the wellbore. Based on steps (3) and (4) of this invention, the starting pressure gradient of five different combustion zones in the fire-driven operation is calculated, and then the total air injection pressure for the fire-driven operation is calculated. The specific data are shown in Table 1.

[0070] Table 1. Calculation results of starting pressure gradient and injection pressure for each combustion zone.

[0071]

[0072] Based on calculations, the starting pressure for fire-driven air injection is approximately 5 MPa. The on-site 8 MPa compressor unit meets the injection conditions, allowing for ignition. The average injection pressure during ignition is 4.2 MPa, gradually decreasing to 3.5 MPa after ignition. Stable production has been maintained for over a year, and the composition of the produced gas and crude oil confirms that it meets high-temperature combustion characteristics.

[0073] In summary, the method, apparatus, and equipment for determining the air injection pressure in high-viscosity reservoir fire-driven operations provided by this invention obtains the additional injection resistance and the starting pressure gradient of different fire-driven combustion zones; and based on the obtained additional injection resistance and starting pressure gradient of different fire-driven combustion zones, accurately calculates the air injection pressure for fire-driven operations in the target reservoir after steam huff and puff preheating. Thus, this method successfully guides the optimization of formation preheating parameters in high-viscosity reservoirs, effectively determines the optimal timing for switching to fire-driven operations and the air injection pressure in high-viscosity reservoirs, achieves stable high-temperature fire-driven displacement, and fills the gap in the calculation method of high-temperature fire-driven air injection pressure in high-viscosity reservoirs. Furthermore, based on the migration characteristics of the combustion zone in the seepage channel between injection and production wells during the fire-flooding process of high-viscosity oil reservoirs, and the range of action of oil displacement and viscosity reduction mechanisms such as high-temperature combustion, crude oil upgrading, and flue gas scavenging, this invention establishes a regional starting pressure gradient and provides a calculation method for the air injection pressure during fire-flooding of high-viscosity oil reservoirs. This solves the current problems of excessive steam injection in high-viscosity oil reservoirs easily causing fire spread and insufficient steam preheating leading to a continuous increase in air injection pressure and the inability of the formation to maintain stable combustion.

[0074] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the air injection pressure in a high-viscosity oil reservoir during fire flooding, the method comprising: Obtain additional gas injection resistance and start-up pressure gradients for different fire-driven combustion zones; Based on the additional gas injection resistance and the starting pressure gradient of the different fire-driven combustion zones, determine the fire-driven air injection pressure of the target reservoir after steam huff and puff preheating. in, Based on the additional gas injection resistance and the starting pressure gradient of different fire-driven combustion zones, the fire-driven air injection pressure of the target reservoir after steam huff and puff preheating is determined using the following formula: In the formula, P is the air pressure injected by the fire drive, in MPa; G i The starting pressure gradients represent different fire-driven combustion zones. G1 is the starting pressure gradient of the already burned zone, G2 is the starting pressure gradient of the high-temperature zone (>200℃), G3 is the starting pressure gradient of the zone where condensate, modified oil, and high-temperature flue gas act together, G4 is the starting pressure gradient of the combustion flue gas zone, and G5 is the starting pressure gradient of the original remaining oil zone. i The widths of different fire-driven combustion zones are represented in meters (m). l1 is the width of the already burned zone, l2 is the width of the high-temperature zone (>200℃), l3 is the width of the zone where condensate, modified oil, and high-temperature flue gas act together, l4 is the width of the combustion flue gas zone, and l5 is the width of the original remaining oil zone. f Additional gas injection resistance, in MPa; in, Wherein, K3 is the reservoir permeability in the zone where condensate, modified oil, and high-temperature flue gas interact, in mD; K4 is the reservoir permeability in the zone where combustion flue gas interacts, in mD; K5 is the reservoir permeability in the original remaining oil zone, in mD; μ3 is the crude oil viscosity in the zone where condensate, modified oil, and high-temperature flue gas interact, in mPa·S; μ4 is the crude oil viscosity in the zone where combustion flue gas interacts, in mPa·S; μ5 is the crude oil viscosity in the original remaining oil zone, in mPa·S; A and B are coefficients; l1 = 0.03t ~ 0.05t; where t is the number of days of reservoir combustion after ignition; l2 = 7; l3 = 10; l4 = 30; l5 is the remaining width obtained by subtracting the sum of the widths of the four regions l1, l2, l3, and l4 from the distance between the injection well and the production well; P f =1.

2. The method for determining the air injection pressure for fire-driven oil reservoirs according to claim 1, wherein, The method further includes: comparing and analyzing the determined fire-driven air injection pressure with the actual injection pressure of the air injection equipment; If the determined fire-driven air injection pressure is less than or equal to the actual injection pressure of the air injection device, then the air injection and ignition are performed directly at the fire-driven air injection pressure. If the determined fire-driven air injection pressure is greater than the actual injection pressure of the air injection equipment, then a second round of steam huff and puff preheating is performed on the target reservoir, and the second fire-driven air injection pressure is re-determined. This process continues until the target reservoir is preheated for the nth round of steam huff and puff, and the determined nth fire-driven air injection pressure is less than or equal to the actual injection pressure of the air injection equipment. In this case, the air injection and ignition are performed at the nth fire-driven air injection pressure.

3. The method for determining the air injection pressure for fire-driven oil reservoirs according to claim 1, wherein, The high-temperature zone >200°C includes: the combustion zone, the coking zone, and the steam zone; The zone where condensate, modified oil, and high-temperature flue gas interact includes: a high-temperature condensate zone, an oil wall, and a first-part residual oil zone; The combustion flue gas action zone is the second part of the remaining oil zone.

4. A device for determining the air injection pressure in a high-viscosity oil reservoir fire drive, the device comprising a processor and a memory; wherein, The memory is used to store machine-executable instructions; The processor is configured to read and execute machine-executable instructions stored in the memory to implement the method as described in any one of claims 1 to 3.

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