A multi-objective-based branch horizontal well trajectory design method

Abstract

The present invention proposes a multi-objective branch horizontal well trajectory design method, which belongs to the technical field of oil extraction and processing industry, and includes the following steps: S1: Based on geological characteristics and development goals, a wellbore trajectory scheme is formed; S2: A thin reservoir fishbone branch wellbore pressure drop model, a formation model, and a branch well productivity model are constructed; S3: A drill friction torque analysis is performed on the wellbore trajectory scheme, and the well inclination angle and the build-up rate are optimized; S4: The safety of the main wellbore horizontal section screen pipe under different well inclination angles and target front distances is analyzed, and the influence of different branch angles on the wellbore stability is analyzed by finite element analysis; S5: Multi-objective optimization is performed on the wellbore trajectory in the wellbore trajectory scheme, and the design parameters in the wellbore trajectory scheme are optimized. The present invention adjusts the wellbore trajectory parameters according to the analysis results, ensures the safety of the drill tool during the running-in process, reduces the risk of accidents during the drilling process, and effectively improves the drilling efficiency and mining benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of oil extraction and processing industry, and specifically relates to a branch horizontal well trajectory design method based on multiple objectives. Background Art

[0002] With the continuous increase in energy demand, the development and utilization of thin reservoirs (thin oil layers or coal reservoirs) as an important clean energy has received more and more attention. In the field of oil and gas exploration and development, horizontal wells have the advantages of increasing the exposed area of ​​oil and gas layers and improving development efficiency. In particular, the use of multi-branch horizontal wells has effectively increased oil and gas production, improved recovery rate, reduced drilling costs, increased recovery rate, and shortened the mining cycle. It has gradually become a common means of developing thin reservoirs (thin oil layers or coal reservoirs).

[0003] Conventional horizontal well development has a limited horizontal section length, generally around 200m, which not only results in low single-well productivity and difficulty in controlling reservoir reserves, but also high construction costs and low single-well comprehensive benefits. With the improvement of drilling technology, the scientific nature of wellbore design has become increasingly important, and it is urgent to use advanced technical means to optimize the wellbore trajectory of thin reservoirs (thin oil layers or coal reservoirs) to improve the penetration ability of the wellbore, enhance productivity and ensure safety. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, a branch horizontal well trajectory design method based on multiple objectives is provided.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] This technical solution proposes a multi-objective branch horizontal well trajectory design method, including the following steps:

[0007] S1: Based on geological characteristics and development objectives, a wellbore trajectory plan is formed, which includes a main wellbore plan and a branch wellbore plan;

[0008] S2: Based on the thin reservoir type, a fishbone branch wellbore pressure drop model, a formation model, and a branch well productivity model are constructed. Thin reservoirs include thin oil layers and coal reservoirs.

[0009] S3: Perform drill friction and torque analysis on the wellbore trajectory plan, adjust the wellbore trajectory parameters according to the analysis results, and optimize the well inclination angle and build-up rate based on the drill friction and torque analysis;

[0010] S4: Analyze the safety of running the screen in the horizontal section of the main wellbore at different well inclination angles and target front distances, and use finite element analysis to analyze the influence of different branch angles on the wellbore stability;

[0011] S5: performing multi-objective optimization on the wellbore trajectory in the wellbore trajectory plan, optimizing the design parameters in the wellbore trajectory plan, and obtaining a final wellbore trajectory plan.

[0012] Preferably, in S1, the geological characteristics of the target block are analyzed to determine the distribution, thickness, inclination and reservoir properties of the oil and gas reservoirs, and based on the analysis of the oil and gas reservoirs, the target layers and target point positions of the main wellbore and each branch wellbore are determined.

[0013] Preferably, in said S2, the gas flow of the thin reservoir is as follows: establishing a gas and water flow model, and constructing a fishbone branch wellbore pressure drop model based on the flow law of the fluid in the horizontal section and the branch confluence;

[0014] Among them, the two-term gas-water migration equation in thin reservoirs is as follows:

[0015] (1);

[0016] In the formula, is the gas phase flow potential, is the water phase flow potential, is the diffusion coefficient of gas in the crack, B is the volume coefficient, S is saturation, is the gas production of the reservoir in a grid volume per unit time, is the water production of the reservoir in a grid volume per unit time;

[0017] Wellbore pressure drop model of herringbone branch wells:

[0018] For branch well section, the formula is as follows:

[0019] (2);

[0020] In the formula, i is the number of nodes from the upstream end of the branch. i part, is the flow rate from the formation into the branch wellbore, is the flow rate flowing into this section from the upstream section adjacent to the branch well section;

[0021] For the main and branch well sections with branches, the formula is as follows:

[0022] (3);

[0023] In the formula, is the flow rate from the formation into the main branch wellbore of this section, is the flow rate from the upstream section adjacent to the main branch well section into this section, is the flow rate from the branch of the well section into the well section, The two subscripts represent the number of the main well section and the number of the branch respectively;

[0024] For the main well section without branches, the formula is as follows:

[0025] (4);

[0026] In the formula, i Indicates that the well section is the first from the upstream end of the main branch. i part, is the flow rate from the upstream section adjacent to the main branch well section into this section, including the sum of all upstream main branch flows and branch flows, It is the flow rate flowing from the formation into the main and branch wellbore of this section.

[0027] Preferably, in S3, the hook load and torque of the horizontal wellbore under different working conditions are calculated, and based on the influence of the friction coefficient, target front distance and water-to-vertical ratio on the friction torque of the drill bit, the reasonable target front distance under different well inclination angles is determined, and the limit value of the casing friction coefficient is greater than 0.2, and the limit value of the open hole friction coefficient is greater than 0.25.

[0028] Preferably, based on the maximum hook load and turntable torque of the drill bit in various working conditions under different friction coefficients, branch angles and branch lengths of the branch wellbore, from the perspective of drilling technology, the branch section inclination rate is less than 8° / 30m, and the branch angle and the length of the inclination section are controlled from the cost aspect. Combined with the requirements for production capacity optimization, the branch wellbore trajectory parameters are optimized by comparing the drilling difficulty under different branch angles and inclination section lengths.

[0029] Preferably, in S5, the multiple objectives include productivity, friction torque, screen safety and well wall mechanical stability, and the design parameters include well inclination angle, target front distance, branch angle, branch length, branch number and branch spacing.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] This application conducts an in-depth analysis of geological conditions and development objectives, and through the reasonable design of the wellbore trajectory of the main wellbore, it can ensure the rationality of the well inclination angle and the target front distance, optimize the production capacity of the branch wells, and combine the fishbone branch wellbore pressure drop model and formation model to simulate the influence of different morphological parameters on the production capacity, determine the optimal branch morphological parameters, and achieve comprehensive optimization of the wellbore trajectory plan, thereby optimizing the production capacity of the branch wells and improving the overall mining efficiency.

[0032] This application analyzes the friction torque and adjusts the wellbore trajectory parameters according to the analysis results to ensure the safety of the drill bit during the lowering process, reduce the risk of accidents during the drilling process, improve drilling efficiency, ensure the mechanical stability of the wellbore wall, and reduce the risk of wellbore collapse. By comprehensively considering factors such as production capacity, friction torque, screen safety and wellbore mechanical stability, multi-objective optimization design is carried out to ensure that the wellbore trajectory design complies with the principles of safety, economy and efficiency, and while meeting various technical requirements, it can reduce mining costs and improve economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0034] Figure 1 It is the overall flow chart of the present invention;

[0035] Figure 2 It is a schematic diagram of the target front distance in the present invention;

[0036] Figure 3 It is a schematic diagram of the wellbore structure in the present invention;

[0037] Figure 4 This is the result diagram of the effect of different branch lengths on the productivity of thin reservoir branch wells;

[0038] Figure 5 This is the result diagram of the impact of different branch angles on the production capacity of thin reservoir branch wells;

[0039] Figure 6 This is the result diagram of the impact of different branch numbers on the production capacity of branch wells in thin reservoirs;

[0040] Figure 7 This is the result diagram of the impact of different branch spacing conditions on the production capacity of thin reservoir branch wells;

[0041] Figure 8 The displacement of the monitoring point in the z direction changes with time at different branch angles Figure 1 ;

[0042] Fig. 9 The displacement of the monitoring point in the z direction changes with time at different branch angles Figure 2 ;

[0043] Fig.10 The displacement of the monitoring point in the z direction changes with time at different branch angles Figure 3 ;

[0044] Fig.11 It is the horizontal projection diagram of multi-branch horizontal well design;

[0045] Fig.12 It is a three-dimensional diagram of the multi-branch horizontal well design. DETAILED DESCRIPTION

[0046] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0047] like Figure 1-Figure 12 As shown, this embodiment proposes a branch horizontal well trajectory design method based on multiple objectives, including the following steps:

[0048] S1: Based on geological characteristics and development objectives, a wellbore trajectory plan is formed. The wellbore trajectory plan includes a main wellbore plan and a branch wellbore plan. The main wellbore plan includes determining the well inclination angle and target front distance, and the branch wellbore plan includes determining the number, angle and length of each branch wellbore;

[0049] S2: Based on the thin reservoir type (thin oil layer or coal reservoir), the wellbore pressure drop model of the fishbone branch well, the formation model, and the branch well productivity model are constructed. The Petrel software can be used to construct the model, simulate and calculate the influence of different morphological parameters on productivity, so as to determine the morphological parameters of the branch well;

[0050] S3: Perform drill tool friction and torque analysis on the wellbore trajectory plan, adjust the wellbore trajectory parameters according to the analysis results to ensure that the drill tool can pass safely during the lowering process, and optimize the parameters such as well inclination angle and build-up rate on the basis of the drill tool friction and torque analysis to ensure the operability and drilling efficiency of the wellbore trajectory. The drilling engineering software Landmark can be used to perform drill tool friction and torque analysis;

[0051] S4: Analyze the safety of running the screen in the horizontal section of the main wellbore at different well inclination angles and target front distances, and determine the wellbore trajectory parameters for safe running of the screen. Finite element analysis software such as FLAC3D can be used to analyze the influence of different branch angles on the wellbore stability and verify the mechanical stability of the wellbore trajectory.

[0052] S5: performing multi-objective optimization on the wellbore trajectory in the wellbore trajectory plan, optimizing the design parameters in the wellbore trajectory plan, and obtaining a final wellbore trajectory plan.

[0053] In S1, the geological characteristics of the target block are analyzed in detail to determine the distribution, thickness, inclination and reservoir properties of the oil and gas reservoirs. Based on the analysis of the oil and gas reservoirs, the target layers and target points of the main wellbore and each branch wellbore are determined to ensure that the wellbore trajectory can penetrate the high-yield layer to the greatest extent.

[0054] In S2, thin reservoirs include thin oil layers and coal reservoirs. The gas flow in thin reservoirs is as follows: a gas and water flow model under dual media is established. By studying the flow pressure drop in the horizontal wellbore and the flow law of the branch confluence, the flow law of the fluid in the horizontal section and the branch confluence is determined, and a fishbone branch wellbore pressure drop model is constructed. The Petrel software can be used to study the law of changes in branch well production capacity under geological conditions.

[0055] Among them, the two-term gas-water migration equation in thin reservoirs is as follows:

[0056] (1);

[0057] In the formula, is the gas phase flow potential, is the water phase flow potential, is the diffusion coefficient of gas in the crack, B is the volume coefficient, S is saturation, is the gas production of the reservoir in a grid volume per unit time, is the water production of the reservoir in a grid volume per unit time;

[0058] Wellbore pressure drop model of herringbone branch wells:

[0059] For branch well section, the formula is as follows:

[0060] (2);

[0061] In the formula, i is the number of nodes from the upstream end of the branch. i part, is the flow rate from the formation into the branch wellbore, is the flow rate flowing into this section from the upstream section adjacent to the branch well section;

[0062] For the main and branch well sections with branches, the formula is as follows:

[0063] (3);

[0064] In the formula, is the flow rate from the formation into the main branch wellbore of this section, is the flow rate from the upstream section adjacent to the main branch well section into this section, is the flow rate from the branch of the well section into the well section, The two subscripts represent the number of the main well section and the number of the branch respectively;

[0065] For the main well section without branches, the formula is as follows:

[0066] (4);

[0067] In the formula, i Indicates that the well section is the first from the upstream end of the main branch. i part, is the flow rate from the upstream section adjacent to the main branch well section into this section, including the sum of all upstream main branch flows and branch flows, It is the flow rate flowing from the formation into the main and branch wellbore of this section.

[0068] In S3, the Wellplan module in the software is used to calculate the hook load and torque of the horizontal wellbore under different working conditions. Based on the influence of friction coefficient, target front distance and water-to-vertical ratio on the friction torque of the drill bit, the reasonable target front distance under different well inclination angles is determined.

[0069] In the process of friction and torque analysis of multi-branch horizontal wells, the larger the limit values ​​of the casing friction coefficient and the open hole friction coefficient under safe running conditions, the smaller the corresponding drilling difficulty and the better the drilling requirements. At the same time, the limit value of the casing friction coefficient should be greater than 0.2, and the limit value of the open hole friction coefficient should be greater than 0.25.

[0070] Based on the maximum hook load and turntable torque of the drilling tool in various working conditions under different friction coefficients, branch angles and branch lengths of branch wells, from the perspective of drilling technology, the branch section inclination rate is less than 8° / 30m. The branch angle and the length of the inclination section are controlled from the cost aspect. Combined with the requirements of production capacity optimization, the drilling difficulty under different branch angles and inclination section lengths is compared to optimize the branch wellbore trajectory parameters.

[0071] In S5, the multiple objectives include productivity, friction torque, screen safety and wellbore mechanical stability, and the design parameters include well inclination angle, target front distance, branch angle, branch length, branch number and branch spacing.

[0072] Through in-depth analysis of geological conditions and development objectives, and through reasonable design of the main wellbore trajectory, the rationality of the well inclination angle and the target front distance can be ensured, and the production capacity of the branch wells can be optimized. Combined with the wellbore pressure drop model and formation model of the coalbed methane fishbone branch well, the influence of different morphological parameters on the production capacity can be simulated, the optimal branch morphological parameters can be determined, and the comprehensive optimization of the wellbore trajectory plan can be achieved, thereby optimizing the production capacity of the branch wells and improving the overall mining efficiency.

[0073] A multi-branch horizontal well is deployed in a thin reservoir block. The wellbore trajectory type is selected and optimized according to the method of this application, including the following steps:

[0074] S11: Geological condition analysis and preliminary wellbore trajectory design

[0075] According to geological conditions, development objectives and adjacent well morphological parameters, the wellbore trajectory of the multi-branch horizontal well was designed, and the parameter value range was determined: the horizontal section length of the main wellbore was 500m, the target front distance was 150-300m, and the well inclination angle was 92°-98°; the branch length of the branch wellbore was 220-500m, the branch angle was 30°-75°, the number of branches was 2-8, and the branch spacing was 25-100m, thus initially forming the wellbore trajectory plan.

[0076] S12: Study on the influence of multi-branch horizontal well morphological parameters on productivity

[0077] Through the establishment of the productivity calculation model and the use of Petrel software to study the productivity change law of branch wells under geological conditions, Figure 4-Figure 7 The results of the effects of different branch lengths, branch angles, branch numbers, and branch spacing on branch well productivity are shown in the figure. Reference parameters for branch wellbore are given from the perspective of productivity: the branch length is preferably 350-400 m; within a certain range, the larger the branch angle, the better; the number of branches is 4-6; and the branch spacing is 50 m or 75 m.

[0078] S13: Determination of morphological parameters of multi-branch horizontal wells based on drilling tool friction torque

[0079] (1) Determination of main wellbore morphological parameters

[0080] Table 1: Reservoir main wellbore drilling tool friction torque data table

[0081]

[0082] It can be seen from Table 1 that when the well inclination angle is 94° or less, safe drilling can be achieved within the range of 150-300 m for the target front distance. The larger the target front distance, the smaller the inclination rate, and the easier it is to achieve inclination. Therefore, combined with the actual situation on site and the experience of adjacent wells, the key parameters of the main wellbore trajectory can be optimized: well inclination angle of 94° and target front distance of 300 m.

[0083] (2) Determination of branch wellbore morphological parameters

[0084] Table 2: Drilling tool friction torque data table at different branch angles

[0085]

[0086] It can be seen from Table 2 that with the increase of branch angle, the length of the deflection section gradually increases, the torque of the rotary table gradually increases, and the hook load decreases. Under the condition of friction coefficient (0.25, 0.3), the drill bit will undergo sinusoidal buckling, and the drill bit can drill safely when the friction coefficient is within (0.2, 0.25).

[0087] Table 3: Drilling tool friction torque data for different branch lengths

[0088]

[0089] It can be seen from Table 3 that as the branch length increases, the disc torque gradually decreases, the hook load fluctuates, and the overall change is not large. When the branch length is ≥400 m, the friction coefficient is required to be higher, and it is recommended to be controlled within (0.15, 0.2). When the branch length is <400 m, the friction coefficient is recommended to be controlled within (0.2, 0.25).

[0090] Table 4: Drilling feasibility analysis table of different branch angles under the condition of branch length of 400 m

[0091]

[0092] The technical requirements for the deflection section are high, and the drilling speed is relatively low, so a longer construction period is required. This increases the operating costs of labor and equipment. As can be seen from Table 4, when designing a branch wellbore, the angle with the main wellbore can be selected between 45° and 60°.

[0093] Table 5: Drilling feasibility analysis table of different deflection rates under the condition of branch angle 60°

[0094]

[0095] It can be seen from Table 5 that only when the length of the branch deflection section is ≥ 225 m is it feasible to construct.

[0096] By analyzing the friction and torque of branch wellbore drilling tools and optimizing the branch morphology from the angle of deflection, the main parameters of branch wellbore of multi-branch horizontal well can be obtained: the branch angle should be controlled at 45-60°, the length of the branch deflection section should be 225 m or more, and the branch length should be less than 400 m.

[0097] S14: Determination of morphological parameters of multi-branch horizontal wells based on safe running of screens

[0098] Table 6: Limit friction coefficient for safe lowering of reservoir main wellbore screen

[0099]

[0100] It can be seen from Table 6 that with the increase of well inclination angle, the requirement for friction coefficient becomes higher and higher, and even the friction coefficient needs to be within (0.1, 0.15), which is difficult to achieve.

[0101] Therefore, from the perspective of safe lowering of the screen pipe, when the well inclination angle is 92-94°, the target front distance can be 150-300 m, and when the well inclination angle is 96°, the target front distance can only be 250-300 m; when the well inclination angle is 98°, the screen pipe is difficult to lower safely.

[0102] Effect of mechanical stability on branch morphology parameters: Figure 8-Figure 10 Schematic diagram of the change of the z-direction displacement of the monitoring point on the well with different branch angles over time Figure 1 , two and three, by Figure 8-Figure 10 It can be seen that the displacement near the intersection first decreases and then increases with the branch angle of 60° as the turning point; the displacement on the main well decreases as the branch angle increases; the displacement on the branch well first decreases and then increases with 45° as the turning point.

[0103] From the perspective of wellbore mechanical stability, when the branch angle is 30°-90°, the overall stability is good, and when the branch angle is 60°, the stability of the intersection is the best.

[0104] S15: Comprehensive optimization of wellbore trajectory

[0105] Based on the perspectives of multiple objectives such as productivity, drill bit friction torque, safe running of screens and mechanical stability, the final morphological parameters of the multi-branch horizontal wellbore trajectory design can be determined as follows: well inclination angle 94°, target front distance 250-300 m, branch angle 45°-60°, branch length 350m-400m, number of branches 4-6, and branch interval 50-75 m.

[0106] Taking one of the morphological parameter combinations as an example, the wellbore trajectory was optimized using Landmark software: the well inclination angle was set to 94°, the horizontal section length of the main wellbore was 500 m, the target front distance of target point A was 300 m, the water-to-vertical ratio was about 2.5:1, the number of branches was 6, the angle of each branch was 60°, the branch length was 400 m, and the branch interval was 50 m. The conclusions are as follows: Fig.11 and Fig.12 As shown, Fig.11 Design horizontal projection diagrams for multi-branch horizontal wells. Fig.12 Design 3D diagrams for multi-branch horizontal wells.

[0107] Table 7: L1 wellbore trajectory of multi-branch horizontal well

[0108]

[0109] Table 8: L2 wellbore trajectory of multi-branch horizontal well

[0110]

[0111] Table 9: L3 wellbore trajectory of multi-branch horizontal well

[0112]

[0113] Table 10: Wellbore trajectory table for multi-branch horizontal well L4

[0114]

[0115] Table 11: L5 wellbore trajectory of multi-branch horizontal well

[0116]

[0117] Table 12: Wellbore trajectory table of multi-branch horizontal well L6

[0118]

[0119] Table 13: Multi-branch horizontal well M1 wellbore trajectory table

[0120]

[0121] By analyzing the friction and torque and adjusting the wellbore trajectory parameters according to the analysis results, the safety of the drill bit during the lowering process is ensured, the risk of accidents during drilling is reduced, the drilling efficiency is improved, the mechanical stability of the wellbore wall is ensured, and the risk of wellbore collapse is reduced. By comprehensively considering factors such as production capacity, friction and torque, screen safety and wellbore mechanical stability, multi-objective optimization design is carried out to ensure that the wellbore trajectory design complies with the principles of safety, economy and efficiency, and while meeting various technical requirements, it can reduce mining costs and improve economic benefits.

[0122] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A multi-objective branch horizontal well trajectory design method, characterized in that: The following steps are involved: S1: Based on geological characteristics and development objectives, a wellbore trajectory plan is formed, which includes a main wellbore plan and a branch wellbore plan; S2: Based on the thin reservoir type, a fishbone branch wellbore pressure drop model, a formation model, and a branch well productivity model are constructed. Thin reservoirs include thin oil layers and coal reservoirs. S3: Perform drill friction and torque analysis on the wellbore trajectory plan, adjust the wellbore trajectory parameters according to the analysis results, and optimize the well inclination angle and build-up rate based on the drill friction and torque analysis; S4: Analyze the safety of running the screen in the horizontal section of the main wellbore at different well inclination angles and target front distances, and use finite element analysis to analyze the influence of different branch angles on the wellbore stability; S5: performing multi-objective optimization on the wellbore trajectory in the wellbore trajectory scheme, optimizing the design parameters in the wellbore trajectory scheme, and obtaining a final wellbore trajectory scheme; In S2, the gas flow in the thin reservoir is as follows: establishing a gas and water flow model, and constructing a fishbone branch wellbore pressure drop model based on the flow law of the fluid in the horizontal section and the branch confluence; Among them, the two-term gas-water migration equation in thin reservoirs is as follows: （1）； In the formula, is the gas phase flow potential, is the water phase flow potential, is the diffusion coefficient of gas in the crack, B is the volume coefficient, S is saturation, is the gas production of the reservoir in a grid volume per unit time, is the water production of the reservoir in a grid volume per unit time; Wellbore pressure drop model of herringbone branch wells: For branch well section, the formula is as follows: （2）； In the formula, i is the number of nodes from the upstream end of the branch. i part, is the flow rate from the formation into the branch wellbore, is the flow rate flowing into this section from the upstream section adjacent to the branch well section; For the main and branch well sections with branches, the formula is as follows: （3）； In the formula, is the flow rate from the formation into the main branch wellbore of this section, is the flow rate from the upstream section adjacent to the main branch well section into this section, is the flow rate from the branch of the well section into the well section, The two subscripts represent the number of the main well section and the number of the branch respectively; For the main well section without branches, the formula is as follows: （4）； In the formula, i Indicates that the well section is the first from the upstream end of the main branch. i part, is the flow rate from the upstream section adjacent to the main branch well section into this section, including the sum of all upstream main branch flows and branch flows, It is the flow rate flowing from the formation into the main and branch wellbore of this section.

2. A multi-objective branch horizontal well trajectory design method according to claim 1, characterized in that: In S1, the geological characteristics of the target block are analyzed to determine the distribution, thickness, inclination and reservoir properties of the oil and gas reservoirs. Based on the analysis of the oil and gas reservoirs, the target layers and target point positions of the main wellbore and each branch wellbore are determined.

3. The multi-objective branch horizontal well trajectory design method according to claim 1, characterized in that: In S3, the hook load and torque of the horizontal wellbore under different working conditions are calculated, and based on the influence of the friction coefficient, target front distance and water-to-vertical ratio on the friction torque of the drill bit, the reasonable target front distance under different well inclination angles is determined, and the limit value of the casing friction coefficient is greater than 0.2, and the limit value of the open hole friction coefficient is greater than 0.

25.

4. A multi-objective branch horizontal well trajectory design method according to claim 3, characterized in that: Based on the maximum hook load and turntable torque of the drilling tool in various working conditions under different friction coefficients, branch angles and branch lengths of branch wells, from the perspective of drilling technology, the branch section inclination rate is less than 8° / 30m. The branch angle and the length of the inclination section are controlled from the cost aspect. Combined with the requirements of production capacity optimization, the drilling difficulty under different branch angles and inclination section lengths is compared to optimize the branch wellbore trajectory parameters.

5. The multi-objective branch horizontal well trajectory design method according to claim 1, characterized in that: In S5, multiple objectives include productivity, friction torque, screen safety and wellbore mechanical stability. Based on maximizing productivity, drilling safely and controlling drilling costs, the wellbore trajectory parameters of multi-branch horizontal wells are designed, including well inclination angle, target front distance, branch angle, branch length, branch number and branch spacing.

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