A hydraulic fracturing pipeline safety evaluation method

Abstract

The application provides a hydraulic fracturing pipeline safety evaluation method, which comprises the following steps: obtaining performance parameters of a fracturing pipeline on site; establishing a three-dimensional model of the fracturing pipeline based on the performance parameters of the fracturing pipeline; performing erosion risk simulation of the fracturing pipeline by using simulation software to obtain an erosion position of the fracturing pipeline and an erosion rate of the erosion position, and converting the erosion rate into an erosion depth; establishing a risk evaluation grade of the fracturing pipeline, and formulating a detection cycle and a pipe replacement time of the fracturing pipeline according to the erosion position, the erosion depth and the risk evaluation grade; performing vibration fatigue risk simulation of the fracturing pipeline by using simulation software to obtain stress and displacement distribution of the fracturing pipeline; and evaluating the safety of the fracturing pipeline during fracturing construction based on the stress and displacement distribution of the fracturing pipeline. The method has little influence on fracturing construction and can ensure the continuity of fracturing construction, and the key positions of the fracturing pipeline where risks occur are determined, so that the pipeline can be checked and replaced in a targeted manner.

Description

Technical Field

[0001] This invention relates to the fields of hydraulic fracturing and pressurized pipeline technology, and specifically to a method for safety evaluation of hydraulic fracturing pipelines. Background Technology

[0002] Hydraulic fracturing is a key technology for shale gas extraction. Its basic principle is as follows: using a surface high-pressure pump unit, a large volume of high-viscosity fluid (fracturing fluid) is injected into the formation through the wellbore, creating high pressure at the bottom of the well. When this pressure exceeds the formation's bearing capacity, fractures form near the bottom of the well. Continued injection of fluid carrying proppant causes the fractures to extend forward. The proppant supports the fractures, forming sand-filled fractures of a certain size with high conductivity. In this way, oil and gas can easily flow into the well through the fractures, achieving increased production and injection.

[0003] To ensure fracturing fluid can be pumped into the formation, a pipeline is needed on the surface to connect the high-pressure pump unit and the wellhead; this is the fracturing pipeline. During fracturing operations, fracturing pipelines often face erosion and wear problems. Erosion and wear typically refer to the structural wear phenomenon that occurs when high-speed sand-containing fluid impacts the structural wall, specifically manifested in the interaction between the liquid-solid two-phase flow inside the pipe and the structural wall. During fracturing operations, the fracturing fluid at the pump outlet of the fracturing truck exhibits uneven flow. At high-pressure components, the fracturing fluid generates a time-varying excitation force on the structural wall, causing fluid-structure interaction vibration in the fracturing pipeline. This vibration not only causes mechanical vibration and environmental noise pollution but can also, in severe cases, lead to catastrophic accidents.

[0004] Current technologies primarily focus on safety issues of oil and gas pipelines under loads such as earthquakes, rockfalls, and landslides. Research on paving loads under fracturing conditions is limited. Furthermore, current pipeline safety evaluation methods mainly target long-distance steel oil and gas pipelines, whose service life and operational intensity differ significantly from fracturing pipelines. Therefore, previous research cannot provide effective references.

[0005] In summary, existing technologies lack a comprehensive and unified approach to hazard assessment of fracturing pipelines used in hydraulic fracturing stations, making it difficult to provide effective references for fracturing operations and to provide a scientific and reasonable basis for the safe operation of fracturing pipelines and their protective design hazards during fracturing operations. Summary of the Invention

[0006] The purpose of this invention is to provide a safety evaluation method for hydraulic fracturing pipelines, in order to solve the problem in the prior art that it is difficult to effectively assess the hazards of fracturing pipelines during hydraulic fracturing operations, and to provide effective reference for hydraulic fracturing operations and scientific and reasonable judgment basis for the protection of fracturing pipelines during hydraulic fracturing operations.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] This invention provides a method for safety evaluation of hydraulic fracturing pipelines, comprising:

[0009] Obtain the performance parameters of the field fracturing pipeline;

[0010] A three-dimensional model of the fracturing pipeline was established based on the performance parameters of the fracturing pipeline.

[0011] Based on the three-dimensional model of the fracturing pipeline, simulation software was used to simulate the erosion risk of the fracturing pipeline, obtain the erosion location and erosion rate of the fracturing pipeline, and convert the erosion rate into erosion depth.

[0012] Establish a risk assessment level for fracturing pipelines, wherein the risk assessment level includes the correspondence between the remaining wall thickness of the fracturing pipeline and the risk level of the fracturing pipeline;

[0013] Based on the risk assessment level and fracturing speed and depth of the fracturing pipeline, the inspection cycle and fitting replacement time of the fracturing pipeline are determined.

[0014] Based on the three-dimensional model of the fracturing pipeline, simulation software was used to simulate the vibration fatigue risk of the fracturing pipeline, and the stress and displacement distribution of the fracturing pipeline were obtained.

[0015] The safety of the fracturing pipeline during fracturing operations is evaluated based on the stress and displacement distribution of the fracturing pipeline.

[0016] Preferably, obtaining the performance parameters of the field fracturing pipeline includes:

[0017] Obtain the geometric parameters of the fracturing pipeline: pipeline diameter and length, pipeline thickness, elbows, and tees;

[0018] Obtain the material properties of fracturing pipelines: pipeline materials, main components of fracturing fluid, and solid particulate materials;

[0019] Obtain fluid characteristics of fracturing pipelines: fluid density and viscosity, proppant solid particles, and flow velocity;

[0020] Obtain the operating conditions of the fracturing pipeline: flow rate, pressure, and temperature.

[0021] Preferably, establishing a three-dimensional model of the fracturing pipeline based on its performance parameters includes:

[0022] Based on the pipeline diameter and length, pipeline thickness, elbow parameters, and the installation position and connection of elbows and tees used in fracturing operations, a three-dimensional model of the fracturing pipeline is constructed.

[0023] Preferably, the step of simulating the erosion risk of the fracturing pipeline using simulation software based on the three-dimensional model of the fracturing pipeline includes:

[0024] The three-dimensional model of the fracturing pipeline was imported into the Fluent module of ANSYS software, and the simulation environment was set according to the material properties and fluid properties of the fracturing pipeline.

[0025] Based on the fluid-solid two-phase flow equation and erosion equation, the erosion risk of fracturing pipelines is simulated.

[0026] The flow equations are solved using the Euler-Lagrange method with fluid as the continuous phase and solid particles as the discrete phase. The changes in particle motion state are solved by differential equations to obtain the internal flow field distribution of the fracturing pipeline and the material loss and erosion distribution of the fracturing pipeline wall.

[0027] The erosion rate at the erosion location is obtained based on the erosion equation.

[0028] Preferably, converting the erosion rate into erosion depth includes:

[0029] If the erosion rate obtained from the simulation is the mass loss rate, then divide the mass loss rate by the density of the fracturing pipeline material to obtain the linear erosion rate.

[0030] If the erosion rate obtained from the simulation is the volume loss rate, then the volume loss rate is taken as the linear erosion rate.

[0031] Multiplying the linear erosion rate by time yields the erosion depth over time.

[0032] Preferably, the establishment of the risk assessment level for the fracturing pipeline includes:

[0033] The risk assessment levels for the fracturing pipeline include intact, minor, moderate, severe, and hazardous.

[0034] For fracturing straight pipes, the following criteria are defined: no reduction in wall thickness indicates good condition; remaining wall thickness ≥ 100 mm indicates mild condition; remaining wall thickness ≥ 90 mm indicates moderate condition; remaining wall thickness ≥ 80 mm indicates severe condition; and remaining wall thickness < 75.90 mm indicates dangerous condition.

[0035] For fracturing bends, the following criteria are defined: no reduction in wall thickness indicates good condition; remaining wall thickness ≥ 160 mm indicates mild condition; remaining wall thickness ≥ 130 mm indicates moderate condition; remaining wall thickness ≥ 100 mm indicates severe condition; and remaining wall thickness < 75.90 mm indicates dangerous condition.

[0036] For fracturing tees, the following criteria are defined: no reduction in wall thickness indicates good condition; remaining wall thickness ≥ 220 mm indicates mild condition; remaining wall thickness ≥ 130 mm indicates moderate condition; remaining wall thickness ≥ 100 mm indicates severe condition; and remaining wall thickness < 75.90 mm indicates dangerous condition.

[0037] Preferably, the step of determining the inspection cycle and fitting replacement time of the fracturing pipeline based on the risk assessment level and fracturing speed and depth includes:

[0038] Based on the location of erosion, plan the key areas and inspection cycles for safety inspection of fracturing pipelines;

[0039] The erosion depth over time is calculated based on the maximum erosion rate. The remaining wall thickness is obtained by subtracting the erosion depth from the original wall thickness of the fracturing pipeline.

[0040] The time required for the fracturing pipeline to meet the replacement criteria is determined by the risk assessment level and remaining wall thickness of the fracturing pipeline; the replacement criteria refer to a remaining wall thickness of less than 75.90 mm.

[0041] Preferably, the method further includes: performing a fracturing pipeline erosion risk simulation, and after replacing the pipe fittings, measuring the erosion depth of the replaced pipe fittings, and recording the measured erosion depth... An empirical formula for fracturing depth is derived by correlating the pressure P, the proppant particle size S, and the operation time t under fracturing conditions:

[0042] ,

[0043] in: , , , , , , , , , These are constant coefficients, obtained through fitting during the optimization process; This refers to the fracturing pressure; The particle size of the proppant used; The operation time for fracturing pipe fittings;

[0044] As field measurement data is accumulated and the empirical formula is continuously optimized, it can be directly applied to the safety evaluation of fracturing pipelines in later stages. Make predictions.

[0045] Preferably, the step of simulating the vibration fatigue risk of the fracturing pipeline using simulation software based on the three-dimensional model of the fracturing pipeline to obtain the stress and displacement distribution of the fracturing pipeline includes:

[0046] The three-dimensional model of the fracturing pipeline was imported into the Fluent + Transition Structural module of ANSYS software for numerical simulation. The boundary stress load data of the flow field was transferred to the solid boundary to perform numerical stress simulation in the solid domain, and the stress change of the pipeline wall under fracturing operation conditions was obtained.

[0047] By adjusting the fixing points and fixing methods of the fracturing pipeline, the influence of pipeline layout on the stress magnitude of the fracturing pipeline can be obtained. Adjusting the fixing points and fixing methods of the pipeline can minimize the stress on the pipeline. If the maximum stress borne by the fracturing pipeline obtained from the simulation is lower than the yield strength of the material, then the fracturing pipeline is reliable.

[0048] The beneficial effects achieved by this invention are as follows:

[0049] This invention offers a convenient evaluation process, minimizes the impact on fracturing operations, ensures the continuity of fracturing operations, and clearly identifies key areas where risks may occur in fracturing pipelines, facilitating targeted inspection and replacement. The identification of fracturing pipeline risk types guides on-site safety assessments. This method not only ensures the normal progress of fracturing operations but also guides safety inspections of fracturing pipelines, guaranteeing on-site safety during fracturing operations. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the hydraulic fracturing pipeline safety evaluation method provided in an embodiment of the present invention;

[0051] Figure 2 This is a three-dimensional model diagram of a fracturing pipeline provided in an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of erosion simulation of a continuous bend in a fracturing pipeline provided in an embodiment of the present invention;

[0053] Figure 4 This is a schematic diagram of erosion simulation of a fracturing pipeline bend provided in an embodiment of the present invention;

[0054] Figure 5 A comparison diagram of erosion with and without erosion defects obtained from the erosion risk simulation of fracturing pipelines provided in this embodiment of the invention.

[0055] Figure 6 The stress distribution diagram of the fracturing pipeline provided in the embodiment of the present invention. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0057] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0058] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0059] It should be emphasized here that the step markers mentioned below are not a limitation on the order of the steps, but should be understood as meaning that the steps can be executed in the order mentioned in the embodiments, or in a different order than in the embodiments, or several steps can be executed simultaneously.

[0060] To address the difficulty of effectively assessing the hazards of fracturing pipelines during hydraulic fracturing operations using existing technologies, this invention proposes a safety evaluation method for fracturing pipelines during hydraulic fracturing operations. For fracturing pipelines, the main risks during fracturing operations include erosion damage from proppant solid particles and vibration fatigue risks due to the uneven flow of fracturing fluid at the pump outlet caused by the fracturing pump. The greatest risks faced by fracturing pipelines during fracturing operations are erosion and vibration fatigue. The most direct impact of erosion on pipelines is the reduction in pipeline wall thickness. If thin-walled fittings are not detected in time, they can easily cause puncture injuries or equipment damage under the high pressure of fracturing. Furthermore, the stress experienced by fracturing pipelines under high pressure can also lead to deformation or even fracture. By combining the fracturing pipeline with its operating conditions during fracturing operations, the erosion risk patterns and stress variation relationships of the fracturing pipeline under these conditions are obtained. This provides guidance for the design, installation, and scientific planning of inspection cycles and fitting replacement for fracturing pipelines.

[0061] Based on the above technical background, embodiments of the present invention provide a method for safety evaluation of hydraulic fracturing pipelines, such as... Figure 1 As shown, it includes the following steps:

[0062] Step S1: Conduct a risk analysis for the fracturing pipeline. The main risks faced by the fracturing pipeline are those arising from its own high-pressure operating conditions.

[0063] Step S2: Obtain the performance parameters of the fracturing pipeline in the field, including: pipeline geometry parameters: pipeline diameter and length, pipeline thickness, elbows, tees; material properties: pipeline material, main components of fracturing fluid, solid particulate material; fluid properties: fluid density and viscosity, proppant solid particles, flow velocity; operating conditions: flow rate, pressure, and temperature.

[0064] Step S3: Establish a simplified 3D model of the fracturing pipeline and set material properties according to the pipeline material;

[0065] Step S4: Perform erosion risk simulation of fracturing pipeline. Import the simplified model from Step S3 into the Fluent module of ANSYS software for numerical simulation calculation. The simulation analysis is based on the fluid-solid two-phase flow equation and the erosion mode equation. The fluid-solid two-phase flow equation includes the continuity equation of turbulent motion, the momentum equation and the erosion model.

[0066] Step S5: Based on the simulation results of Step S4, obtain the erosion location and erosion rate of the fracturing pipeline in the simplified model, and determine the inspection cycle and pipe replacement time of the fracturing pipeline based on the erosion location and erosion rate.

[0067] Based on the location of erosion, plan the key areas and inspection cycles for safety inspection of the fracturing pipeline; calculate the degree of reduction in the fracturing pipeline wall thickness based on the maximum erosion rate, compare it with the safety level of the fracturing pipeline wall thickness, calculate the time when the fracturing pipeline reaches the point of needing to replace the fittings (when the remaining wall thickness of the fitting is less than 75.90 mm), and then replace the fittings.

[0068] Step S6: Perform vibration fatigue risk simulation of fracturing pipeline. Import the simplified model from step S3 into the Fluent + Transition Structural module in ANSYS software for numerical simulation. Transfer the boundary stress load data of the flow field to the solid boundary and perform numerical simulation of the solid domain. Finally, in the post-processing stage, relevant data such as flow velocity and pressure of the flow field can be obtained. In the structural module, the vibration characteristics analysis of the solid domain can be obtained.

[0069] Step S7: Based on the simulation results of step S6, obtain the stress and displacement distribution of the fracturing pipeline in the simplified model;

[0070] Step S8: Evaluate the safety of the fracturing pipeline during fracturing operations based on the stress and displacement distribution of the fracturing pipeline.

[0071] In this embodiment of the invention, a three-dimensional model of the fracturing pipeline is constructed based on the pipeline diameter and length, pipeline thickness, elbow parameters, and the installation positions and connections of elbows and tees used in fracturing operations. Figure 2 As shown, the 3D model of the fracturing pipeline is imported into the Fluent module of ANSYS software. The simulation environment is set according to the materials used, including pipeline materials, main components of fracturing fluid, and main components of proppant.

[0072] In this embodiment of the invention, a simulation of the erosion risk of a fracturing pipeline is performed, and the simulation results are as follows: Figure 3 , Figure 4 and Figure 5As shown. Based on the simulation results, the locations of key erosion damage in the fracturing pipeline were determined, and the maintenance time for these key erosion damage locations was planned based on the maximum erosion rate.

[0073] During the simulation, the continuity equation for the continuous phase is:

[0074] ,

[0075] Discrete phase continuity equation:

[0076] ,

[0077] Continuous phase momentum equation:

[0078] ,

[0079] Discrete phase momentum equation:

[0080] ,

[0081] in , These are the volume fractions of the continuous phase and the discrete phase, respectively. , , These represent the densities of the continuous phase and the discrete phase, respectively. , They are continuous phases in direction and Instantaneous velocity component in the direction; , Discrete phases direction and Instantaneous velocity component in the direction; , Indicating two directions, in the formula, represents the quantity of molecular position relative to . , Differential in direction, For the stress tensor, this term represents the stress in space. Differentiation in direction; For the fixed stress tensor, this term represents the stress space. Differentiation in direction; For gravity in Components in direction; For pressure; These are interphase forces, including virtual mass forces, pressure gradient forces, and interphase drag.

[0082] During hydraulic fracturing, solid particles collide with the equipment wall under the influence of high-speed fluid. In this embodiment of the invention, the flow equation is solved based on the Euler-Lagrange method, with the fluid as the continuous phase and the solid particles as the discrete phase. The changes in particle motion state are solved by differential equations, thereby obtaining the particle trajectory and energy transfer changes. This model can explore the interaction between solid particles and fluid. In numerical simulation calculations, the two do not affect each other, thus obtaining the flow field distribution inside the fracturing pipeline and the material loss and erosion distribution of the manifold wall.

[0083] In this embodiment of the invention, the erosion model is as follows:

[0084] ,

[0085] in, It represents the erosion and wear mass of particles on a unit area per unit time on the structural wall surface. This represents the average mass flow rate of the particles. This represents the number of particles colliding with the structural wall. It is a function of particle diameter; The impact angle between the particle flow path and the structural wall; is the impact angle function of the particle; is the relative velocity function of the particles with respect to the fracturing pressure; This is a function of the relative velocity of the particles; for solid particles such as quartz sand, the value is generally taken as 2.6. This represents the wall area of ​​the tube wall where the particles collide.

[0086] It should be noted that the erosion rate in Fluent simulation software is usually given in the form of mass loss rate (kg / m²-s) or volume loss rate (m / s), which needs to be converted into erosion depth over time.

[0087] The conversion relationship between maximum erosion rate and erosion depth in FLuent is as follows:

[0088] A1. Determine the material density (ρ): The fracturing pipeline material is 30CrMo steel, an alloy structural steel with good mechanical properties and wear resistance. Its density is typically around 7850 kg / m³.

[0089] A2. Conversion based on erosion rate type:

[0090] ①If the erosion rate is the mass loss rate ( ):

[0091] The linear erosion rate is obtained by dividing the mass loss rate by the material density. ):

[0092] ,

[0093] in: The linear erosion rate is expressed in m / s. The mass loss rate is expressed in kg / m²-s. ρ represents the density of the erosion material, in kg / m³.

[0094] ②If the erosion rate is the volume loss rate ( ):

[0095] Linear erosion rate ( Equals volume loss rate:

[0096] ,

[0097] in: The linear erosion rate is expressed in m / s. The volume loss rate is expressed in m / s.

[0098] A3. Calculate the erosion depth over time ( ):

[0099] Erosion depth equals linear erosion rate multiplied by time ( ):

[0100] ,

[0101] in: Erosion time, in seconds; The depth of erosion is in meters (m).

[0102] Numerous factors influence the maximum erosion rate during fracturing operations, and a single erosion simulation cannot fully reflect the erosion rate of the fracturing pipeline. In this embodiment of the invention, erosion simulation of the fracturing pipeline is performed in a simulation environment set according to the fracturing operation conditions to determine the key erosion locations and the maximum erosion rate. The timing of the first fracturing pipeline inspection and the replacement of pipe fittings are determined to avoid frequent maintenance and reduced construction efficiency. Then, an empirical formula is introduced to recalculate the erosion depth. Specifically, the erosion damage depth of the replaced pipe fittings is measured, and the erosion depth is calculated. Pressure in fracturing conditions The particle size of the proppant used and homework time The deep empirical formula is derived through correlation calculation:

[0103] ,

[0104] in: , , , , , , , , , These are constant coefficients, obtained through fitting during the optimization process; This refers to the fracturing pressure; The particle size of the proppant used; This refers to the operation time of the fracturing pipe fitting.

[0105] As field measurement data accumulates, empirical formulas can be continuously optimized and the database enriched. In subsequent pipeline safety assessments, these empirical formulas can be used to refine the formulas. Predictions can reduce safety assessment time, avoid excessive impact on fracturing operations, and ensure continuous operation.

[0106] In this embodiment of the invention, the erosion depth is calculated based on the maximum erosion rate, which corresponds to the degree of reduction in the fracturing pipeline wall thickness. The time required for the fracturing pipeline to reach the point of needing to replace the fittings (when the remaining fitting wall thickness is less than 75.90 mm) is calculated by referring to the fracturing pipeline risk assessment indicators. The remaining wall thickness is the original wall thickness minus the erosion depth.

[0107] In this embodiment of the invention, the simplified model from step S3 is imported into the Fluent + TransitionStructural module of ANSYS software for numerical simulation. The boundary stress load data of the flow field is transferred to the solid boundary to perform numerical simulation of the solid domain, thereby obtaining the stress variation of the pipe wall under fracturing operation conditions. Figure 6 As shown, the red area represents the region of maximum stress.

[0108] The stress in fracturing pipelines is affected not only by fracturing pressure and fracturing fluid velocity but also by the pipeline layout; all factors should be fully considered. Following the principle of minimum pipeline stress, a pipeline is considered reliable when the maximum stress it experiences is below the material's yield strength.

[0109] The risk level of a pipeline is determined by evaluating the erosion and stress changes. In this embodiment, the risk evaluation index of the fracturing pipeline is set as shown in Table 1 below. In Table 1, the remaining wall thickness is the original wall thickness of the pipeline minus the degree of reduction in the wall thickness of the fracturing pipeline (i.e., the erosion depth).

[0110] Table 1 Risk Assessment Indicators for Fracturing Pipelines

[0111]

[0112] When the erosion risk of a fracturing pipeline is at a dangerous level, it indicates that the pipeline is unreliable and prone to accidents such as punctures and perforations. In such cases, it is necessary to replace excessively thin parts of the pipeline and install isolation and protection measures around the pipeline to prevent injury from splashing materials. Regarding pipeline stress risk, the principle of minimum pipeline stress should be followed; if the maximum stress experienced by the fracturing pipeline is lower than the material's yield strength, the pipeline is considered reliable.

[0113] This invention uses erosion risk and stress fatigue risk of fracturing pipelines as important indicators for safety evaluation. An erosion simulation environment is constructed based on fracturing operation parameters. The simulation identifies weak points and key protection areas in the fracturing pipeline, and estimates the pipeline wall thickness decay time based on the maximum erosion rate, guiding the determination of pipeline maintenance opportunities and fitting replacement cycles. Stress simulation is used to consider stress changes in the pipeline, taking into account both the dynamic factors of fracturing fluid flow and the static factors of manifold layout. The safety evaluation of the fracturing pipeline is achieved through erosion risk and stress fatigue risk indicators.

[0114] Using the method of this invention, an erosion risk simulation was performed on a certain construction high-pressure pipe, and the erosion rates were obtained as shown in Table 2 below.

[0115] Table 2. Fracturing rate (kg / m²-s) in high-pressure tubing during fracturing operations

[0116]

[0117] Among them, 0.065mm, 0.065mm, 0.210mm, and 0.420mm are several typical values ​​in the range of proppant concentration variation during construction.

[0118] As shown in Table 2, the location with the highest erosion rate in the pipe during fracturing operations is the tee position. The average erosion rate for all fracturing conditions yields an erosion rate of 4.85 × 10⁻⁶ for the fracturing tee. -04 The fracturing elbow punching rate is 3.24 × 10⁻⁶. -04 The fracturing straight pipe flushing rate is 5.15 × 10⁻⁶. -05 .

[0119] Based on the fracturing bend erosion rate, the erosion depth is calculated as a time-varying value, as shown in Table 3 below.

[0120] Table 3. Data on wall thickness reduction in bends during fracturing operations

[0121]

[0122] The calculated working time for the fracturing bend to reach its wall thickness limit is 350 hours. This is basically consistent with the maximum time currently used for pipelines in fracturing operations.

[0123] Furthermore, pipeline vibration fatigue risk simulation is performed. The constructed three-dimensional model of the fracturing pipeline is imported into the Fluent + Transition Structural module in ANSYS software for numerical simulation. The boundary stress load data of the flow field is transferred to the solid boundary for numerical simulation of the solid domain. Finally, in the post-processing stage, relevant data such as flow velocity and pressure of the flow field can be obtained, and the vibration characteristics analysis of the solid domain can be obtained in the structural module.

[0124] Based on the simulation results, the stress and displacement distribution of the fracturing pipeline in the simplified model are obtained to evaluate the safety of the fracturing pipeline during fracturing operations. The evaluation considers two factors: the reduction in pipeline wall thickness due to erosion and the stress fatigue damage caused by the pipeline's installation and fixing methods. When the wall thickness of the large-diameter pipeline is greater than 75.9 mm, the pipeline is considered to have high safety and only requires periodic inspection. When the wall thickness of the large-diameter pipeline is less than 75.9 mm, more frequent inspections are needed to prevent rapid wall thickness decay leading to puncture or breakage accidents. The boundary stress load data of the flow field are transferred to the solid boundary for numerical stress simulation in the solid domain. By adjusting the fixing points and methods of the fracturing pipeline, the influence of pipeline layout on the stress magnitude can be obtained. Adjusting the fixing points and methods to minimize the stress on the pipeline, and considering the pipeline reliable when the maximum stress borne by the fracturing pipeline is lower than the material's yield strength, indicates that the pipeline is reliable.

[0125] Based on the above technical solution, the embodiments of the present invention offer convenience in the evaluation process, have minimal impact on fracturing operations, ensure the continuity of fracturing operations, and clearly identify key areas where risks may occur in fracturing pipelines, facilitating targeted inspection and replacement of pipelines. Clarifying the types of risks in fracturing pipelines can guide on-site safety assessments during fracturing operations. This method not only ensures the normal progress of fracturing operations but also guides safety inspections of fracturing pipelines, guaranteeing on-site safety during fracturing operations.

[0126] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for safety evaluation of hydraulic fracturing pipelines, characterized in that, include: Obtain the performance parameters of the field fracturing pipeline; A three-dimensional model of the fracturing pipeline was established based on the performance parameters of the fracturing pipeline. Based on the three-dimensional model of the fracturing pipeline, simulation software was used to simulate the erosion risk of the fracturing pipeline, obtain the erosion location and erosion rate of the fracturing pipeline, and convert the erosion rate into erosion depth. Establish a risk assessment level for fracturing pipelines, wherein the risk assessment level includes the correspondence between the remaining wall thickness of the fracturing pipeline and the risk level of the fracturing pipeline; Based on the risk assessment level and fracturing speed and depth of the fracturing pipeline, the inspection cycle and fitting replacement time of the fracturing pipeline are determined. Based on the three-dimensional model of the fracturing pipeline, simulation software was used to simulate the vibration fatigue risk of the fracturing pipeline, and the stress and displacement distribution of the fracturing pipeline were obtained. The safety of the fracturing pipeline during fracturing operations is evaluated based on the stress and displacement distribution of the fracturing pipeline.

2. The method for safety evaluation of hydraulic fracturing pipelines according to claim 1, characterized in that, The acquisition of performance parameters of the field fracturing pipeline includes: Obtain the geometric parameters of the fracturing pipeline: pipeline diameter and length, pipeline thickness, elbows, and tees; Obtain the material properties of fracturing pipelines: pipeline materials, main components of fracturing fluid, and solid particulate materials; Obtain fluid characteristics of fracturing pipelines: fluid density and viscosity, proppant solid particles, and flow velocity; Obtain the operating conditions of the fracturing pipeline: flow rate, pressure, and temperature.

3. The method for safety evaluation of hydraulic fracturing pipelines according to claim 2, characterized in that, The process of establishing a three-dimensional model of the fracturing pipeline based on its performance parameters includes: A three-dimensional model of the fracturing pipeline is constructed based on the pipeline diameter and length, pipeline thickness, elbow parameters, and the installation position and connection of elbows and tees used in fracturing operations.

4. The method for safety evaluation of hydraulic fracturing pipelines according to claim 3, characterized in that, The simulation of erosion risk of the fracturing pipeline, based on the three-dimensional model of the fracturing pipeline, is performed using simulation software, including: The three-dimensional model of the fracturing pipeline was imported into the Fluent module of ANSYS software, and the simulation environment was set according to the material properties and fluid properties of the fracturing pipeline. Based on the fluid-solid two-phase flow equation and erosion equation, the erosion risk of fracturing pipelines is simulated. The flow equations are solved using the Euler-Lagrange method with fluid as the continuous phase and solid particles as the discrete phase. The changes in particle motion state are solved by differential equations to obtain the internal flow field distribution of the fracturing pipeline and the material loss and erosion distribution of the fracturing pipeline wall. The erosion rate at the erosion location is obtained based on the erosion equation.

5. The method for safety evaluation of hydraulic fracturing pipelines according to claim 4, characterized in that, The process of converting the erosion rate into erosion depth includes: If the erosion rate obtained from the simulation is the mass loss rate, then divide the mass loss rate by the density of the fracturing pipeline material to obtain the linear erosion rate. If the erosion rate obtained from the simulation is the volume loss rate, then the volume loss rate is taken as the linear erosion rate. Multiplying the linear erosion rate by time yields the erosion depth over time.

6. The method for safety evaluation of hydraulic fracturing pipelines according to claim 1, characterized in that, The establishment of risk assessment levels for fracturing pipelines includes: The risk assessment levels for the fracturing pipeline include intact, mild, moderate, severe, and hazardous. For fracturing straight pipes, the following criteria are defined: no reduction in wall thickness indicates good condition; remaining wall thickness ≥ 100 mm indicates mild condition; remaining wall thickness ≥ 90 mm indicates moderate condition; remaining wall thickness ≥ 80 mm indicates severe condition; and remaining wall thickness < 75.90 mm indicates dangerous condition. For fracturing bends, the following criteria are defined: no reduction in wall thickness indicates good condition; remaining wall thickness ≥ 160 mm indicates mild condition; remaining wall thickness ≥ 130 mm indicates moderate condition; remaining wall thickness ≥ 100 mm indicates severe condition; and remaining wall thickness < 75.90 mm indicates dangerous condition. For fracturing tees, the following criteria are defined: no reduction in wall thickness indicates good condition; remaining wall thickness ≥ 220 mm indicates mild condition; remaining wall thickness ≥ 130 mm indicates moderate condition; remaining wall thickness ≥ 100 mm indicates severe condition; and remaining wall thickness < 75.90 mm indicates dangerous condition.

7. The method for safety evaluation of hydraulic fracturing pipelines according to claim 6, characterized in that, The process of establishing the inspection cycle and fitting replacement time for the fracturing pipeline based on the risk assessment level and fracturing speed and depth includes: Based on the location of erosion, plan the key areas and inspection cycles for safety inspection of fracturing pipelines; The erosion depth over time is calculated based on the maximum erosion rate. The remaining wall thickness is obtained by subtracting the erosion depth from the original wall thickness of the fracturing pipeline. The time required for the fracturing pipeline to meet the replacement criteria is determined by the risk assessment level and remaining wall thickness of the fracturing pipeline; the replacement criteria refer to a remaining wall thickness of less than 75.90 mm.

8. The method for safety evaluation of hydraulic fracturing pipelines according to claim 7, characterized in that, The method further includes: simulating the erosion risk of the fracturing pipeline, and after replacing the pipe fittings, measuring the erosion depth of the replaced pipe fittings, and recording the measured erosion depth... An empirical formula for fracturing depth is derived by correlating the pressure P, the proppant particle size S, and the operation time t under fracturing conditions: ， in: , , , , , , , , , These are constant coefficients, obtained through fitting during the optimization process; This refers to the fracturing pressure; The particle size of the proppant used; The operation time for fracturing pipe fittings; As field measurement data is accumulated and the empirical formula is continuously optimized, it can be directly applied to the safety evaluation of fracturing pipelines in later stages. Make predictions.

9. The method for safety evaluation of hydraulic fracturing pipelines according to claim 3, characterized in that, Based on the three-dimensional model of the fracturing pipeline, simulation software is used to simulate the vibration fatigue risk of the fracturing pipeline, obtaining the stress and displacement distribution of the fracturing pipeline, including: The three-dimensional model of the fracturing pipeline was imported into the Fluent + Transition Structural module of ANSYS software for numerical simulation. The boundary stress load data of the flow field was transferred to the solid boundary to perform numerical stress simulation in the solid domain, and the stress change of the pipe wall under fracturing operation was obtained. By adjusting the fixing points and fixing methods of the fracturing pipeline, the influence of pipeline layout on the stress magnitude of the fracturing pipeline can be obtained. Adjusting the fixing points and fixing methods of the pipeline can minimize the stress on the pipeline. If the maximum stress borne by the fracturing pipeline obtained from the simulation is lower than the yield strength of the material, then the fracturing pipeline is reliable.

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