Method for determining flue gas assisted steam huff and puff gas injection timing

Abstract

This invention relates to oil and gas field development technology and discloses a method for determining the timing of flue gas-assisted steam injection. The method includes the following steps: S1, obtaining experimental data on constant composition expansion, multi-stage degassing, and injection expansion in the target block; S2, determining a gas-liquid balance constant table based on the experimental data; S3, determining the average pressure P near the well bottom; S4, determining the cumulative oil production N of the steam injection with flue gas assistance based on P and the pressure P0 during flue gas-assisted steam injection. y Cumulative oil production N from steam injection c S5, according to N y and N c Calculate the cumulative increase in oil production ΔN from flue gas-assisted steam huff and puff; S6. Calculate the profit increase E from flue gas-assisted steam huff and puff based on ΔN; S7. Plot the relationship curve between E and P0; S8. Determine the timing of gas injection for flue gas-assisted steam huff and puff based on the relationship curve. This method can improve the development effect of steam huff and puff in heavy oil reservoirs and increase the reservoir recovery rate.

Description

Technical Field

[0001] This invention relates to oil and gas field development technology, specifically to a method for determining the timing of flue gas-assisted steam huff and puff injection. Background Technology

[0002] Flue gas-assisted steam injection (FGA) technology involves injecting flue gas (such as nitrogen and carbon dioxide) from a boiler along with steam into the formation. This gas then interacts with the crude oil in the formation before production. The injected flue gas plays a crucial role in improving the fluidity of the crude oil, expanding its reach, and providing thermal insulation. Switching to FGA after steam injection can effectively expand the steam reach, reduce the viscosity of the formation crude oil, and improve the recovery rate of steam injection. The timing of FGA injection is critical for the transition from steam injection to FGA. Determining the right timing for FGA injection is essential for improving the economic benefits and development effectiveness of the oilfield.

[0003] If flue gas-assisted steam injection is performed too early, it will lead to higher oilfield development costs and poorer economic benefits; if flue gas-assisted steam injection is performed too late, it will lead to poorer viscosity reduction effect of flue gas and lower oilfield recovery rate.

[0004] Therefore, there is an urgent need to provide a method for determining the timing of flue gas-assisted steam huff and puff. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide a method for determining the timing of flue gas-assisted steam huff and puff. This method can improve the development effect of steam huff and puff in heavy oil reservoirs and increase the recovery rate of the reservoir.

[0006] This invention provides a method for determining the timing of flue gas-assisted steam huff and puff, comprising the following steps:

[0007] S1. Test the constant composition expansion experimental data, multi-stage degassing experimental data and gas injection expansion experimental data of the target block;

[0008] S2. Determine the gas-liquid equilibrium constant table based on the constant composition expansion experimental data, the multi-stage degassing experimental data, and the gas injection expansion experimental data.

[0009] S3. Determine the average pressure P near the bottom of the well during the steam injection process based on the gas-liquid balance constant table.

[0010] S4. Initially, set an average pressure near the bottom of the steam injection well as the pressure P0 during flue gas-assisted steam injection. Based on the average pressure P near the bottom of the well and the pressure P0 during flue gas-assisted steam injection, determine the cumulative oil production N of steam injection with flue gas assistance. yCumulative oil production N from steam injection c ;

[0011] S5. Based on the cumulative oil production N of the steam injection-to-flue gas-assisted steam injection, y and the cumulative oil production N from the steam injection c Calculate the cumulative increase in oil production ΔN from flue gas-assisted steam huff and puff;

[0012] S6. Calculate the profit increase value E of flue gas-assisted steam huff and puff based on the cumulative oil production increase value ΔN of the flue gas-assisted steam huff and puff.

[0013] S7. Plot the relationship curve between the profit increase value E of the flue gas-assisted steam huff and puff and the pressure P0 when the flue gas-assisted steam huff and puff is transferred.

[0014] S8. Determine the timing of the flue gas auxiliary steam injection based on the relationship curve.

[0015] Preferably, in step S1, the method for testing the constant composition expansion experimental data, the multi-stage degassing experimental data, and the gas injection expansion experimental data of the target block includes: selecting crude oil from the oilfield surface separator and casing gas, blending the formation crude oil according to the original gas-oil ratio under formation temperature and formation pressure conditions, and conducting constant composition expansion experiments, multi-stage degassing experiments, and gas injection expansion experiments in a PVT cylinder.

[0016] More preferably, the constant composition expansion experiment includes: transferring the compound oil sample into the PVT cylinder, initially with a pressure higher than the bubble point pressure, then gradually reducing the pressure, statistically analyzing the corresponding crude oil volume and condensate gas volume in the PVT cylinder under different pressures, and calculating the ratio of the crude oil volume to the condensate gas volume. During this process, the compound oil sample is observed through an observation window, and the pressure is recorded when the first batch of bubbles appears in the compound oil sample, and this pressure is taken as the bubble point pressure of the compound oil sample.

[0017] The process of the multi-stage degassing experiment includes: at the beginning of degassing, the pressure in the PVT cylinder is set to the bubble point pressure and the temperature is the original formation temperature; the pressure is reduced, and the gas begins to separate from the crude oil. After equilibrium is reached, the separated gas is discharged from the PVT cylinder. The above operation is repeated until the pressure in the PVT cylinder drops to the set minimum pressure. The dissolved gas-oil ratio of the oil sample in the PVT cylinder is recorded under different pressures.

[0018] The method for the gas injection expansion experiment includes: transferring flue gas and the compound oil sample into the PVT cylinder at a molar ratio of A:1, allowing the flue gas and the compound oil sample to mix thoroughly, pressurizing until the flue gas is completely dissolved, and recording the pressure and volume at this point; repeating the above operation according to the molar ratio of flue gas to the compound oil sample of 0:1, 2A:1, 3A:1, and 4A:1; wherein A is 0.1-0.24.

[0019] Preferably, in step S2, the method for determining the gas-liquid equilibrium constant table includes: using WinPro software to fit the constant composition expansion experimental data, the multi-stage degassing experimental data, and the gas injection expansion experimental data obtained in step S1 to determine the critical temperature, critical pressure, eccentricity factor, molar mass, and volume offset coefficient of each component of crude oil, and using the WinPro software to output the gas-liquid equilibrium constant table.

[0020] Preferably, in step S3, the method for determining the average pressure P near the bottom of the well includes: establishing a numerical simulation model of steam injection based on the gas-liquid balance constant table in step S2, performing numerical simulation calculations using the stars module in CMG, setting the simulation duration to t, outputting the pressure of each grid near the bottom of the well during the steam injection production process, and calculating the average pressure P near the bottom of the well.

[0021] The formula for calculating the average pressure P near the bottom of the well is shown in equation (1):

[0022]

[0023] Where Pi is the pressure of the i-th grid near the steam injection well, and n is the total number of grids.

[0024] More preferably, in step S4, the cumulative oil production N of the steam injection converted to flue gas-assisted steam injection is... y and the cumulative oil production N from the steam injection c The determination method includes: during the steam injection numerical simulation in step S3, the average pressure P near the bottom of the well continuously decreases. When the average pressure P near the bottom of the well drops to the pressure P0 at the time of the flue gas-assisted steam injection, the flue gas-assisted steam injection numerical simulation is performed. After the total production time of steam injection and flue gas-assisted steam injection reaches t, the cumulative oil production N of the steam injection and flue gas-assisted steam injection is output. y During the numerical simulation of steam injection in step S3, the average pressure P near the bottom of the well continuously decreases. When the average pressure P near the bottom of the well drops to the pressure P0 required for the flue gas-assisted steam injection, steam injection continues. After the production time of steam injection reaches t, the cumulative oil production N of the steam injection is output. c .

[0025] Preferably, in step S5, the calculation formula for the cumulative increase in oil production ΔN of the flue gas-assisted steam huff and puff is as shown in formula (2):

[0026] ΔN=N y -N c (2).

[0027] Preferably, in step S6, the method for calculating the profit increase value E of the flue gas-assisted steam huff and puff includes: based on the cumulative oil production increase value ΔN obtained in step S5, combined with the future value V of crude oil sales revenue from the flue gas-assisted steam huff and puff. iny Future value of crude oil sales revenue from steam throughput V inc The cost of flue gas-assisted steam injection (V) outy The cost of steam throughput V outc Calculate the profit increase E of the flue gas-assisted steam injection;

[0028] The future value V of the crude oil sales revenue from flue gas-assisted steam huff and puff iny The calculation formula is shown in formula (3):

[0029]

[0030] The future value V of the steam-blown crude oil sales revenue inc The calculation formula is shown in equation (4):

[0031]

[0032] The cost of flue gas-assisted steam huff and puff, V outy The calculation formula is shown in formula (5):

[0033]

[0034] The cost V of the steam throughput outc The calculation formula is shown in equation (6):

[0035]

[0036] Combining equations (2) and (6), we can obtain the expression for the profit increase E of the flue gas-assisted steam injection compared to steam injection, as shown in equation (7):

[0037]

[0038] Where T is the total number of years of steam injection and flue gas auxiliary steam injection; G is the crude oil price; i is the discount rate; α is the rate of increase in crude oil price; T0 is the number of years of steam injection; P y Annual operating costs for flue gas injection; Pc β represents the annual operating cost of steam throughput; β represents the annual operating cost increase rate.

[0039] Preferably, in step S7, the method for plotting the relationship curve between the profit increase value E of the flue gas-assisted steam injection and the pressure P0 during the flue gas-assisted steam injection includes: decreasing the pressure P0 during the flue gas-assisted steam injection proportionally, repeating steps S4 to S6 until the maximum number of iterations is reached, and plotting the relationship curve between the profit increase value E of the flue gas-assisted steam injection and the pressure P0 during the flue gas-assisted steam injection in a rectangular coordinate system.

[0040] Preferably, in step S8, the method for determining the injection timing of the flue gas-assisted steam huff and puff includes: in the relationship curve obtained in step S7, the average pressure P near the bottom of the well corresponding to the maximum increase in profit E of the flue gas-assisted steam huff and puff is the injection timing of the flue gas-assisted steam huff and puff.

[0041] The beneficial effects of the present invention through the above technical solution are as follows:

[0042] The present invention provides a method for determining the timing of flue gas-assisted steam huff and puff injection. Based on constant composition expansion experimental data, multi-stage degassing experimental data, and injection expansion experimental data of crude oil, a gas-liquid balance constant table of flue gas dissolved in crude oil was obtained. On this basis, a numerical simulation model of steam huff and puff and flue gas-assisted steam huff and puff was established. Based on the cumulative increase in oil production corresponding to different flue gas-assisted steam huff and puff pressure timings obtained from numerical simulation, a method for determining the timing of flue gas-assisted steam huff and puff injection was established using the net present value method. This method can effectively guide the efficient development of heavy oil thermal recovery and is of great significance for improving the development effect and increasing the recovery rate of heavy oil reservoirs through steam huff and puff.

[0043] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0044] Figure 1 This is a flowchart of the method for determining the timing of flue gas-assisted steam injection according to the present invention;

[0045] Figure 2 This is the table of gas-liquid equilibrium constants output after fitting in this invention;

[0046] Figure 3 This is a graph showing the variation of the average pressure P near the bottom of the well over time in this invention;

[0047] Figure 4 This is the relationship curve between the profit increase value E of flue gas-assisted steam huff and puff in this invention and the pressure P0 when switching to flue gas-assisted steam huff and puff. Detailed Implementation

[0048] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0049] As mentioned above, the basic embodiment of the present invention provides a method for determining the timing of flue gas-assisted steam huff and puff injection, such as... Figure 1 As shown, it includes the following steps:

[0050] S1. Test the constant composition expansion experimental data, multi-stage degassing experimental data and gas injection expansion experimental data of the target block;

[0051] S2. Determine the gas-liquid equilibrium constant table based on the constant composition expansion experimental data, the multi-stage degassing experimental data, and the gas injection expansion experimental data.

[0052] S3. Determine the average pressure P near the bottom of the well during the steam injection process based on the gas-liquid balance constant table.

[0053] S4. Initially, set an average pressure near the bottom of the steam injection well as the pressure P0 during flue gas-assisted steam injection. Based on the average pressure P near the bottom of the well and the pressure P0 during flue gas-assisted steam injection, determine the cumulative oil production N of steam injection with flue gas assistance. y Cumulative oil production N from steam injection c ;

[0054] S5. Based on the cumulative oil production N of the steam injection-to-flue gas-assisted steam injection, y and the cumulative oil production N from the steam injection c Calculate the cumulative increase in oil production ΔN from flue gas-assisted steam huff and puff;

[0055] S6. Calculate the profit increase value E of flue gas-assisted steam huff and puff based on the cumulative oil production increase value ΔN of the flue gas-assisted steam huff and puff.

[0056] S7. Plot the relationship curve between the profit increase value E of the flue gas-assisted steam huff and puff and the pressure P0 when the flue gas-assisted steam huff and puff is transferred.

[0057] S8. Determine the timing of the flue gas auxiliary steam injection based on the relationship curve.

[0058] In the description of the embodiments of the present invention, the determination of the timing of auxiliary steam huff and puff injection for heavy oil flue gas is taken as an example. Specifically, heavy oil refers to crude oil with a specific gravity greater than 0.90 and a degassed crude oil viscosity of 100 mPa·s or more at the oil layer temperature. According to the viscosity of heavy oil, it can be divided into: ordinary heavy oil (degassed oil viscosity of 100-10000 mPa·s at the oil layer temperature, specific gravity greater than 0.90) and extra-heavy oil (degassed oil viscosity of 1×10⁻⁶ mPa·s at the oil layer temperature). 4 -5×10 4 mPa·s (specific gravity greater than 0.95) and extra-heavy oil (degassed oil viscosity at reservoir temperature is 5×10⁻⁶ mPa·s, specific ... 4 (above mPa·S, with a specific gravity greater than 0.98).

[0059] The determination method provided in the above-described basic embodiments of the present invention, based on the constant composition expansion experimental data, multi-stage degassing experimental data, and gas injection expansion experimental data of crude oil, obtains a gas-liquid balance constant table of flue gas dissolved in crude oil. Using this gas-liquid balance constant table, the average pressure P near the bottom of the well during the steam huff and puff production process is determined. Based on this, a numerical simulation model of steam huff and puff and flue gas-assisted steam huff and puff is established to determine the cumulative oil production N of steam huff and puff and flue gas-assisted steam huff and puff. y Cumulative oil production N from steam injection c The study calculated the increase in oil production ΔN corresponding to different flue gas-assisted steam injection pressure timings. Using the net present value method, a method for determining the timing of flue gas-assisted steam injection was established, which can effectively guide the efficient development of heavy oil thermal recovery and is of great significance for improving the development effect of steam injection in heavy oil reservoirs and increasing the recovery rate of crude oil.

[0060] In one specific embodiment of the present invention, step S1, the method for testing the constant composition expansion experimental data, the multi-stage degassing experimental data, and the gas injection expansion experimental data of the target block includes: selecting crude oil from the oilfield surface separator and casing gas, blending the formation crude oil according to the original gas-oil ratio under formation temperature and pressure conditions, and conducting constant composition expansion experiments, multi-stage degassing experiments, and gas injection expansion experiments in a PVT cylinder. Using the above method to obtain the constant composition expansion experimental data, multi-stage degassing experimental data, and gas injection expansion experimental data of the target block can accurately reflect the information of the actual reservoir and improve the accuracy of the experiments.

[0061] As a specific embodiment of the present invention, the constant composition expansion experiment includes: transferring the compound oil sample into the PVT cylinder, initially with a pressure higher than the bubble point pressure, then gradually reducing the pressure, statistically analyzing the corresponding crude oil volume and condensate gas volume in the PVT cylinder under different pressures, and calculating the ratio of the crude oil volume to the condensate gas volume. During this process, the compound oil sample is observed through an observation window, and the pressure is recorded when the first batch of bubbles appears in the compound oil sample, and this pressure is taken as the bubble point pressure of the compound oil sample. The multi-stage degassing experiment includes: at the start of degassing, setting the pressure in the PVT cylinder to the bubble point pressure and the temperature to the original formation temperature; reducing the pressure, and the gas begins to separate from the crude oil, leveling off... After balancing, the separated gas is discharged from the PVT cylinder. The above operation is repeated until the pressure in the PVT cylinder drops to the set minimum pressure. The dissolved gas-oil ratio of the oil sample in the PVT cylinder at different pressures is recorded. The method of the gas injection expansion experiment includes: transferring flue gas and the compound oil sample into the PVT cylinder at a molar ratio of A:1, so that the flue gas and the compound oil sample are fully mixed, and pressurizing until the flue gas is completely dissolved, and recording the pressure and volume at this time; repeating the above operation according to the molar ratio of flue gas to the compound oil sample of 0:1, 2A:1, 3A:1, 4A:1; where A is 0.1-0.24, specifically 0.1, 0.15, 0.2, 0.24, or any value between the aforementioned values. The bubble point pressure of the compound oil sample can be determined by the above constant composition expansion experiment, the dissolved gas-oil ratio at different pressures can be obtained by the above multi-stage degassing experiment, and the saturation pressure when different flue gases are injected into the compound oil sample by the above gas injection expansion experiment.

[0062] In this invention, the dissolved gas-oil ratio of the oil sample during the multi-stage degassing experiment refers to the volume ratio of dissolved gas in the oil sample to the volume of degassed crude oil under standard ground conditions. The calculation method for the dissolved gas-oil ratio under different pressures is: (volume of gas removed from crude oil under standard conditions - volume of condensate gas under the current pressure) / volume of degassed crude oil.

[0063] In one specific embodiment of the present invention, step S2, the method for determining the gas-liquid equilibrium constant table, includes: using WinPro software to fit the constant composition expansion experimental data, the multi-stage degassing experimental data, and the gas injection expansion experimental data obtained in step S1, to determine the critical temperature, critical pressure, eccentricity factor, molar mass, and volume offset coefficient of each component of the crude oil, and using the WinPro software to output the gas-liquid equilibrium constant table. This method can quickly determine the gas-liquid equilibrium constant table and accurately reflect the information of the crude oil.

[0064] In a specific embodiment of the present invention, in step S3, the method for determining the average pressure P near the bottom of the well includes: based on the gas-liquid balance constant table in step S2, establishing a numerical simulation model of steam injection, using the stars module in CMG to perform numerical simulation calculations, setting the simulation duration to t, outputting the pressure of each grid near the bottom of the well during the steam injection production process, and calculating the average pressure P near the bottom of the well.

[0065] The formula for calculating the average pressure P near the bottom of the well is shown in equation (1):

[0066]

[0067] Where Pi is the pressure (MPa) of the i-th grid near the steam injection well, and n is the total number of grids. The numerical model of steam injection established based on the gas-liquid balance constant table can accurately simulate the pressure of each grid near the bottom of the well during the steam injection production process, and then calculate the average pressure P near the bottom of the well through equation (1).

[0068] In one specific embodiment of the present invention, in step S4, the cumulative oil production N of the steam injection converted to flue gas-assisted steam injection is... y and the cumulative oil production N from the steam injection c The determination method includes: during the steam injection numerical simulation in step S3, the average pressure P near the bottom of the well continuously decreases. When the average pressure P near the bottom of the well drops to the pressure P0 at the time of the flue gas-assisted steam injection, the flue gas-assisted steam injection numerical simulation is performed. After the total production time of steam injection and flue gas-assisted steam injection reaches t, the cumulative oil production N of the steam injection and flue gas-assisted steam injection is output. y During the numerical simulation of steam injection in step S3, the average pressure P near the bottom of the well continuously decreases. When the average pressure P near the bottom of the well drops to the pressure P0 required for the flue gas-assisted steam injection, steam injection continues. After the production time of steam injection reaches t, the cumulative oil production N of the steam injection is output. c .

[0069] In one specific embodiment of the present invention, in step S5, the calculation formula for the cumulative increase in oil production ΔN of the flue gas-assisted steam huff and puff is shown in formula (2):

[0070] ΔN=N y -N c (2).

[0071] In one specific embodiment of the present invention, the calculation method for the profit increase value E of the flue gas-assisted steam huff and puff in step S6 includes: based on the cumulative oil production increase value ΔN of the flue gas-assisted steam huff and puff obtained in step S5, combined with the future value V of crude oil sales revenue from the flue gas-assisted steam huff and puff. iny Future value of crude oil sales revenue from steam throughput V inc The cost of flue gas-assisted steam injection (V) outy The cost of steam throughput V outc Calculate the profit increase E of the flue gas-assisted steam injection;

[0072] The future value V of the crude oil sales revenue from flue gas-assisted steam huff and puff iny The calculation formula is shown in formula (3):

[0073]

[0074] The future value V of the steam-blown crude oil sales revenue inc The calculation formula is shown in equation (4):

[0075]

[0076] The cost of flue gas-assisted steam huff and puff, V outy The calculation formula is shown in formula (5):

[0077]

[0078] The cost V of the steam throughput outc The calculation formula is shown in equation (6):

[0079]

[0080] Combining equations (2) and (6), we can obtain the expression for the profit increase E of the flue gas-assisted steam injection compared to steam injection, as shown in equation (7):

[0081]

[0082] Where T is the total number of years of steam injection and flue gas auxiliary steam injection; G is the crude oil price; i is the discount rate; α is the rate of increase in crude oil price; T0 is the number of years of steam injection; P y Annual operating costs for flue gas injection; P c Let β be the annual operating cost of steam injection; β be the annual operating cost increase rate. Using the above formula, the profit increase E of flue gas-assisted steam injection can be calculated quickly and accurately.

[0083] In a specific embodiment of the present invention, the method for plotting the relationship curve between the profit increase E of the flue gas-assisted steam huff and puff and the pressure P0 during the flue gas-assisted steam huff and puff in step S7 includes: progressively decreasing the pressure P0 during the flue gas-assisted steam huff and puff, repeating steps S4 to S6 until the maximum number of iterations is reached, and plotting the relationship curve between the profit increase E of the flue gas-assisted steam huff and puff and the pressure P0 during the flue gas-assisted steam huff and puff in a rectangular coordinate system. The relationship curve obtained by the above method can effectively guide the efficient development of heavy oil thermal recovery, improve the recovery rate, and is applicable to actual production.

[0084] In a specific embodiment of the present invention, in step S8, the method for determining the injection timing of the flue gas-assisted steam huff and puff includes: in the relationship curve obtained in step S7, the average pressure P near the bottom of the well corresponding to the maximum increase in profit E of the flue gas-assisted steam huff and puff is the injection timing of the flue gas-assisted steam huff and puff.

[0085] The timing of flue gas-assisted steam huff and puff injection is determined based on the basic parameters of a certain oil reservoir. The basic parameters are: reservoir temperature 70℃, average porosity 0.32, and average permeability 2565×10⁻⁶. -3 μm 2 The viscosity of the underground crude oil is 2909 mPa·s, and the original formation pressure is 14.5 MPa. According to a particularly preferred embodiment of the present invention, a method for determining the timing of flue gas-assisted huff and puff injection is provided, such as... Figure 1 As shown, it includes the following steps:

[0086] S1. Test the constant composition expansion test data, multi-stage degassing test data and gas injection expansion test data of the target block: Select crude oil from the oilfield surface separator and casing gas, and reconstitute the formation crude oil according to the original gas-oil ratio under the conditions of formation temperature (75℃) and formation pressure (14.5MPa). Conduct constant composition expansion test, multi-stage degassing test and gas injection expansion test in the PVT cylinder.

[0087] (1) Constant composition expansion experiment: The compound oil sample was transferred to the PVT cylinder, the initial pressure was set to 18 MPa, and then the pressure was gradually reduced. The corresponding crude oil and condensate gas volumes in the PVT cylinder were counted. The bubble point pressure of the oil sample was determined by observing the window (the pressure corresponding to the first batch of bubbles is the bubble point pressure). When the pressure was lower than the bubble point pressure, the pressure was further reduced. The crude oil and condensate gas volumes in the PVT cylinder were counted. The constant composition expansion experiment data obtained by the experiment are shown in Table 1. It can be seen that the bubble point pressure of the oil sample is 1.1 MPa.

[0088] Table 1

[0089] relative volume 0.9903 0.9917 0.994 0.9963 0.9989 1 1.0286

[0090] (2) Multi-stage degassing experiment: At the beginning of degassing, the pressure in the PVT cylinder is set to the bubble point pressure and the temperature is the original formation temperature. When the pressure is reduced, the gas begins to separate from the crude oil. After equilibrium is reached, the separated gas is discharged from the PVT cylinder. The above steps are repeated until the pressure in the PVT cylinder drops to the set minimum pressure. The experimental data of multi-stage degassing obtained are shown in Table 2. It can be seen that the dissolved gas-oil ratio of the oil sample is 8.1. When the pressure decreases, the crude oil is degassed and the dissolved gas-oil ratio decreases.

[0091] Table 2

[0092] Dissolved gas-oil ratio 8.1 4.2 2.7 1.3

[0093] (3) Gas Injection Expansion Experiment: Flue gas was transferred into the PVT cylinder at a molar fraction of 20% in the oil sample, allowing the flue gas to mix thoroughly with the oil sample. The pressure was increased until all the flue gas dissolved, and the pressure and volume were recorded. The above experiment was repeated with flue gas molar fractions of 40%, 60%, and 80% in the oil sample. The gas injection expansion experiment data obtained are shown in Table 3. It can be seen that the higher the molar fraction of flue gas, the greater the saturation pressure of the crude oil.

[0094] Table 3

[0095] Saturation pressure / MPa 4.10 7.50 11.43 19.45 37.83

[0096] S2. Input the constant composition expansion experimental data of crude oil (see Table 1), multi-stage degassing experimental data (see Table 2), and gas injection expansion experimental data (see Table 3) into the fluid fitting software WinProp. Fit the experimental data by adjusting the parameters of each component of crude oil. The adjusted parameters of each component of crude oil are shown in Table 4.

[0097] Table 4

[0098]

[0099]

[0100] After fitting, Winprop software is used to output a table of gas-liquid equilibrium constants, as shown below. Figure 2 As shown, from Figure 2 It can be seen that as the temperature increases, the gas-liquid equilibrium constant increases, and the solubility of flue gas in crude oil decreases; as the pressure increases, the gas-liquid equilibrium constant decreases, and the solubility of flue gas in crude oil increases.

[0101] S3. Determine the average pressure near the wellbore during the steam injection production process. Based on the gas-liquid balance constant table obtained in step S2, and combined with the oilfield parameters of the target block, establish a numerical simulation model for steam injection. Use the Stars module in CMG for numerical simulation calculations, set the simulation duration to 8 years, output the pressure of each grid near the wellbore during the steam injection production process, and select 9 grids to calculate the average pressure P near the wellbore. The curve of the average pressure P near the wellbore changing with production time is shown below. Figure 3 As shown.

[0102] The formula for calculating the average pressure P near the bottom of the well is:

[0103]

[0104] Where Pi is the pressure of the i-th grid near the steam injection well, in MPa; n is the total number of grids.

[0105] S4. Calculate the cumulative oil production N of steam injection with flue gas auxiliary steam injection. y Cumulative oil production N from steam injection c In the numerical simulation of steam injection in step S3, when the average pressure P near the bottom of the well drops to 13 MPa, a numerical simulation of flue gas-assisted steam injection is performed. After the total production time of steam injection and flue gas-assisted steam injection reaches 8 years, the cumulative oil production N of flue gas after steam injection is output. y The output is 96,000 tons. Based on the model in step S3, another model is set up to continue the steam injection numerical simulation when the average pressure P near the bottom of the well drops to 13 MPa. The total time is 8 years before the cumulative steam injection oil production N is output. c It is 87,000 tons.

[0106] S5. Calculate the cumulative increase in oil production ΔN caused by flue gas-assisted steam huff and puff. The formula for calculating the cumulative increase in oil production ΔN caused by flue gas-assisted steam huff and puff is:

[0107] ΔN=N y -N c (2);

[0108] The cumulative oil production N of the steam injection assisted by flue gas obtained in step S4 is calculated as follows: y Cumulative oil production N from steam injection c Substituting into equation (2), we can obtain that the cumulative increase in oil production ΔN for flue gas-assisted steam injection is 0.9 million tons compared to steam injection.

[0109] Step S6: Calculate the profit increase E from flue gas-assisted steam huff and puff. Based on the cumulative oil production increase ΔN obtained in step S5, combined with the future value V of crude oil sales revenue from flue gas-assisted steam huff and puff. inyFuture value of crude oil sales revenue from steam throughput V inc The cost of flue gas-assisted steam injection (V) outy The cost of steam throughput V outc Calculate the profit increase E from flue gas-assisted steam injection.

[0110] Future value of flue gas-assisted steam huff and puff crude oil sales revenue V iny The calculation formula is shown in formula (3):

[0111]

[0112] Future value of steam throughput crude oil sales revenue V inc The formula for calculation is:

[0113]

[0114] Cost of flue gas-assisted steam injection V outy It can be represented as:

[0115]

[0116] Cost of steam throughput V outc It can be represented as:

[0117]

[0118] Where T is the total number of years of steam injection and flue gas auxiliary steam injection; G is the crude oil price; i is the discount rate; α is the rate of increase in crude oil price; T0 is the number of years of steam injection; P y Annual operating costs for flue gas injection; P c β represents the annual operating cost of steam throughput; β represents the annual operating cost increase rate.

[0119] Combining equations (2) and (6), we can obtain the expression for the profit increase E of flue gas-assisted steam injection compared to steam injection:

[0120]

[0121] The price of crude oil is 4,000 yuan / ton, the discount rate is 2.3%, the crude oil price increase rate is 3.2%, the annual operating cost of flue gas injection is 100,000 yuan, and the annual operating cost increase rate is 1.5%. Using formula (7), it is calculated that the profit increase value E of flue gas auxiliary steam injection is 470,000 yuan compared with steam injection.

[0122] S7. Plot the relationship curve between the profit increase value E of flue gas-assisted steam huff and puff and the pressure P0 during flue gas-assisted steam huff and puff. In a specific embodiment of the invention, the pressure P0 during flue gas-assisted steam huff and puff decreases by 0.5 MPa from 13 MPa. Steps S4 to S6 are repeated, and the corresponding profit increase value E of flue gas-assisted steam huff and puff is calculated. The maximum number of iterations is set to 12. The resulting relationship curve between the profit increase value E of flue gas-assisted steam huff and puff and the pressure P0 during flue gas-assisted steam huff and puff is shown below. Figure 4 As shown.

[0123] S8. Determine the timing of gas injection for flue gas-assisted steam injection. The relationship curve between the profit increase E from flue gas-assisted steam injection obtained in step S7 and the pressure P0 at the time of switching to flue gas-assisted steam injection ( Figure 4 It can be seen that when the pressure P0 is less than 11 MPa during flue gas-assisted steam huff and puff, the profit increase increases with increasing pressure; when the pressure P0 is greater than 11 MPa, the profit increase decreases with increasing pressure; and when the pressure P0 is 11 MPa, the profit reaches its maximum of 3.54 million yuan. Therefore, when the average pressure P0 near the steam huff and puff well drops to 11 MPa during steam huff and puff production, flue gas-assisted steam huff and puff should be implemented.

[0124] The method provided by the above preferred embodiments can improve the development effect of steam huff and puff in heavy oil reservoirs and increase the recovery rate of the reservoirs.

[0125] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for determining the timing of flue gas-assisted steam huff and puff, characterized in that, Includes the following steps: S1. Select crude oil from the oilfield surface separator and casing gas, and blend the formation crude oil under formation temperature and pressure conditions according to the original gas-oil ratio. Conduct constant composition expansion experiments, multi-stage degassing experiments, and gas injection expansion experiments in a PVT cylinder to obtain constant composition expansion experiment data, multi-stage degassing experiment data, and gas injection expansion experiment data for the target block. The gas injection expansion experiment method includes: transferring flue gas and blended oil sample into the PVT cylinder at a molar ratio of A:1, allowing the flue gas and blended oil sample to be fully mixed, pressurizing until the flue gas is completely dissolved, and recording the pressure and volume at this time; repeating the above operation according to the molar ratio of flue gas to blended oil sample of 0:1, 2A:1, 3A:1, and 4A:1; where A is 0.1-0.

24. S2. Determine the gas-liquid equilibrium constant table based on the constant composition expansion experimental data, the multi-stage degassing experimental data, and the gas injection expansion experimental data. S3. Determine the average pressure near the bottom of the well during the steam injection process based on the aforementioned gas-liquid balance constant table. P ; S4. Initially, set the average pressure near the bottom of the steam injection well as the pressure during auxiliary steam injection using flue gas. P 0, based on the average pressure near the bottom of the well. P and the pressure during the flue gas-assisted steam huff and puff. P 0. Determine the cumulative oil production from steam injection to flue gas-assisted steam injection. N y Cumulative oil production from steam injection N c ; S5. Based on the cumulative oil production from the steam injection to flue gas-assisted steam injection... N y and the cumulative oil production from the steam huff and puff N c Calculate the cumulative increase in oil production Δ due to flue gas-assisted steam injection. N ; S6, Based on the cumulative increase in oil production Δ of the flue gas-assisted steam huff and puff N Calculate the profit increase from flue gas-assisted steam injection. E ; S7. Calculate the profit increase value of the flue gas-assisted steam huff and puff. E Pressure during flue gas-assisted steam huff and puff P The relationship curve of 0; S8. Determine the timing of the flue gas auxiliary steam injection based on the relationship curve.

2. The determination method according to claim 1, characterized in that, The constant composition expansion experiment includes: transferring the compound oil sample into the PVT cylinder, initially with a pressure higher than the bubble point pressure, then gradually reducing the pressure, statistically analyzing the corresponding crude oil volume and condensate gas volume in the PVT cylinder under different pressures, and calculating the ratio of the crude oil volume to the condensate gas volume. During this process, the compound oil sample is observed through an observation window, and the pressure is recorded when the first batch of bubbles appears in the compound oil sample, and this pressure is taken as the bubble point pressure of the compound oil sample. The multi-stage degassing experiment includes: at the start of degassing, the pressure in the PVT cylinder is set to the bubble point pressure, and the temperature is the original formation temperature; the pressure is reduced, and gas begins to separate from the crude oil. After equilibrium is reached, the separated gas is discharged from the PVT cylinder. The above operation is repeated until the pressure in the PVT cylinder drops to the set minimum pressure. The dissolved gas-oil ratio of the oil sample in the PVT cylinder is recorded under different pressures.

3. The determining method according to claim 1 or 2, characterized in that, In step S2, the method for determining the gas-liquid equilibrium constant table includes: using WinPro software to fit the constant composition expansion experimental data, the multi-stage degassing experimental data and the gas injection expansion experimental data obtained in step S1, determining the critical temperature, critical pressure, eccentricity factor, molar mass and volume offset coefficient of each component of crude oil, and using the WinPro software to output the gas-liquid equilibrium constant table.

4. The determining method according to claim 1 or 2, characterized in that, In step S3, the average pressure near the bottom of the well P The determination method includes: establishing a numerical simulation model of steam huff and puff based on the gas-liquid balance constant table in step S2, performing numerical simulation calculations using the stars module in CMG, and setting the simulation duration to [value missing]. t The pressure of each grid near the bottom of the well during the output steam injection process is calculated, and the average pressure near the bottom of the well is calculated. P ; The average pressure near the bottom of the well P The calculation formula is shown in formula (1): （1）； in, Pi The first one near the steam injection well i The pressure of each grid, n This represents the total number of grid cells.

5. The determination method according to claim 4, characterized in that, In step S4, the cumulative oil production from the steam injection to flue gas-assisted steam injection is... N y and the cumulative oil production from the steam huff and puff N c The determination method includes: during the steam injection numerical simulation in step S3, the average pressure near the bottom of the well. P The pressure continues to decrease until the average pressure near the bottom of the well is reached. P The pressure drops to the level of the auxiliary steam injection in the flue gas. P At 0:00, numerical simulation of flue gas-assisted steam huff and puff was conducted, and the total production time of steam huff and puff combined with flue gas-assisted steam huff and puff reached [a certain value]. t Then, the cumulative oil production of the steam injection system converted to flue gas-assisted steam injection is output. N y During the steam injection numerical simulation in step S3, the average pressure near the bottom of the well is... P The pressure continues to decrease until the average pressure near the bottom of the well is reached. P The pressure drops to the level of the auxiliary steam injection in the flue gas. P At 0:00, continue steam injection until the steam injection production time reaches [time value missing]. t Then, the cumulative oil production from the steam huff and puff is output. N c .

6. The determining method according to claim 1 or 2, characterized in that, In step S5, the cumulative increase in oil production Δ of the flue gas-assisted steam huff and puff is... N The calculation formula is shown in formula (2): （2）。 7. The determining method according to claim 1 or 2, characterized in that, In step S6, the profit increase value of the flue gas-assisted steam huff and puff is... E The calculation method includes: based on the cumulative increase in oil production Δ obtained in step S5 using the flue gas-assisted steam huff and puff. N The future value of crude oil sales revenue combined with flue gas-assisted steam huff and puff. V iny Future value of crude oil sales revenue from steam throughput V inc Cost of flue gas-assisted steam injection V outy and the cost of steam throughput V outc Calculate the profit increase from the flue gas-assisted steam injection. E ; Future value of the flue gas-assisted steam huff and puff crude oil sales revenue V iny The calculation formula is shown in formula (3): （3）； Future value of the steam throughput crude oil sales revenue V inc The calculation formula is shown in equation (4): （4）； The cost of flue gas-assisted steam huff and puff V outy The calculation formula is shown in formula (5): （5）； The cost of the steam throughput V outc The calculation formula is shown in equation (6): （6）； Combining equations (2) and (6), we can obtain the profit increase of the flue gas-assisted steam injection compared to steam injection. E The expression for is shown in equation (7): （7）； in, T Total service life of steam injection and auxiliary steam injection for flue gas transfer; G For crude oil prices; i The discount rate; α The rate of increase in crude oil prices; T 0 represents the number of years for steam injection; P y Annual operating costs for injecting flue gas; P c Annual operating costs for steam throughput; β The annual operating cost increase rate.

8. The determining method according to claim 1 or 2, characterized in that, In step S7, the profit increase value of the flue gas-assisted steam huff and puff is... E Pressure during flue gas-assisted steam huff and puff P The method for plotting the relationship curve includes: decreasing the pressure of the flue gas-assisted steam huff and puff in a proportional manner. P 0. Repeat steps S4 to S6 until the maximum number of iterations is reached. Plot the profit increase value of the flue gas-assisted steam injection in a Cartesian coordinate system. E Pressure during flue gas-assisted steam huff and puff P The relationship curve between 0 and 0.

9. The determining method according to claim 1 or 2, characterized in that, In step S8, the method for determining the injection timing of the flue gas-assisted steam injection includes: in the relationship curve obtained in step S7, the profit increase value of the flue gas-assisted steam injection. E The average pressure near the bottom of the well corresponding to the maximum value P The timing of gas injection for the auxiliary steam injection of the flue gas.

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