Exploitation method for improving gas injection recovery after fracturing of horizontal well by using straight well pressure regulation

Abstract

The present application relates to oil and gas field development technical field, disclose a kind of using straight well pressure regulation improves the recovery of gas injection after horizontal well fracturing Exploitation method, comprising: step S1.Determine the strong connection position of fracture network between horizontal well;Step S2.Establish straight well and horizontal well combination well pattern system;Step S3.Select the injection of pressure regulating fluid medium system straight well, using straight well pressure regulation balance regional formation pressure;Step S4.Use combination well pattern to carry out CO2 group throughput;Step S5: repeat step S3-S4, carry out next round operation, until the production of horizontal well and straight well reaches economic limit production.The exploitation method of the present application uses straight well horizontal well combination well pattern to adjust formation pressure and stress distribution, so that the production effect of horizontal well CO2 throughput is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development, in particular to a mining method for improving gas injection recovery after horizontal well fracturing by using straight well pressure regulation. BACKGROUND

[0002] Field tests show that whether the CO2 huff and puff gas cavity is closed and whether the formation pressure is increased become the key factors affecting the recovery of dense oil horizontal well fracturing after gas injection. The interwell fracture connection mode, connection degree, pressure distribution and its complexity are complex and variable, and it is difficult to achieve only by using horizontal well to adjust the formation pressure.

[0003] At present, CO2 huff and puff operation is mostly carried out by two horizontal wells in a general gas injection mode, gas channeling is obvious, and the production effect is poor. From the point of view of oil production technology, the selective gas injection technology of coiled tubing + packer is not mature, and the construction risk of full well section gel temporary plugging + CO2 huff and puff mode is very large. Therefore, there is an urgent need for a mining method that can further improve the recovery of horizontal wells under the condition of fracture network connection after horizontal well volume fracturing.

[0004] Patent document CN112302608A discloses a horizontal well pre-pressing fluid development method based on three-dimensional fracturing well network, which comprises the following steps: step 1: deploying a target horizontal well in the oil layer, the target horizontal well is not fractured; deploying a first horizontal well parallel to the target horizontal well on the upper part of the horizontal section of the target horizontal well, and fracturing the first horizontal well to form a fracture perpendicular to the direction of the horizontal section of the target horizontal well; deploying a straight well around the target horizontal well, and fracturing the straight well to form a fracture parallel to the direction of the horizontal section of the target horizontal well, and the position is lower than that of the target horizontal well; step 2: in the state that the target horizontal well is not fractured and not produced, injecting energy supplementing fluid into the formation with the first horizontal well and the straight well as injection wells; step 3: after completing the injection of energy supplementing fluid into the formation, fracturing the target horizontal well and opening the well for production; at the same time, the first horizontal well and the straight well as injection wells are converted into oil production wells and opened for production. The technical scheme of the patent overcomes the disadvantages of traditional pre-gas injection technology, fully utilizes the high conductivity fractures and gravity in the fracture network, enhances the formation energy, improves the flow capacity of crude oil, forms a more complex fracture network, and finally realizes the suppression of production decline during the whole life cycle of the horizontal well after production, prolongs the stable production period, and improves the recovery. However, the technical scheme of the patent is only for the development of original oil reservoir, which does not meet the actual situation of current oil field development, and is not applicable to the oil field well which has been deployed with multiple horizontal wells and formed fracture network by volume fracturing. SUMMARY

[0005] The present application aims to solve at least one of the technical problems existing in the prior art or related art, and provides a mining method for improving gas injection recovery after horizontal well fracturing by using straight well pressure regulation, which adjusts formation pressure and stress distribution by using straight well and horizontal well combined well pattern, so that the production effect of CO2 huff and puff in the horizontal well is greatly improved.

[0006] To achieve the above technical purposes, the present application adopts the following technical solutions:

[0007] A mining method for improving gas injection recovery after horizontal well fracturing by using straight well pressure regulation, the method comprising the following steps:

[0008] Step S1. Determine the strong connectivity position of the fracture network between the horizontal wells: comprehensively analyze regional geologic logging data, microseismic monitoring data, high-frequency pressure monitoring data and fracturing operation data, calculate the fracture connectivity coefficient of each section between the wells, and determine the strong connectivity well section position of the fracture connectivity coefficient in the set interval range;

[0009] Step S2. Establish a combined well pattern system of straight well and horizontal well: set a straight well at the strong connectivity well section position of the fracture network, and complete the well by casing perforation;

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

[0011] Step S4. Develop CO2 huff and puff by using the combined well pattern: develop synchronous CO2 huff and puff operation of the two horizontal wells according to the set gas injection amount, gas injection speed, soak time and production system; at the same time, if the straight well and the horizontal well are matrix connected, the straight well develops synchronous CO2 huff and puff operation according to the set operation parameters;

[0012] Step S5: Repeat steps S3-S4 to develop the next round of operation until the production of the horizontal well and the straight well reaches the economic limit production.

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

[0014]

[0015] In the above formula: C is the fracture connectivity coefficient of each section between the wells; k is the unit conversion coefficient, dimensionless; μ is the viscosity of 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 fracture, 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 discharge, L / min.

[0016] Further, the interwell Young's modulus E, Poisson's ratio v and minimum horizontal principal stress σ are obtained by using geologic logging data.h ;

[0017] According to the microseismic monitoring data, a half-fracture length L is obtained.

[0018] According to the high-frequency pressure monitoring data of the adjacent well, a fracture fluid pressure P is obtained. f ;

[0019] According to the fracturing construction data, a net pressure ΔP in the fracture is obtained.

[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 strong connectivity well section position.

[0021] Further, in step S2, according to the direction perpendicular to the horizontal section, the straight well is arranged at the middle position of the well spacing of the two horizontal wells; according to the direction parallel to the horizontal section, the straight well is arranged at the midpoint position of the fracture network strong connectivity section.

[0022] Further, in step S2, the number of the straight well is ≥1.

[0023] Further, the step S3 specifically includes:

[0024] Step S301. Test: inject water containing tracer into the straight well according to the set displacement, monitor the tracer time of the two side horizontal wells, and determine the water channeling channel volume of the straight well according to the water injection displacement and the tracer time;

[0025] Step S302. Select agent: according to the size relationship between the water channeling channel volume of the straight well and the straight well control pore volume, the connectivity type between the horizontal sections of the two horizontal wells is judged, and the pressure regulating fluid medium system is selected according to the connectivity type;

[0026] Step S303. Pressure regulation: inject the pressure regulating fluid medium system into the straight well to establish a high-pressure wall of the straight well to block the direct connection between the two side horizontal wells.

[0027] Further, in the step S302, according to the size relationship between the water channeling channel volume of the straight well and the straight well control pore volume, the connectivity type between the horizontal sections of the two horizontal wells is judged, which specifically includes:

[0028] Calculate the straight well control pore volume;

[0029] If the water channeling channel volume of the straight well ≥ the straight well control pore volume, it is judged as matrix connectivity;

[0030] If the water channeling channel volume of the straight well < the straight well control pore volume, it is judged as fracture connectivity.

[0031] Further, the calculation formula of the straight well control pore volume is:

[0032] Further, the calculation formula of the straight well control pore volume is:

[0033] In the formula, V0 is the vertical well control pore volume, m 3 ; d is the well spacing, m; a is the length of each stage of horizontal well fracturing section, m; h is the oil reservoir thickness, m; Porosity, decimal.

[0034] Further, in the step S302, the pressure regulating fluid medium system is selected according to the connectivity type, and specifically comprises:

[0035] If the matrix connectivity, the water and surfactant profile control system is selected, and the system viscosity at the formation temperature is the underground crude oil viscosity;

[0036] If the fracture connectivity, the water and temperature responsive gel temporary plugging agent is selected, and the temperature responsive temporary plugging agent has the following characteristics:

[0037] In the range of ±5℃ of the oil reservoir temperature, the viscosity can be increased to 50-500 times of the underground crude oil viscosity, and in the range of +(15-25)℃ of the oil reservoir temperature, the viscosity is reduced to the underground crude oil viscosity.

[0038] Further, in the step S303, the standard of the vertical well high pressure wall is that the vertical wellhead pressure is increased by more than 15 MPa after the pressure regulating fluid medium system is injected.

[0039] Further, in the step S4, the two-side horizontal well synchronous CO2 huff and puff operation is carried out according to the set gas injection amount, gas injection speed, soak time and production system, wherein:

[0040] The gas injection amount is 5000-10000t, the gas injection speed is 100-200t / d, the soak time is 30-60 days, and the production system is 3-5mm choke pressure control production.

[0041] Further, in the step S4, if the vertical well and the horizontal well are matrix connectivity, the vertical well adopts the set operation parameters to carry out the CO2 huff and puff operation synchronously, wherein:

[0042] The gas injection amount is 0.2 times of the horizontal well, the gas injection speed is 0.3 times of the horizontal well, and the soak time and the production system are the same as the horizontal well.

[0043] Further, the step S5 further comprises:

[0044] Before the step S3 of repeatedly injecting the pressure regulating fluid medium system into the vertical well, the connectivity strength of the vertical well and the horizontal well is monitored:

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

[0046] If the connectivity strength is reduced, first inject water with a temperature 15-25 DEG C higher than the oil layer temperature into the vertical well to deblock the early-stage temporary plugging agent, and then inject a profile control and flooding system of water and a surfactant.

[0047] Compared with the prior art, the present application has the following beneficial effects:

[0048] (1) The mining method for improving gas injection recovery after horizontal well fracturing by using vertical well pressure regulation provided by the present application adjusts the formation pressure and stress distribution by using vertical well horizontal well combined well pattern, so that the CO2 huff and puff production effect of the horizontal well is greatly improved. It has been verified that the single well oil increment after temporary plugging in the fracture strong connectivity area is 16900 tons, the recovery ratio is increased by 6.77%, and the input-output ratio is 1.90; the single well oil increment after huff and puff in the matrix strong connectivity area combined well pattern is 12300 tons, the recovery ratio is increased by 4.91%, and the input-output ratio is 2.46.

[0049] (2) Compared with the prior art patent document CN112302608A, the mining method for improving gas injection recovery after horizontal well fracturing by using vertical well pressure regulation provided by the present application proposes a method for determining the strong connectivity position of the fracture network between horizontal wells and a method for regulating pressure and channeling by using a combined well pattern pressure regulating fluid medium system, which can efficiently develop the existing unconventional reservoir development well pattern. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 The flow chart of the mining method of the present application is shown in the figure;

[0051] Figure 2 The recovery ratio comparison curve of different schemes under the fracture strong connectivity condition of Example 1 of the present application is shown in the figure;

[0052] Figure 3 The recovery ratio comparison curve of different schemes under the matrix strong connectivity condition of Example 2 of the present application is shown in the figure. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0054] In combination with Figure 1 the figure, the present application provides a mining method for improving gas injection recovery after horizontal well fracturing by using vertical well pressure regulation, which comprises the following steps:

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

[0056] The formula for calculating the fracture connectivity coefficient of each section between wells is:

[0057]

[0058] In the above formula (1), C is the fracture connectivity coefficient of each 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 fracture, 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 operation displacement, L / min.

[0059] In the above formula (1), the interwell Young's modulus E, Poisson's ratio v and minimum horizontal principal stress σ h are obtained from geological logging data; the half-fracture length L is obtained from microseismic monitoring data; the fluid pressure P f in the fracture is obtained from adjacent well high-frequency pressure monitoring data; and the net pressure ΔP in the fracture is obtained from fracturing operation data.

[0060] If the fracture connectivity coefficient of the corresponding well section is 0.9-1, the well section is defined as the strong connectivity well section position.

[0061] Step S2. Establish a combination well pattern system of vertical wells and horizontal wells: set vertical wells at the strong connectivity position of the fracture network, and complete the well with casing perforation.

[0062] In this step S2, the vertical well is set at the middle position of the well spacing of two horizontal wells in the direction perpendicular to the horizontal section, and at the midpoint position of the strong connectivity section of the fracture network in the direction parallel to the horizontal section.

[0063] The number of vertical wells set is ≥1, which can be determined according to the actual number of strong connectivity well sections of horizontal wells.

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

[0065] Step S301. Test: inject water containing a tracer into the vertical well at a set displacement, while monitoring the tracer arrival time of the two horizontal wells, and determine the water channeling channel volume of the vertical well according to the water injection displacement and the tracer arrival time.

[0066] Step S302. Selecting agent: judging the connection type between the horizontal sections of the two horizontal wells according to the size relationship between the water channeling passage volume of the vertical well and the vertical well control pore volume, and selecting the pressure regulating fluid medium system according to the connection type.

[0067] Wherein, the connection type between the horizontal sections of the two horizontal wells is judged according to the size relationship between the water channeling passage volume of the vertical well and the vertical well control pore volume, and specifically includes:

[0068] The vertical well control pore volume is calculated as follows:

[0069]

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

[0071] If the water channeling passage volume of the vertical well > the vertical well control pore volume, it is judged as matrix connection;

[0072] If the water channeling passage volume of the vertical well < the vertical well control pore volume, it is judged as fracture connection.

[0073] The pressure regulating fluid medium system is selected according to the connection type, and specifically includes:

[0074] If it is matrix connection, a profile control system of water and surfactant is selected, and the system viscosity at the formation temperature is the underground crude oil viscosity;

[0075] If it is fracture connection, a water and temperature responsive gel temporary plugging agent is selected, and the temperature responsive temporary plugging agent has the following characteristics:

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

[0077] Step S303. Pressure regulation: injecting the pressure regulating fluid medium system into the vertical well to establish a vertical well high pressure wall to block the direct connection between the two horizontal wells.

[0078] Wherein, the standard for establishing the vertical well high pressure wall is that after injecting the pressure regulating fluid medium system, the vertical well wellhead pressure is increased by more than 15 MPa.

[0079] Step S4. Developing CO2 group huff and puff by using the combined well pattern, which refers to that the adjacent two wells or multiple wells simultaneously perform CO2 huff and puff, injection-simmering-production synchronous operation, and pressure cooperation, so as to prevent gas channeling between the wells. This step specifically includes:

[0080] According to the set gas injection amount, gas injection speed, soaking time and drainage and production system, the two-side horizontal well synchronous CO2 huff and puff operation is carried out, the gas injection amount is 5000-10000t, the gas injection speed is 100-200t / d, the soaking time is 30-60 days, and the drainage and production system is 3-5mm nozzle pressure control production.

[0081] At the same time, if the vertical well and the horizontal well are in matrix communication, the vertical well adopts the set operation parameter to carry out the CO2 huff and puff operation, the gas injection amount is 0.2 times of the horizontal well, the gas injection speed is 0.3 times of the horizontal well, and the soaking time and the drainage and production system are the same as those of the horizontal well.

[0082] Step S5: repeating steps S3-S4, carrying out the next round operation until the horizontal well and the vertical well reach the economic limit production.

[0083] Wherein, before repeating step S3 to inject the pressure regulating fluid medium system into the vertical well, the communication strength of the vertical well and the horizontal well is monitored:

[0084] If the communication strength is enhanced, the pressure regulating fluid medium system is selected to be water and temperature response type gel temporary plugging agent;

[0085] If the communication strength is reduced, first, water with a temperature of 15-25℃ higher than the temperature of the oil layer is injected into the vertical well to deblock the early temporary plugging agent, and then a profile control system of water and a surfactant is selected for injection.

[0086] Example 1

[0087] The mining method for improving the gas injection recovery rate of the horizontal well after fracturing by using the vertical well pressure regulation in the embodiments of the application is used to mine the horizontal well group with strong fracture communication.

[0088] Two horizontal wells are produced after volume fracturing, and there is a strong fracture communication section between the two wells. The single well control reserve is 250,000 tons, and the current production is 2 years, the first year single well cumulative oil production is 0.84 tons, the two years single well cumulative oil production is 1.23 tons, and the recovery degree is 4.91%. According to the volume fracturing depletion type decline development, it is predicted that in 10 years, the monthly decline rate is 0.01, the single well cumulative oil production is 3.13 tons, and the recovery degree is 12.56%.

[0089] Based on the above basic scheme, the following three schemes are set up for comparison:

[0090] The first scheme is: without temporary plugging the strong fracture communication section, one horizontal well carries out CO2 huff and puff operation, and the gas injection amount of the horizontal well is 30,000 tons;

[0091] The second scheme is: without temporary plugging the strong fracture communication section, two horizontal wells carry out CO2 huff and puff operation, and the gas injection amount of the two horizontal wells is 60,000 tons.

[0092] The third scheme is to temporarily block the strong fracture connection section, and to perform CO2 group huff and puff operation on two horizontal wells, and the gas injection amount of the two horizontal wells is 60,000 tons; meanwhile, a straight well is drilled and temporarily blocked, and the specific operation is as follows: a straight well is arranged at the position of the strong fracture connection section, the straight well is drilled by casing perforation, the water and temperature responsive gel temporary blocking agent is injected into the straight well, the straight well is used to balance the formation pressure of the region, and the temporary blocking operation is performed.

[0093] The related economic cost is that the injection of 1 ton of CO2 is 500 yuan, the drilling and completion cost of the straight well is 8 million yuan, and the injection cost of the temperature responsive gel temporary blocking agent is 200,000 yuan.

[0094] The related technical parameters are that the CO2 huff and puff is 5 rounds, 1 round of huff and puff per year, and the single well gas injection amount of the horizontal well is 6,000 tons.

[0095] Table 1 is a statistical table of technical and economic indicators of different schemes under the condition of strong fracture connection, and the recovery ratio comparison curve of different schemes under the condition of strong fracture connection is as shown in Figure 2 .

[0096] Table 1 is a statistical table of technical and economic indicators of different schemes under the condition of strong fracture connection, and the recovery ratio comparison curve of different schemes under the condition of strong fracture connection is as shown in

[0097]

[0098] From table 1, it can be seen that the first scheme invests 30 million yuan, and the income is only 3.59 million yuan, which is not economically feasible; the second scheme is basically balanced in investment and output, and the economic benefit is general; the third scheme has the best technical scheme and economic benefit, and the single well oil increment of the third scheme based on the first scheme is 16.9 thousand tons, the recovery ratio is increased by 6.77%, and the input-output ratio is 1.90.

[0099] Example 2

[0100] The exploitation method for improving the gas injection recovery ratio of the horizontal well after fracturing by using the straight well pressure regulation in the embodiment of the present application is used to exploit the horizontal well group with strong matrix connection.

[0101] Two horizontal wells are produced after volume fracturing, and there is a strong matrix connection section between the two wells. The single well control reserve is 250,000 tons, and the current production is 2 years, the first year single well cumulative oil production is 0.84 thousand tons, the two-year single well cumulative oil production is 1.23 thousand tons, and the recovery degree is 4.91%. According to the volume fracturing depletion type decline development, it is predicted that in 10 years, the monthly decline rate is 0.01, the single well cumulative oil production is 3.13 thousand tons, and the recovery degree is 12.56%.

[0102] The above-mentioned basic scheme is taken as a reference, and the following three schemes are set up for comparison:

[0103] The first scheme is that no straight well is arranged for profile control and flooding, and only two horizontal wells are subjected to CO2 huff and puff. The matrix strong connectivity section is subjected to profile control, and two horizontal wells are subjected to CO2 huff and puff operation. The gas injection amount of the two horizontal wells is 60,000 tons.

[0104] The second scheme is that a straight well is arranged for profile control, and only two horizontal wells are subjected to CO2 huff and puff after profile control. The matrix strong connectivity section is subjected to profile control, and one straight well is drilled for profile control operation. The profile control operation steps are as follows: a straight well is arranged at the position of the matrix strong connectivity section, the straight well is drilled by casing perforation, a water and surfactant profile control system is selected to be injected into the straight well, the formation pressure of the region is balanced by the straight well, and the profile control operation is performed. After profile control, two horizontal wells are subjected to CO2 huff and puff operation. The gas injection amount of the two horizontal wells is 60,000 tons.

[0105] The third scheme is that a straight well is arranged for profile control, and two horizontal wells and one straight well are subjected to CO2 huff and puff after profile control. The matrix strong connectivity section is subjected to profile control, and one straight well is drilled for profile control operation. The profile control operation steps are as follows: a straight well is arranged at the position of the matrix strong connectivity section, the straight well is drilled by casing perforation, a water and surfactant profile control system is selected to be injected into the straight well, the formation pressure of the region is balanced by the straight well, and the profile control operation is performed. After profile control, two horizontal wells and one straight well are subjected to CO2 huff and puff operation. The gas injection amount of the two horizontal wells is 60,000 tons, and the gas injection amount of the straight well is 6,000 tons.

[0106] The relevant economic cost is that the injection of 1 ton of CO2 is 500 yuan, the drilling and completion cost of the straight well is 8 million yuan, and the injection of the surfactant profile control system is 0.5 million yuan.

[0107] The relevant technical parameter is that CO2 huff and puff is 5 rounds, 1 round is huffed and puffed in 2 years, and the single well gas injection amount of the horizontal well is 6,000 tons.

[0108] Table 2 is a statistical table of technical and economic indexes of different schemes under the condition of matrix strong connectivity, and the corresponding recovery ratio comparison curves of different schemes under the condition of matrix strong connectivity are as shown in Figure 3

[0109] Table 2 Technical and economic index statistical table of different schemes under the condition of matrix strong connectivity

[0110]

[0111] It can be seen from Table 2 that the three schemes have technical and economic benefits, but the third scheme has better technical and economic benefits and better technical effects. On the basis of the first scheme, the single well oil increment of the third scheme is 12,300 tons, the recovery ratio is increased by 4.91%, and the input-output ratio is 2.46.

[0112] ​The above merely illustrates the embodiments of the present application, but should not be used to limit the present application. Any modification, equivalent replacement, and improvement within the scope of the present application should be included in the protection scope of the present application.

Claims

1. A mining method for improving gas injection recovery after fracturing of a horizontal well by using a straight well pressure regulation, characterized in that, The method comprises the following steps: Step S1. Determining the position of the strong fracture network connecting well section between horizontal wells: comprehensively analyzing regional geological logging data, microseismic monitoring data, high-frequency pressure monitoring data and fracturing operation data, calculating the fracture connecting coefficient of each section between wells, and determining the position of the strong fracture network connecting well section in the set interval range; The calculation formula of the fracture connecting coefficient of each section between wells is: In the above formulae: C is the fracture intercommunication coefficient for each section between wells; k is the unit conversion coefficient, dimensionless; If the fracture connecting coefficient of the corresponding well section is 0.9-1, the well section is defined as the position of the strong fracture network connecting well section; viscosity of the fracturing fluid, mPa-s; L half-length of the fracture, m; v Poisson's ratio, decimal; fluid pressure in the fracture, MPa; minimum horizontal principal stress, MPa; interwell Young's modulus, MPa; net pressure in the fracture, MPa; Q For construction discharge, L / min; Step S2. Establishing a combined well pattern system of vertical wells and horizontal wells: setting vertical wells at the position of the strong fracture network connecting well section, and completing the well by casing perforation; Step S3. Selecting a pressure regulating fluid medium system to inject into the vertical well, and using the vertical well to regulate and balance the formation pressure in the region; Step S4. Developing CO2 group huff and puff by using the combined well pattern: developing synchronous CO2 huff and puff operation of the two horizontal wells according to the set gas injection amount, gas injection speed, soaking time and production system; at the same time, if the vertical well and the horizontal well are matrix connected, the vertical well develops synchronous CO2 huff and puff operation according to the set operation parameters; Step S5: repeating steps S3-S4 to develop the next round of operation until the production of the horizontal well and the vertical well reaches the economic limit production. In step S2, the vertical well is arranged at the middle position of the well spacing of the two horizontal wells in the direction perpendicular to the horizontal section; and the vertical well is arranged at the midpoint position of the strong fracture network connecting section in the direction parallel to the horizontal section.

2. The method of recovery according to claim 1, wherein, Using geologic well logging data, interwell Young's modulus E , Poisson's ratio In step S2, the number of the vertical wells is ≥1. , and minimum horizontal principal stress are obtained; According to the microseismic monitoring data, it is obtained that the half slit length is 0.5 m L ; Applying the high-frequency pressure monitoring data of the adjacent well, it is obtained that the fluid pressure in the fracture P f ; From the fracturing job data, the net pressure ΔP in the fracture is obtained: P .

3. The method of recovery according to claim 1, wherein, The step S3 specifically comprises:

4. The method of recovery according to claim 3, wherein, Step S301. Testing: injecting water containing a tracer into the vertical well according to the set displacement, monitoring the tracer breakthrough time of the two horizontal wells at the same time, and determining the water channeling channel volume of the vertical well according to the water injection displacement and the tracer breakthrough time; 5. The method of recovery according to claim 1, wherein, Step S302. Selecting agent: judging the connection type between the horizontal sections of the two horizontal wells according to the size relationship between the water channeling channel volume of the vertical well and the vertical well control pore volume, and selecting the pressure regulating fluid medium system according to the connection type; Step S303. Pressure regulation: injecting the pressure regulating fluid medium system into the vertical well to establish a high pressure wall of the vertical well to block the direct connection between the two horizontal wells. In step S302, the connection type between the horizontal sections of the two horizontal wells is judged according to the size relationship between the water channeling channel volume of the vertical well and the vertical well control pore volume, which specifically comprises: Calculating the vertical well control pore volume; 6. The method of recovery according to claim 5, wherein, If the water channeling channel volume of the vertical well ≥ the vertical well control pore volume, it is judged as matrix connection; If the water channeling channel volume of the vertical well < the vertical well control pore volume, it is judged as fracture connection. The calculation formula of the vertical well control pore volume is: φ 7. The method of recovery according to claim 6, wherein, φ is the porosity, which is a decimal number. V 0= d / 2× a × h × In step S302, the pressure regulating fluid medium system is selected according to the connection type, which specifically comprises: In the above formula, V 0 is the vertical well control pore volume, m 3 ; d is the well spacing, m; a is the length of each stage of horizontal well fracturing, m; h is the oil reservoir thickness, m ; If it is matrix connection, a water and surfactant profile control system is selected, and the system viscosity at the formation temperature is the underground crude oil viscosity; 8. A method of extraction according to claim 6 or 7, characterised in that, If it is fracture connection, a water and temperature responsive gel temporary plugging agent is selected, and the temperature responsive gel temporary plugging agent has the following characteristics: ​ ​ The viscosity can be increased to 50-500 times of the viscosity of the underground crude oil within the range of ±5 ℃ of the reservoir temperature, and the viscosity can be reduced to the viscosity of the underground crude oil within the range of + (15-25) ℃ of the reservoir temperature.

9. The method of recovery according to claim 5, wherein, In the step S303, the criterion for establishing the high-pressure wall of the vertical well is that the pressure at the wellhead of the vertical well is increased by more than 15 MPa after the injection of the pressure-adjusting fluid medium system.

10. The method of recovery according to claim 1, wherein, In the step S4, the synchronous CO2 huff and puff operation of the two horizontal wells is carried out according to the set injection amount, injection speed, soaking time and production system, wherein: The injection amount is 5000-10000 t, the injection speed is 100-200 t / d, the soaking time is 30-60 days, and the production system is 3-5 mm choke pressure control production.

11. The method of recovery according to claim 10, wherein, In the step S4, if the vertical well and the horizontal well are in matrix communication, the vertical well carries out the CO2 huff and puff operation with the set operation parameters. The injection amount is 0.2 times of that of the horizontal well, the injection speed is 0.3 times of that of the horizontal well, and the soaking time and the production system are the same as those of the horizontal well.

12. The method of recovery according to claim 1, wherein, The step S5 further comprises: Before the step S3 of injecting the pressure-adjusting fluid medium system into the vertical well is repeated, the communication strength between the vertical well and the horizontal well is monitored. If the communication strength is enhanced, the pressure-adjusting fluid medium system is selected to be water and a temperature-responsive gel temporary plugging agent; If the communication strength is reduced, water with a temperature 15-25 ℃ higher than the reservoir temperature is first injected into the vertical well to deblock the temporary plugging agent, and then a water and surfactant profile control system is selected for injection.

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