A method for analyzing the dynamics of a drill string for producing natural gas hydrates without a riser, considering vortex-induced vibration

Abstract

The application discloses a kind of to consider vortex-induced vibration's without riser exploitation natural gas hydrate drill string dynamics analysis method, comprising: establishing seawater section drill string dynamics model and vortex-induced vibration model, calculate current force component and drill string dynamics response data;The dynamic parameters of seawater section O-shaped grid are mapped to stratum section contact mechanics grid, generate adaptive transition layer grid, and calculate the dynamic synchronization and real-time update of dynamic parameters are realized;Establish stratum section drill string dynamics model, calculate dynamic contact force, and dynamically adjust friction coefficient according to vortex-induced vibration frequency, introduce rock brittle fracture model to analyze stress distribution and trajectory deviation;The energy input of seawater section is compared and verified with dissipated energy of stratum section, and the fatigue damage index of drill string is calculated and parameter optimization instruction is triggered.The application effectively solves the problem that the dynamic parameter transmission accuracy of riserless drill string between seawater section and stratum section is insufficient, dynamic synchronization is poor and multi-physical field coupling is insufficient.

Description

Technical Field

[0001] This invention belongs to the field of natural gas hydrate extraction and drill string dynamics analysis, and more specifically, it relates to a drill string dynamics analysis method for extracting natural gas hydrates without a riser, taking into account vortex-induced vibration. Background Technology

[0002] Natural gas hydrate, often called "combustible ice" due to its ice-like appearance and flammability, is an ice-like crystalline substance formed from natural gas and water under low temperature and high pressure conditions. Its main component is methane. As a highly promising new energy source, natural gas hydrate has enormous reserves globally, widely distributed in deep-sea sediments and permafrost zones. It is estimated that the carbon content of global natural gas hydrate is about twice that of existing fossil fuels, demonstrating its vast reserves and making it an important research direction for addressing future energy needs.

[0003] However, the extraction of natural gas hydrates faces numerous challenges. On the one hand, the extraction environment is complex, often occurring in harsh conditions such as the deep sea or polar regions, making extraction extremely difficult. For example, in deep-sea areas, it is necessary to cope with enormous water pressure, low temperatures, and complex marine geological conditions. On the other hand, extraction technologies are still immature, and existing extraction methods, such as depressurization, thermal shock, and injection, all have certain limitations. Taking depressurization as an example, although the principle is relatively simple—that is, to decompose natural gas hydrates into natural gas and water by reducing formation pressure—in practical applications, it may lead to problems such as formation collapse and hydrate regeneration, affecting extraction efficiency and safety.

[0004] In deep-sea natural gas hydrate extraction, riserless extraction methods are gaining increasing attention. Compared to traditional riser extraction, this method offers advantages such as lower cost and greater operational flexibility, making it particularly suitable for shallow natural gas hydrate extraction. However, riserless extraction also presents new challenges. For instance, the drill string is directly exposed to the complex marine environment in the seawater section, making it more susceptible to factors such as ocean currents, which can trigger complex dynamic problems like vortex-induced vibrations, seriously threatening drill string safety and the smooth progress of extraction.

[0005] Drill string dynamics is the study of the force and motion characteristics of a drill string during drilling, and it is of great significance for ensuring drilling safety and improving drilling efficiency. Currently, drill string dynamics research has achieved certain results in conventional drilling, establishing various mechanical models that consider the interaction between the drill string, drilling fluid, and wellbore, enabling a certain degree of analysis and prediction of drill string forces, deformations, and vibrations. However, in the dynamic analysis of drill strings without risers, there is a problem of insufficient accuracy in the transfer of dynamic parameters between the seawater section and the formation section, leading to the accumulation of initial condition errors in the formation section analysis, which in turn affects the reliability of drill string safety assessment. The root cause of this problem lies in: ① Parameter format mismatch: The model meshing methods of the seawater segment (based on fluid domain slices and O-type grids) and the formation segment (based on contact mechanics discretized grids) are different, which requires cross-grid interpolation when transferring parameters, and is prone to introducing errors.

[0006] ② Poor synchronization of dynamic response data: The time-varying characteristics of vortex-induced vibration in contact with the formation require real-time updates of parameters, but the traditional static transmission mechanism cannot meet the dynamic coupling requirements.

[0007] ③ The multiphysics coupling effect is not fully correlated: the ocean current force in the seawater section and the contact force in the formation section are not fully coupled during the transmission process, resulting in distortion of the overall dynamic behavior simulation of the drill string.

[0008] In summary, existing dynamic analysis methods for riserless drill strings have significant shortcomings when dealing with the complex conditions of deep-sea natural gas hydrate extraction. There is an urgent need for a new analysis method that can improve the accuracy of dynamic parameter transfer between the seawater section and the formation section, meet the requirements for dynamic response data synchronization, and fully correlate multi-physics coupling effects, so as to ensure the safe and efficient operation of riserless drill strings in the deep-sea natural gas hydrate extraction process. Summary of the Invention

[0009] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a method for dynamic analysis of drill strings used in the extraction of natural gas hydrates without a riser, taking into account vortex-induced vibration.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: a method for dynamic analysis of drill string for the extraction of natural gas hydrates without a riser, considering vortex-induced vibration, comprising the following steps: Based on the drill string geometry parameters and marine environment parameters, a dynamic model of the seawater section drill string was constructed, and vortex-induced vibration modeling of the seawater section drill string was performed based on the wake oscillator theory. The vibration amplitude and frequency of the seawater section drill string were calculated. At the same time, the ocean current force components of each fluid domain slice were calculated based on the Navier-Stokes equations, and the axial tension, torque and displacement time history data of the seawater section drill string were obtained. A parameter transfer interface is established at the mudline boundary. A hybrid interpolation algorithm is used to map the dynamic parameters of the O-type grid in the seawater section to the contact mechanics grid in the formation section. An adaptive transition layer grid is generated at the mudline boundary. At the same time, a two-way feedback channel is established at the mudline boundary to implement two-way coupled iterative calculation, so as to realize the dynamic synchronization and real-time update of the dynamic parameters of the seawater section and the formation section. A dynamic model of the drill string in the formation section is established based on the initial conditions of the transmission. The dynamic contact force between the drill string and the well wall in the formation section is calculated by using the Coulomb friction model combined with Hertz contact theory. The friction coefficient is dynamically adjusted according to the vortex-induced vibration frequency. A rock brittle fracture model is introduced to simulate the stress distribution and trajectory deviation of the drill string in the formation section during the drill bit cutting process. A comparative analysis of the energy input from the seawater section and the energy dissipated from the formation section is conducted. When the energy error exceeds a set threshold, the proportional coefficient of the transmission parameters is dynamically adjusted. The fatigue damage index of the drill string is calculated based on Miner's linear cumulative damage theory. When the fatigue damage index exceeds a set threshold, a parameter optimization command is triggered.

[0011] As a preferred embodiment, the specific process of vortex-induced vibration modeling is as follows: First, based on the wake oscillator theory, the seawater section of the drill string is divided into multiple independent fluid domain slices along the axial direction, and each slice is discretized using an O-type grid; then, the vortex shedding frequency of each slice is calculated using the Strouhal number relationship, and the wake oscillator equations are solved simultaneously to obtain the vibration amplitude and frequency of the seawater section of the drill string in the downstream and cross-flow directions; finally, based on the calculated vortex shedding frequency, the wake oscillator equations are constructed. The Strauhal number relation is as follows:

[0012] In the formula, The angular frequency of vortex shedding; These are Strauhal numbers; Local ocean current velocity at the depth of each slice; The outer diameter of the drill string in the seawater section; The equation for the wake oscillator is:

[0013] In the formula, This refers to the downstream vibration displacement of the drill string in the seawater section. This is the fluid damping coefficient; The coupling coefficient of the wake oscillator; This represents the downstream acceleration of the drill string in the seawater section.

[0014] As a preferred embodiment, the specific process of calculating the current force components of each fluid domain slice based on the Navier-Stokes equations and obtaining the axial tension, torque, and displacement time history data of the seawater section drill string is as follows: Based on the Navier-Stokes equations, computational fluid dynamics software is used to numerically solve the flow field around the seawater section drill string to obtain the current force components of each slice, including the axial force, radial force, and torque distribution, and the axial tension, torque, and displacement time history data of the seawater section drill string are calculated in combination with the seawater section drill string dynamic model. The basic form of the Navier-Stokes equations is:

[0015] In the formula, ρ For fluid density; u This is the velocity vector; t For time; pThe pressure borne by the fluid element; μ For fluid dynamic viscosity; F It is an external force.

[0016] As a preferred embodiment, the specific process of the hybrid interpolation algorithm is as follows: first, the spatial distribution of key dynamic parameters is calculated in each slice of the O-type grid in the seawater section using Lagrange interpolation; then, the interpolated key dynamic parameters are mapped to the nodes of the contact mechanics grid in the formation section using radial basis functions; and at the same time, a residual feedback mechanism is introduced in the transition layer grid to correct errors.

[0017] As a preferred embodiment, the specific process for calculating the spatial distribution of key dynamic parameters in each slice of the O-type grid in the seawater section using Lagrange interpolation is as follows: key nodes are selected in each fluid domain slice, including the grid center point and control points uniformly distributed along the boundary; the displacement and stress information of each key node are calculated using fluid dynamics software to form a set of known data points for interpolation calculation; a polynomial interpolation function is constructed using the known data point set through the Lagrange interpolation method, so that the interpolation function accurately matches the corresponding displacement and stress values ​​at each known data point, thereby obtaining the spatial distribution of drill string displacement and stress in each slice of the O-type grid in the seawater section; The expression for the interpolation function is:

[0018] In the formula, x The position to be interpolated; The coordinates of the known data points; For the physical quantity values ​​corresponding to known data points, the interpolation function is... The calculated value is the prediction result for the position to be interpolated.

[0019] As a preferred embodiment, the specific process of mapping the interpolated key dynamic parameters to the nodes of the formation section contact mechanics grid using radial basis functions is as follows: The coordinates of all nodes on the formation section contact mechanics grid are determined, and the displacement and stress values ​​of the drill string in the seawater section are extracted from the O-type grid of the seawater section as input information for subsequent mapping; an interpolation equation system is established using the Gaussian kernel function as the radial basis function, and a spatial continuous function is constructed to describe the distribution pattern of the known data points; the constructed spatial continuous function is applied to all target nodes of the formation section contact mechanics grid to calculate the displacement and stress values ​​of the drill string corresponding to each node; the least squares method is used to optimize the weighting coefficients to minimize the error between the mapped data and the original data.

[0020] As a preferred embodiment, the specific process of introducing a residual feedback mechanism into the transition layer mesh for error correction is as follows: Interpolation error is calculated in the transition layer mesh. Local interpolation error is calculated by comparing the interpolated displacement and stress values ​​with the reference values.

[0021] In the formula, The value obtained from interpolation; For reference only; If local interpolation error R If the set threshold is exceeded, adaptive mesh refinement is triggered, adding computing nodes in areas with large errors and re-performing interpolation calculations.

[0022] As a preferred embodiment, the specific process of the bidirectional coupled iterative calculation is as follows: First, after the calculation is completed at each time step, the key dynamic parameters of the seawater section drill string are extracted, including the vibration amplitude, downstream vibration displacement and axial tension of the seawater section drill string. These data are then packaged into a standardized format and transmitted to the formation section drill string dynamic model in real time. Then, after receiving the data transmitted from the seawater section, the formation section drill string calculates the dynamic contact force between the formation section drill string and the well wall at that time step, and feeds it back to the seawater section drill string dynamic model, based on the current contact state between the formation section drill string and the well wall. The contact reaction force received in the seawater section is treated as an external load term and added to the drill string dynamics model of the seawater section, resulting in the modified drill string dynamics model of the seawater section:

[0023] in, Forces acting on fluids; The mass matrix of the drill string in the seawater section; The damping matrix of the drill string in the seawater section; Here is the stiffness matrix of the drill string in the seawater section; K Here is the stiffness matrix of the drill string in the seawater section; x This represents the displacement vector of the drill string in the seawater section after correction for external loads.

[0024] As a preferred embodiment: the comparative analysis of the input energy in the seawater section and the dissipated energy in the formation section, and the dynamic adjustment of the proportional coefficient of the transmission parameters when the energy error exceeds a set threshold, specifically involves: comparing and analyzing the input energy in the seawater section and the dissipated energy in the formation section to ensure overall energy conservation; when the energy error exceeds 5%, dynamically adjusting the proportional coefficient of the key power parameters until the energy error is less than 5%; The energy input in the seawater section is calculated from the work done by the ocean current on the drill string in the seawater section, mainly including the energy input caused by axial tension and vortex-induced vibration; the energy dissipated in the formation section includes frictional energy loss and energy consumption generated during rock fracturing, and the frictional energy loss is calculated using the following formula:

[0025] In the formula, E f This is due to frictional energy loss; F f Friction; v This represents the relative slip velocity.

[0026] As a preferred embodiment, the calculation of the drill string fatigue damage index based on Miner's linear cumulative damage theory specifically involves: extracting stress time history data at the mudline and drill bit connection, calculating the drill string fatigue damage index D based on Miner's linear cumulative damage theory, and triggering a parameter optimization command when D exceeds 0.8. The parameter optimization command includes reducing the drill string rotation speed or adjusting the drilling fluid density. The expression for Miner's linear cumulative damage theory is as follows:

[0027] In the formula, D The fatigue damage index of the drill string; This represents the number of loop iterations. This refers to the fatigue life of a material under a specific stress amplitude.

[0028] The present invention has the following advantages due to the adoption of the above technical solutions: 1. Improve the accuracy of cross-mesh parameter transfer: This invention develops a hybrid interpolation algorithm that combines Lagrange interpolation with radial basis functions (RBF). This algorithm accurately maps the dynamic parameters of the seawater segment mesh to the nodes of the formation segment contact mechanics mesh, ensuring the consistency of parameter spatial distribution. Simultaneously, an adaptive transition layer mesh is set at the mudline boundary, utilizing local refinement and mesh deformation techniques to achieve a smooth transition between the seawater and formation segments, effectively reducing interpolation errors. This improvement significantly enhances the accuracy of cross-mesh parameter transfer, providing more accurate initial conditions for subsequent dynamic analysis.

[0029] 2. Achieve dynamic data synchronization and real-time updates: This invention employs a bidirectional coupling iterative algorithm, establishing a bidirectional feedback channel at the mudline boundary. After each time step of calculation in the seawater section, the updated parameters (such as vortex-induced vibration amplitude) are immediately transmitted to the formation section, while simultaneously receiving contact reaction force data from the formation section to correct the drill string motion equations in the seawater section model. This dynamic data synchronization and real-time update mechanism effectively solves the problem that traditional static transmission mechanisms cannot meet the requirements of dynamic coupling, ensuring the timeliness and accuracy of drill string dynamics analysis.

[0030] 3. Enhance the coupling correlation of multiphysics fields: A vortex-induced vibration-contact force coupling equation is embedded in the parameter transfer interface. The vibration response amplitude of the seawater section is used as the dynamic excitation term of the contact friction force in the formation section, and the expression for the friction coefficient in the Coulomb friction model is modified to vary with the vibration frequency. Global energy conservation verification is performed by comparing the input energy of the seawater section with the dissipated energy of the formation section, and the proportional coefficient of the transfer parameters is dynamically adjusted to ensure the overall energy balance of the coupled model. This improvement enhances the correlation of multi-physics coupling between the seawater and formation sections, making the simulation of the overall dynamic behavior of the drill string more realistic and reliable.

[0031] 4. Provide reliable technical support for drill string safety assessment: By employing high-precision cross-grid transfer, dynamic data synchronization, and multiphysics coupling enhancement, this invention effectively solves the accuracy and real-time issues of parameter transfer between the seawater section and the formation section. This not only improves the reliability of drill string dynamics analysis but also provides solid technical support for the safety assessment of riserless drill strings in deep-sea natural gas hydrate extraction, helping to reduce safety risks during the extraction process and ensuring the smooth progress of extraction operations. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings: Figure 1 This is a schematic flowchart of a drill string dynamics analysis method for extracting natural gas hydrates without a riser, according to an embodiment of the present invention. Figure 2 This is a flowchart illustrating the hybrid interpolation algorithm in this invention. Figure 3 This is a schematic diagram of the global energy conservation verification and safety assessment process in this invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0034] This invention provides a method for dynamic analysis of drill string in riserless gas hydrate extraction considering vortex-induced vibration. The method includes: establishing a drill string dynamic model and a vortex-induced vibration model for the seawater section; calculating ocean current force components and drill string dynamic response data; mapping the dynamic parameters of the O-type grid in the seawater section to the contact mechanics grid in the formation section, generating an adaptive transition layer grid, and calculating and realizing dynamic synchronization and real-time updating of dynamic parameters; establishing a drill string dynamic model for the formation section, calculating dynamic contact forces, and dynamically adjusting the friction coefficient according to the vortex-induced vibration frequency; introducing a rock brittle fracture model to analyze stress distribution and trajectory deviation; comparing and verifying the input energy in the seawater section and the dissipated energy in the formation section; calculating the drill string fatigue damage index and triggering parameter optimization commands. This invention effectively solves the problems of insufficient accuracy in dynamic parameter transfer, poor dynamic synchronization, and insufficient multi-physics coupling between the seawater and formation sections of riserless drill strings.

[0035] The following is a detailed description, with reference to the accompanying drawings, of the drilling string dynamics analysis method for extracting natural gas hydrates without a riser, considering vortex-induced vibration, provided by an embodiment of the present invention.

[0036] Please see Figure 1 This invention proposes a dynamic analysis method for drilling strings in the extraction of natural gas hydrates without a riser, considering vortex-induced vibration, comprising the following steps: S100. Dynamic characteristics analysis of the drill string in the seawater section: S101. Based on drill string geometric parameters (including drill string length, outer diameter and inner diameter) and marine environmental parameters (including ocean current velocity and drilling fluid density), a dynamic model of the drill string in the seawater section is constructed using the finite element method. S102. Regarding vortex-induced vibration modeling, firstly, based on the wake oscillator theory, the seawater section of the drill string is divided into multiple independent fluid domain slices along the axial direction. Each slice is discretized using an O-type mesh to ensure that the hydrodynamic characteristics of the vortex shedding region are accurately described. Then, the vortex shedding frequency of each slice is calculated using the Strouhal number relationship, and the wake oscillator equations are solved simultaneously to obtain the vibration amplitude and frequency of the seawater section of the drill string in the downstream (Y-axis) and transverse (Z-axis) directions, so as to accurately describe the vibration response of the seawater section of the drill string under the action of fluid. Finally, based on the calculated vortex shedding frequency, the wake oscillator equations are constructed. The Strauhal number relation is:

[0037] In the formula, The angular frequency of vortex shedding; These are Strauhal numbers; Local ocean current velocity at the depth of each slice; This refers to the outer diameter of the drill string in the seawater section.

[0038] The equation for the wake oscillator is:

[0039] In the formula, This refers to the downstream vibration displacement of the drill string in the seawater section. This is the fluid damping coefficient; The coupling coefficient of the wake oscillator; This represents the downstream acceleration of the drill string in the seawater section.

[0040] S104. For ocean current force calculation, based on the Navier-Stokes equations, the computational fluid dynamics software (ANSYS Fluent) is used to numerically solve the flow field around the seawater section of the drill string to obtain the ocean current force components of each slice, including axial force, radial force and torque distribution. Combined with the dynamic model of the seawater section drill string, the axial tension, torque and displacement time history data of the seawater section drill string are calculated to ensure the accurate transmission of dynamic parameters in time and space.

[0041] The basic form of the Navier-Stokes equations is:

[0042] In the formula, ρ For fluid density; u The velocity vector; t For time; p The pressure borne by the fluid element; μ For fluid dynamic viscosity; F It is an external force.

[0043] S200. Cross-mesh parameter transfer and dynamic synchronization: S201. Establish a high-precision parameter transfer interface at the mudline boundary to solve the problem of dynamic parameter transfer between the seawater section and the formation section; S202. A hybrid interpolation algorithm is adopted. First, the spatial distribution of key dynamic parameters (including displacement and stress) of the drill string in the seawater section is calculated in each slice of the O-type grid in the seawater section by Lagrange interpolation. Then, the interpolated key dynamic parameters are mapped to the nodes of the contact mechanics grid in the formation section using radial basis functions (using Gaussian kernel function). At the same time, a residual feedback mechanism is introduced in the transition layer grid to correct errors, ensuring the consistency of the spatial distribution and the accuracy of transmission of key dynamic parameters. S203. Generate an adaptive transition layer mesh. Insert the transition layer mesh at the mudline boundary. Through local refinement and mesh deformation techniques, achieve a smooth transition between the seawater section and the stratigraphic section meshes, and eliminate interpolation abrupt errors.

[0044] S204. Implement bidirectional coupling iterative calculation, establish a bidirectional feedback channel at the mudline boundary, and transmit the updated vibration amplitude and axial tension parameters of the drill string in the seawater section to the formation section after each time step of calculation is completed. At the same time, receive the contact reaction force data of the formation section, correct the dynamic model of the drill string in the seawater section, and realize dynamic data synchronization and real-time updating.

[0045] S300. Drill string-formation coupling analysis of the formation section: S301. Based on the transmitted initial conditions, establish a dynamic model of the drill string in the formation section; S302. Conduct contact mechanics modeling, use the Coulomb friction model combined with Hertz contact theory to calculate the dynamic contact force between the drill string and the well wall in the formation section, and dynamically adjust the friction coefficient according to the vortex-induced vibration frequency of each slice to make the dynamic model of the drill string in the formation section more consistent with the actual contact state. S303. Conduct an analysis of the interaction between the drill string and the rock in the formation section, introduce a brittle fracture model of the rock to simulate the stress distribution and trajectory deviation of the drill string in the formation section during the drill bit cutting process, and use the finite element method to iteratively solve the dynamic equilibrium equation of the stress state of the drill string in the formation section, dynamically update the displacement and stress distribution of the drill string in the formation section, analyze the influencing factors of trajectory deviation, and provide a theoretical basis for optimizing drilling parameters.

[0046] The dynamic equilibrium equation for the stress state of the drill string in the formation section is as follows:

[0047] In the formula, The mass matrix of the drill string in the formation section; The damping matrix of the drill string in the formation section; This represents the stiffness matrix of the drill string in the formation section; u This represents the displacement vector of the drill string in the formation section; This refers to the cutting force of the drill bit. This is the reaction force of the strata.

[0048] S400. Global Energy Conservation Verification and Safety Assessment: S401. Please refer to Figure 3 A comparative analysis was conducted on the input energy (work done by ocean currents) in the seawater section and the dissipated energy (friction energy, rock fracturing energy) in the formation section to ensure overall energy conservation. When the energy error exceeded 5%, the proportional coefficient of key dynamic parameters was dynamically adjusted to ensure that the energy error was less than 5%, thus guaranteeing the physical consistency of the calculation process and the stability and accuracy of the coupled model (i.e., the overall calculation framework formed by combining the drill string dynamics model of the seawater section and the drill string dynamics model of the formation section). The energy input in the seawater section is calculated from the work done by the ocean current on the drill string in the seawater section, mainly including the energy input caused by axial tension and vortex-induced vibration; the energy dissipated in the formation section includes frictional energy loss and energy consumption generated during rock fracturing, and the frictional energy loss is calculated using the following formula:

[0049] In the formula, E f This is due to frictional energy loss; F f Friction; v Relative slip velocity; S402. Extract stress time history data at the mudline and drill bit connection, calculate the drill string fatigue damage index based on Miner's linear cumulative damage theory, and trigger parameter optimization commands when the drill string fatigue damage index in the formation section exceeds 0.8 to reduce the risk of drill string fatigue damage and ensure the safety and stability of the drilling process. Parameter optimization commands include reducing drill string rotation speed or adjusting drilling fluid density to change the stress state of the drill string in the formation section, slow down the fatigue accumulation rate, and extend the system's service life. The expression for Miner's linear cumulative damage theory is as follows:

[0050] In the formula, D The fatigue damage index of the drill string; This represents the number of loop iterations. This refers to the fatigue life of a material under a specific stress amplitude.

[0051] In the above embodiments, preferably, please refer to Figure 2 Step S202, "Calculating the spatial distribution of key dynamic parameters of the drill string in the seawater section within each slice of the O-type grid in the seawater section using Lagrange interpolation," specifically includes: First, select key nodes within each fluid domain slice. Key nodes include the grid center point and control points evenly distributed along the boundary. Then, the displacement and stress information of each key node are calculated using fluid dynamics software to form a set of known data points for interpolation calculation; Finally, using these known data points, a polynomial interpolation function is constructed using the Lagrange interpolation method, so that the interpolation function accurately matches the corresponding displacement and stress values ​​at each known data point, thereby obtaining the spatial distribution of displacement and stress of the drill string in the seawater section within each slice of the O-type grid in the seawater section.

[0052] The expression for the interpolation function is:

[0053] In the formula, x The position to be interpolated; The coordinates of the known data points; For the physical quantity values ​​corresponding to known data points, the interpolation function is... The calculated value is the predicted result for the position to be interpolated. During the interpolation process, the interpolation basis function is used. This method ensures that the interpolation polynomial strictly satisfies the given data values ​​at known data points, while maintaining reasonable smoothness throughout the entire grid domain. It guarantees the continuity of displacement and stress within the O-type grid in the seawater section, improving the accuracy of key dynamic parameters transferred from the seawater section to the formation section.

[0054] In the above embodiments, preferably, step S202, "mapping the interpolated key dynamic parameters to the nodes of the formation contact mechanics grid using radial basis functions (employing Gaussian kernel functions)," specifically includes: First, the coordinates of all nodes on the contact mechanics grid of the formation section are determined. At the same time, the displacement and stress values ​​of the drill string in the seawater section are extracted from the O-type grid of the seawater section as input information for subsequent mapping. Then, using the Gaussian kernel function Using radial basis functions, an interpolation equation system is established to construct a spatially continuous function to describe the distribution pattern of known data points; where... r The Euclidean distance between the interpolation point and the known point is... Shape parameters used to control local fitting ability; Finally, the constructed spatial continuity function is applied to all target nodes of the contact mechanics grid of the formation section to calculate the displacement and stress values ​​of the drill string corresponding to each node in the formation section. At the same time, the least squares method is used to optimize the weighting coefficients to minimize the error between the mapped data and the original data, thereby improving the interpolation accuracy.

[0055] The above method can achieve smooth and continuous transmission of key dynamic parameters at the boundary between the seawater section and the stratigraphic section, effectively reducing interpolation errors and improving the stability and accuracy of coupled calculations.

[0056] In the above embodiments, preferably, step S202, "introducing a residual feedback mechanism in the transition layer mesh for error correction," specifically includes: Interpolation error is calculated in the transition layer mesh. Local interpolation error is calculated by comparing the interpolated displacement and stress values ​​with reference values ​​obtained from finite element simulation or experimental data.

[0057] In the formula, The value obtained from interpolation; For reference only. If there is a local interpolation error... RIf the error exceeds a set threshold (e.g., 10%), adaptive mesh refinement is triggered. Adaptive refinement uses a local mesh refinement strategy to add computational nodes in areas with large errors, insert new mesh points, and re-perform interpolation calculations. This method enhances the accuracy and stability of parameter transfer from the seawater section to the formation section, reduces local mechanical response distortion caused by interpolation errors, and improves the reliability of dynamic analysis results.

[0058] In the above embodiments, preferably, the "bidirectional coupled iterative calculation" in step S204 specifically includes: First, after the calculation is completed at each time step, the key dynamic parameters of the seawater section drill string are extracted, including the vibration amplitude, downstream vibration displacement and axial tension of the seawater section drill string. These data are then packaged into a standardized format and transmitted to the formation section drill string dynamic model in real time. Then, after receiving the data transmitted from the seawater section, the formation section drill string calculates the dynamic contact force between the formation section drill string and the well wall at that time step, and feeds it back to the seawater section drill string dynamic model, based on the current contact state between the formation section drill string and the well wall. The contact reaction force received in the seawater section is treated as an external load term and added to the drill string dynamics model of the seawater section, resulting in the modified drill string dynamics model of the seawater section:

[0059] in, Forces acting on fluids; The mass matrix of the drill string in the seawater section; The damping matrix of the drill string in the seawater section; Here is the stiffness matrix of the drill string in the seawater section; x This represents the displacement vector of the drill string in the seawater section after correction for external loads.

[0060] The following example, using the extraction of natural gas hydrates in a deep-sea area, further illustrates the drill string dynamics analysis method for extracting natural gas hydrates without a riser. The relevant actual parameters of the drill string are as follows: Drill string length: L = 1000m Drill string outer diameter: = 0.2m Drill string inner diameter: d = 0.15m Ocean current velocity: v = 2m / s Drilling fluid density: ρ m =1200kg / m3 Static friction coefficient: μ0 = 0.3 Vibration coupling coefficient: α = 0.1 Strouhal number: St = 0.2 Fluid density: ρ = 1025 kg / m³ 3 Hydrodynamic viscosity: μ = 0.001 Pa·s Drill string mass: m = 50000 kg (uniformly distributed, can be accurately calculated based on actual material density, etc.) Stiffness matrix K: (Determined based on drill string material properties and structure; a diagonal matrix; main diagonal elements) Axial stiffness lateral stiffness ) Damping matrix C: (where Rayleigh damping is used, taken empirically) , , (where M is the mass matrix, determined by the drill string mass) Analyze according to the steps described above: Analysis of the dynamic characteristics of the drill string in the seawater section: Vortex-induced vibration modeling: The drill string is divided into n = 100 fluid domain slices along the axial direction, and each slice is divided using an O-type mesh. The vortex shedding angular frequency is calculated based on the Strouhal number relationship.

[0061] The equations for the wake oscillator are constructed, and numerical methods (such as the Runge-Kutta method) are used to solve for the vibration amplitude and frequency in the downstream (Y-axis) and transverse (Z-axis) directions. The downstream vibration amplitude is obtained after solving. =0.05m, frequency =0.3Hz; transverse vibration amplitude =0.03m, frequency =0.32Hz.

[0062] Ocean current force calculation: Based on the Navier-Stokes equations, the flow field around the drill string was numerically solved using ANSYS Fluent software. A computational domain was set, and the flow field on and around the drill string surface was meshed with 500,000 meshes (adjustable according to actual conditions). The k-ε turbulence model was used. The ocean current force components of each slice were calculated, and then the axial tension, torque, and displacement time history data were obtained. The calculation showed that at a certain time t = 10s, the axial tension T = 80,000 N, the torque Mt = 5,000 N·m, and the displacement x = 0.1 m.

[0063] Cross-mesh parameter transfer and dynamic synchronization: Hybrid interpolation algorithm: Within each slice of the O-type grid in the seawater section, the grid center and boundary points are selected as key nodes, and the spatial distribution of displacement and stress is calculated using Lagrange interpolation. Then, based on the node coordinates of the contact mechanics grid in the stratigraphic section, a Gaussian kernel function is used to map the interpolated parameters to the stratigraphic section grid, and the weighting coefficients are optimized using the least squares method. In the transition layer grid, the calculated interpolation error R = 8%, which does not exceed the threshold of 10%, so no adaptive grid refinement is required.

[0064] Adaptive transition layer mesh generation: A transition layer mesh is inserted at the mudline boundary. Through local refinement and mesh deformation techniques, a smooth transition between the seawater section and the stratigraphic section mesh is achieved. The local refinement area of ​​the transition layer mesh is 1m above and below the mudline boundary, with a refinement factor of 1.5.

[0065] Two-way coupled iterative calculation: The seawater segment calculation module performs calculations at each time step (time step size). After completing the numerical calculation at t = 0.01s, key dynamic parameters such as vortex-induced vibration amplitude and axial tension are transmitted to the formation section module. Upon receiving the data, the formation section module calculates the contact reaction force and feeds it back to the seawater section module to correct the drill string motion equations. At t = 10s, the contact reaction force calculated by the formation section is... =10000N. The motion equation of the seawater section is corrected based on this force. The motion equation is solved by the explicit time integration method (central difference method) to update the displacement and velocity of the drill string.

[0066] Drill string-formation coupling analysis of the formation section: Contact mechanics modeling: based on the eddy-induced vibration frequency transmitted in the seawater section =0.3Hz, =0.32Hz, calculate the correction amount for the friction coefficient: (at t = 10s) Dynamic friction coefficient

[0067] The dynamic contact force between the drill string and the wellbore is calculated using the Coulomb friction model combined with Hertzian contact theory. Normal contact force F n =20000 N Then friction The contact force was solved using the Newton-Raphson iterative method, and the convergence condition was met after 5 iterations.

[0068] Drill string-rock interaction analysis: A brittle rock fracture model is introduced to simulate the stress distribution and trajectory deviation of the drill string in the formation section during drill bit cutting. Drill bit cutting force F b =15000 N , formation reaction force F r=12000 N The dynamic equilibrium equations were solved iteratively using the finite element method, combined with an adaptive mesh refinement strategy. Local mesh refinement was performed in the drill bit-rock contact area, increasing the mesh count by 20%. Higher-order time integration methods (such as the Newmark method) were employed to ensure numerical stability during the computation. The stress distribution and trajectory offset of the drill string at t = 10s were calculated, with the maximum stress being... =100MPa, trajectory offset is =0.02m.

[0069] Global energy conservation verification and safety assessment: Energy balance verification: Calculate the input energy of the seawater section and the work done by the ocean current within t = 10s. =1,000,000 J. Calculate the dissipated energy and frictional energy of the formation. (Relative slip velocity v = 0.05 m / s), rock fracture energy Er = 20000 J (calculated based on the brittle fracture model), total dissipated energy W_{out} = E_{f} + E_{r} = 3000 + 20000 = 23000 J. Energy error is... Adjust the proportional coefficient of the transfer parameters (to 0.8 times the original value), recalculate, and continue until the energy error is less than 5%.

[0070] Dynamic safety early warning: Extract stress time history data at the mudline and drill bit connection, and calculate fatigue life based on Miner's linear cumulative damage theory. At t = 10s, the stress amplitude at the mudline... The number of cycles n1 = 1000, and the fatigue life of the material under this stress amplitude N1 = 10000 cycles; stress amplitude at the drill bit connection. Number of loops Next, the fatigue life of the material under this stress amplitude. Second-rate.

[0071] Calculate the fatigue damage index: At this point, the system is operating normally. If D exceeds 0.8, a parameter optimization command is triggered, such as reducing the drill string speed or adjusting the drilling fluid density.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for dynamic analysis of drill string in the extraction of natural gas hydrates without a riser, considering vortex-induced vibration, characterized in that, Includes the following steps: Based on the drill string geometry parameters and marine environment parameters, a dynamic model of the seawater section drill string was constructed, and vortex-induced vibration modeling of the seawater section drill string was performed based on the wake oscillator theory. The vibration amplitude and frequency of the seawater section drill string were calculated. At the same time, the ocean current force components of each fluid domain slice were calculated based on the Navier-Stokes equations, and the axial tension, torque and displacement time history data of the seawater section drill string were obtained. A parameter transfer interface is established at the mudline boundary. A hybrid interpolation algorithm is used to map the dynamic parameters of the O-type grid in the seawater section to the contact mechanics grid in the formation section. An adaptive transition layer grid is generated at the mudline boundary. At the same time, a two-way feedback channel is established at the mudline boundary to implement two-way coupled iterative calculation, so as to realize the dynamic synchronization and real-time update of the dynamic parameters of the seawater section and the formation section. A dynamic model of the drill string in the formation section is established based on the initial conditions of the transmission. The dynamic contact force between the drill string and the well wall in the formation section is calculated by using the Coulomb friction model combined with Hertz contact theory. The friction coefficient is dynamically adjusted according to the vortex-induced vibration frequency. A rock brittle fracture model is introduced to simulate the stress distribution and trajectory deviation of the drill string in the formation section during the drill bit cutting process. A comparative analysis of the energy input from the seawater section and the energy dissipated from the formation section is conducted. When the energy error exceeds a set threshold, the proportional coefficient of the transmission parameters is dynamically adjusted. The fatigue damage index of the drill string is calculated based on Miner's linear cumulative damage theory. When the fatigue damage index exceeds a set threshold, a parameter optimization command is triggered.

2. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 1, characterized in that, The specific process of vortex-induced vibration modeling is as follows: First, based on the wake oscillator theory, the seawater section of the drill string is divided into multiple independent fluid domain slices along the axial direction, and each slice is discretized using an O-type grid; then, the vortex shedding frequency of each slice is calculated using the Strauhal number relationship, and the wake oscillator equations are solved simultaneously to obtain the vibration amplitude and frequency of the seawater section of the drill string in the downstream and cross-flow directions; finally, based on the calculated vortex shedding frequency, the wake oscillator equations are constructed. The Strauhal number relation is as follows: ； In the formula, The angular frequency of vortex shedding; These are Strauhal numbers; Local ocean current velocity at the depth of each slice; The outer diameter of the drill string in the seawater section; The equation for the wake oscillator is: ； In the formula, This refers to the downstream vibration displacement of the drill string in the seawater section. This is the fluid damping coefficient; The coupling coefficient of the wake oscillator; This represents the downstream acceleration of the drill string in the seawater section.

3. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 2, characterized in that, The specific process of calculating the ocean current force components of each fluid domain slice based on the Navier-Stokes equations and obtaining the axial tension, torque and displacement time history data of the seawater section drill string is as follows: Based on the Navier-Stokes equations, the flow field around the seawater section drill string is numerically solved using computational fluid dynamics software to obtain the ocean current force components of each slice, including the distribution of axial force, radial force and torque, and the axial tension, torque and displacement time history data of the seawater section drill string are calculated in combination with the dynamic model of the seawater section drill string. The basic form of the Navier-Stokes equations is: ； In the formula, ρ For fluid density; u This is the velocity vector; t For time; p The pressure borne by the fluid element; μ For fluid dynamic viscosity; F It is an external force.

4. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 1, characterized in that, The specific process of the hybrid interpolation algorithm is as follows: First, the spatial distribution of key dynamic parameters is calculated in each slice of the O-type grid in the seawater section by Lagrange interpolation. Then, the interpolated key dynamic parameters are mapped to the nodes of the contact mechanics grid in the formation section using radial basis functions. At the same time, a residual feedback mechanism is introduced in the transition layer grid to correct errors.

5. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 4, characterized in that, The specific process for calculating the spatial distribution of key dynamic parameters in each slice of the O-type grid in the seawater section using Lagrange interpolation is as follows: Key nodes are selected within each fluid domain slice, including the grid center point and control points uniformly distributed along the boundary; displacement and stress information of each key node are calculated using fluid dynamics software to form a set of known data points for interpolation calculation; a polynomial interpolation function is constructed using the known data point set through the Lagrange interpolation method, ensuring that the interpolation function accurately matches the corresponding displacement and stress values ​​at each known data point, thus obtaining the spatial distribution of drill string displacement and stress within each slice of the O-type grid in the seawater section. The expression for the interpolation function is: ； In the formula, x The position to be interpolated; The coordinates of the known data points; For the physical quantity values ​​corresponding to known data points, the interpolation function is... The calculated value is the prediction result for the position to be interpolated.

6. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 5, characterized in that, The specific process of mapping the interpolated key dynamic parameters to the nodes of the formation section contact mechanics grid using radial basis functions is as follows: First, determine the coordinates of all nodes on the formation section contact mechanics grid. Simultaneously, extract the displacement and stress values ​​of the drill string in the seawater section from the O-type grid of the seawater section as input information for subsequent mapping. Second, establish an interpolation equation set using the Gaussian kernel function as the radial basis function, constructing a spatially continuous function to describe the distribution pattern of the known data points. Third, apply the constructed spatially continuous function to all target nodes of the formation section contact mechanics grid, calculating the displacement and stress values ​​of the drill string corresponding to each node in the formation section. Fourth, optimize the weighting coefficients using the least squares method to minimize the error between the mapped data and the original data.

7. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 6, characterized in that, The specific process of introducing a residual feedback mechanism into the transition layer mesh for error correction is as follows: Interpolation error is calculated in the transition layer mesh. Local interpolation error is calculated by comparing the interpolated displacement and stress values ​​with the reference values. ； In the formula, The value obtained from interpolation; For reference only; If local interpolation error R If the set threshold is exceeded, adaptive mesh refinement is triggered, adding computing nodes in areas with large errors and re-performing interpolation calculations.

8. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 7, characterized in that, The specific process of the bidirectional coupled iterative calculation is as follows: First, after the calculation is completed at each time step, the key dynamic parameters of the seawater section drill string are extracted, including the vibration amplitude, downstream vibration displacement and axial tension of the seawater section drill string. These data are then packaged into a standardized format and transmitted to the formation section drill string dynamic model in real time. Then, after receiving the data transmitted from the seawater section, the formation section drill string calculates the dynamic contact force between the formation section drill string and the well wall at that time step, and feeds it back to the seawater section drill string dynamic model, based on the current contact state between the formation section drill string and the well wall. The contact reaction force received in the seawater section is treated as an external load term and added to the drill string dynamics model of the seawater section, resulting in the modified drill string dynamics model of the seawater section: ； in, Forces acting on fluids; The mass matrix of the drill string in the seawater section; The damping matrix of the drill string in the seawater section; Here is the stiffness matrix of the drill string in the seawater section; x This represents the displacement vector of the drill string in the seawater section after correction for external loads.

9. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 8, characterized in that, The comparison and analysis of the input energy in the seawater section and the dissipated energy in the formation section, and the dynamic adjustment of the proportional coefficient of the transmission parameters when the energy error exceeds the set threshold, specifically involves: comparing and analyzing the input energy in the seawater section and the dissipated energy in the formation section to ensure overall energy conservation; when the energy error exceeds 5%, dynamically adjusting the proportional coefficient of the key power parameters until the energy error is less than 5%; The energy input in the seawater section is calculated from the work done by the ocean current on the drill string in the seawater section, mainly including the energy input caused by axial tension and vortex-induced vibration; the energy dissipated in the formation section includes frictional energy loss and energy consumption generated during rock fracturing, and the frictional energy loss is calculated using the following formula: ； In the formula, E f This is due to frictional energy loss; F f Friction; v This represents the relative slip velocity.

10. The method for dynamic analysis of drill string for extracting natural gas hydrates without a riser according to claim 9, characterized in that, The calculation of the drill string fatigue damage index based on Miner's linear cumulative damage theory specifically involves: extracting stress time history data at the mudline and drill bit connection, calculating the drill string fatigue damage index D based on Miner's linear cumulative damage theory, and triggering a parameter optimization command when D exceeds 0.

8. The parameter optimization command includes reducing the drill string rotation speed or adjusting the drilling fluid density. The expression for Miner's linear cumulative damage theory is as follows: ； In the formula, D The fatigue damage index of the drill string; This represents the number of loop iterations. This refers to the fatigue life of a material under a specific stress amplitude.

Images