Evaluation Methods for Air Foam Flooding Development in Low-Permeability Reservoirs

Abstract

This invention discloses a method for evaluating the development effect of air foam flooding in low-permeability reservoirs, specifically implemented according to the following steps: dividing the reservoir into injection-production units, collecting dynamic production data of these units, calculating the instantaneous gas-liquid ratio, instantaneous pressure-flow index, and instantaneous apparent resistance coefficient to obtain the trend of injection capacity changes; statistically analyzing the cumulative air foam injection volume and the cumulative oil, water, and gas production of the wells to calculate the trend of foam resistance factor changes over time; calculating the reserve utilization degree and monthly production decline rate to evaluate the oil displacement effect of the wells in the block; determining the weight values ​​of each evaluation factor using fuzzy mathematical hierarchical analysis and expert scoring to construct an evaluation system; and quantitatively and comprehensively evaluating the air foam flooding development effect of the reservoir using the evaluation system combined with a graded scoring method. This invention has high applicability, a simpler process, and good results, making it suitable for evaluating the development effect of air foam flooding.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development technology, specifically relating to a method for evaluating the development effect of air foam flooding in low-permeability reservoirs. Background Technology

[0002] In my country's crude oil reserves, low-permeability reservoirs account for over 30%, a significant proportion. During development, the productivity of these reservoirs has been increasing year by year, indicating their enormous exploration and development potential. Current technologies utilize conventional waterflooding for oil displacement. However, due to well-developed fractures and strong heterogeneity, waterflooding can easily occur during the waterflooding stage due to crossflow along fractures. Therefore, air foam flooding has been proposed as a production enhancement measure. Air foam flooding combines air and foam flooding, using foam for profile control and air for oil displacement. It integrates the advantages of both, improving both sweep efficiency and recovery rate. The timing of the transition from waterflooding to air foam flooding affects the reservoir's effectiveness. Generally, in low water-cut stages, water control is the primary method for production enhancement, while in high water-cut stages, water control is the primary method. Therefore, evaluating the production enhancement effect of air foam flooding at different stages is crucial.

[0003] To address the challenges of evaluating the effectiveness of air foam flooding development, which involves numerous influencing factors, each with varying modes and degrees of impact, and even the inability to quantitatively assess certain factors, current evaluation methods primarily rely on water flooding for low-permeability reservoir development. However, this approach suffers from several drawbacks: First, it focuses on a specific stage of water flooding, lacking adaptability to the overall development stages of the reservoir. Second, the parameter ranges for evaluation indicators are based on conventional oil and gas reservoir development, which is somewhat unsuitable for air foam flooding in low-permeability reservoirs. Third, existing evaluation methods cannot fully reflect the development effectiveness of air foam flooding. Summary of the Invention

[0004] The purpose of this invention is to provide a method for evaluating the development effect of air foam flooding in low-permeability reservoirs, which solves the problem that existing methods for evaluating the development effect of low-permeability reservoirs mainly rely on water flooding, which has poor adaptability and poor effect.

[0005] The technical solution adopted in this invention is a method for evaluating the development effect of air foam flooding in low-permeability reservoirs, which is implemented according to the following steps:

[0006] Step 1: Divide the injection and extraction units;

[0007] Step 2: Collect monthly production dynamic data for different injection and extraction units;

[0008] Step 3: Calculate the instantaneous gas-liquid ratio, instantaneous pressure-flow index, and instantaneous apparent resistance coefficient of each injection-production unit using the production dynamic data collected in Step 2, and obtain the trend of injection capacity change of different units.

[0009] Step 4: Calculate the cumulative air foam injection volume of the injection wells and the cumulative oil, water and gas production of the production wells in the injection-production unit, and calculate the trend of the foam resistance factor over time.

[0010] Step 5: Calculate the reserve utilization level and monthly production decline rate of the injection-production unit after air foam injection to evaluate the oil displacement effect of the block's oil wells;

[0011] Step 6: Using the data obtained in Steps 4 and 5 as evaluation factors, the weight values ​​of each evaluation factor are determined by fuzzy mathematical hierarchical analysis and expert scoring method to construct an evaluation system. The evaluation system is then combined with the graded calculation scoring method to conduct a quantitative comprehensive evaluation of the air foam flooding development effect of the reservoir.

[0012] The invention is further characterized in that,

[0013] The specific process of dividing injection-production units is as follows: In the same reservoir, taking the injection well as the center, the connectivity between wells is determined by using the reservoir plane tracer test technology after air foam injection and the production dynamic change characteristics of the oil wells around the injection well after air foam injection, and the injection-production units are divided.

[0014] Monthly production dynamic data includes the monthly injection volume and pressure of air foam and water in injection wells, as well as the monthly oil production, monthly fluid production, monthly gas production, and water cut of production wells.

[0015] The specific process of step 3 is as follows:

[0016] Step 3.1, calculate the instantaneous gas-liquid ratio of the injection well;

[0017]

[0018] The gas-liquid ratio ω of the injection well is calculated by the volume of injected air and foam; it has no unit. g The air injection volume, m 3 q f m is the foam injection volume. 3 / d;

[0019] Step 3.2: Calculate the instantaneous foam pressure-flow rate index and the air pressure-flow rate index respectively;

[0020]

[0021] The foam pressure-flow index (PH) is calculated by the ratio of the pressure differential of the foam injection well to the injection rate. f Unit MPa·d / m 3 ;P hf The injection pressure in the foam injection well is MPa; ρ is the density of the injected fluid, kg / m³. 3 h represents the injection well depth, in meters; ΔP fFor friction loss along the friction path, MPa; P e P represents the mean formation pressure, in MPa; wf The bottom-hole flowing pressure for foam injection wells is measured in MPa.

[0022]

[0023] The air pressure flow index PH is calculated by the ratio of the pressure difference at the air injection well to the injection rate. g MPa·d / m 3 ;P gf Injection pressure of the air injection well, MPa; P wg The bottom-hole flowing pressure for foam injection wells is measured in MPa.

[0024] Step 3.3, calculate the instantaneous apparent drag coefficient;

[0025]

[0026]

[0027] The apparent resistance coefficient R′ is calculated as the ratio of the foam pressure-flow index to the water pressure-flow index; pH f The foam pressure-flow index is expressed in MPa·d / m³. 3 ;PH w The pressure-flow index is expressed in MPa·d / m³. 3 q w The volume of water injected is in meters (m). 3 / d;q w The volume of water injected is in meters (m). 3 / d, B w μ is the volume index of water, which has no unit. w The viscosity of water is expressed in mPa·s; r e Let r be the decompression radius of the injection well, in meters (m); w K is the radius of the well, in meters; S is the skin coefficient, which has no unit; K e For effective penetration, 10 -3 μm 2 H represents the effective thickness, in meters (m).

[0028] Step 3.4: The injection capacity of the injection well is evaluated by calculating the changing trends of the pressure-flow index and apparent resistance coefficient of the injection well. The larger the pressure-flow index, the better the sealing, and the smaller the apparent resistance coefficient, the stronger the air foam injection capacity.

[0029] The specific calculation process for step 4 is as follows:

[0030]

[0031] In the formula, the drag factor is f, which has no unit; w mThe mass gas-liquid ratio is given; it has no unit. (m) w The original water content of the injection and production unit, 10 4 t;m o For cumulative oil production, 10 4 t; Δm w The difference between the injected water and the produced water, 10 4 t; Δm represents the mass change within the injection-production unit, 10 4 t.

[0032] The resistance factor f in equation (6) reflects the degree of change of foam in the injection and production unit. When f equals 0, it indicates that the foaming rate and defoaming rate in the block are equal, indicating that the foam drive in the injection and production unit has reached an ideal stable state. When f > 0, the gas-liquid ratio of foam at the bottom increases, indicating that the gas ratio inside the block increases. When f < 0, the gas-liquid ratio of foam at the bottom decreases, and the defoaming rate of foam accelerates. The closer |f| is to 0, the better the stability of foam.

[0033] In step 5, the monthly oil and water production data of the producing wells collected in step 2 are used, combined with the gas-liquid ratio calculated in step 3, to calculate the reserve utilization level and monthly production decline rate of the injection-production unit.

[0034] Step 5.1: Calculate the reserve utilization level of the injection and production unit;

[0035] lg(W p +mI g +c)=a+bN p (7)

[0036] N w =7.54b-0.969 (8)

[0037] R OM =N w / N (9)

[0038] In the formula, R OM For the degree of utilization of reserves, decimal; W p For cumulative water production, 10 4 m 3 ;I g For cumulative gas injection volume, 10 4 m 3 m is a constant related to the injected gas-liquid ratio; c is a constant; a is a constant; b is a constant; N p For cumulative oil production, 10 4 m 3 N w For water-driven storage (mobile oil storage), 10 4 m 3 N represents the geological reserves of the oil reservoir, 104 m 3 ;

[0039] Equation (7) describes the degree of reserve utilization of the injection and production units before and after air foam flooding. It is an important parameter reflecting the expansion of the swept volume of air foam. If the degree of reserve utilization is greater than 0.6, the injected air foam will have a better effect on expanding the swept volume.

[0040] Step 5.2, calculate the monthly decline rate of production;

[0041]

[0042] q represents oil well production, m 3 / mon;q r The oil well production rate corresponding to the start time of the water drive to air foam drive transition, m 3 / mon;D r The rate of decline corresponds to the reference point; t r Reference time; t is production time; mon; n is the decreasing exponent;

[0043] D r This describes the production decline rate at the production end of the injection-production unit. When the production decline rate during the air foam flooding stage decreases by 30% compared to the water flooding production decline rate, the injected air foam has a better oil enhancement effect.

[0044] Step 5.3: Calculate the decrease in water content;

[0045] S wr =S wi -S w,min (11)

[0046] S wr The percentage decrease in water content; S wi S represents the initial moisture content at the start of foam flooding, in %; w，min This represents the lowest moisture content during the air foam drive stage, at %.

[0047] S wr This describes the rate of water cut decline at the production end of the injection-production unit, assuming the water cut decline rate S... wr When the concentration is greater than 5%, the injected air foam plays a good role in sealing.

[0048] The specific process of step 6 is as follows:

[0049] Step 6.1, the specific steps of the fuzzy mathematical hierarchical analysis method are as follows: compare the evaluation factors pairwise according to the hierarchical analysis scaling table to establish a judgment matrix, and solve for the largest eigenvector of the judgment matrix X.

[0050] The judgment matrix is:

[0051]

[0052] Step 6.1.1: Calculate the product M of the elements in each row of the judgment matrix. i :

[0053]

[0054] In the formula, x ij To determine the elements in a matrix; n is the order of the matrix;

[0055] Step 6.1.2, calculate M i nth root

[0056]

[0057] Step 6.1.3, for standardization;

[0058]

[0059] Where Wi is the weight value of the evaluation factor being sought.

[0060] Step 6.2 Quantitatively evaluate the effectiveness of air foam flooding in the reservoir using a graded scoring method.

[0061] Step 6.2 uses a graded scoring method to compare each factor with the established evaluation system. When the indicator reaches "good", the evaluation factor score is the weighted value; when the indicator is "average", the score is the weighted score * (a + b * (parameter value - lower limit of the threshold) / (upper limit of the threshold - lower limit of the threshold)) where a + b = 1, a = 0.4, b = 0.6; when the indicator is below "poor", the score is a * weighted score. Finally, the weighted values ​​of all evaluation factors are added together to obtain the final score as the comprehensive score.

[0062] The overall score rating criteria are as follows: an overall score <0.75 is poor; an overall score between 0.75 and 0.85 is average; and an overall score ≥0.85 is excellent.

[0063] The beneficial effects of this invention are as follows: This invention addresses the principles and processes of air foam flooding, defining the effectiveness characteristics of oil wells and water wells in the injection-production unit after air foam flooding. It defines the calculation methods for the pressure-flow index and apparent resistance coefficient of the injection well in the air foam flooding stage, the degree of reserve control in the production well, increases the evaluation of injection capacity and improves the degree of reserve control at the production end, quantifies the importance of each factor, and obtains a suitable method for evaluating the development effect of air foam flooding. This invention has high applicability, a simpler process, reliable results, and is suitable for widespread application. Attached Figure Description

[0064] Figure 1 This is a diagram showing the distribution of injection and production units in a low-permeability reservoir using the air foam flooding development effect evaluation method in this invention embodiment.

[0065] Figure 2 This is a pressure-flow index diagram of the method for evaluating the development effect of air foam flooding in low-permeability reservoirs in this embodiment of the invention. Detailed Implementation

[0066] The present invention will now be described in detail with reference to specific embodiments.

[0067] The present invention provides a method for evaluating the development effect of air foam flooding in low-permeability reservoirs, which is implemented according to the following steps:

[0068] Step 1: Divide the injection and extraction units;

[0069] The specific process of dividing injection-production units is as follows: In the same reservoir, taking the injection well as the center, the connectivity between wells is determined by using the reservoir plane tracer test technology after air foam injection and the production dynamic change characteristics of the oil wells around the injection well after air foam injection, and the injection-production units are divided.

[0070] Step 2: Collect monthly production dynamic data for different injection and extraction units;

[0071] Monthly production dynamic data includes the monthly injection volume and pressure of air foam and water in injection wells, as well as the monthly oil production, monthly fluid production, monthly gas production, and water cut of production wells.

[0072] Step 3: Calculate the instantaneous gas-liquid ratio, instantaneous pressure-flow index, and instantaneous apparent resistance coefficient of each injection-production unit using the production dynamic data collected in Step 2, and obtain the trend of injection capacity change of different units.

[0073] Step 3.1, calculate the instantaneous gas-liquid ratio of the injection well;

[0074]

[0075] The gas-liquid ratio ω of the injection well is calculated by the volume of injected air and foam; it has no unit. g The air injection volume, m 3 q f m is the foam injection volume. 3 / d;

[0076] Step 3.2: Calculate the instantaneous foam pressure-flow rate index and the air pressure-flow rate index respectively;

[0077]

[0078] The foam pressure-flow index (PH) is calculated by the ratio of the pressure differential of the foam injection well to the injection rate. f Unit MPa·d / m 3 ;P hf The injection pressure in the foam injection well is MPa; ρ is the density of the injected fluid, kg / m³. 3 h represents the injection well depth, in meters; ΔP f For friction loss along the friction path, MPa; P e P represents the mean formation pressure, in MPa; wf The bottom-hole flowing pressure for foam injection wells is measured in MPa.

[0079]

[0080] The air pressure flow index PH is calculated by the ratio of the pressure difference at the air injection well to the injection rate. g MPa·d / m 3 ;P gf Injection pressure of the air injection well, MPa; P wg The bottom-hole flowing pressure for foam injection wells is measured in MPa.

[0081] Step 3.3, calculate the instantaneous apparent drag coefficient;

[0082]

[0083]

[0084] The apparent resistance coefficient R′ is calculated as the ratio of the foam pressure-flow index to the water pressure-flow index; pH f The foam pressure-flow index is expressed in MPa·d / m³. 3 ;PH w The pressure-flow index is expressed in MPa·d / m³. 3 q w The volume of water injected is in meters (m). 3 / d;q w The volume of water injected is in meters (m). 3 / d, B w μ is the volume index of water, which has no unit. w The viscosity of water is expressed in mPa·s; r e Let r be the decompression radius of the injection well, in meters (m); w K is the radius of the well, in meters; S is the skin coefficient, which has no unit; K e For effective penetration, 10 -3 μm 2 H represents the effective thickness, in meters (m).

[0085] Step 3.4: The injection capacity of the injection well is evaluated by calculating the changing trends of the pressure-flow index and apparent resistance coefficient of the injection well. The larger the pressure-flow index, the better the sealing, and the smaller the apparent resistance coefficient, the stronger the air foam injection capacity.

[0086] Step 4: Calculate the cumulative air foam injection volume of the injection wells and the cumulative oil, water and gas production of the production wells in the injection-production unit, and calculate the trend of the foam resistance factor over time.

[0087]

[0088] In the formula, the drag factor is f, which has no unit; w m The mass gas-liquid ratio is given; it has no unit. (m) w The original water content of the injection and production unit, 10 4 t;m o For cumulative oil production, 10 4 t; Δm w The difference between the injected water and the produced water, 10 4 t; Δm represents the mass change within the injection-production unit, 10 4 t.

[0089] The resistance factor f in equation (6) reflects the degree of foam variation within the injection-production unit. When f equals 0, it indicates that the foaming rate and defoaming rate within the block are roughly equal, signifying that the foam drive in the injection-production unit has reached an ideal stable state. When f > 0, the gas-liquid ratio of the foam at the bottom increases, indicating an increase in the gas ratio within the block. When f < 0, the gas-liquid ratio of the foam at the bottom decreases, and the foam defoaming rate accelerates. Therefore, the closer |f| is to 0, the better the foam stability.

[0090] Step 5: Calculate the reserve utilization level and monthly production decline rate of the injection-production unit after air foam injection to evaluate the oil displacement effect of the block's oil wells;

[0091] Using the monthly oil production and monthly water production of the production wells collected in step 2, and combined with the gas-liquid ratio calculated in step 3, the reserve utilization level and monthly production decline rate of the injection-production unit are calculated.

[0092] Step 5.1: Calculate the reserve utilization level of the injection and production unit;

[0093] lg(W p +mI g +c)=a+bN p (7)

[0094] N w =7.54b-0.969 (8)

[0095] R OM =Nw / N (9)

[0096] In the formula, R OM For the degree of utilization of reserves, decimal; W p For cumulative water production, 10 4 m 3 ;I g For cumulative gas injection volume, 10 4 m 3 m is a constant related to the injected gas-liquid ratio; c is a constant; a is a constant; b is a constant; N p For cumulative oil production, 10 4 m 3 N w For water-driven storage (mobile oil storage), 10 4 m 3 N represents the geological reserves of the oil reservoir, 10 4 m 3 ;

[0097] Equation (7) describes the degree of reserve utilization of the injection and production units before and after air foam flooding. It is an important parameter reflecting the expansion of the swept volume of air foam. If the degree of reserve utilization is greater than 0.6, the injected air foam will have a better effect on expanding the swept volume.

[0098] Step 5.2, calculate the monthly decline rate of production;

[0099]

[0100] q represents oil well production, m 3 / mon;q r The oil well production rate corresponding to the start time of the water drive to air foam drive transition, m 3 / mon;D r The rate of decline corresponds to the reference point; t r Reference time; t is production time; mon; n is the decreasing exponent;

[0101] D r This describes the production decline rate at the production end of the injection-production unit. When the production decline rate during the air foam flooding stage decreases by 30% compared to the water flooding production decline rate, the injected air foam has a better oil enhancement effect.

[0102] Step 5.3: Calculate the decrease in water content;

[0103] S wr =S wi -S w,min (11)

[0104] S wr The percentage decrease in water content; S wiS represents the initial moisture content at the start of foam flooding, in %; w，min This represents the lowest moisture content during the air foam drive stage, at %.

[0105] S wr This describes the rate of water cut decline at the production end of the injection-production unit, assuming the water cut decline rate S... wr When the concentration is greater than 5%, the injected air foam plays a good role in sealing.

[0106] Step 6: Using the data obtained in Steps 4 and 5 as evaluation factors, the weight values ​​of each evaluation factor are determined by fuzzy mathematical hierarchical analysis and expert scoring method to construct an evaluation system. The evaluation system is then combined with the graded calculation scoring method to conduct a quantitative comprehensive evaluation of the air foam flooding development effect of the reservoir.

[0107] Step 6.1, the specific steps of the fuzzy mathematical hierarchical analysis method are as follows: compare the evaluation factors pairwise according to the hierarchical analysis scaling table to establish a judgment matrix, and solve for the largest eigenvector of the judgment matrix X.

[0108] The judgment matrix is:

[0109]

[0110] Step 6.1.1: Calculate the product M of the elements in each row of the judgment matrix. i :

[0111]

[0112] In the formula, x ij To determine the elements in a matrix; n is the order of the matrix;

[0113] Step 6.1.2, calculate M i nth root

[0114]

[0115] Step 6.1.3, for standardization;

[0116]

[0117] Where Wi is the weight value of the evaluation factor being sought;

[0118] Step 6.2 Quantitatively evaluate the effectiveness of air foam flooding in the reservoir using a graded scoring method.

[0119] The graded scoring method compares each factor with the established evaluation system. During calculation, when an indicator reaches "Good," the evaluation factor score is assigned a weighted value; when the indicator is "Average," the score = weighted score * (a + b * (parameter value - lower limit of the threshold) / (upper limit of the threshold - lower limit of the threshold)), where a + b = 1, a = 0.4, and b = 0.6; when the indicator is below "Poor," the score = a * weighted score. Finally, the weighted values ​​of all evaluation factors are added together to obtain the final score as the comprehensive score. The comprehensive score rating criteria are: comprehensive score < 0.75 is poor; comprehensive score 0.75–0.85 is average; comprehensive score ≥ 0.85 is excellent.

[0120] Example

[0121] The method for evaluating the development effect of air foam flooding in low-permeability reservoirs in this embodiment is implemented according to the following steps:

[0122] Step 1, divide the injection and extraction units into units Liu 76-60, such as... Figure 1 As shown; the division of injection and production units will combine reservoir planar tracer testing technology and the production dynamics of wells around the injection well after air foam injection to determine the inter-well connectivity.

[0123] Step 2: Collect monthly production dynamic data of injection and production unit Liu76-60, including monthly injection volume and injection pressure of air foam and water in injection wells, and monthly oil production, monthly fluid production, monthly gas production and water cut of production wells.

[0124] Step 3: Calculate the instantaneous gas-liquid ratio and instantaneous pressure-flow index for each injection-production unit using the production dynamic data collected in Step 2. Figure 2 As shown, the instantaneous apparent drag coefficient reveals the trend of injection capacity variation for different units;

[0125] Step 4: Calculate the cumulative air foam injection volume of the injection wells and the cumulative oil, water, and gas production of the production wells in the injection-production unit, and calculate the trend of the foam resistance factor over time; Calculate the cumulative air foam injection volume of the injection wells and the cumulative oil, water, and gas production of the production wells in the injection-production unit, and calculate the foam resistance factor as 0.2.

[0126] Step 5: Calculate the reserve utilization rate and monthly production decline rate of the injection-production unit after air foam injection to evaluate the oil displacement effect of the block's oil wells; after air foam injection, the reserve utilization rate of the injection-production unit is 68.8%, the monthly production decline rate during the water drive stage is 1.19%, and the monthly production decline rate during the air foam drive stage is 0.88%, evaluating the oil displacement effect of the block's oil wells, with a water cut decrease of 6.89%;

[0127] Step 6: Using the data obtained in Steps 4 and 5 as evaluation factors, determine the weight values ​​of each evaluation factor using the fuzzy analytic hierarchy process (AHP) and expert scoring method to construct an evaluation system. The specific steps of the fuzzy analytic hierarchy process are as follows: compare the evaluation factors pairwise according to the analytic hierarchy scale table, as shown in Table 1 below:

[0128] Table 1 Comparison of Evaluation Factors

[0129]

[0130] Based on Table 1, the weight values ​​of each evaluation factor were determined using fuzzy mathematical hierarchical analysis and expert scoring methods, as shown in Table 2.

[0131] Table 2 Weight values ​​of each evaluation factor

[0132]

[0133] The air foam flooding development effect of the reservoir was quantitatively evaluated by combining the evaluation system with the graded calculation score method: the comprehensive score of the injection and production unit was calculated to be 0.88, indicating that the development effect of this example is good.

[0134] This invention establishes a comprehensive evaluation method and system for the adaptability of air foam flooding based on fuzzy mathematics. Using this method, the development effect of air foam flooding in low-permeability reservoirs is evaluated. By analyzing production dynamic data, the influence of different operating conditions on air foam flooding is obtained, and finally, methods with superior comprehensive performance are calculated and selected. This solves the problem that existing evaluations of low-permeability reservoir development effects mainly rely on water flooding, which has poor adaptability and effectiveness. Air injection is safe and controllable, and economic benefits are significantly improved, further proving the effectiveness of air foam flooding technology. This is of great significance for the subsequent exploration, testing, and application of related supporting processes, thereby eliminating potential production safety hazards.

Claims

1. A method for evaluating the development effect of air foam flooding in low-permeability reservoirs, characterized in that, The specific steps are as follows: Step 1: Divide the injection and extraction units; Step 2: Collect monthly production dynamic data for different injection and extraction units; Step 3: Calculate the instantaneous gas-liquid ratio, instantaneous pressure-flow index, and instantaneous apparent resistance coefficient of each injection-production unit using the production dynamic data collected in Step 2, and obtain the trend of injection capacity change of different units. Step 4: Calculate the cumulative air foam injection volume of the injection wells and the cumulative oil, water and gas production of the production wells in the injection-production unit, and calculate the trend of the foam resistance factor over time. Step 5: Calculate the reserve utilization level and monthly production decline rate of the injection-production unit after air foam injection to evaluate the oil displacement effect of the block's oil wells; Step 6: Using the data obtained in Steps 4 and 5 as evaluation factors, the weight values ​​of each evaluation factor are determined by fuzzy mathematical hierarchical analysis and expert scoring method to construct an evaluation system. The evaluation system is then combined with the graded calculation score method to conduct a quantitative comprehensive evaluation of the air foam flooding development effect of the reservoir. The specific process of dividing the injection-production unit is as follows: In the same reservoir, with the injection well as the center, the inter-well connectivity is determined by using the reservoir plane tracer test technology after air foam injection and the production dynamic change characteristics of the oil wells around the injection well after air foam injection, and the injection-production unit is divided. The monthly production dynamic data includes the monthly injection volume and injection pressure of air foam and water in the injection wells, and the monthly oil production, monthly fluid production, monthly gas production and water cut of the oil production wells. The specific process of step 3 is as follows: Step 3.1, calculate the instantaneous gas-liquid ratio of the injection well; （1） The gas-liquid ratio of the injection well is calculated by the volume of injected air and foam. No unit; q g The air injection volume, m 3 , q f m is the foam injection volume. 3 / d; Step 3.2: Calculate the instantaneous foam pressure-flow rate index and the air pressure-flow rate index respectively; （2） The foam pressure-flow index is calculated by the ratio of the pressure differential at the foam injection well to the injection rate. PH f Unit MPa·d / m 3 ; P hf Inject pressure into the foam injection well, MPa; ρ The density of the injected fluid, kg / m³ 3 h represents the injection well depth, in meters; ΔP f Friction loss along the friction path, MPa; P e The mean formation pressure is expressed in MPa. P wf The bottom-hole flowing pressure for foam injection wells is measured in MPa. （3） The air pressure-flow rate index is calculated by the ratio of the pressure difference at the air injection well to the injection rate. PH g MPa·d / m 3 ; P gf Inject pressure into the air injection well, MPa; P wg The bottom-hole flowing pressure for foam injection wells is measured in MPa. Step 3.3, calculate the instantaneous apparent drag coefficient; （4） （5） The apparent drag coefficient is calculated by dividing the foam pressure-flow index by the water pressure-flow index. ; PH f The foam pressure-flow index is expressed in MPa·d / m³. 3 ; PH w The pressure-flow index is expressed in MPa·d / m³. 3 q w The volume of water injected is in meters (m). 3 / d;q w The volume of water injected is in meters (m). 3 / d, B w This is the volume coefficient of water, and it has no unit. μ w Where is the viscosity of water, mPa·s; r e Let the depressurization radius of the injection well be m; r w Let be the radius of the well, in meters. S is the epidermal coefficient, which has no unit. K e For effective penetration, 10 -3 μm 2 ; H Effective thickness, in meters (m); Step 3.4: The injection capacity of the injection well is evaluated by calculating the changing trends of the pressure-flow index and apparent resistance coefficient of the injection well. The larger the pressure-flow index, the better the sealing; the smaller the apparent resistance coefficient, the stronger the air foam injection capacity. The specific calculation process for step 4 is as follows: (6) In the formula, the drag factor is f No unit; w m This is the gas-liquid ratio by mass of injected liquid; it has no unit. m w The original water content of the injection and production unit, 10 4 t; m o For cumulative oil production, 10 4 t; Δ m w The difference between the injected water and the produced water, 10 4 t; Δ m For the quality changes within the injection-production unit, 10 4 t; The drag factor in equation (6) f This reflects the degree of change in foam within the injection-production unit, when f When the value equals 0, it indicates that the foaming rate and defoaming rate within the block are roughly equal, signifying that the foam flooding in the injection and production unit has reached an ideal stable state; when... f When the gas-liquid ratio is greater than 0, the gas-liquid ratio of the foam at the bottom of the earth increases, indicating that the proportion of gas inside the block increases; when f When the gas-liquid ratio is less than 0, the foam defoaming rate decreases at the ground level. f The closer a value is to 0, the more stable the bubble is.

2. The method for evaluating the development effect of air foam flooding in low-permeability reservoirs according to claim 1, characterized in that, In step 5, the monthly oil production and monthly water production of the producing wells collected in step 2 are used, combined with the gas-liquid ratio calculated in step 3, to calculate the reserve utilization level and monthly production decline rate of the injection-production unit: Step 5.1: Calculate the reserve utilization level of the injection and production unit; （7） （8） （9） In the formula, R OM The decimal represents the degree of resource utilization. W p For cumulative water production, 10 4 m 3 ; I g For cumulative gas injection volume, 10 4 m 3 ; m It is a constant related to the injected gas-liquid ratio; c It is a constant; a It is a constant; b It is a constant; N p For cumulative oil production, 10 4 m 3 ; N w For water-driven storage, 10 4 m 3 ; N For oil reservoir geological reserves, 10 4 m 3 ; Equation (7) describes the degree of reserve utilization of the injection and production units before and after air foam flooding. It is an important parameter reflecting the expansion of the swept volume of air foam. If the degree of reserve utilization is greater than 0.6, the injected air foam will have the effect of expanding the swept volume. Step 5.2, calculate the monthly decline rate of production; （10） q For oil well production, m 3 / mon; q r The oil well production rate corresponding to the start time of the water drive to air foam drive transition, m 3 / mon; D r The rate of decline corresponds to the reference point; t r For reference only; t For production time, mon; n A decreasing exponent; D r This describes the production decline rate at the production end of the injection-production unit. When the production decline rate during the air foam flooding stage decreases by 30% compared to the water flooding production decline rate, the injected air foam has a better oil enhancement effect. Step 5.3: Calculate the decrease in water content; （ 11） S wr The percentage decrease in water content, % S wi The initial moisture content of the foam flooding system is %; S w，min This represents the lowest moisture content during the air foam drive stage, at % %. S wr This describes the rate of water cut decrease at the production end of the injection-production unit. When the water cut decreases... S wr When the concentration is greater than 5%, the injected air foam acts as a sealant.

3. The method for evaluating the development effect of air foam flooding in low-permeability reservoirs according to claim 2, characterized in that, The specific process of step 6 is as follows: Step 6.1, the specific steps of the fuzzy mathematical hierarchical analysis method are as follows: compare the evaluation factors pairwise according to the hierarchical analysis scaling table to establish a judgment matrix, and solve for the largest eigenvector of the judgment matrix X. The judgment matrix is: X= Step 6.1.1: Calculate the product of the elements in each row of the judgment matrix. M i : （12） In the formula, x ij To determine the elements in a matrix; n Let be the order of the matrix; Step 6.1.2, Calculation M i of n Root ; （13） Step 6.1.3, for standardization; （14） Among them, W i The weight values ​​of the evaluation factors are to be determined. Step 6.2 Quantitatively evaluate the effectiveness of air foam flooding in the reservoir using a graded scoring method.

4. The method for evaluating the development effect of air foam flooding in low-permeability reservoirs according to claim 3, characterized in that, Step 6.2 uses a tiered scoring method to compare each factor with the established evaluation system. During calculation, when an indicator reaches "good," the evaluation factor score is assigned a weighted value; when the indicator is "average," the score is assigned a weighted value. (a+b) (Parameter value - Lower limit of threshold) / (Upper limit of threshold - Lower limit of threshold)) where a + b = 1, a = 0.4, b = 0.6; when the indicator is lower than "poor", the score is a. The final score is calculated by adding up the weighted values ​​of all evaluation factors.

5. The method for evaluating the development effect of air foam flooding in low-permeability reservoirs according to claim 4, characterized in that, The overall score rating criteria are as follows: an overall score <0.75 is considered poor; an overall score between 0.75 and 0.85 is considered average. A score of ≥0.85 is considered excellent.

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