A parametric response experimental method for a coupled system of offshore platform-riser-subsea wellhead

Abstract

This invention provides an experimental method for the parametric response of a coupled system of an offshore platform-riser-subsea wellhead, belonging to the technical field of riser systems. This method uses the configuration parameters of an actual offshore drilling riser system as a basis, and determines the parameters of the similarity ratio, model material, and structural dimensions based on similarity theory and truncation design theory. The various devices are fastened together using flanges and bolts. The heave amplitude and frequency of the six-degree-of-freedom excitation platform and the drilling fluid circulation device are adjusted to control the drilling fluid flow rate and pressure within the riser string. Multiple sets of metal strain gauges are attached to different positions on the riser string, and a three-part force meter is installed at the top and bottom of the riser system. By analyzing and processing the collected data, this method can solve the problem of unclear mechanisms affecting the parametric excitation vibration of the pressure-controlled drilling riser coupled system under complex loads.

Description

Technical Field

[0001] This invention belongs to the technical field of riser systems, and more specifically, relates to a parametric response experimental method for a coupled system of offshore platform-riser-subsea wellhead. Background Technology

[0002] As onshore oil and gas resource extraction becomes increasingly challenging, oil and gas development is gradually shifting towards deep-sea and ultra-deep-sea areas to meet the growing energy demand. Unlike onshore drilling, deep-water drilling involves a smaller gap between formation pressure and fracture pressure, a narrower safe density window for drilling operations, greater difficulty in wellbore pressure control, and frequent occurrences of complex downhole situations such as overflows and leaks. This leads to extended non-productive time, increased drilling costs, and a higher risk of major safety accidents such as blowouts, polluting the marine environment and endangering the personal safety of workers. To address the problem of well control in deep-water formations with narrow density windows, Managed Pressure Drilling (MPD) technology is a crucial technology for achieving safe and efficient drilling in deep and ultra-deep water. Its core involves real-time monitoring and precise control of bottom hole pressure through MPD high-pressure riser devices, deck pressure control equipment, and back pressure control pipelines. By adjusting back pressure within the tubing string and regulating drilling fluid flow rate, the bottom hole pressure is maintained within the safe density window, ensuring efficient and safe deep-water drilling operations.

[0003] Research has revealed that significant progress has been made in the basic theoretical research and practical application of controlled pressure drilling (MPD) technology both domestically and internationally. However, there are few reports on the parametric vibration response analysis of the tubing system in the offshore platform-riseer-subsea wellhead coupling system under the combined effects of drilling platform heave, high pressure inside the tubing, and drilling fluid velocity. The load on the controlled pressure drilling riser coupling system is more complex than that on a conventional drilling riser system. Summary of the Invention

[0004] In view of this, the present invention provides a parametric excitation response experimental method for a coupled system of offshore platform-riseer-subsea wellhead, which can solve the problem of unclear mechanism of influence of parameter excitation vibration on the coupled system of pressure-controlled drilling riser under complex loads.

[0005] This invention is implemented as follows:

[0006] This invention provides a parametric response experimental method for a coupled system of an offshore platform-riser-subsea wellhead, comprising the following specific steps:

[0007] S10: This experimental method is truly close to actual operations, selecting the configuration of an actual offshore drilling riser system as the basis. However, due to the large size of the actual offshore drilling riser system and limitations imposed by experimental conditions and site, a similarity-scaled experimental study is necessary. Appropriate similarity criteria are selected based on the specific experimental requirements and the experimental object. In this experiment, the primary consideration is the parametrically excited lateral vibration response of the coupled system of the offshore platform-riser-subsea wellhead; therefore, geometric similarity, Cauchy similarity, and Froude similarity criteria are prioritized. Since the scaled-down model still far exceeds the scale of the experimental pool, to meet experimental requirements, the equivalent water depth truncation design theory is adopted. That is, after scaling down according to similarity theory, the boundary motion conditions of the truncation point are applied to the top of the experimental model based on the maximum experimental water depth requirement.

[0008] Among them, the geometric similarity criterion is:

[0009] Cauchy's similarity criterion:

[0010] Froude's similarity criterion:

[0011] In the formula: λ represents the scaling ratio, the subscripts s and m represent the physical model and the scaled-down model, respectively; L represents the model length, B represents the model width; ρ represents the model fluid density, V represents the model characteristic velocity, E represents the model elastic modulus; and g is the gravitational acceleration.

[0012] Based on the scaling relationships between various physical quantities, the model material (in this experimental method, the actual riser material is X80 steel with an elastic modulus E = 210 GPa; based on the determined scaling ratio, the final material is copper with an elastic modulus of 108 GPa, mainly to complete the design of the bending stiffness of the scaled model; the corresponding duct scaled model is selected as aluminum alloy material), structural dimensions (including length, mass, inner and outer diameters of the pipe column, bending stiffness, etc.), and other important parameters are determined to complete the design of each component of the experimental device; the correction coefficient γ in the table represents the ratio of seawater density to freshwater density, generally γ = 1.025.

[0013] Table 1: Relationship between scale conversions of physical quantities

[0014]

[0015] S20: The various devices are fastened together using flanges and bolts;

[0016] S30: After the entire apparatus is installed, design the required internal pressure value of the tubular column according to the pressure scaling conversion relationship determined in the table, specifically: The corresponding drilling fluid flow rate value is the actual drilling operation condition. The design of the parametric test operation condition is completed. The drilling fluid flow rate and pressure in the riser string are controlled by adjusting the heave amplitude and frequency of the six-degree-of-freedom excitation platform and adjusting the drilling fluid circulation device, so as to simulate the parametric vibration during actual marine riser pressure control drilling operations.

[0017] The heave amplitude of the six-degree-of-freedom excitation platform is calculated according to the requirements:

[0018]

[0019] In the formula, S represents the amplitude displacement of heave, m; s1 is the initial displacement, m; and ω is the frequency of the amplitude displacement, rad / s.

[0020] S40: By attaching multiple sets of metal strain gauges at different positions of the riser string, and installing a three-part force meter at the top and bottom of the riser system, real-time acquisition of experimental data on the para-stress response of the riser system under different platform heave amplitudes and frequencies, as well as different drilling fluid flow rates and pressures is achieved.

[0021] S50: By analyzing and processing the collected data, modal vibration analysis, parametric vibration displacement analysis, and tubing axial force analysis of the coupled system of offshore platform-riseer-subsea wellhead are completed under parameter excitation.

[0022] The overall experimental setup is designed and manufactured using similarity theory and truncation design theory to determine important parameters such as similarity ratio, material of scaled-down experimental model, and structural dimensions. The overall experimental setup includes a six-degree-of-freedom excitation platform, tensioner model, expansion joint device, upper flexible joint, riser system, lower flexible joint, blowout preventer assembly, guide string model, subsea wellhead system, drilling fluid circulation device, three-part force meter testing device, stress-strain acquisition instrument, acquisition card, and data transmission pipeline. All devices are fastened together using flanges and bolts.

[0023] Based on the above technical solution, the experimental method for parametric response of a coupled system of offshore platform-riser-subsea wellhead according to the present invention can be further improved as follows:

[0024] Before conducting the parametric excitation response experiment, the natural frequencies of the diaphragm coupling system were first measured through multiple sets of impact experiments to determine the required platform excitation frequency range for parametric excitation vibration. The specific steps are as follows:

[0025] A fixed force is applied to the riser column, causing the riser system to undergo free decay motion, while strain data is collected in real time on a computer.

[0026] Furthermore, during the impact test, a drilling fluid circulation device was used to select different pressures and drilling fluid flow rates to simulate the changes in pressure and flow rate inside the riser string during actual controlled pressure drilling operations, so as to measure the natural frequency of the riser string when the inside of the string is filled with high pressure and high drilling fluid flow rate.

[0027] Furthermore, the strain signal collected in the impact experiment is a time-domain sinusoidal response signal. Using MATLAB software, it is transformed into a frequency-domain signal through Fourier transform. The frequency value corresponding to the sudden change in vibration amplitude after Fourier transform is extracted, that is, the frequency of modal vibration during the free decay process of the riser string after impact is obtained, and the data is recorded to complete the natural frequency analysis of the offshore platform-riser-subsea wellhead coupling system.

[0028] The main formula for the Fourier transform is:

[0029] Assuming the stress-strain signal has a period of T, find the corresponding angular frequency. According to the Fourier transform formula, the stress-strain periodic signal can be expressed as:

[0030]

[0031] In the formula A n a n b n These are the Fourier transform coefficients;

[0032]

[0033] Signal data acquisition and presentation are generally divided into two types: time-domain signals and frequency-domain signals. These two signal storage types are essentially the same; they simply interpret the actual meaning of the signal from different perspectives.

[0034] The time-domain sinusoidal response signal is a signal that changes with time. For natural frequency analysis, it is necessary to transform the time-domain response signal into the frequency-domain response signal to understand the amplitude signal change caused by the corresponding frequency.

[0035] Furthermore, the specific steps for controlling the drilling fluid flow rate and pressure within the riser string by adjusting the heave amplitude and frequency of the six-degree-of-freedom excitation platform and adjusting the drilling fluid circulation device to simulate the parametric vibration during actual marine riser pressure control drilling operations are as follows:

[0036] The first step is to use a drilling fluid circulation device to change the pressure inside the riser string and the flow rate of the drilling fluid to simulate actual pressure-controlled drilling operations.

[0037] The second step is to adjust the heave amplitude and heave frequency of the six-degree-of-freedom excitation platform based on the multiple relationship between the excitation frequency of the parametric excitation vibration and the natural frequency of the tubular coupling system.

[0038] The third step involves changing the heave amplitude and frequency of the six-degree-of-freedom excitation platform and adjusting the internal pressure and drilling fluid velocity of the tubing string through the drilling fluid circulation device. This completes the excitation vibration response analysis of the deep-water controlled-pressure drilling riser coupling system under different riser string pressures and drilling fluid velocities. A stress-strain device is used to collect the excitation vibration response data of the riser coupling system in real time.

[0039] Different platform heave amplitudes and frequencies will change the effective axial tension of the tubing string. Changes in the effective axial tension parameters will cause lateral vibration of the riser, which is the parameter-excited vibration of the deepwater drilling riser system.

[0040] Furthermore, the lateral vibration caused by the change in the effective axial tension parameter of the riser string is the parameter-excited vibration of the deepwater drilling riser system.

[0041] Furthermore, the three-part force meter device is a resistance strain gauge sensor, and its axial direction needs to be calibrated before the experiment to ensure the accuracy of the collected data.

[0042] The three-component force meter testing device used can simultaneously measure the full force information in space (Cartesian coordinate system), namely, three force components and three torque components. In this experiment, a three-component force meter device was installed at the top of the tensioner experimental model and the riser experimental model, and at the contact point between the bottom of the riser experimental model and the BOP experimental model, to measure the variation law of effective axial tension under the excitation vibration of the offshore platform-riser-subsea wellhead coupled system parameters.

[0043] The three-part force meter device can be a three-part force sensor with a range of ±3000 kg in the axial direction, ±1000 kg in the transverse and longitudinal directions, and a measurement error of 0.6-1.2 kg.

[0044] The calibration formula for the three-part force apparatus used in this experimental method is as follows:

[0045] F1 = -5843.15·ε + 12.46;

[0046] F2 = -5328.65·ε - 5.24;

[0047] Where F represents the calculated axial force in N; ε is the resistance strain signal measured by the three-part force meter.

[0048] Furthermore, regarding the lateral force on the riser pipe column, the experiment utilizes a spring installed in the middle of the riser pipe to provide an approximate static lateral load, in order to simulate the actual lateral external loads such as ocean currents experienced by the riser system under actual marine conditions. Based on the magnitude of the lateral force required by the experiment, the spring stiffness and length are designed to meet the required lateral static load.

[0049] The calculation formula for the design of springs under lateral static loads is as follows:

[0050] F = K·x;

[0051]

[0052] In the formula, F represents the required lateral static load force, N; x is the spring elongation, m; K is the elastic stiffness of the spring, N / m; G is the shear modulus of the spring material; d is the spring wire diameter, m; d1 is the spring mean diameter, m; and n is the effective number of coils of the spring.

[0053] Furthermore, the specific steps for analyzing and processing the collected data are as follows:

[0054] First, a low-pass Chebyshev Type I filter is performed. Based on different data signals, appropriate cutoff frequency, sampling frequency, and filter order are selected to eliminate data errors caused by noise or other experimental errors, improve analysis accuracy, separate useful signals from noise, and obtain a sinusoidal periodic function with good linearity and waveform.

[0055] Furthermore, the specific steps for completing the modal vibration analysis, parametric vibration displacement analysis, and tubing axial force analysis under parametric excitation of the offshore platform-riseer-subsea wellhead coupled system include:

[0056] After filtering the data collected from various measuring points under different working conditions, Fourier transform was performed. The signal change during parametric vibration was determined by using the multiple relationship between the excitation frequency of the parameters and the natural frequency of the system when the coupled system of the offshore platform-riseer-subsea wellhead under parametric vibration. The nodal bending moment M was calculated from the strain value measured in the experiment. The bending moment value at the measuring point was fitted with a sixth-order polynomial using MATLAB software to obtain the function M(z) of the bending moment as a function of the coupled system position. The displacement distribution function y(z) of the coupled system was obtained by performing a quadratic integral on M(z) using MATLAB program.

[0057]

[0058] In the formula, M is the bending moment at the measuring point, N·m; ε is the bending stress at the section, dimensionless; R is the radius of the column in the scaled-down experimental model, m; and EI is the bending stiffness, N·m. 2 ; y(z) is the system displacement distribution function, m.

[0059] In this experiment, the DH3817F strain acquisition system was used to acquire parametric vibration stress and strain data of the coupled system of offshore platform-riselet-subsea wellhead. This included the acquisition drive software system and the acquisition system chassis. The acquisition system chassis has 16 signal channels, so 16 sets of metal strain gauges were attached to the guide tube and riser string. The strain gauges were attached densely to the guide tube, near the wellhead, and at the top of the riser, as stress concentration is more likely to occur in these areas from a theoretical analysis perspective. Before each experiment, each channel was zeroed out to ensure the accuracy of the acquired data.

[0060] The metal strain gauges are attached to different positions on the guide tube and riser model using a half-bridge method. Since the entire device is installed in a water tank to simulate the marine environment, the metal strain gauges are protected with waterproof adhesive to prevent failure. The metal strain gauges are connected to the stress-strain acquisition system via signal input lines to complete the acquisition of stress-strain data of the excitation vibration response of the offshore platform-riser-subsea wellhead coupling system.

[0061] Compared with existing technologies, the beneficial effects of the parametric vibration response experimental method for a coupled system of offshore platform-riseer-subsea wellhead provided by this invention are as follows: First, based on the configuration parameters of an actual offshore drilling riser system, and based on similarity theory and truncation design theory, important parameters such as the similarity ratio of the scaled experiment, model material, and structural dimensions are determined. The design of each component of the experimental device is then completed, and the devices are fastened together using flanges and bolts. After the overall device is installed, the parametric vibration response law of the pressure-controlled drilling riser coupled system during actual offshore drilling operations is studied by changing the heave amplitude and frequency of the six-degree-of-freedom excitation platform and by using a drilling fluid circulation device to change multiple variable parameters such as the pressure inside the pipe and the drilling fluid flow rate. This experimental research method simultaneously considers multiple loads such as platform heave motion, high pressure inside the pipe, and drilling fluid flow rate, as well as the coupling interaction between the various components of the offshore platform-riseer-subsea wellhead system, providing a reference for safe operation of deep-water pressure-controlled drilling risers. Attached Figure Description

[0062] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0063] Figure 1 A schematic diagram of the parametric response experimental model of the coupled system of offshore platform-riser-subsea wellhead.

[0064] Figure 2 This is a flowchart of the experimental analysis method for the parametric response of the offshore platform-riser-subsea wellhead coupling system of the present invention;

[0065] The attached diagram lists the components represented by each number as follows:

[0066] 1. Six-degree-of-freedom excitation platform; 2. Tensioner system; 3. Upper flexible joint; 4. Expansion joint device; 5. First three-part force gauge testing device; 6. Metal strain gauge; 7. Riser system model; 8. Spring; 9. Lower flexible joint; 10. Second three-part force gauge testing device; 11. Blowout preventer assembly; 12. Conduit model; 13. Subsea wellhead device; 14. Drilling fluid circulation device; 15. High-pressure water pump; 16. Flow meter device; 17. Pressure metering device; 18. Stress-strain acquisition system; 19. Signal input line. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0068] like Figure 2 The image shown is a first embodiment of a parametric response experimental method for a coupled system of an offshore platform-riser-subsea wellhead provided by the present invention. This embodiment includes the following specific steps:

[0069] S10: Based on the configuration parameters of the actual marine drilling riser system, and based on similarity theory and truncation design theory, determine the parameters of the similarity ratio, model material, and structural dimensions for the scaled-down experiment, and complete the design of each component of the experimental device.

[0070] S20: The various devices are fastened together using flanges and bolts;

[0071] S30: After the overall device is installed, the drilling fluid flow rate and pressure in the riser string are controlled by adjusting the heave amplitude and frequency of the six-degree-of-freedom excitation platform and the drilling fluid circulation device, so as to simulate the para-excited vibration during actual marine riser pressure control drilling operations.

[0072] S40: By attaching multiple sets of metal strain gauges at different positions of the riser string, and installing a three-part force meter at the top and bottom of the riser system, real-time acquisition of experimental data on the para-stress response of the riser system under different platform heave amplitudes and frequencies, as well as different drilling fluid flow rates and pressures is achieved.

[0073] S50: By analyzing and processing the collected data, modal vibration analysis, parametric vibration displacement analysis, and tubing axial force analysis of the coupled system of offshore platform-riseer-subsea wellhead are completed under parameter excitation.

[0074] Parallel-excited vibration (PEV) is a special form of vibration. The external excitation for PEV is not applied to the system as an external force, but rather indirectly achieved through the periodic changes in the system's internal parameters. Due to the platform's heave motion, the axial force on the tubing varies with the platform's movement, causing changes in the stiffness of the riser system, resulting in PEV in the horizontal direction. Resonance occurs when the external excitation frequency is close to or a multiple of the system's natural frequency. While the amplitude-frequency response curve for ordinary resonance is a series of scattered points, PEV occurs across a range of regions. Even if the excitation frequency is far from the natural frequency, PEV will occur if the parameter excitation falls into the unstable region, making it more difficult to avoid. For deep-sea marine structural systems, with increasing water depth and complex service environments, PEV is highly susceptible to occur, leading to tubing failure and fluid leakage, causing significant economic losses and environmental pollution.

[0075] Among them, such as Figure 1 As shown, the model device includes various devices used in marine controlled pressure drilling riser operations, including a six-degree-of-freedom excitation platform 1, a tensioner system 2, an upper flexible joint 3, an expansion joint device 4, a riser system model 7, a lower flexible joint 9, a blowout preventer assembly 11, a guide tube model 12, a subsea wellhead device 13, a drilling fluid circulation device 14, a first three-part force meter testing device 5, a second three-part force meter testing device 10, and a stress and strain acquisition device 18;

[0076] The six-degree-of-freedom excitation platform 1 simulates an actual offshore drilling platform. Certain amplitude and frequency parameters are set for the platform to realize the platform's heave and sag operations under ocean currents and waves. A real-time displacement response excitation is given to the top of the riser, causing the axial force of the riser system 7 to change with the platform's heave and sag motion. This excitation has a significant impact on the lateral vibration of the riser system 7.

[0077] The top of the riser system model 7 is connected to the main body of the six-degree-of-freedom excitation platform 1 via tensioner 2. Tensioner model 2 is connected to flexible joint 3 and expansion joint 4. In the experiment, expansion joint 4 is simplified to a spring device. During the platform's heave motion, the heave compensation device is a very important device. Large heave displacement will cause the flexible joint to rotate too much and the riser system to bend excessively, resulting in failure or even breakage. The six-degree-of-freedom excitation platform 1 transmits the tension force to the expansion joint 4 and then to the riser system 7 through tensioner 2. When the platform heaves, the expansion joint 4 can provide a real-time changing tension force to the top of the riser while compensating for a certain displacement, thus converting the displacement excitation of the platform into force excitation, so that the axial force of the riser system 7 changes in real time with the platform's heave motion.

[0078] After the design of each component in the experiment is completed, the material, number of coils, wire diameter, and center diameter of the expansion joint device 4 are set according to the weight of the overall device and the requirements for heave displacement to determine the stiffness and length requirements of the expansion joint model 4.

[0079] The drilling fluid circulation device 14 injects drilling fluid into the riser string 7 through a high-pressure water pump 15 to simulate the circulation process of drilling fluid during actual drilling operations. The flow meter 16 and pressure meter 17 are used to monitor the high pressure and drilling fluid flow rate in the pipe in real time to match the actual marine pressure controlled drilling operation. The high-pressure water pump 15, flow meter 16 and pressure meter 17 are designed according to the experimental requirements to meet the experimental requirements.

[0080] Among them, the first three-part force meter testing device 5 can complete the real-time measurement of the effective axial tension of the offshore platform-riseer-subsea wellhead coupling system under different platform heave amplitudes and frequencies, as well as under high pressure and drilling fluid flow rate in the pipe, to observe the parametric excitation vibration response caused by the pipe string under different axial tensions, and at the same time obtain the variation law of the axial force of the pipe string under the action of high pressure and drilling fluid flow rate in the pipe.

[0081] The metal strain gauge 6 is attached to different positions on the guide tube and riser model using a half-bridge method. Since the entire device is installed in a water tank to simulate the marine environment, the metal strain gauge is protected with waterproof adhesive to prevent failure. The metal strain gauge 6 is connected to the stress-strain acquisition system 18 via signal input line 19 to complete the acquisition of stress-strain data of the excitation vibration response of the marine platform-riser-subsea wellhead coupling system.

[0082] like Figure 2 In this experiment, the DH3817F strain acquisition system was used to acquire parametric vibration stress and strain data of the coupled system of offshore platform-rise manifold-subsea wellhead. This included the acquisition drive software system and the acquisition system chassis. The acquisition system chassis has 16 signal channels, so 16 sets of metal strain gauges were attached to the guide tube and riser string. The strain gauges were attached more densely to the guide tube, near the wellhead, and at the top of the riser, as stress concentration is more likely to occur in these areas from a theoretical analysis perspective. In addition, each channel was zeroed out before each experiment to ensure the accuracy of the data acquisition.

[0083] The experiment mainly studies the vibration response analysis of the high-pressure riser under the heave of the platform. The six-degree-of-freedom excitation platform 1 is used to simulate the longitudinal heave excitation. For the lateral force of the riser, a spring 8 is used at approximately the middle of the riser to provide an approximate static lateral load, simulating the actual lateral external loads such as ocean currents experienced by the riser system in actual marine conditions. The stiffness and length of the spring are designed according to the magnitude of the lateral force required by the experiment to meet the required lateral static load.

[0084] Figure 2 In data processing, due to experimental errors such as the vibration of the six-degree-of-freedom excitation platform, irregular water flow in the water tank, and interference from the transmission line, the measured parameter excitation vibration strain response data fluctuates. However, the waveform exhibits a sinusoidal function pattern consistent with the platform's motion period. Therefore, to ensure the accuracy of the experiment, low-pass Chebyshev Type I filtering is performed before data analysis. By reasonably adjusting the cutoff frequency, sampling frequency, and filter order, data errors caused by noise or other experimental errors are eliminated, improving the analysis accuracy and separating useful signals from noise. A sinusoidal periodic function with good linearity and waveform is obtained.

[0085] Figure 2 Before conducting parametric excitation vibration response, the natural frequency of the system is first determined. A knocking vibration experiment of the offshore platform-riser-subsea wellhead coupled system is carried out to determine the overall natural frequency of the system.

[0086] After the experimental setup for the offshore platform-riser-subsea wellhead coupling system was completed, the natural frequencies of the riser coupling system were first measured through multiple sets of impact tests to determine the platform excitation frequency range required for parametric excitation vibration. A fixed force was applied to the riser string, causing the riser system to undergo free decay motion, while strain data was recorded and acquired in real time on a computer. During the impact tests, drilling fluid circulation device 14 was used to simulate the changes in pressure and velocity within the riser string during actual controlled-pressure drilling operations by selecting different pressures and drilling fluid flow rates. This allowed for the measurement of the riser's natural frequencies when the string was filled with high pressure and high drilling fluid velocity.

[0087] Figure 2The test data obtained from the impact experiment on the offshore platform-riser-subsea wellhead coupling system includes strain data. Signal data acquisition is generally presented in two formats: time-domain and frequency-domain. These two signal storage types are essentially the same, only interpreting the actual meaning of the signal from different perspectives. The strain signal acquired in the impact experiment is a time-domain sinusoidal response signal, which changes over time. For natural frequency analysis, it is necessary to transform the time-domain response signal into a frequency-domain response signal to understand the amplitude signal change caused by the corresponding frequency. The stress-strain time-domain response signal measured in the impact experiment is transformed into a frequency-domain signal through Fourier transform. The frequency value corresponding to the sudden change in vibration amplitude after Fourier transform is extracted, i.e., the frequency of modal vibration during the free decay process of the tubing after impact. This data is recorded to complete the natural frequency analysis of the offshore platform-riser-subsea wellhead coupling system.

[0088] Figure 2 Based on the measured natural frequency of the offshore platform-riseer-subsea wellhead coupling system, a parametric vibration response experiment of the offshore platform-riseer-subsea wellhead coupling system was conducted. The drilling fluid circulation device 14 was used to change the pressure and drilling fluid flow rate in the high-pressure tubing to simulate actual pressure-controlled drilling operations. The heave amplitude and frequency of the six-degree-of-freedom excitation platform 1 were adjusted according to the multiple relationship between the excitation frequency when parametric excitation vibration occurs and the natural frequency of the tubing coupling system. Different platform heave amplitudes and frequencies alter the effective axial tension of the tubing string. Changes in the effective axial tension parameter cause lateral vibration of the riser, which is the parameter-excited vibration of the deep-water drilling riser system. In the experiment, the parameter-excited vibration response analysis of the deep-water controlled-pressure drilling riser coupling system under different tubing string pressures and drilling fluid velocities was completed by changing the heave amplitude and frequency of the six-degree-of-freedom excitation platform 1 and by adjusting the internal pressure and drilling fluid flow rate of the drilling fluid circulation device 14. The stress-strain acquisition system 18 was used to collect the parameter-excited vibration response data of the controlled-pressure drilling riser coupling system in real time.

[0089] This invention comprehensively considers the parametric excitation vibration response analysis under the combined effects of platform heave motion, high pressure inside the pipe, and drilling fluid flow velocity. A six-degree-of-freedom platform excitation device 1 is used to achieve heave excitation, while a drilling fluid circulation device 14 is used to change the high pressure inside the pipe and the drilling fluid flow velocity to simulate actual offshore controlled pressure drilling operations. The parametric excitation vibration response analysis of the offshore platform-riseer-subsea wellhead coupled system is considered under the influence of multiple factors. Simultaneously, the first three-part force meter testing device 5 and the second three-part force meter testing device 10 are used to measure in real time the influence of any factor on the axial force of the pipe string caused by changes in platform heave amplitude, heave frequency, high pressure inside the pipe, and drilling fluid flow velocity. This invention more closely reflects actual operating conditions. Furthermore, high-precision testing devices are used to complete data acquisition, enabling modal analysis, parametric excitation vibration displacement analysis, and pipe string axial tension analysis under parametric excitation vibration of the coupled system, providing a theoretical reference for deepwater controlled pressure drilling riser operations.

[0090] Specifically, the principle of this invention is as follows: During use, based on the configuration parameters of an actual offshore drilling riser system, and using similarity theory and truncation design theory, the parameters of the similarity ratio for the scaled experiment, model material, and structural dimensions are determined to complete the design of each component of the experimental device. Each device is fastened together using flanges and bolts. After the overall device is installed, the drilling fluid velocity and pressure within the riser string are controlled by adjusting the heave amplitude and frequency of the six-degree-of-freedom excitation platform and adjusting the drilling fluid circulation device to simulate the parametric vibration during actual offshore riser pressure control drilling operations. Multiple sets of metal strain gauges are attached to different positions on the riser string, and a three-part force meter is installed at the top and bottom of the riser system to collect real-time experimental data on the parametric response of the riser system under different platform heave amplitudes and frequencies, as well as different drilling fluid velocities and pressures. By analyzing and processing the collected data, modal analysis, parametric vibration displacement analysis, and axial force analysis of the string are completed under the parametric excitation of the offshore platform-riser-subsea wellhead coupled system.

Claims

1. A parametric response experimental method for a coupled system of offshore platform-riser-subsea wellhead, characterized in that, The method comprises the following specific steps: S10: Based on the similar theory and the truncation design theory, the scale experiment similarity ratio, the model material, and the structural size parameters are determined according to the actual marine drilling riser system configuration parameters, and the design of each component of the experimental device is completed; the equivalent water depth truncation design theory is adopted, that is, according to the similarity theory after scaling, the boundary motion condition of the truncation point is applied to the top of the experimental model according to the maximum experimental water depth requirement; S20: The experimental device comprises a six-degree-of-freedom excitation platform (1), a tensioner system (2), an upper flexible joint (3), an expansion joint device (4), a riser system model (7), a lower flexible joint (9), a blowout preventer group (11), a guide pipe model (12), an underwater wellhead device (13), a drilling fluid circulating device (14), and a first three-component force instrument testing device (5), a second three-component force instrument testing device (10), and a stress-strain acquisition device (18); the devices are fastened and connected through flanges and bolts; the riser system model (7) is connected to the main body of the six-degree-of-freedom excitation platform (1) through the tensioner system (2) at the top, and the tensioner system (2) is connected to the expansion joint device (4) through the upper flexible joint (3); the six-degree-of-freedom excitation platform (1) transmits the tensioning force to the expansion joint device (4) and then to the riser system model (7) through the tensioner system (2), so that the expansion joint device (4) provides a real-time changing tensioning force to the top of the riser while compensating for a certain displacement when the platform heaves, the displacement excitation of the platform is converted into force excitation, and the axial force of the riser system model (7) changes in real time with the heaving motion of the platform; S30: After the overall device is installed, the heave amplitude and frequency of the six-degree-of-freedom excitation platform and the drilling fluid circulating device are adjusted to control the flow rate and pressure of the drilling fluid in the riser string, so as to simulate parametrically excited vibration in actual marine riser managed pressure drilling operations; the heave amplitude of the six-degree-of-freedom excitation platform ; in the formula, the heave amplitude displacement is m; the initial displacement is m; the heave amplitude frequency is ; The specific steps comprise: Firstly, the drilling fluid circulating device is used to change the internal pressure and the flow rate of the drilling fluid of the riser string, and the actual managed pressure drilling operation is simulated; Secondly, the heave amplitude and the heave frequency of the six-degree-of-freedom excitation platform are adjusted according to the multiple relationship between the excitation frequency of the parameter excitation vibration and the natural frequency of the pipe string coupling system; Thirdly, the heave amplitude and the frequency of the six-degree-of-freedom excitation platform are changed, and the internal pressure and the flow rate of the drilling fluid are adjusted through the drilling fluid circulating device, the parameter excitation vibration response analysis of the deepwater managed pressure drilling riser coupling system under different riser string pressures and drilling fluid flow rates is completed, and the stress-strain device is used to collect the parameter excitation vibration response data of the riser coupling system in real time; S40: A plurality of groups of metal strain gauges are pasted at different positions of the riser string, a three-component force instrument device is installed at the top and the bottom of the riser system respectively, and the real-time collection of the parameter excitation response experimental analysis data of the riser system under different platform heave amplitudes and frequencies and different drilling fluid flow rates and pressures is completed. S50: The collected data is analyzed and processed, first low-pass Chebyshev I filter processing is performed, according to different data signals, appropriate cut-off frequency, sampling frequency and filter order are selected, data errors caused by noise or other experimental errors are excluded, analysis accuracy is improved, useful signals and noise are separated, analysis accuracy is improved, linear and waveform good sinusoidal periodic function is obtained; modal shape analysis, parametric vibration displacement analysis and pipe string axial force analysis of the offshore platform-riser-underwater wellhead coupling system under parametric excitation are completed, the data collected by different working conditions of each measuring point are filtered and Fourier transformed, the multiple relationship between the parametric excitation frequency and the natural frequency of the system when the offshore platform-riser-underwater wellhead coupling system occurs parametric vibration is used to determine the signal change when parametric vibration occurs; the bending moment of the node is calculated from the strain value measured in the experiment, the bending moment value of the measuring point is obtained by using the sixth polynomial fitting method to obtain the function of the bending moment with the change of the position of the coupling system by using MATLAB software, and the distribution function of the displacement of the coupling system is obtained by using MATLAB program for secondary integration calculation; ； ； where M is the measured point bending moment, ; is the bending strain value at the cross section, dimensionless; R is the scaled experimental model pipe string radius, m; EI is the bending stiffness, ; y(z) is the system displacement distribution function, m.

2. The method according to claim 1, wherein, Before the parametric response experiment, the natural frequency of the riser coupling system is measured through a plurality of knocking experiments to determine the required platform excitation frequency range when parametric excitation vibration occurs, the specific steps are as follows: The fixed force is used to knock on the riser string, the riser system is in free decay motion, and the strain data is collected in real time on the computer.

3. The method according to claim 2, wherein, During the knocking test, the drilling fluid circulating device is used to select different pressure and drilling fluid flow rate values to simulate the change of the internal pressure and flow rate of the riser string in the actual managed pressure drilling operation process, so as to measure the natural frequency of the riser string corresponding to the high pressure and high drilling fluid flow rate in the pipe string.

4. The method according to claim 3, wherein, The strain signal collected in the knocking experiment is a time domain sinusoidal response signal, which is converted into a frequency domain signal by using MATLAB software through Fourier transform, the frequency value corresponding to the sudden change of the vibration amplitude after Fourier transform is extracted, that is, the frequency of the modal vibration of the riser string during the free decay process after the knocking is completed, and the data is recorded, and the natural frequency analysis of the offshore platform-riser-underwater wellhead coupling system is completed.

5. The method according to claim 4, wherein, The transverse vibration caused by the change of the effective axial tension parameter of the riser string is the parametric excitation vibration of the deepwater drilling riser system.

6. The method according to claim 5, wherein, The three-component instrument device is a resistance strain sensor, and the axial direction needs to be calibrated before the experiment, that is, the quantitative relationship between the measured value and the force is determined to ensure the accuracy of the collected data.

7. The method according to claim 6, wherein, For the transverse force of the riser string, the spring installed in the middle position of the riser is used to provide transverse approximate static load in the experiment to simulate the transverse external load of the riser system in the actual marine working condition, according to the size of the transverse force required by the experiment, the spring stiffness and length are designed to meet the requirement of the required transverse static load.

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