Mining method for improving gas injection recovery ratio after horizontal well fracturing through vertical well pressure regulation

Abstract

The invention relates to the technical field of oil and gas field development, and discloses a mining method for improving the gas injection recovery ratio after horizontal well fracturing through vertical well pressure regulation. S2, establishing a vertical well and horizontal well combined well pattern system; s3, a pressure regulating fluid medium system is selected to be injected into the vertical well, and the formation pressure of the area is balanced through pressure regulation of the vertical well; s4, CO2 group huff and puff are carried out through the combined well pattern; and S5, the steps S3 to S4 are repeated, and the next round of operation is carried out until the yield of the horizontal well and the vertical well reaches the economic limit yield. According to the mining method, the formation pressure and stress distribution are adjusted through the vertical well and horizontal well combined well pattern, so that the CO2 huff and puff production effect of the horizontal well is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a production method for improving the recovery rate of gas injection after fracturing of a horizontal well by utilizing vertical well pressure regulation. Background Art

[0002] Field tests have shown that whether the CO2 intake and exhaust gas cavity is closed and whether the formation pressure is increased are key factors affecting the recovery of tight oil horizontal wells after fracturing and gas injection. The connection mode and degree of fractures between horizontal wells are complex and changeable, and the pressure distribution is extremely complex. It is difficult to adjust the formation pressure using only horizontal wells.

[0003] At present, CO2 huff and puff operations are mostly carried out by injecting gas in two horizontal wells, which results in obvious gas channeling and poor production effect. From the perspective of oil production process conditions, the selective gas injection process of coiled tubing + packer is immature, and the construction risk of the full-well gel temporary plugging + CO2 huff and puff method is very high. Therefore, there is an urgent need for a production method that can further improve the recovery rate of horizontal wells when the fracture network is connected after volume fracturing of horizontal wells.

[0004] Patent document CN112302608A discloses a method for developing a horizontal well by injecting fluid before fracturing based on a three-dimensional fracturing well network, the method comprising: step 1: deploying a target horizontal well in the oil layer, and the target horizontal well is not fractured; deploying a first horizontal well parallel to the target horizontal well at the upper part of the horizontal section of the target horizontal well, and fracturing the first horizontal well to form a crack perpendicular to the horizontal section of the target horizontal well; deploying vertical wells around the target horizontal well, and fracturing the vertical wells to form a crack parallel to the horizontal section of the target horizontal well and lower than the horizontal section of the target horizontal well; step 2: when the target horizontal well is not fractured and is not in production, using the first horizontal well and the vertical well as injection wells to inject energy replenishing fluid into the formation; step 3: after completing the injection of the formation energy replenishing fluid, fracturing the target horizontal well and starting production; at the same time, the first horizontal well and the vertical well used as injection wells are converted into oil production wells and started production. The technical solution of this patent overcomes the disadvantages of single-well injection of traditional advanced gas injection technology, gives full play to the role of high-conductivity fractures and gravity in the fracture network, enhances formation energy, improves crude oil flowability, and forms a more complex fracture network, ultimately achieving the inhibition of production decline throughout the life cycle of horizontal wells after production, prolongs the stable production period, and improves the recovery rate; however, the technical solution of this patent is only for the development of original oil reservoirs, which does not conform to the actual situation of current oil field development, and is not suitable for oil field wells that have now deployed multiple horizontal wells on a large scale and carried out volume fracturing to form a fracture network connection. Summary of the invention

[0005] The present invention aims to solve at least one technical problem existing in the prior art or related technology, and provides a production method for improving the gas injection recovery rate after horizontal well fracturing by regulating the pressure of a vertical well, and adjusting the formation pressure and stress distribution by using a combined well network of vertical wells and horizontal wells, so that the CO2 throughput production effect of the horizontal well is greatly improved.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A method for increasing the recovery rate of gas injection after fracturing of a horizontal well by regulating the pressure of a vertical well, the method comprising the following steps:

[0008] Step S1. Determine the location of strong connection of fracture networks between horizontal wells: comprehensively analyze regional geological logging data, microseismic monitoring data, high-frequency pressure monitoring data and fracturing construction data, calculate the fracture connectivity coefficient of each section between wells, and determine the location of the strongly connected well section with fracture connectivity coefficient within a set range;

[0009] Step S2. Establishing a vertical well and horizontal well combination well pattern system: setting a vertical well at the location of the well section with strong connection of the seam network, and completing the well with casing perforation;

[0010] Step S3. Select a pressure regulating fluid medium system and inject it into the vertical well, and use the vertical well to regulate the pressure and balance the regional formation pressure;

[0011] Step S4. Carry out CO2 group huff and puff using the combined well pattern: carry out CO2 huff and puff operations in the horizontal wells on both sides synchronously according to the set gas injection volume, gas injection speed, well shut-in time and drainage system; at the same time, if the vertical well and the horizontal well are connected by the matrix, the vertical well adopts the set operation parameters to carry out CO2 huff and puff operations synchronously;

[0012] Step S5: Repeat steps S3-S4 to carry out the next round of operations until the production of horizontal wells and vertical wells reaches the economic limit production.

[0013] Furthermore, in step S1, the calculation formula for the fracture connectivity coefficient of each section between wells is:

[0014]

[0015] In the above formula: C is the connectivity coefficient of each fracture section between wells; k is the unit conversion coefficient, dimensionless; μ is the viscosity of the fracturing fluid, mPa·s; L is the half fracture length, m; v is the Poisson's ratio, decimal; P f is the fluid pressure in the crack, MPa; σ h is the minimum horizontal principal stress, MPa; E is the interwell Young's modulus, MPa; ΔP is the net pressure in the fracture, MPa; Q is the construction displacement, L / min.

[0016] Furthermore, the geological logging data are used to obtain the following inter-well Young's modulus E, Poisson's ratio ν and minimum horizontal principal stress σh ;

[0017] According to the microseismic monitoring data, we can obtain: half crack length L;

[0018] The high-frequency pressure monitoring data of adjacent wells were used to obtain the following fluid pressure in the fracture: f ;

[0019] Obtained through fracturing construction data: net pressure ΔP in the fracture.

[0020] Further, in step S1, if the fracture connectivity coefficient of the corresponding well section is calculated to be 0.9-1, the well section is defined as a strongly connected well section position.

[0021] Furthermore, in step S2, the vertical well is set at the middle position of the distance between the two horizontal wells in a direction perpendicular to the horizontal section; and in a direction parallel to the horizontal section, the vertical well is set at the midpoint of the strongly connected section of the fracture network.

[0022] Furthermore, in step S2, the number of vertical wells is ≥1.

[0023] Furthermore, the step S3 specifically includes:

[0024] Step S301. Testing: Inject water containing tracers into the vertical well at a set rate, monitor the time it takes for tracers to appear in the horizontal wells on both sides, and determine the volume of the water channel in the vertical well based on the water injection rate and the time it takes for tracers to appear;

[0025] Step S302. Selecting agents: judging the type of connection between the horizontal sections of two horizontal wells according to the relationship between the volume of the vertical well water channel and the volume of the vertical well controlled pores, and selecting the pressure regulating fluid medium system according to the type of connection;

[0026] Step S303. Pressure regulation: inject a pressure regulating fluid medium system into the vertical well to build a vertical well high-pressure wall to prevent the horizontal wells on both sides from being directly connected.

[0027] Furthermore, in step S302, the type of connection between the horizontal sections of the two horizontal wells is determined according to the size relationship between the volume of the vertical well water channel and the volume of the vertical well controlled pores, specifically including:

[0028] Calculate the controlled pore volume of vertical wells;

[0029] If the vertical well water channel volume is greater than or equal to the vertical well controlled pore volume, it is judged to be matrix connected;

[0030] If the volume of the vertical well water channel is less than the vertical well controlled pore volume, the fracture is judged to be connected.

[0031] Furthermore, the calculation formula for the vertical well controlled pore volume is:

[0032]

[0033] In the above formula, V0 is the controlled pore volume of the vertical well, m 3 ; d is the well spacing, m; a is the length of each level of fracturing in the horizontal well, m; h is the thickness of the oil layer, m; is the porosity, a decimal.

[0034] Furthermore, in step S302, the pressure regulating fluid medium system is selected according to the connection type, specifically including:

[0035] If the matrix is ​​connected, a water and surfactant displacement system is selected, and the system viscosity at the formation temperature is the viscosity of the underground crude oil;

[0036] If the cracks are connected, water and a temperature-responsive gel temporary plugging agent are selected, and the characteristics of the temperature-responsive temporary plugging agent are:

[0037] When the oil layer temperature is within the range of ±5℃, the viscosity can rise to 50-500 times the viscosity of underground crude oil. When the oil layer temperature is within the range of +(15-25)℃, the viscosity drops to the viscosity of underground crude oil.

[0038] Furthermore, in step S303, the standard for establishing the vertical well high-pressure wall is that after the pressure-regulating fluid medium system is injected, the vertical well head pressure increases by more than 15 MPa.

[0039] Furthermore, in step S4, according to the set gas injection volume, gas injection speed, well shut-in time and drainage system, synchronous CO2 huff-and-puff operations are carried out in the horizontal wells on both sides, wherein:

[0040] The gas injection volume is 5000-10000t, the gas injection speed is 100-200t / d, the soaking time is 30-60 days, and the drainage system is 3-5mm oil nozzle pressure controlled production.

[0041] Furthermore, in step S4, if the vertical well and the horizontal well are matrix-connected, the vertical well adopts set operating parameters to synchronously carry out CO2 huff-and-puff operations; wherein:

[0042] The gas injection volume is 0.2 times that of a horizontal well, the gas injection speed is 0.3 times that of a horizontal well, and the soaking time and drainage system are the same as those of a horizontal well.

[0043] Furthermore, the step S5 further includes:

[0044] Before repeating step S3 to inject the pressure regulating fluid medium system into the vertical well, monitor the connectivity strength between the vertical well and the horizontal well:

[0045] If the connectivity strength is enhanced, the pressure regulating fluid medium system is selected to be water and a temperature-responsive gel temporary plugging agent;

[0046] If the connectivity strength is reduced, water with a temperature 15-25°C higher than the oil layer temperature is first injected into the vertical well to remove the temporary plugging agent, and then a water and surfactant control and displacement system is selected for injection.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] (1) The present invention provides a production method for improving the recovery rate of gas injection after fracturing of horizontal wells by using vertical well pressure regulation. The vertical well and horizontal well combination well pattern is used to adjust the formation pressure and stress distribution, so that the CO2 huff and puff production effect of the horizontal well is greatly improved. It has been verified that the oil production of a single well after temporary plugging of the strongly connected fracture area is 16,900 tons, the recovery rate is increased by 6.77%, and the input-output ratio reaches 1.90; the oil production of a single well after huff and puff of the combined well pattern in the strongly connected matrix area is 12,300 tons, the recovery rate is increased by 4.91%, and the input-output ratio reaches 2.46;

[0049] (2) Compared with the existing patent document CN112302608A, the present application provides a production method for improving the gas injection recovery rate after horizontal well fracturing by using vertical well pressure regulation, proposes a method for determining the location of strong connectivity between horizontal well fracture networks and a method for pressure regulation and sealing of fluid medium systems using a combined well network pressure regulation, and can efficiently develop existing unconventional oil reservoirs with development well networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a flow chart of the mining method of the present invention;

[0051] Figure 2 This is a comparison curve of recovery rates of different schemes under the condition of strong fracture connectivity in Example 1 of the present invention;

[0052] Figure 3 This is a comparison curve of recovery factors of different schemes under the condition of strong matrix connectivity in Example 2 of the present invention. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] Combination Figure 1 As shown, the present invention provides a production method for improving the recovery rate of gas injection after fracturing of horizontal wells by regulating the pressure of vertical wells, and the method comprises the following steps:

[0055] Step S1. Determine the location of the strongly connected fracture network between horizontal wells: comprehensively analyze the regional geological logging data, microseismic monitoring data, high-frequency pressure monitoring data and fracturing construction data, calculate the fracture connectivity coefficient of each section between wells, and determine the location of the strongly connected well section.

[0056] Among them, the calculation formula for the fracture connectivity coefficient of each section between wells is:

[0057]

[0058] In the above formula (1), C is the connectivity coefficient of each fracture segment between wells; k is the unit conversion coefficient, dimensionless; μ is the viscosity of the fracturing fluid, mPa·s; L is the half fracture length, m; v is the Poisson's ratio, decimal; P f is the fluid pressure in the crack, MPa; σ h is the minimum horizontal principal stress, MPa; E is the interwell Young's modulus, MPa; ΔP is the net pressure in the fracture, MPa; Q is the construction displacement, L / min.

[0059] In the above formula (1), the inter-well Young's modulus E, Poisson's ratio ν and minimum horizontal principal stress σ are obtained using geological logging data: h ; Obtain half fracture length L based on microseismic monitoring data; Obtain fracture fluid pressure P using adjacent well high-frequency pressure monitoring data f ; Obtained through fracturing construction data: net pressure ΔP in the fracture.

[0060] If the fracture connectivity coefficient of the corresponding well section is calculated to be 0.9-1, the well section is defined as a strongly connected well section.

[0061] Step S2. Establishing a vertical well and horizontal well combination well pattern system: setting vertical wells at the locations where the seam network is strongly connected, and completing the wells through casing perforation.

[0062] In step S2, the vertical well is set at the middle position of the distance between two horizontal wells in a direction perpendicular to the horizontal section; and the vertical well is set at the midpoint of the strongly connected section of the fracture network in a direction parallel to the horizontal section.

[0063] The number of the vertical wells is ≥1, which can be determined based on the number of actually strongly connected well sections of the horizontal wells.

[0064] Step S3. Select a pressure regulating fluid medium system and inject it into the vertical well, and use the vertical well to regulate the pressure and balance the regional formation pressure, specifically including:

[0065] Step S301. Test: Inject water containing tracers into the vertical well at a set rate, monitor the time it takes for tracers to appear in the horizontal wells on both sides, and determine the volume of the water channel in the vertical well based on the water injection rate and the time it takes for tracers to appear.

[0066] Step S302. Selecting agents: Based on the relationship between the volume of the vertical well water channel and the volume of the vertical well controlled pores, determine the type of connectivity between the horizontal sections of the two horizontal wells, and select a pressure regulating fluid medium system based on the connectivity type.

[0067] Among them, the type of connectivity between the horizontal sections of two horizontal wells is determined based on the relationship between the volume of the vertical well water channel and the volume of the vertical well controlled pores, including:

[0068] Calculate the controlled pore volume of a vertical well:

[0069]

[0070] In the above formula, V0 is the controlled pore volume of the vertical well, m 3 ; d is the well spacing, m; a is the length of each level of fracturing in the horizontal well, m; h is the thickness of the oil layer, m; is the porosity, a decimal;

[0071] If the vertical well water channel volume is greater than the vertical well controlled pore volume, it is judged to be matrix connected;

[0072] If the volume of the vertical well water channel is less than the vertical well controlled pore volume, the fracture is judged to be connected.

[0073] Select the pressure regulating fluid medium system according to the connection type, including:

[0074] If the matrix is ​​connected, a water and surfactant displacement system is selected, and the system viscosity at the formation temperature is the viscosity of the underground crude oil;

[0075] If the cracks are connected, water and a temperature-responsive gel temporary plugging agent are selected, and the characteristics of the temperature-responsive temporary plugging agent are:

[0076] When the oil layer temperature is within the range of ±5℃, the viscosity can rise to 50-500 times the viscosity of underground crude oil. When the oil layer temperature is within the range of +(15-25)℃, the viscosity drops to the viscosity of underground crude oil.

[0077] Step S303. Pressure regulation: inject a pressure regulating fluid medium system into the vertical well to build a vertical well high-pressure wall to prevent the horizontal wells on both sides from being directly connected.

[0078] Among them, the standard for establishing a vertical well high-pressure wall is: after injecting the pressure-regulating fluid medium system, the wellhead pressure of the vertical well increases by more than 15MPa.

[0079] Step S4. Use the combined well network to carry out CO2 group huff and puff. CO2 group huff and puff means: two or more adjacent wells carry out CO2 huff and puff at the same time, injection-stem-production synchronous operation, pressure coordination, so as to prevent gas channeling between wells. This step specifically includes:

[0080] According to the set gas injection volume, gas injection rate, well soaking time and drainage system, the synchronous CO2 huff-and-puff operation of the horizontal wells on both sides is carried out. The gas injection volume is 5000-10000t, the gas injection rate is 100-200t / d, the well soaking time is 30-60 days, and the drainage system is 3-5mm oil nozzle pressure control production;

[0081] At the same time, if the vertical well and the horizontal well are connected by the matrix, the vertical well will carry out CO2 huff-and-puff operations synchronously using the set operating parameters, the gas injection volume is 0.2 times that of the horizontal well, the gas injection speed is 0.3 times that of the horizontal well, and the soaking time and drainage system are the same as those of the horizontal well.

[0082] Step S5: Repeat steps S3-S4 to carry out the next round of operations until the production of horizontal wells and vertical wells reaches the economic limit production.

[0083] Before repeating step S3 to inject the pressure regulating fluid medium system into the vertical well, the connectivity strength between the vertical well and the horizontal well is monitored:

[0084] If the connectivity strength is enhanced, the pressure regulating fluid medium system is selected to be water and a temperature-responsive gel temporary plugging agent;

[0085] If the connectivity strength is reduced, water with a temperature 15-25°C higher than the oil layer temperature is first injected into the vertical well to remove the temporary plugging agent, and then a water and surfactant control and displacement system is selected for injection.

[0086] Example 1

[0087] In the embodiment of the present invention, a production method for improving the recovery rate of gas injection after fracturing of a horizontal well by regulating the pressure of a vertical well is used to produce a horizontal well group with strongly connected fractures.

[0088] Two horizontal wells were produced after volume fracturing, and there is a strong fracture connection section between the two wells. The controlled reserves of a single well are 250,000 tons. Currently, it has been in production for 2 years. The cumulative oil production of a single well in the first year is 8,400 tons, and the cumulative oil production of a single well in two years is 12,300 tons, with a recovery rate of 4.91%. According to the volume fracturing depletion decline development, it is predicted that in 10 years, the monthly decline rate will be 0.01, the cumulative oil production of a single well will be 31,300 tons, and the recovery degree will be 12.56%.

[0089] Taking the above basic scheme as reference, the following three schemes are set for comparison:

[0090] The first option is: do not temporarily plug the strongly connected section of the fracture, and perform CO2 huff-and-puff operations in one horizontal well, with a gas injection volume of 30,000 tons;

[0091] The second option is: do not temporarily plug the strongly connected fracture section, and perform CO2 group huff-and-puff operations in two horizontal wells, with a gas injection volume of 60,000 tons;

[0092] The third option is to temporarily plug the strongly connected section of the fracture and perform CO2 group huff-and-puff operations in two horizontal wells with an injection volume of 60,000 tons. At the same time, drill a vertical well and perform temporary plugging operations. The specific operations are as follows: set up a vertical well at the location of the strongly connected section of the fracture, drill a vertical well by casing perforation, select water and temperature-responsive gel temporary plugging agents to be injected into the vertical well, use the vertical well pressure regulation to balance the regional formation pressure, and perform temporary plugging operations.

[0093] The relevant economic costs are: 500 yuan for injecting 1 ton of CO2, 8 million yuan for vertical well drilling and completion, and 200,000 yuan for injecting temperature-responsive gel temporary plugging agent.

[0094] The relevant technical parameters are: 5 rounds of CO2 throughput, 1 round of throughput every 2 years, and 6,000 tons of gas injection per horizontal well.

[0095] Table 1 below is a statistical table of technical and economic indicators of different schemes under the condition of strong fracture connectivity. The corresponding recovery factor comparison curves of different schemes under the condition of strong fracture connectivity are as follows: Figure 2 shown.

[0096] Table 1 Statistics of technical and economic indicators of different schemes under the condition of strong crack connectivity

[0097]

[0098] From Table 1, we can see that: the first option has an investment of 30 million yuan and a return of only 3.59 million yuan, which is economically not feasible; the second option has a basic balance between input and output and average economic benefits; the third option has the best technical and economic benefits. Based on option 1, the third option has an increase in oil production per well of 16,900 tons, a recovery rate increase of 6.77%, and an input-output ratio of 1.90.

[0099] Example 2

[0100] The embodiment of the present invention discloses a production method for improving the recovery rate of gas injection after fracturing of a horizontal well by regulating the pressure of a vertical well, and produces a horizontal well group with strong matrix connectivity.

[0101] Two horizontal wells were produced after volume fracturing, and there is a strong matrix connection section between the two wells. The controlled reserves of a single well are 250,000 tons. Currently, it has been in production for 2 years. The cumulative oil production of a single well in the first year is 8,400 tons, and the cumulative oil production of a single well in two years is 12,300 tons, with a recovery rate of 4.91%. According to the volume fracturing depletion decline development, it is predicted that in 10 years, the monthly decline rate will be 0.01, the cumulative oil production of a single well will be 31,300 tons, and the recovery degree will be 12.56%.

[0102] Taking the above basic scheme as reference, the following three schemes are set for comparison:

[0103] The first option is: no vertical wells are set for regulation and displacement, and only two horizontal wells are used for CO2 huff and puff. The matrix strong connection section is regulated and displacement is carried out, and two horizontal wells are used for CO2 huff and puff operations, with a gas injection volume of 60,000 tons.

[0104] The second option is to set up vertical wells for adjustment and displacement, and only two horizontal wells will perform CO2 huff and puff after adjustment and displacement. Adjustment and displacement are performed on the strongly connected section of the matrix, and one vertical well is drilled for adjustment and displacement operations. The adjustment and displacement operation steps are: set up a vertical well at the location of the strongly connected section of the matrix, drill one vertical well by casing perforation, select water and surfactant adjustment and displacement system to inject into the vertical well, use the vertical well pressure regulation to balance the regional formation pressure, and perform adjustment and displacement operations. After adjustment and displacement, the two horizontal wells perform CO2 huff and puff operations, and the gas injection volume of the two horizontal wells is 60,000 tons.

[0105] The third option is to set up vertical wells for adjustment and displacement, and after adjustment and displacement, two horizontal wells and one vertical well will perform CO2 huff and puff. Adjustment and displacement are performed on the strongly connected section of the matrix, and one vertical well is drilled for adjustment and displacement operations. The adjustment and displacement operation steps are to set up a vertical well at the location of the strongly connected section of the matrix, drill one vertical well by casing perforation, select water and surfactant adjustment and displacement system to inject into the vertical well, use the vertical well pressure regulation to balance the regional formation pressure, and perform adjustment and displacement operations. After adjustment and displacement, two horizontal wells and one vertical well will perform CO2 huff and puff operations, with the gas injection volume of the two horizontal wells being 60,000 tons and the gas injection volume of the one vertical well being 6,000 tons.

[0106] The relevant economic costs are: 500 yuan for injecting 1 ton of CO2, 8 million yuan for vertical well drilling and completion, and 500,000 yuan for injecting surfactant displacement system.

[0107] The relevant technical parameters are: 5 rounds of CO2 throughput, 1 round of throughput every 2 years, and 6,000 tons of gas injection per horizontal well.

[0108] Table 2 below is a statistical table of technical and economic indicators of different schemes under the condition of strong matrix connectivity. The recovery factor comparison curves of different schemes under the condition of strong matrix connectivity are as follows: Figure 3 shown.

[0109] Table 2 Statistics of technical and economic indicators of different schemes under the condition of strong matrix connectivity

[0110]

[0111] From Table 2, we can see that all three options have technical and economic benefits, but the technical and economic benefits of Option 3 are better, and the technical effect is better. Based on Option 1, Option 3 increases the oil production per well by 12,300 tons, increases the recovery rate by 4.91%, and achieves an input-output ratio of 2.46.

[0112] The above description is only an embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the application scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. A mining method for improving the recovery rate of gas injection after horizontal well fracturing by using vertical well pressure regulation, characterized in that: The method comprises the following steps: Step S1. Determine the location of strong connection of fracture networks between horizontal wells: comprehensively analyze regional geological logging data, microseismic monitoring data, high-frequency pressure monitoring data and fracturing construction data, calculate the fracture connectivity coefficient of each section between wells, and determine the location of the strongly connected well section with fracture connectivity coefficient within a set range; Step S2. Establishing a vertical well and horizontal well combination well pattern system: setting a vertical well at the location of the well section with strong connection of the seam network, and completing the well with casing perforation; Step S3. Select a pressure regulating fluid medium system and inject it into the vertical well, and use the vertical well to regulate the pressure and balance the regional formation pressure; Step S4. Carry out CO2 group huff and puff using the combined well pattern: carry out CO2 huff and puff operations in the horizontal wells on both sides synchronously according to the set gas injection volume, gas injection speed, well shut-in time and drainage system; at the same time, if the vertical well and the horizontal well are connected by the matrix, the vertical well adopts the set operation parameters to carry out CO2 huff and puff operations synchronously; Step S5: Repeat steps S3-S4 to carry out the next round of operations until the production of horizontal wells and vertical wells reaches the economic limit production.

2. The method according to claim 1, characterized in that In step S1, the calculation formula of the fracture connectivity coefficient of each section between wells is: In the above formula: C is the connectivity coefficient of each fracture section between wells; k is the unit conversion coefficient, dimensionless; μ is the viscosity of the fracturing fluid, mPa·s; L is the half fracture length, m; v is the Poisson's ratio, decimal; P f is the fluid pressure in the crack, MPa; σ h is the minimum horizontal principal stress, MPa; E is the interwell Young's modulus, MPa; ΔP is the net pressure in the fracture, MPa; Q is the construction displacement, L / min.

3. The method according to claim 2, characterized in that Using geological logging data to obtain: inter-well Young's modulus E, Poisson's ratio ν and minimum horizontal principal stress σ h ; According to the microseismic monitoring data, we can obtain: half crack length L; The high-frequency pressure monitoring data of adjacent wells were used to obtain the following fluid pressure in the fracture: f ; Obtained through fracturing construction data: net pressure ΔP in the fracture.

4. The method according to any one of claims 1 to 3, characterized in that: In step S1, if the fracture connectivity coefficient of the corresponding well section is calculated to be 0.9-1, the well section is defined as a strongly connected well section position.

5. The method according to claim 1, characterized in that In step S2, the vertical well is set at the middle position of the distance between two horizontal wells in a direction perpendicular to the horizontal section; and in a direction parallel to the horizontal section, the vertical well is set at the midpoint of the strongly connected section of the fracture network.

6. The method according to claim 5, characterized in that In step S2, the number of vertical wells is ≥1.

7. The method according to claim 1, characterized in that The step S3 specifically includes: Step S301. Testing: Inject water containing tracers into the vertical well at a set rate, monitor the time it takes for tracers to appear in the horizontal wells on both sides, and determine the volume of the water channel in the vertical well based on the water injection rate and the time it takes for tracers to appear; Step S302. Selecting agents: judging the type of connection between the horizontal sections of two horizontal wells according to the relationship between the volume of the vertical well water channel and the volume of the vertical well controlled pores, and selecting the pressure regulating fluid medium system according to the type of connection; Step S303. Pressure regulation: inject a pressure regulating fluid medium system into the vertical well to build a vertical well high-pressure wall to prevent the horizontal wells on both sides from being directly connected.

8. The method according to claim 7, characterized in that In step S302, judging the type of connection between the horizontal sections of two horizontal wells according to the relationship between the volume of the vertical well water channel and the volume of the vertical well controlled pores specifically includes: Calculate the controlled pore volume of vertical wells; If the vertical well water channel volume is greater than or equal to the vertical well controlled pore volume, it is judged to be matrix connected; If the volume of the vertical well water channel is less than the vertical well controlled pore volume, the fracture is judged to be connected.

9. The method according to claim 8, characterized in that The calculation formula for the vertical well controlled pore volume is: In the above formula, V0 is the controlled pore volume of the vertical well, m 3 ; d is the well spacing, m; a is the length of each level of fracturing in the horizontal well, m; h is the thickness of the oil layer, m; is the porosity, a decimal.

10. The method according to claim 8 or 9, characterized in that: In step S302, the pressure regulating fluid medium system is selected according to the connection type, specifically including: If the matrix is ​​connected, a water and surfactant displacement system is selected, and the system viscosity at the formation temperature is the viscosity of the underground crude oil; If the cracks are connected, water and a temperature-responsive gel temporary plugging agent are selected, and the characteristics of the temperature-responsive temporary plugging agent are: When the oil layer temperature is within the range of ±5℃, the viscosity can rise to 50-500 times the viscosity of underground crude oil. When the oil layer temperature is within the range of +(15-25)℃, the viscosity drops to the viscosity of underground crude oil.

11. The method according to claim 7, characterized in that In step S303, the standard for establishing the vertical well high pressure wall is: after the pressure regulating fluid medium system is injected, the vertical well head pressure increases by more than 15 MPa.

12. The method according to claim 1, characterized in that In step S4, according to the set gas injection volume, gas injection speed, well shut-in time and drainage system, synchronous CO2 huff-and-puff operations are carried out on the horizontal wells on both sides, wherein: The gas injection volume is 5000-10000t, the gas injection speed is 100-200t / d, the soaking time is 30-60 days, and the drainage system is 3-5mm oil nozzle pressure controlled production.

13. The method according to claim 12, characterized in that In step S4, if the vertical well and the horizontal well are connected by the matrix, the vertical well adopts the set operation parameters to synchronously carry out CO2 huff and puff operations; wherein: The gas injection volume is 0.2 times that of a horizontal well, the gas injection speed is 0.3 times that of a horizontal well, and the soaking time and drainage system are the same as those of a horizontal well.

14. The method according to claim 1, characterized in that The step S5 further comprises: Before repeating step S3 to inject the pressure regulating fluid medium system into the vertical well, monitor the connectivity strength between the vertical well and the horizontal well: If the connectivity strength is enhanced, the pressure regulating fluid medium system is selected to be water and a temperature-responsive gel temporary plugging agent; If the connectivity strength is reduced, water with a temperature 15-25°C higher than the oil layer temperature is first injected into the vertical well to remove the temporary plugging agent, and then a water and surfactant control and displacement system is selected for injection.

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