Performance analysis and optimization method for optical fiber logging while drilling of complex oil and gas well

Abstract

The invention discloses a performance analysis and optimization method for optical fiber logging while drilling of a complex oil and gas well, and the method comprises the steps: building a structural model of an optical fiber in a detected oil and gas well tubular column based on the working condition of optical fiber logging while drilling; analyzing transmission characteristics of the optical fiber while drilling to obtain an energy loss calculation strategy of the optical fiber in the oil-gas well pipe column; performing energy loss simulation analysis on the structural model of the optical fiber in the tubular column based on an energy loss calculation strategy; performing flow field stress simulation on the structural model of the optical fiber in the tubular column by using the finite element analysis model, and performing mechanical property analysis on the optical fiber while drilling of the tubular column according to a simulation result; and determining a comprehensive optimization scheme of optical fiber logging while drilling based on the energy loss simulation result and the mechanical property analysis result of the tubular column optical fiber while drilling. By deeply analyzing and simulating the transmission characteristics, the energy loss and the mechanical stability of the optical fiber while drilling, powerful technical support is provided for improving the reliability and the accuracy of an optical fiber while drilling logging system in a complex oil and gas well environment.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas well monitoring, and in particular to a performance analysis and optimization method for fiber optic logging while drilling of complex oil and gas wells. Background Art

[0002] With the continuous development of oil and gas extraction technology, the exploration, development and production of oil and gas wells are facing more and more complex challenges. Traditional oil and gas well monitoring methods mainly rely on cables, sensors and other traditional physical monitoring equipment. However, these technologies have poor reliability and durability under long-term, high-temperature, high-pressure and corrosive environments, resulting in problems such as signal attenuation, sensor failure and high maintenance costs during data transmission. In order to overcome these shortcomings, the oil and gas industry has gradually begun to explore the use of fiber optic technology for intelligent transmission and monitoring.

[0003] At present, fiber-optic logging while drilling technology monitors various parameters in the well in real time by embedding optical fibers into the pipe string of oil and gas wells, and transmits the collected data to the ground through the optical fiber transmission system. Optical fiber sensors can not only withstand extreme temperatures, pressures, chemical corrosion and electromagnetic interference, but also realize remote real-time monitoring and high-precision measurement. This makes the fiber-optic logging while drilling system an effective tool for intelligent monitoring, real-time decision-making and dynamic optimization of oil and gas wells, with great advantages such as long transmission distance, large bandwidth, strong anti-interference ability and low cost. However, in the existing fiber-optic logging while drilling technology, due to the loss of optical fiber and the influence of environmental changes, the measurement results are often inconsistent or the accuracy is insufficient, which affects the subsequent production decision and resource evaluation of oil and gas wells. In addition, the working environment of oil and gas wells may cause problems such as bending, stretching and breaking of optical fibers, affecting the measurement accuracy, but the current technology usually makes it difficult to integrate the energy loss simulation and mechanical performance analysis results, and it is impossible to formulate a comprehensive and reliable optimization plan for the fiber-optic logging while drilling system.

[0004] Therefore, the present invention proposes a performance analysis and optimization method for fiber optic logging while drilling in complex oil and gas wells, conducts in-depth analysis and simulation of the transmission characteristics and mechanical stability of the optical fiber in the tubing string in fiber optic logging while drilling, optimizes the transmission reliability and accuracy of the optical fiber in the complex oil and gas well environment, and thus provides more accurate and stable data support for oil and gas exploration and production. Summary of the invention

[0005] In view of this, the present invention provides a performance analysis and optimization method for fiber optic logging while drilling in complex oil and gas wells, so as to solve the technical problems of unstable monitoring data transmission in existing fiber optic logging while drilling technology and poor stability and durability in complex oil and gas well environments.

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

[0007] In a first aspect, the present invention provides a performance analysis and optimization method for fiber optic logging while drilling in complex oil and gas wells, comprising:

[0008] Based on the working conditions of fiber-optic logging while drilling, a structural model of the optical fiber in the pipe string of the oil and gas well being tested is established;

[0009] Analyze the transmission characteristics of the optical fiber while drilling to obtain the energy loss calculation strategy of the optical fiber in the oil and gas well string;

[0010] Based on the energy loss calculation strategy, an energy loss simulation analysis is performed on the structural model of the optical fiber in the pipe string;

[0011] Using a finite element analysis model to simulate the flow field stress of the structural model of the optical fiber in the pipe string, and performing a mechanical performance analysis on the optical fiber while drilling the pipe string according to the flow field stress simulation results;

[0012] Based on the energy loss simulation results and mechanical property analysis results of the optical fiber while drilling of the pipe string, a comprehensive optimization scheme for optical fiber logging while drilling is determined.

[0013] Furthermore, the structural model of the optical fiber in the tested oil and gas well string is, from inside to outside, a fiber core, a cladding and a protective layer;

[0014] The material of the fiber core is set to be pure quartz glass; the material of the cladding is set to be quartz glass doped with impurities; and the protective layer is set to be polyethylene material.

[0015] Furthermore, the analysis of the transmission characteristics of the optical fiber in the pipe string to obtain the energy loss calculation strategy of the optical fiber while drilling includes:

[0016] By means of approximate analysis of planar waveguide theory, a bending loss calculation model of the optical fiber in the column is established;

[0017] According to the influence of temperature on the material properties and geometric dimensions of the optical fiber, a temperature loss calculation model of the optical fiber energy loss in the pipe column affected by temperature is established;

[0018] A comprehensive energy loss calculation strategy for the optical fiber in the column is obtained according to the bending loss calculation model and the temperature loss calculation model.

[0019] Furthermore, the temperature loss calculation model of the optical fiber energy loss in the pipe string affected by temperature is expressed by the formula:

[0020]

[0021] Among them, U and W are normalized lateral propagation constants, ΔT is the temperature change value, a and β are coefficients, R is the bending radius, and v is the propagation velocity.

[0022] Furthermore, the energy loss simulation analysis of the structural model of the optical fiber in the pipe string based on the energy loss calculation strategy includes:

[0023] Setting the physical parameters and working environment parameters of the optical fiber structure model in the pipe string in the simulation software;

[0024] Setting boundary conditions and meshing the optical fiber structure model in the pipe string;

[0025] Based on the physical parameters and the working environment parameters, the optical signal transmission of the optical fiber in the pipe string during the drilling process is simulated to generate a simulation result.

[0026] Furthermore, the energy loss simulation analysis of the structural model of the optical fiber in the pipe string based on the energy loss calculation strategy also includes:

[0027] Importing the simulation results into data visualization software;

[0028] Draw the relationship curve between temperature and bending loss, and analyze the change trend of optical fiber loss under different temperature conditions;

[0029] Draw the relationship curve between bending radius and bending loss, and analyze the loss characteristics of optical fiber under different bending radii;

[0030] Draw a curve showing the relationship between communication wavelength and bending loss, and analyze the variation of optical fiber loss at different wavelengths.

[0031] Furthermore, the flow field force simulation of the structural model of the optical fiber in the pipe string using the finite element analysis model includes:

[0032] Import the structural model of the optical fiber in the pipe string into the finite element analysis tool, and load the grid of the drilling fluid flow field calculation model;

[0033] Use non-Newtonian fluid to simulate the flow of drilling fluid;

[0034] The steady-state structure simulation model is used to simulate the flow field stress of the optical fiber when the drill rod is stationary and the drill rod is rotating.

[0035] Furthermore, the mechanical properties analysis of the optical fiber while drilling the pipe string according to the flow field calculation results includes:

[0036] The optical fiber is simplified into a thin rod model with uniform mass distribution and regular cross section;

[0037] Based on the force balance principle and elastic mechanics theory, a tension calculation model for optical fiber is established;

[0038] According to the tension calculation model and the flow field force simulation results of the optical fiber, the comprehensive influence of the optical fiber length, drilling fluid density and flow velocity is jointly analyzed, and the influence surface diagram of the multi-dimensional parameters is drawn to identify the sensitive areas and limit conditions of the tension.

[0039] Furthermore, the optical fiber tension calculation model is expressed by the formula:

[0040]

[0041] Where T represents the tension of the optical fiber, ρ f is the drilling fluid density, A is the cross-sectional area of ​​the optical fiber, v is the fluid velocity, ρ w is the density of the optical fiber material, g is the acceleration due to gravity, P r is the radial pressure, and z is the position coordinate of the optical fiber in the axial direction.

[0042] Furthermore, the combined analysis of the combined effects of optical fiber length, drilling fluid density and flow rate includes:

[0043] The axial tensile deformation of the optical fiber generated under the axial pressure is calculated based on the elastic modulus;

[0044] The equiaxial strain generated by the uniform radial compression of the optical fiber under the action of fluid pressure is calculated based on the Poisson's ratio;

[0045] Calculate the elongation of the optical fiber caused by thermal expansion due to temperature change based on the thermal expansion coefficient;

[0046] The optical fiber deformation caused by axial pressure, radial pressure and temperature change is superimposed and calculated to obtain the comprehensive elongation of the optical fiber.

[0047] Compared with the prior art, the present invention provides the following advantages:

[0048] (1) Based on the actual environment of LWD work, the structural model of the optical fiber is established, which can accurately describe the physical state, geometric shape and working environment of the optical fiber in the string, providing a basis for the subsequent energy loss analysis and mechanical property analysis of the optical fiber in the string, and helping to systematically evaluate the transmission loss and force changes of the optical fiber in a complex environment.

[0049] (2) Through energy loss simulation analysis and mechanical property evaluation, a comprehensive evaluation of the optical fiber while drilling can be carried out to identify the possible failure risks of the optical fiber, formulate protective measures and optimize the optical fiber system, reduce the probability of failure, and improve the reliability and service life of the system.

[0050] (3) By integrating the results of energy loss simulation and mechanical properties analysis, a comprehensive optimization plan for the optical fiber while drilling is formulated. At the same time, the transmission characteristics and mechanical properties of the optical fiber are optimized to ensure that the optical fiber can provide high-quality data in harsh environments and withstand the influence of multiple factors such as fluid, temperature and pressure.

[0051] Through in-depth analysis and simulation of optical fiber transmission characteristics, energy loss, and mechanical stability, the present invention ensures that optical fiber can provide high-quality data transmission during logging while drilling and withstand the influence of multiple factors during the logging while drilling process, thereby improving the reliability of the optical fiber system while drilling and further improving the accuracy of logging data obtained by the system in complex oil and gas well environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic diagram of the process flow of the performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells provided by the present invention;

[0053] Figure 2 A schematic diagram of the optical fiber structure provided by the present invention;

[0054] Figure 3 A schematic diagram of mesh division of the optical fiber simulation model provided by the present invention. DETAILED DESCRIPTION

[0055] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0056] See also Figure 1 This embodiment provides a performance analysis and optimization method for fiber optic logging while drilling in complex oil and gas wells, including:

[0057] Step S101: based on the working conditions of optical fiber logging while drilling, establish an optical fiber structure model in the tested oil and gas well string;

[0058] Step S102: Analyze the transmission characteristics of the optical fiber while drilling to obtain the energy loss calculation strategy of the optical fiber in the pipe string;

[0059] Step S103: performing energy loss simulation analysis according to the energy loss calculation strategy and the optical fiber structure model in the pipe string;

[0060] Step S104: using a finite element analysis model to perform flow field calculation on the optical fiber structure model in the pipe string, and performing mechanical property analysis on the optical fiber while drilling the pipe string according to the flow field calculation result;

[0061] Step S105: Determine a comprehensive optimization scheme for optical fiber logging while drilling based on the energy loss simulation results and mechanical property analysis results of the optical fiber logging while drilling of the pipe string.

[0062] The method of this embodiment, firstly, by establishing a fiber structure model, can accurately describe the physical state, geometric shape and working environment of the optical fiber in the pipe column, can reflect the actual layout of the optical fiber in the pipe column, avoid the influence of idealized assumptions on the results, and thus improve the accuracy and reliability of the model. Secondly, through the analysis of transmission characteristics and energy loss, problems in signal transmission (such as signal attenuation, noise influence, etc.) can be identified in advance. Thirdly, using the finite element analysis model to simulate the flow field force and perform mechanical performance analysis can help identify the mechanical risks that may cause optical fiber damage, and carry out protective design in advance to avoid optical fiber damage or performance degradation caused by external forces. Finally, the optimization plan is formulated based on the comprehensive energy loss simulation and mechanical performance analysis results, which not only takes into account the signal quality, but also takes into account the mechanical reliability of the optical fiber, which can not only improve the accuracy and stability of optical fiber measurement, but also ensure its durability in complex environments, and avoid data interruption or measurement errors caused by optical fiber failure.

[0063] As a preferred embodiment, in step S101, firstly, according to the actual working conditions in the logging while drilling process, a fiber optic structure model in the pipe string suitable for the complex working conditions of the oil and gas well is established. Due to the complex conditions such as high temperature, high pressure and strong corrosion in the working environment of the oil and gas well, the design of the fiber optic structure must ensure that it can work stably under these harsh environments. Therefore, the material selection and layer design of the fiber optic structure need to be paid special attention to ensure that it can provide accurate measurement and data transmission in the entire oil and gas production process.

[0064] According to the special working environment of optical fiber logging while drilling, the optical fiber structure model in the measured oil and gas well string is as follows from the inside to the outside: fiber core, cladding and protective layer.

[0065] like Figure 2 As shown, Figure 2The figure is a schematic diagram of the optical fiber structure model. The outermost layer of the optical fiber structure model is the coating layer (protective layer) with a diameter of 250μm. Its main function is to protect the optical fiber from physical damage in the external environment. It also has certain heat resistance and corrosion resistance. This layer usually uses high temperature and high pressure resistant polymer materials or coatings with excellent insulation to adapt to the special working environment of oil and gas wells. The middle layer is the cladding with a diameter of 125μm. It is mainly made of quartz glass doped with impurities. The function of the cladding is to wrap the core layer inside, and confine the optical signal to the core through the principle of total reflection to avoid signal leakage. At the same time, it can also enhance the tensile strength and mechanical properties of the optical fiber, ensuring that the optical fiber can operate stably for a long time in the complex oil and gas well environment. The selection of cladding materials and the incorporation of impurities help to improve the durability and stability of the optical fiber. The innermost layer is the core, with a diameter between 5μm and 50μm, made of pure quartz glass material. The core is the core part of optical fiber transmission, and its quality directly determines the transmission quality and sensitivity of optical fiber signals. The reason for using pure quartz glass is that it has lower light loss and higher transmission efficiency, and can maintain good optical properties under extreme conditions such as high temperature, high pressure and chemical corrosion.

[0066] As a preferred embodiment, in step S102, the transmission characteristics of the optical fiber while drilling are analyzed to obtain the energy loss calculation strategy of the optical fiber in the oil and gas well string, including:

[0067] By means of approximate analysis of planar waveguide theory, a bending loss calculation model of the optical fiber in the column is established;

[0068] According to the influence of temperature on the material properties and geometric dimensions of the optical fiber, a temperature loss calculation model of the optical fiber energy loss in the pipe column affected by temperature is established;

[0069] A comprehensive energy loss calculation strategy for the optical fiber in the column is obtained according to the bending loss calculation model and the temperature loss calculation model.

[0070] Specifically, we first conduct an approximate analysis of the planar waveguide theory. The planar waveguide theory is an approximate method for describing the optical waveguide structure in optical fiber propagation, and is usually used to analyze the bending loss problem of optical fiber. Considering that the optical fiber in the string will be affected by bending during the drilling process, the magnitude of the bending loss is closely related to the bending radius, propagation wavelength, and geometric characteristics of the optical fiber. The optical fiber bending loss is expressed by the formula:

[0071]

[0072] Where A is a constant related to the material and geometric properties of the optical fiber, R is the radius of the fiber bend, and λ is the wavelength of the propagating light.

[0073] From the above formula, it can be seen that the bending loss is inversely proportional to the bending radius R and proportional to the propagation wavelength λ. A smaller bending radius will result in a larger loss, while a longer wavelength (such as near-infrared wavelength) will result in a higher loss. This is critical for the design of optical fiber while drilling, especially in the complex oil and gas well drilling process, where the bending loss may significantly affect the transmission performance of the optical fiber.

[0074] Secondly, during the drilling process, temperature change is a factor that cannot be ignored, so it is also necessary to analyze the impact of temperature on optical fiber energy loss. As the temperature changes, the material properties (such as refractive index) and geometric dimensions of the optical fiber will change, thereby affecting the transmission loss of the optical fiber. By establishing a calculation model for the influence of temperature on the energy loss of the optical fiber while drilling, the functional expression of the optical fiber power and loss coefficient caused by temperature change can be obtained as follows:

[0075]

[0076] Among them, U and W are normalized lateral propagation constants, ΔT is the temperature change value, a and β are coefficients, R is the bending radius, and v is the propagation velocity.

[0077] Finally, a comprehensive energy loss calculation strategy for the optical fiber in the column is obtained according to the bending loss calculation model and the temperature loss calculation model.

[0078] The comprehensive energy loss calculation strategy combines bending loss and temperature loss to obtain the total energy loss of the fiber under drilling conditions. The comprehensive energy loss is the superposition effect of bending loss and temperature loss. The comprehensive energy loss α total =α b +μ·α e (ΔT), μ represents the weighting coefficient.

[0079] By combining the planar waveguide theory to analyze the optical fiber bending loss and considering the effect of temperature on the optical fiber, it is possible to accurately predict the energy loss of the optical fiber in the oil and gas well string, effectively capture the impact of complex environmental changes on the optical fiber performance, and improve the reliability of the optical fiber system while drilling in practical applications. By accurately calculating the bending loss and temperature loss, the structure, material and installation method of the optical fiber while drilling can be optimized to reduce the loss, improve the transmission efficiency, and ensure more stable and reliable data transmission.

[0080] As a preferred embodiment, in step S103, an energy loss simulation analysis is performed on the structural model of the optical fiber in the pipe string based on the energy loss calculation strategy, including:

[0081] The physical parameters and working environment parameters of the optical fiber structure model in the pipe string are set in the simulation software; it should be noted that the physical parameters here include setting the wavelength and step of the optical signal, setting the bending radius and effective refractive index of the optical fiber, and the range and step of the temperature change in the oil and gas well, etc.;

[0082] Setting boundary conditions and meshing the optical fiber structure model in the pipe string;

[0083] Based on the physical parameters and the working environment parameters, the optical signal transmission of the optical fiber in the pipe string during the drilling process is simulated to generate a simulation result.

[0084] As a specific embodiment, firstly, the geometric model of the optical fiber is imported into the simulation software, and the geometric structure of the optical fiber includes a circular core region and a cladding region wrapped around the core. Then, the physical parameters are set, and the selected optical signal wavelengths are short waves of 600nm and 800nm, and long waves of 1300nm and 1600nm, the scanning step is set to 100nm, and the bending radius is an integer between 8mm and 15mm.

[0085] When setting the working environment parameters of the drilling process, considering that the temperature in the well usually varies widely during actual drilling construction, up to 160°C, and may also face a harsh low temperature environment below zero, the temperature change range is set to -50°C to 150°C, and the temperature scanning step is set to 10°C. In addition, in order to improve the efficiency of searching for solutions, the search reference condition of the analysis mode is set to the effective refractive index (1.446) or the core refractive index of the optical fiber. In some embodiments, the search mode uses the effective mode refractive index and searches within an absolute value range of 300 around the offset (that is, the search range is 1.446±0.300, and the effective refractive index range of the search is approximately between 1.146 and 1.746) to ensure that the closest solution is obtained, and within the given fiber or waveguide parameter range, the finally selected mode is most suitable for the application conditions in the well, so that the optical signal is stably and efficiently propagated.

[0086] like Figure 3 As shown in the figure, after the physical parameters and working environment parameters are set, it is necessary to mesh the geometric structure of the optical fiber model. Appropriate meshing can ensure that the mode propagation characteristics of the optical fiber are accurately described. The mode characteristics of the optical fiber, especially the effective refractive index and field intensity distribution, are often closely related to the geometric shape of the optical fiber. Decomposing the calculation area into small units helps to accurately simulate the propagation process of the mode in the optical fiber. Since the changes in the light field are usually more drastic in the core area, a finer mesh is used in the core area to improve the calculation accuracy; a coarser mesh can be used in the cladding area to save computing resources, but it is necessary to ensure that the propagation characteristics of the optical fiber mode can be accurately described.

[0087] After completing the model setting and calculation, check the model settings in the simulation software, including geometric parameters, material properties, boundary conditions, and meshing. Solve after ensuring that they are correct, and use post-processing tools to analyze the calculation results to generate field intensity distribution maps in the core and cladding, and intuitively display the mode distribution through color gradients and contour maps.

[0088] As a specific embodiment, performing energy loss simulation analysis on the structural model of the optical fiber in the pipe string based on the energy loss calculation strategy also includes:

[0089] Import simulation results into data visualization software;

[0090] Draw the relationship curve between temperature and bending loss, analyze the change trend of optical fiber loss under different temperature conditions, mark the key points, such as temperature threshold or significant change point, and clarify the impact of temperature on optical fiber performance;

[0091] Draw a curve of the relationship between bending radius and bending loss to show the loss characteristics of optical fiber at different bending radii; analyze the critical bending radius to determine the radius below which the bending loss increases sharply;

[0092] Draw the relationship curve between communication wavelength and bending loss, study the variation law of optical fiber loss at different wavelengths, compare the distribution characteristics of mode fields at different wavelengths, and clarify the optimization direction of wavelength selection for optical fiber performance;

[0093] Organize and analyze the data charts to ensure that the charts are clear and the parameters are fully labeled.

[0094] Through multi-faceted simulation analysis of optical fiber performance, combined with data visualization and detailed parameter analysis, the accuracy, efficiency and stability of optical fiber logging system design can be greatly improved. It can not only provide a reliable basis for the optimization of optical fiber systems, but also reduce the number of actual tests and experiments, save costs and time, and improve the reliability and life of the entire system.

[0095] As a preferred embodiment, in step S104, a finite element analysis model is used to perform flow field calculation on the optical fiber structure model in the pipe string, including:

[0096] Import the structural model of the optical fiber in the pipe string into the finite element analysis tool, and load the grid of the drilling fluid flow field calculation model;

[0097] Use non-Newtonian fluid to simulate the flow of drilling fluid;

[0098] The steady-state structure simulation model is used to simulate the stress conditions of the optical fiber when the drill rod is stationary and when the drill rod is rotating.

[0099] Specifically, firstly, the structural model of the optical fiber in the pipe string is imported into the module to perform flow field calculation.

[0100] Load the flow field calculation model grid, consider the influence of gravity and buoyancy during the calculation process, and use non-Newtonian fluid to simulate the flow of mud. Set the physical parameters and fluid characteristics: The drilling fluid physical parameters are set to 1.08g / cm 3 , the flow index is 0.737, and the consistency coefficient is 1.07. The model inlet is the velocity boundary condition, and the inlet velocity is 2.6g / cm 3 .

[0101] The structural simulation part adopts a steady-state structural simulation model, and the external forces acting on the optical fiber are its own gravity, buoyancy and the force of the fluid on the optical fiber.

[0102] Taking into account the different working conditions during drilling, simulations are performed in two states: static state and rotating state. Since the drill rod and the upper end of the optical fiber are connected together in a fully constrained state, the optical fiber is static when the drill rod is static, and rotates when the drill rod rotates.

[0103] The results of actual calculation and analysis of the drill pipe in both stationary and rotating states are as follows: when the optical fiber is stationary, the maximum stress of the optical fiber is 204MPa, and when the optical fiber is rotating, the maximum stress is also 204MPa.

[0104] As a preferred embodiment, the mechanical properties of the optical fiber while drilling the pipe string are analyzed according to the flow field calculation results, including:

[0105] The optical fiber is simplified into a thin rod model with uniform mass distribution and regular cross section;

[0106] Based on the force balance principle and elastic mechanics theory, a tension calculation model for optical fiber is established;

[0107] According to the tension calculation model and the flow field force simulation results of the optical fiber, the comprehensive influence of the optical fiber length, drilling fluid density and flow velocity is jointly analyzed, and the influence surface diagram of the multi-dimensional parameters is drawn to identify the sensitive areas and limit conditions of the tension.

[0108] As a specific embodiment, the optical fiber is first simplified into an ideal thin rod model with uniform mass distribution and regular cross-section.

[0109] Based on the principle of force balance and elastic mechanics theory, the optical fiber tension calculation model is established as follows:

[0110]

[0111] Where T represents the tension of the optical fiber, ρ f is the drilling fluid density, A is the cross-sectional area of ​​the optical fiber, v is the fluid velocity, ρ wis the density of the optical fiber material, g is the acceleration due to gravity, P r is the radial pressure, and z is the position coordinate of the optical fiber in the axial direction.

[0112] As the length of the optical fiber increases, the gravity and fluid resistance of the optical fiber will increase significantly, causing the tension to increase linearly along the axial direction. Therefore, in long optical fiber application scenarios such as fiber-optic logging while drilling, special attention should be paid to the maximum tension value at the lower end to avoid the optical fiber from breaking due to exceeding the tensile limit.

[0113] The density of drilling fluid directly affects the buoyancy and fluid pressure of the optical fiber. As the density of drilling fluid increases, the tension of the optical fiber may increase first and then decrease. The increase in flow rate leads to a significant increase in the resistance of the fluid to the optical fiber. Especially in high-speed drilling operations, the swaying force on the optical fiber may become the main source of tension.

[0114] By jointly analyzing the combined effects of fiber length, drilling fluid density and flow rate and drawing the influence surface diagram of multi-dimensional parameters, sensitive areas and extreme conditions of tension can be identified.

[0115] Specifically, under the action of axial pressure, the optical fiber produces axial tensile deformation, and its strain can be calculated by the elastic modulus E, and the formula is:

[0116]

[0117] Among them, ε 轴向 is the axial strain, σ 轴向 is the axial pressure, and E is the elastic modulus of the optical fiber material.

[0118] Under the action of fluid pressure, the optical fiber is uniformly compressed in the radial direction, and its equiaxial strain can be calculated by Poisson's ratio, as follows:

[0119] ε radial = -ν·ε axial,

[0120] Where ε radial is the radial strain and ν is the Poisson's ratio.

[0121] Temperature changes will cause thermal expansion of the optical fiber, and its elongation can be obtained from the thermal expansion coefficient:

[0122] ΔL=L0·α·ΔT,

[0123] Where ΔL is the thermal expansion length of the optical fiber, L0 is the original length of the optical fiber, α is the thermal expansion coefficient of the optical fiber material, and ΔT is the temperature change.

[0124] Therefore, the combined effect of axial pressure, radial pressure and temperature change on optical fiber deformation is analyzed to obtain the comprehensive elongation of the optical fiber:

[0125] ΔL 总 =ΔL 轴向+ΔL 径向 +ΔL 热膨胀 .

[0126] As a specific embodiment, in step S105, the final optimization plan will start from multiple dimensions such as optical fiber materials, optical fiber layout, transmission characteristics, structural design, monitoring mechanism, etc., and comprehensively consider factors such as temperature, pressure, fluid, mechanical vibration in oil and gas wells. By optimizing the transmission capacity, mechanical stability and reliability of the optical fiber, the overall performance of the while-drilling optical fiber logging system is improved, thereby ensuring the accuracy, stability and efficiency of the logging data.

[0127] Specifically, for different oil and gas well environments to be tested, combined with the energy loss, signal attenuation and mechanical properties data of the optical fiber in the oil and gas well string, the signal acquisition and processing algorithm is adjusted to ensure the accuracy and consistency of the measurement data. Through adaptive signal processing technology, the measurement errors caused by environmental changes are reduced, and the adaptability of the optical fiber logging system to complex downhole environments is enhanced. At the same time, according to the flow field force simulation results, the material and structural design of the optical fiber are improved to increase its tensile, compressive and vibration resistance, ensuring that it can still maintain good mechanical properties during long-term operation. Based on the simulation results of energy loss, the design parameters of the optical fiber such as the optical fiber core diameter, refractive index, and cladding structure are adjusted to minimize transmission losses.

[0128] In summary, the present invention proposes a performance analysis and optimization method for fiber optic logging while drilling in complex oil and gas wells. First, according to the actual working conditions in the process of logging while drilling, a fiber optic structure model in the pipe string that can be used for complex working conditions of oil and gas wells is established. According to the established fiber optic structure model in the pipe string, the energy loss of the fiber optic while drilling in the pipe string is calculated. According to the established simulation model, finite element flow field calculation is performed, and the mechanical performance analysis of the fiber optic while drilling in the pipe string is performed. Through the above process, the present invention designs a new set of complete and effective methods for analyzing the intelligent transmission of fiber optic wellbore data while drilling in complex oil and gas wells, which provides effective ideas and methods for in-depth analysis of the feasibility of fiber optic communication while drilling and other similar fiber optic communication problems in the engineering field.

[0129] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A performance analysis and optimization method for fiber optic logging while drilling in complex oil and gas wells, characterized in that: include: Based on the working conditions of fiber-optic logging while drilling, a structural model of the optical fiber in the pipe string of the oil and gas well being tested is established; Analyze the transmission characteristics of the optical fiber while drilling to obtain the energy loss calculation strategy of the optical fiber in the oil and gas well string; Based on the energy loss calculation strategy, an energy loss simulation analysis is performed on the structural model of the optical fiber in the pipe string; Using a finite element analysis model to simulate the flow field stress of the structural model of the optical fiber in the pipe string, and performing a mechanical performance analysis on the optical fiber while drilling the pipe string according to the flow field stress simulation results; Based on the energy loss simulation results and mechanical property analysis results of the optical fiber while drilling of the pipe string, a comprehensive optimization scheme for optical fiber logging while drilling is determined.

2. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 1, characterized in that: The analysis of the transmission characteristics of the optical fiber in the pipe string to obtain the energy loss calculation strategy of the optical fiber while drilling includes: By means of approximate analysis of planar waveguide theory, a bending loss calculation model of the optical fiber in the column is established; According to the influence of temperature on the material properties and geometric dimensions of the optical fiber, a temperature loss calculation model of the optical fiber energy loss in the pipe column affected by temperature is established; A comprehensive energy loss calculation strategy for the optical fiber in the column is obtained according to the bending loss calculation model and the temperature loss calculation model.

3. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 2, characterized in that: The temperature loss calculation model of the optical fiber energy loss in the pipe column affected by temperature is expressed by the formula: Among them, U and W are normalized lateral propagation constants, ΔT is the temperature change value, a and β are coefficients, R is the bending radius, and v is the propagation velocity.

4. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 1, characterized in that: The energy loss simulation analysis of the structural model of the optical fiber in the pipe string based on the energy loss calculation strategy includes: Setting the physical parameters and working environment parameters of the optical fiber structure model in the pipe string in the simulation software; Setting boundary conditions and meshing the optical fiber structure model in the pipe string; Based on the physical parameters and the working environment parameters, the optical signal transmission of the optical fiber in the pipe string during the drilling process is simulated to generate a simulation result.

5. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 4, characterized in that: The energy loss simulation analysis of the structural model of the optical fiber in the pipe string based on the energy loss calculation strategy also includes: Importing the simulation results into data visualization software; Draw the relationship curve between temperature and bending loss, and analyze the change trend of optical fiber loss under different temperature conditions; Draw the relationship curve between bending radius and bending loss, and analyze the loss characteristics of optical fiber under different bending radii; Draw a curve showing the relationship between communication wavelength and bending loss, and analyze the variation of optical fiber loss at different wavelengths.

6. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 1, characterized in that: The method of using a finite element analysis model to simulate the flow field stress of the structural model of the optical fiber in the pipe string includes: Import the structural model of the optical fiber in the pipe string into the finite element analysis tool, and load the grid of the drilling fluid flow field calculation model; Use non-Newtonian fluid to simulate the flow of drilling fluid; The steady-state structure simulation model is used to simulate the flow field stress of the optical fiber when the drill rod is stationary and the drill rod is rotating.

7. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 6, characterized in that: The mechanical property analysis of the optical fiber while drilling the pipe string according to the flow field calculation result includes: The optical fiber is simplified into a thin rod model with uniform mass distribution and regular cross section; Based on the force balance principle and elastic mechanics theory, a tension calculation model for optical fiber is established; According to the tension calculation model and the flow field force simulation results of the optical fiber, the comprehensive influence of the optical fiber length, drilling fluid density and flow velocity is jointly analyzed, and the influence surface diagram of the multi-dimensional parameters is drawn to identify the sensitive areas and limit conditions of the tension.

8. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 7, characterized in that: The optical fiber tension calculation model is expressed by the formula: Where T represents the tension of the optical fiber, ρ f is the drilling fluid density, A is the cross-sectional area of ​​the optical fiber, v is the fluid velocity, ρ w is the density of the optical fiber material, g is the acceleration due to gravity, P r is the radial pressure, and z is the position coordinate of the optical fiber in the axial direction.

9. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 7, characterized in that: The combined analysis of the combined effects of optical fiber length, drilling fluid density and flow rate includes: The axial tensile deformation of the optical fiber generated under the axial pressure is calculated based on the elastic modulus; The equiaxial strain generated by the uniform radial compression of the optical fiber under the action of fluid pressure is calculated based on the Poisson's ratio; Calculate the elongation of the optical fiber caused by thermal expansion due to temperature change based on the thermal expansion coefficient; The optical fiber deformation caused by axial pressure, radial pressure and temperature change is superimposed and calculated to obtain the comprehensive elongation of the optical fiber.

10. The performance analysis and optimization method of fiber optic logging while drilling for complex oil and gas wells according to claim 1, characterized in that: The structural model of the optical fiber in the tested oil and gas well string is as follows from the inside to the outside: a fiber core, a cladding and a protective layer; The material of the fiber core is set to be pure quartz glass; the material of the cladding is set to be quartz glass doped with impurities; and the protective layer is set to be polyethylene material.

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