Gas injection dynamic chart of top gas injection drive after water drive of oil reservoir and establishment method of gas injection dynamic chart

Abstract

The invention discloses a gas injection dynamic chart of top gas injection drive after water drive of an oil reservoir and an establishment method of the gas injection dynamic chart. The establishment method comprises the following steps that S1, an oil well gas channeling equation of top gas injection drive after water drive considering gravity, capillary force and injection-production driving force is established; s2, according to the oil well gas channeling equation, a gas injection dynamic chart relational expression universal for the whole oil reservoir converted from water drive to gas drive is established; s3, according to a gas drive rule of a production curve, searching factors with oil reservoir characteristics and engineering characteristic influences, and revising the gas injection dynamic chart relational expression by adopting the factors; and S4, making the gas injection dynamic plate according to the revised gas injection dynamic plate relational expression. According to the method, the influence of oil reservoir and engineering factors such as gravity, capillary force and injection-production driving force which exist on the gas-liquid interface at the same time on the gas content is considered, the actual situation is better met, the method can be suitable for gas drive dynamic analysis of any type, and technical support is provided for gas drive dynamic analysis after water drive.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a gas injection dynamic chart for top gas injection after water flooding of an oil reservoir and a method for establishing the same. Background Art

[0002] With the continuous advancement of oil and gas exploration and development, many developed oil fields are gradually entering the high or ultra-high water-cut stage. High-water-cut oil fields face numerous challenges. To address these challenges, research into new approaches and methods for improving oil recovery is essential. Gas injection, with its strong adaptability to formations, high injection rates, and minimal reservoir damage, has become an effective method for improving oil recovery in high-water-cut oil fields, demonstrating broad application prospects.

[0003] The waterflooding development effect evaluation system plays an important role in the development of waterflooding reservoirs. The waterflooding characteristic curve is an effective method for evaluating waterflooding effects and is widely used in oil fields. However, there is a lack of similar universal charts in gas injection dynamic analysis, making it difficult to judge the effectiveness of gas flooding dynamics and measures in engineering applications. Summary of the Invention

[0004] In response to the above problems, the present invention aims to provide a dynamic gas injection map for top gas injection after water flooding of an oil reservoir and a method for establishing the same, which can effectively judge the gas injection stability and predict the recovery rate of gas-driven oil reservoirs, providing a reference for adjusting subsequent oil reservoir development plans and improving the recovery rate of gas-driven oil reservoirs.

[0005] The technical solutions of the present invention are as follows: In one aspect, a method for establishing a gas injection dynamic map for top gas injection after water flooding of an oil reservoir is provided, comprising the following steps: S1: Establish the gas crossflow equation for oil wells with top gas injection after water flooding considering gravity, capillary force and injection-production driving force; S2: establishing a general gas injection dynamic diagram relationship for the entire reservoir when switching from water drive to gas drive based on the oil well gas crossover equation; S3: Finding factors having an impact on reservoir characteristics and engineering characteristics based on the gas drive law of the production curve, and revising the gas injection dynamic chart relationship using the factors to obtain a revised gas injection dynamic chart relationship; S4: Producing a gas injection dynamic diagram according to the revised gas injection dynamic diagram relationship.

[0006] Preferably, in step S1, the oil well gas crosstalk equation is: (1) Where: is the air void fraction, dimensionless; is the moisture content, dimensionless; is the gas phase viscosity, ; is the gas phase permeability, ; is the oil phase permeability, ; is the oil phase viscosity, ; is the capillary pressure gradient, ; is the density difference between oil and gas, ; is the acceleration due to gravity, ; is the reservoir dip, °; is the injection-production pressure gradient, ; is the gas phase density, .

[0007] Preferably, in step S2, the relationship between the gas injection dynamic diagram is: (2) (3) Where: is the air void fraction, dimensionless; is the reservoir fluid characteristic parameter, dimensionless; is the degree of recovery, dimensionless; is the recovery factor, dimensionless; is the actual abandoned gas content of the reservoir, dimensionless; are rock and fluid property parameters, dimensionless; is the irreducible water saturation, dimensionless.

[0008] Preferably, in step S3, the factors include the permeability variation coefficient, the oil / gas flow rate ratio, and the effective swept area, and the revised gas injection dynamic diagram relationship is: (4) (5) Where: is the effective swept area, ; is the coefficient of variation of permeability, dimensionless; is the oil-gas flow rate ratio, dimensionless; is the total area of oil layer, ; is the number of oil wells, mouth; is the oil leakage area controlled by a single well, .

[0009] Preferably, the rock and fluid property parameters are obtained by fitting a permeability ratio curve, and the fitting formula of the permeability ratio curve is: (6) Where: K ro is the relative permeability of the oil phase, mD; K rg is the relative permeability of the gas phase, mD; a and b are both rock and fluid property parameters, dimensionless; is the oil saturation, dimensionless.

[0010] Preferably, the actual abandoned gas content of the oil reservoir is 90%.

[0011] On the other hand, a dynamic gas injection map for top gas injection after water flooding of an oil reservoir is also provided, which is established using any of the above-mentioned methods for establishing a dynamic gas injection map for top gas injection after water flooding of an oil reservoir.

[0012] The beneficial effects of the present invention are: The present invention takes into account the influence of reservoir and engineering factors such as gravity, capillary force and injection-production drive on the gas content at the gas-liquid interface. It is more in line with the actual situation and can be applied to any type of gas-driven state analysis, providing technical support for the analysis of gas-driven state after water drive. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 Schematic diagram of a rock permeability ratio curve result in a specific embodiment; Figure 2 A schematic diagram of a gas injection dynamic diagram result before revision in a specific embodiment; Figure 3 This is a schematic diagram of a production curve result in a specific embodiment; Figure 4 A schematic diagram of the revised gas injection dynamic diagram results in a specific embodiment; Figure 5 This is a schematic diagram of the gas injection dynamic graph results under different water saturation conditions in a specific embodiment; Figure 6 Schematic diagram of gas injection dynamic diagram results under different inclination angles in a specific embodiment; Figure 7 It is a schematic diagram of the gas injection dynamic diagram results under different injection-production pressure gradient conditions in a specific embodiment; Figure 8Schematic diagram of the dynamic results of gas injection under different capillary pressure gradient conditions in a specific embodiment. DETAILED DESCRIPTION

[0015] The present invention is further described below with reference to the accompanying drawings and examples. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those commonly understood by those of ordinary skill in the art to which this application belongs. The use of similar words such as "include" or "comprising" in the present invention means that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0016] In one aspect, the present invention provides a method for establishing a gas injection dynamic map for top gas injection after water flooding in an oil reservoir, comprising the following steps: S1: Establish the gas channeling equation for oil wells with top gas injection after water flooding, considering gravity, capillary force and injection-production driving force.

[0017] In a specific embodiment, the oil well gas crosstalk equation is: (1) Where: is the air void fraction, dimensionless; is the moisture content, dimensionless; is the gas phase viscosity, ; is the gas phase permeability, ; is the oil phase permeability, ; is the oil phase viscosity, ; is the capillary pressure gradient, ; is the density difference between oil and gas, ; is the acceleration due to gravity, ; is the reservoir dip, °; is the injection-production pressure gradient, ; is the gas phase density, .

[0018] In the above embodiment, the oil well gas crosstalk equation is derived by the following steps: First, the relationship between gas holdup and injection-production rate is established based on the injection-production balance principle. The results are shown below: (7) Where: is the oil production rate, ; is the injection speed, .

[0019] Then, considering the Darcy flow of the fluid, the reservoir and oil well characteristic parameters (such as injected gas viscosity, oil-gas viscosity difference, reservoir inclination, etc.) are substituted into Equation (7) to obtain the oil well gas channeling equation shown in Equation (1).

[0020] S2: Based on the oil well gas crossover equation, a universal gas injection dynamic diagram relationship for the entire reservoir from water drive to gas drive is established.

[0021] In a specific embodiment, the relationship between the gas injection dynamic diagram is: (2) (3) Where: is the air void fraction, dimensionless; is the reservoir fluid characteristic parameter, dimensionless; is the degree of recovery, dimensionless; is the recovery factor, dimensionless; is the actual abandoned gas content of the reservoir, dimensionless; are rock and fluid property parameters, dimensionless; is the irreducible water saturation, dimensionless.

[0022] In the above embodiment, the gas injection dynamic diagram relationship is derived by the following steps: First, according to formula (1), the following relationship is established: (8) Where: is the gas phase relative permeability, ; is the relative permeability of the oil phase, .

[0023] Then, the calculation formula of rock and fluid property parameter b is established based on the oil-gas seepage relationship: (9) Where: a is the rock and fluid property parameter, dimensionless; is the oil saturation, dimensionless.

[0024] The calculation formula considering oil saturation and residual oil saturation during gas injection is: (10) (11) Where: is the residual oil saturation during gas injection, dimensionless.

[0025] By combining the above equations (8)-(11), the dynamic diagram relationship of gas injection shown in (2)-(3) of the present invention can be obtained.

[0026] In a specific embodiment, the rock and fluid property parameters are obtained by fitting a permeability ratio curve, and the fitting formula of the permeability ratio curve is: (6) Where: K ro is the relative permeability of the oil phase, mD; K rg is the relative permeability of the gas phase, mD; a and b are both rock and fluid property parameters, dimensionless; is the oil saturation, dimensionless.

[0027] S3: Finding factors having influence on reservoir characteristics and engineering characteristics according to the gas drive law of the production curve, and revising the gas injection dynamic diagram relationship using the factors to obtain a revised gas injection dynamic diagram relationship.

[0028] In a specific embodiment, the factors include permeability variation coefficient, oil / gas flow rate ratio, and effective swept area, and the revised gas injection dynamic diagram relationship is: (4) (5) Where: is the effective swept area, ; is the coefficient of variation of permeability, dimensionless; is the oil-gas flow rate ratio, dimensionless; is the total area of oil layer, ; is the number of oil wells, mouth; is the oil leakage area controlled by a single well, .

[0029] In the above embodiment, the revised gas injection dynamic diagram relationship is derived by the following steps: First, the rock and fluid property parameters b are revised using the oil saturation area weighting method to make them applicable to the entire reservoir: (12) (13) Where: is the average saturation of a single well, dimensionless; are the revised rock and fluid property parameters, dimensionless.

[0030] Then, considering the influence of oil and gas viscosity difference and formation heterogeneity, there is a certain difference between the calculated recovery rate and the actual recovery rate of the reservoir. The permeability variation coefficient and oil and gas flow rate ratio are used to revise the gas injection dynamic chart relationship to obtain the revised gas injection dynamic chart relationship shown in Equations (4) and (5).

[0031] In a specific embodiment, the actual abandoned gas content of the oil reservoir is 90%. It should be noted that the actual abandoned gas content of the oil reservoir in this embodiment is only a preferred embodiment. When using the present invention, this parameter can be set according to the actual abandoned gas content of the target oil reservoir.

[0032] S4: Producing a gas injection dynamic diagram according to the revised gas injection dynamic diagram relationship.

[0033] On the other hand, the present invention also provides a dynamic gas injection map for top gas injection after water flooding of an oil reservoir, which is established using any of the above-mentioned methods for establishing a dynamic gas injection map for top gas injection after water flooding of an oil reservoir.

[0034] In a specific embodiment, taking the oil reservoir in Block X as an example, a gas injection dynamic map is established by using the method for establishing a gas injection dynamic map for top gas injection after water flooding of the oil reservoir according to the present invention, specifically comprising the following steps: (1) Obtain the characteristic parameters of the reservoir and wells in Block X. Some of the results are shown in Table 1: Table 1 Reservoir and well characteristic parameters in Block X

[0035] (2) Establish the gas crossover equation for top gas injection after water flooding, considering gravity, capillary force and injection-production driving force as shown in equation (1); (3) Establish the gas injection dynamic diagram relationship for the entire reservoir from water drive to gas drive as shown in equations (2)-(3); In this embodiment, the rock permeability ratio curve is as follows: Figure 1 As shown, the rock and fluid property parameter b is obtained as 21.97 by fitting using formula (6).

[0036] In this example, the actual abandoned gas content of the reservoir is 90%, and the relationship between the gas injection dynamic diagram is: (14) The gas injection dynamic diagram obtained by drawing the formula (14) is as follows: Figure 2 As shown; (4) Finding factors that have an impact on reservoir characteristics and engineering characteristics based on the gas drive law of the production curve, and revising the gas injection dynamic chart relationship using the factors to obtain a revised gas injection dynamic chart relationship; In this embodiment, the production curve is as follows Figure 3 As shown, the factors include the permeability variation coefficient ( ), oil-gas flow rate ratio ( ) and the effective swept area ( ), the revised gas injection dynamic diagram relationship is as follows: (15) (5) According to the revised relationship between the dynamic diagram of gas injection, the dynamic diagram of gas injection is produced. The result is as follows: Figure 4 shown.

[0037] from Figure 4 As can be seen, the predicted total recovery for Block X after water flooding and natural gas injection is 51.5%. Furthermore, a laboratory experiment predicted a total recovery of 54.43%. This comparison shows that the predictions of the present invention are very close to the experimental results, with an error of only 5.38%. The recovery predicted by the present invention is reliable.

[0038] In addition to using the gas injection dynamic chart to predict the recovery rate, the gas injection dynamic chart can also be used to determine the production dynamics of the X block. Above the predicted recovery rate curve indicates unstable production, and below the predicted recovery rate curve indicates stable production.

[0039] In another specific embodiment, the same method as the above embodiment is used to draw gas injection dynamic charts under different water saturations, different inclination angles, different injection-production pressure gradients, and different capillary pressure gradients. The results are as follows: Figure 5-8 shown.

[0040] In summary, the present invention can generate a dynamic gas injection chart that is consistent with actual operating conditions, providing technical support for recovery rate prediction and production performance evaluation. Compared with existing technologies, the present invention represents a significant improvement.

[0041] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for establishing a dynamic gas injection map for top gas injection after water flooding in an oil reservoir, characterized in that: The following steps are involved: S1: Establish the gas crossflow equation for oil wells with top gas injection after water flooding considering gravity, capillary force and injection-production driving force; S2: establishing a general gas injection dynamic diagram relationship for the entire reservoir when switching from water drive to gas drive based on the oil well gas crossover equation; S3: Finding factors having an impact on reservoir characteristics and engineering characteristics based on the gas drive law of the production curve, and revising the gas injection dynamic chart relationship using the factors to obtain a revised gas injection dynamic chart relationship; S4: Producing a gas injection dynamic diagram according to the revised gas injection dynamic diagram relationship.

2. The method for establishing a dynamic gas injection map for top gas injection after water flooding in an oil reservoir according to claim 1, characterized in that: In step S1, the oil well gas crossover equation is: （1） Where: is the air void fraction, dimensionless; is the moisture content, dimensionless; is the gas phase viscosity, ; is the gas phase permeability, ; is the oil phase permeability, ; is the oil phase viscosity, ; is the capillary pressure gradient, ; is the density difference between oil and gas, ; is the acceleration due to gravity, ; is the reservoir dip, °; is the injection-production pressure gradient, ; is the gas phase density, .

3. The method for establishing a dynamic gas injection map for top gas injection after water flooding in an oil reservoir according to claim 2, characterized in that: In step S2, the relationship between the gas injection dynamic diagram is: （2） （3） Where: is the air void fraction, dimensionless; is the reservoir fluid characteristic parameter, dimensionless; is the degree of recovery, dimensionless; is the recovery factor, dimensionless; is the actual abandoned gas content of the reservoir, dimensionless; are rock and fluid property parameters, dimensionless; is the irreducible water saturation, dimensionless.

4. The method for establishing a dynamic gas injection map for top gas injection after water flooding in an oil reservoir according to claim 3, characterized in that: In step S3, the factors include the permeability variation coefficient, the oil-gas flow rate ratio, and the effective swept area. The revised relationship of the gas injection dynamic diagram is: （4） （5） Where: is the effective swept area, ; is the coefficient of variation of permeability, dimensionless; is the oil-gas flow rate ratio, dimensionless; is the total area of oil layer, ; is the number of oil wells, mouth; is the oil leakage area controlled by a single well, .

5. The method for establishing a dynamic gas injection map for top gas injection after water flooding in an oil reservoir according to claim 4, characterized in that: The rock and fluid property parameters are obtained by fitting the permeability ratio curve. The fitting formula of the permeability ratio curve is: （6） Where: K ro is the relative permeability of the oil phase, mD; K rg is the relative permeability of the gas phase, mD; a and b are both rock and fluid property parameters, dimensionless; is the oil saturation, dimensionless.

6. The method for establishing a dynamic gas injection map for top gas injection after water flooding in an oil reservoir according to claim 4 or 5, characterized in that: The actual abandoned gas content of the oil reservoir is 90%.

7. A dynamic gas injection diagram for top gas injection after water flooding in an oil reservoir, characterized in that: The method for establishing a gas injection dynamic diagram of top gas injection after water flooding of an oil reservoir according to any one of claims 1 to 6 is used to establish the gas injection dynamic diagram.

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