A method for calculating reserves of fracture-cavity carbonate reservoirs for gas drive

Abstract

The present invention belongs to the technical field of petroleum development, and in particular, relates to a method for calculating gas-driven reserves in fracture-cavity carbonate reservoirs, and the specific steps are: obtaining correction coefficients of gravity differentiation influencing factors through numerical simulation experiments; calculating the pre-corrected gas-driven reserves of the actual reservoir; correcting the pre-corrected gas-driven reserves of the actual reservoir using the correction coefficients of gravity differentiation influencing factors, and obtaining the corrected gas-driven reserves and the corrected gas-driven degree of the actual reservoir. The present invention simulates and constructs a fine conceptual model based on actual reservoir parameters and injection-production dynamic data to accurately characterize reservoir and fluid characteristics, and takes into account the influence of gravity differentiation influencing factors on reserve calculation. By introducing correction coefficients, the calculation results of gas-driven reserves are more in line with the actual conditions of fracture-cavity carbonate reservoirs, providing a reliable basis for reservoir development.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum development, and in particular relates to a method for calculating reserves for gas drive in fracture-cavity carbonate reservoirs. Background Art

[0002] The Ordovician reservoirs in Tahe Oilfield are carbonate fracture-cave reservoirs. They are special reservoir types, deep burial, high temperature and high salinity, large characteristic scale of reservoir space, and extremely strong heterogeneity. The reservoir space has both large caves and dissolution pores and fractures of different scales. The production declines rapidly, the recovery rate is low, the development unit types are diverse, and the development mode is diverse. With the continuous deepening of development, the main area of ​​Tahe has entered the medium-to-high water content stage, the contradiction between oil and water is prominent, the remaining oil potential is difficult to tap, and the reserves are unevenly utilized, which seriously restricts the efficient development of the oilfield. Improving the recovery rate has become a key research direction. Gas injection drive has received widespread attention, especially gas injection gravity drive, which can effectively utilize the gravity differentiation factor caused by the oil and gas density difference to exploit the remaining oil. Nitrogen injection development began in 2012 and achieved good results.

[0003] At present, domestic and foreign research focuses on gas injection parameters and other aspects. The calculation methods include those based on material balance and numerical simulation, but they face challenges such as high gas injection cost, difficult to control gas channeling, and the need to improve the accuracy of reserve calculation. In the future, we should focus on reducing costs, controlling gas channeling, improving reserve calculation methods, and exploring the mechanism of improving oil recovery.

[0004] At present, a lot of research has been carried out on gas injection-assisted gravity drainage technology at home and abroad. For example, Cardwell Jr WT and Parsons RL proposed the gravity drainage theory, and the gas-assisted gravity drive theory has also achieved results and has been applied in many blocks. This theory is applicable to homogeneous and fractured reservoirs; Craig et al.'s research shows that strengthening the factors affecting gravity differentiation can improve the recovery rate and is affected by the injection rate; Sun Jianfang et al. established a method for calculating the total reserves of well groups based on the PDA analysis method; Zhu Guiliang constructed a method for calculating the reasonable gas injection volume of gas-driven well groups in fault-karst reservoirs. However, fracture-cavity reservoirs have deficiencies in the quantitative and qualitative evaluation and calculation methods of large-scale nitrogen drive reserves. At present, some areas have entered the stage of large-scale nitrogen drive development, but due to the lack of methods suitable for the evaluation and calculation of nitrogen injection reserves, it is difficult to quantify the overall gas drive status of large residual hills and structural highs and the potential for sustainable nitrogen injection. Therefore, there is an urgent need to develop a method for calculating the reserves of fracture-cavity reservoir-scale nitrogen injection based on actual reservoir models, so as to achieve a quantitative assessment of the optimization and adjustment potential of unit-scale nitrogen flooding.

[0005] The patent "Experimental device and experimental method for determining the efficiency of nitrogen and nitrogen foam assisted gravity flooding" (CN109707352B) provides an experimental device for determining nitrogen and nitrogen foam assisted gravity flooding, which has a simulated core, including an injection system, a temperature control system, a back pressure control system and a data acquisition system, and designs an experimental method based on the above experimental device, which can effectively determine the difference in crude oil recovery between nitrogen assisted gravity drive and nitrogen and nitrogen foam assisted gravity drive, and provide guidance for methods of increasing recovery through gas drive and chemical drive. However, it does not mention how to calculate or describe the reserves for nitrogen drive.

[0006] The patent "A method and device for determining the degree of reserve utilization in carbonate fracture-cave systems" (CN116335652A) provides an experimental device for determining nitrogen and nitrogen foam-assisted gravity flooding, which has a simulated core, including an injection system, a temperature control system, a back pressure control system and a data acquisition system. The experimental method is designed based on the above experimental device, which can effectively determine the difference in crude oil recovery between nitrogen-assisted gravity drive and nitrogen and nitrogen foam-assisted gravity drive, and provide guidance for methods of increasing recovery through gas drive and chemical drive. Although the patent mentions a method for determining the degree of reserve utilization, the device is too complicated. Summary of the invention

[0007] The present invention aims to provide a method for calculating gas-driven reserves in fracture-cavity carbonate reservoirs to solve the problems existing in the prior art, provide a reliable basis for reservoir development, and improve the recovery rate. The present invention evaluates gas-driven reserves, establishes a calculation method, analyzes the law of remaining oil, provides a basis for optimization and adjustment, and also provides a reference for similar reservoirs.

[0008] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0009] The specific steps of the reserve calculation method for gas drive in fracture-cavity carbonate reservoirs are as follows:

[0010] (1) Obtain the correction coefficients of gravity differentiation influencing factors through numerical simulation experiments;

[0011] (2) The calculated gas drive reserves of the actual reservoir before correction;

[0012] (3) The pre-correction gas-driven reserves of the actual reservoir are corrected using the correction coefficient of gravity differentiation influencing factors to obtain the post-correction gas-driven reserves and post-correction gas-driven degree of the actual reservoir.

[0013] The specific steps of step (1) are:

[0014] Using the geological design module of tNavigator software, adjust the geological parameters, fluid parameters and production parameters of the conceptual model, export the simulation results, and obtain the gas drive reserves before correction of the conceptual model. N 模型。

[0015] The geological parameters are grid attributes, such as grid step, depth, porosity, permeability, temperature, etc. In areas with complex reservoir changes, the grid step is set to a smaller value to accurately describe the reservoir characteristics; in areas with relatively uniform reservoirs, the grid step is appropriately increased to improve calculation efficiency. The depth range is ensured to be consistent with the actual reservoir depth; according to the core analysis data, the porosity of different regions is assigned, the porosity of the karst development area is set to 0.2-0.3, and the matrix porosity is set to 0.05-0.1; combined with the well test data, the high permeability channel and low permeability area are assigned respectively, the high permeability fracture permeability is set to 1000mD-5000mD, and the matrix permeability is set to 1mD-10mD; the temperature is set to 100℃-120℃ according to the reservoir temperature measurement data.

[0016] The fluid parameters are fluid properties, such as dissolved gas-oil ratio (RS), rock compressibility, oil-water interface, oil-gas interface, viscosity, density, components, etc. Set the dissolved gas-oil ratio according to the analysis results of oil and gas samples; determine the rock compressibility based on rock mechanics experiments, and determine the positions of the oil-water interface and oil-gas interface based on reservoir geological research and input them into the software. Since it is a gas injection development, the PVT model selects the component model, and inputs the component information of the fluid (such as the content of components such as C1, C7, C10, etc.) and temperature (such as 100°C) according to the results of oil and gas composition analysis.

[0017] The production parameters are well data, such as injection fluid, gas injection rate, bottom hole pressure or liquid production of production wells, production time, etc. According to the actual distribution of well locations in the reservoir and the development plan, the locations of production wells and gas injection wells are determined in the model. Gas injection wells are arranged in high parts of the structure to utilize the influence of gravity differentiation factors to enable gas to better displace crude oil; production wells are arranged in low parts or favorable production areas to facilitate the outflow of crude oil. For gas injection wells, nitrogen is selected as the injection fluid, and the gas injection rate is set according to the reservoir characteristics and development experience; for production wells, the bottom hole pressure or liquid production of the production well can be selected and the production time can be set.

[0018] (1-2) Import the simulation results into PetrelRE software to obtain the corrected gas-driven reserves of the conceptual model. .

[0019] (1-3) Calculate the correction coefficient of gravity differentiation influencing factors:

[0020] C = N模型 ’ / N 模型 ;

[0021] in, C It is the correction coefficient of gravity differentiation influencing factors, dimensionless; N 模型 ’ is the corrected gas-driven reserves of the conceptual model, m 3 ; N 模型 is the gas-driven reserves before correction of the conceptual model, m 3 .

[0022] During the gas drive process, the density difference between nitrogen and crude oil will cause different forces on different fluids, affecting their movement trajectories, so overburden will occur during the displacement process. Therefore, when calculating the reserves of gas drive, the influence of gravity differentiation factors needs to be included. In order to adjust this influence, a correction factor needs to be introduced. C To correct the calculation results of the used reserves.

[0023] In step (2), the actual reservoir reserves before correction for gas drive are N 实际 The calculation formula is:

[0024] ;

[0025] in, N 实际 is the gas drive reserves of the actual reservoir before correction, m 3 ; R is the actual radius of the gas drive oil front, m ; h is the oil layer thickness, m ; is the porosity, dimensionless; S g is the gas saturation and is dimensionless.

[0026] Among them, the radius of the gas drive oil front in the actual reservoir is R The calculation formula is:

[0027] ;

[0028] in, R is the actual radius of the gas drive oil front, m ; is the dimensionless radius of the gas drive oil front, dimensionless; is the well radius, m.

[0029] Dimensionless radius of the gas drive oil front in an actual reservoir The calculation process is:

[0030] ;

[0031] in, is the dimensionless radius of the gas drive oil front, dimensionless; T D The gas drive oil front has dimensionless time and dimensionless; It is the dimensionless moving velocity of the gas drive oil front, dimensionless.

[0032] (2-1) According to the relationship curve between the injected gas fraction and the gas saturation, the derivative of the injected gas fraction with respect to the gas saturation is obtained: .

[0033] (2-2) Calculation of dimensionless migration velocity of gas-driven oil front in actual reservoir based on actual reservoir parameters ;

[0034] ;

[0035] in, is the dimensionless moving velocity of the gas drive oil front, dimensionless; q is the gas injection rate, m 3 / d ; B is the gas volume coefficient, dimensionless; h is the oil layer thickness, m ; is the porosity, dimensionless; S g is the gas saturation, dimensionless; It is the derivative of injected gas fraction with respect to gas saturation, dimensionless; r is the radial distance, m .

[0036] (2-3) Calculate the dimensionless time of the gas drive oil front in the actual reservoir;

[0037] ;

[0038] in, T D The gas drive oil front has dimensionless time and dimensionless; Q g is the underground volume of total gas injection, m 3 ; q w is the water injection speed, m3 / s ; B w is the volume coefficient of water, dimensionless; t w is the water injection time, s ; is the well radius, m;h is the oil layer thickness, m ; is the porosity and is dimensionless.

[0039] (2-4) Calculate the dimensionless radius of the gas drive oil front in the actual reservoir ;

[0040] ;

[0041] in, is the dimensionless radius of the gas drive oil front, dimensionless; T D The gas drive oil front has dimensionless time and dimensionless; It is the dimensionless moving velocity of the gas drive oil front, dimensionless.

[0042] In step (3), the calculation formula for the corrected gas drive reserves of the actual reservoir is:

[0043] ;

[0044] in, C It is the correction coefficient of gravity differentiation and other influencing factors, dimensionless; is the corrected gas drive reserves of the actual reservoir, m 3 ; is the gas drive reserves of the actual reservoir before correction, m 3 .

[0045] In step (3), the calculation formula for the corrected gas drive degree of the actual reservoir is:

[0046] ;

[0047] in, is the corrected gas drive reserves of the actual reservoir, m 3 ; is the actual reservoir reserves before gas flooding, m 3 , E It is the corrected gas displacement effect of the actual reservoir and is dimensionless.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) More accurate calculation of reserves. The present invention takes into account the influence of gravity differentiation factors on reserve calculation, and introduces a correction coefficient to make the gas-driven reserve calculation results more in line with the actual situation of fracture-cavity carbonate reservoirs. The existing technology does not fully consider this complex factor when calculating reserves, resulting in large deviations in the calculation results. The present invention can accurately quantify the reserves of the affected area of ​​gas drive, provide a reliable basis for the accurate formulation of development plans, optimize gas injection parameters and well network layout, and improve recovery rate.

[0050] (2) Applicable to complex reservoir characteristics. Fracture-cavity carbonate reservoirs are highly heterogeneous, and existing calculation methods are not well adapted to this. The present invention derives formulas and simulates based on actual reservoir parameters (such as porosity, permeability, oil layer thickness, etc.) and injection and production dynamic data, constructs a fine conceptual model to accurately characterize reservoir and fluid characteristics, and can effectively handle complex reservoirs. It provides a universal reserve calculation and evaluation method for reservoirs with different geological conditions and exploitation stages, broadens the scope of application, and improves the technical level of reservoir development.

[0051] (3) Optimize development decision support. The present invention forms a systematic calculation process and a multi-parameter evaluation system, covering reserve calculation, correction coefficient determination and utilization degree analysis, providing all-round data for development decision-making. With the help of software numerical simulation and correction coefficient calculation, the gas drive effect and reserve utilization trend can be accurately predicted, helping developers to understand the mining dynamics, plan and adjust the gas injection and oil production strategies in advance, realize dynamic optimization of the development process, avoid ineffective mining, enhance the flexibility and scientificity of the development plan, and improve the economic benefits and efficiency of development. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a flow chart of the present invention.

[0053] Figure 2 This is the conceptual model constructed in the present invention.

[0054] Figure 3 The actual block diagrams and conceptual model diagrams of the STOIIP before and after air drive are shown after the tNavigator file in the present invention is imported into petrelRE, wherein A is the actual block diagram of the STOIIP before air drive, B is the actual block diagram of the STOIIP after air drive, C is the conceptual model diagram of the STOIIP before air drive, and D is the conceptual model diagram of the STOIIP after air drive.

[0055] Figure 4 It is a comparative diagram of the case where the gravity differentiation influencing factor is not considered and the case where the gravity differentiation influencing factor is considered when calculating the gas drive reserves in the present invention, wherein A does not consider the effect of the gravity differentiation influencing factor, and B considers the effect of the gravity differentiation influencing factor. DETAILED DESCRIPTION

[0056] Example 1

[0057] A production well in Tahe Oilfield, the oil layer thickness of the well is known , porosity , well radius , gas injection rate , total gas injection underground volume , gas volume coefficient , water injection speed , the volume coefficient of water , water injection time .

[0058] The specific steps of the oil reservoir gas drive reserve calculation method are as follows:

[0059] (1) The correction coefficients of gravity differentiation influencing factors are obtained through numerical simulation experiments.

[0060] (1-1) Using the geological design module of tNavigator software, adjust the geological parameters, fluid parameters and production parameters of the conceptual model, export the simulation results, and obtain the gas drive reserves before correction for a series of conceptual models. N 模型。

[0061] The grid step size is adjusted according to the actual reservoir characteristics and data accuracy requirements. In areas with complex reservoir changes, the grid step size is set to 5m×5m×2m; in areas with relatively uniform reservoirs, the grid step size is set to 10m×10m×5m.

[0062] According to geological research results and actual measurement data, the corrected depth range is consistent with the actual reservoir depth, such as 4700m-5100m), porosity (according to core analysis data, the porosity of different regions is assigned, such as the porosity of karst development area is set to 0.2-0.3, and the matrix porosity is set to 0.05 - 0.1), permeability (combined with well test data, high permeability channels and low permeability areas are assigned separately, such as the permeability of high permeability fractures is set to 1000mD-5000mD, and the matrix permeability is set to 1mD-10mD), temperature (according to reservoir temperature measurement data, set to 100°C-120°C) and other parameters.

[0063] According to the analysis results of oil and gas samples, the dissolved gas-oil ratio (RS) was set to 100 at depth = 4800 and 200 at depth = 5015. The rock compressibility was determined according to rock mechanics experiments (e.g., compressibility = 5×10 -5 bar -1) and input it into the software; determine the positions of the oil-water interface (such as 5060m) and the oil-gas interface (such as 4600m) based on reservoir geological research and set them accurately in the software; because it is gas injection development, the PVT model selects the component model, and according to the results of oil and gas composition analysis, input the component information of the fluid (such as the content of C1, C7, C10, etc.), as well as the temperature (such as 100℃), etc.

[0064] According to the actual well location distribution and development plan of the reservoir, the location of production wells and gas injection wells is determined in the model. For example, gas injection wells are arranged in the high part of the structure to make use of the gravity differentiation factor to make gas better displace crude oil; production wells are arranged in the low part or favorable production area to facilitate the outflow of crude oil.

[0065] Set reasonable production parameters. For gas injection wells, choose nitrogen as the injection fluid, and set the gas injection rate (consistent with actual production) based on reservoir characteristics and development experience; for production wells, you can choose to input the bottom hole pressure or liquid production of the production well (consistent with actual production) and set the production time (must be longer than the production time).

[0066] Click the Run button to start the program. After the program runs correctly, choose to export the model in the data. format file in the software, then switch to the simulation module, import the exported data. format file, and run the program again for simulation calculations.

[0067] After the simulation is completed, go to the Reports option, select Save Graphs and Properties Binaries, and obtain four files: ①Grids in *.EGRID format (containing grid information), ②Initial property cubes (initial property data), ③Calculated property cubes (calculated property data), and ④Summary files (summary files, containing key information and result statistics during the simulation process).

[0068] (1-2) Import the simulation results into PetrelRE software to obtain the corrected gas-driven reserves for a series of conceptual models. ;

[0069] Import the above four files into the software in sequence, and use the Filter function to calculate the STOIIP before and after gas drive. For example, if the STOIIP before gas drive is 1,000,000 m³ and the STOIIP after gas drive is 800,000 m³, then the corrected gas drive reserves are 1000000 - 800000 = 200000 m³.

[0070] (1-3) Calculate the correction coefficient of gravity differentiation influencing factors:

[0071] C = N 模型 ’ / N 模型 ;

[0072] in, C is Correction coefficient of gravity differentiation influencing factors, dimensionless; N 模型 ’ is the corrected gas-driven reserves of the conceptual model, m 3 ; N 模型 is the gas-driven reserves before correction of the conceptual model, m 3 .

[0073] ;

[0074] After a large number of simulation experiments, the correction coefficient of the production well was obtained. .

[0075] (2) The calculated gas-driven reserves of the actual reservoir before correction.

[0076] (2-1) According to the relationship curve between the injected gas fraction and the gas saturation, the derivative of the injected gas fraction with respect to the gas saturation is obtained: ;

[0077] The gas saturation of the production well was measured ,have to; .

[0078] (2-2) Calculation of dimensionless migration velocity of gas-driven oil front in actual reservoir based on actual reservoir parameters ;

[0079] ;

[0080] ;

[0081] in, is the dimensionless moving velocity of the gas drive oil front, dimensionless; q is the gas injection rate, m 3 / d ; B is the gas volume coefficient, dimensionless; h is the oil layer thickness, m ; is the porosity, dimensionless; S g is the gas saturation, dimensionless; It is the derivative of injected gas fraction with respect to gas saturation, dimensionless; r is the radial distance, m .

[0082] (2-3) Calculate the dimensionless time of the gas drive oil front in the actual reservoir;

[0083] ;

[0084] in, T D The gas drive oil front has dimensionless time and dimensionless; Q g is the total underground volume of gas injection, m 3 ; q w is the water injection speed, m 3 / s ; B w is the volume coefficient of water, dimensionless; t w is the water injection time, s ; is the well radius, m;h is the oil layer thickness, m ; is the porosity and is dimensionless.

[0085] (2-4) Calculate the dimensionless radius of the gas drive oil front in the actual reservoir ;

[0086] ;

[0087] in, is the dimensionless radius of the gas drive oil front, dimensionless; T D The gas drive oil front has dimensionless time and dimensionless; It is the dimensionless moving velocity of the gas drive oil front, dimensionless.

[0088] (2-5) Radius of the gas-to-oil front in an actual reservoir R The calculation formula is:

[0089] ;

[0090] in, R is the actual radius of the gas drive oil front, m ; is the dimensionless radius of the gas drive oil front, dimensionless; is the well radius, m .

[0091] (2-6) Actual reservoir reserves before correction for gas drive N 实际 The calculation formula is:

[0092] ;

[0093] ;

[0094] in, N 实际 is the gas drive reserves of the actual reservoir before correction, m 3 ; R is the actual radius of the gas drive oil front, m ; h is the oil layer thickness, m ; is the porosity, dimensionless; S g is the gas saturation and is dimensionless.

[0095] (3) The pre-correction gas-driven reserves of the actual reservoir are corrected using the correction coefficient of gravity differentiation influencing factors to obtain the post-correction gas-driven reserves and post-correction gas-driven degree of the actual reservoir.

[0096] The calculation formula for the corrected gas drive reserves of the actual reservoir is:

[0097] ;

[0098] in, C It is the correction coefficient of gravity differentiation and other influencing factors, dimensionless; is the corrected gas drive reserves of the actual reservoir, m 3 ; is the gas drive reserves of the actual reservoir before correction, m 3 .

[0099] The calculation formula for the corrected gas drive degree of the actual reservoir is:

[0100] ;

[0101] E =10740÷1000000=1.07%;

[0102] in, is the corrected gas drive reserves of the actual reservoir, m 3 ; is the actual reservoir reserves before gas flooding, m 3 , E It is the corrected gas displacement effect of the actual reservoir and is dimensionless.

Claims

1. A method for calculating gas drive reserves in fracture-cavity carbonate reservoirs, characterized in that: The specific steps are: (1) Obtain the correction coefficients of gravity differentiation influencing factors through numerical simulation experiments; (1-1) Using the geological design module of tNavigator software, adjust the geological parameters, fluid parameters and production parameters of the conceptual model, export the simulation results, and obtain the gas drive reserves before correction of the conceptual model. N 模型 ; The geological parameters include grid step size, depth, porosity, permeability, and temperature; The fluid parameters include dissolved gas-oil ratio, rock compressibility, oil-water interface, oil-gas interface, viscosity, density, fluid component information, and temperature; The production parameters include injected fluid, gas injection rate, bottom hole pressure or liquid production of production wells, production time, location of production wells, and location of gas injection wells; (1-2) Import the simulation results into PetrelRE software to obtain the corrected gas-driven reserves of the conceptual model. N 模型 ’ ; (1-3) Calculate the correction coefficient of gravity differentiation influencing factors: C = N 模型 ’ / N 模型 ； in, C It is the correction coefficient of gravity differentiation influencing factors, dimensionless; N 模型 ’ is the corrected gas-driven reserves of the conceptual model, m 3 ; N 模型 is the gas-driven reserves before correction of the conceptual model, m 3 ; (2) The calculated gas drive reserves of the actual reservoir before correction; ； in, N 实际 is the gas drive reserves of the actual reservoir before correction, m 3 ; R is the actual radius of the gas drive oil front, m ; h is the oil layer thickness, m ; is the porosity, dimensionless; S g is the gas saturation, dimensionless; (3) Using the correction coefficient of gravity differentiation influencing factors, the pre-correction gas-driven reserves of the actual reservoir are corrected to obtain the post-correction gas-driven reserves and post-correction gas-driven degree of the actual reservoir; ； in, C It is the correction coefficient of gravity differentiation and other influencing factors, dimensionless; is the corrected gas drive reserves of the actual reservoir, m 3 ; is the corrected gas drive reserves of the actual reservoir, m 3 ; ； in, is the corrected gas drive reserves of the actual reservoir, m 3 ; is the actual reservoir reserves before gas flooding, m 3 , E is the corrected gas displacement degree of the actual reservoir, dimensionless; The radius of the gas drive oil front in the actual reservoir R The calculation formula is: ； in, R is the actual radius of the gas drive oil front, m ; is the dimensionless radius of the gas drive oil front, dimensionless; is the well radius, m ; The dimensionless radius of the gas drive oil front of the actual reservoir The calculation process is: (2-1) According to the relationship curve between the injected gas fraction and the gas saturation, the derivative of the injected gas fraction with respect to the gas saturation is obtained: ; (2-2) Calculation of dimensionless migration velocity of gas-driven oil front in actual reservoir based on actual reservoir parameters ; ； in, is the dimensionless moving velocity of the gas drive oil front, dimensionless; q is the gas injection rate, m 3 / d ; B is the gas volume coefficient, dimensionless; h is the oil layer thickness, m ; is the porosity, dimensionless; S g is the gas saturation, dimensionless; It is the derivative of injected gas fraction with respect to gas saturation, dimensionless; r is the radial distance, m ; (2-3) Calculate the dimensionless time of the gas drive oil front in the actual reservoir; ； in, T D The gas drive oil front has dimensionless time and dimensionless; Q g is the total underground volume of gas injection, m³ ; q w is the water injection speed, m 3 / s ; B w is the volume coefficient of water, dimensionless; t w is the water injection time, s ; is the well radius, m;h is the oil layer thickness, m ; is the porosity, dimensionless; (2-4) Calculate the dimensionless radius of the gas drive oil front in the actual reservoir ; ； in, is the dimensionless radius of the gas drive oil front, dimensionless; T D The gas drive oil front has dimensionless time and dimensionless; It is the dimensionless moving velocity of the gas drive oil front, dimensionless.

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