A method for quantitative safety evaluation of a tailpipe hanger

Abstract

The application provides a tailpipe hanger quantitative safety evaluation method, and belongs to the technical field of high-temperature and high-pressure deep well production. The application establishes a finite element mechanics entity model of a position where a tailpipe hanger is located, converts the finite element mechanics entity model of the position where the tailpipe hanger is located into a finite element mechanics grid model; performs finite element simulation and simulation on a pressure gradient of the tailpipe hanger and an outer wall of a tieback cylinder thereof; establishes a prediction model of the pressure gradient of the outer wall of the pipe string varying with internal pressure; establishes a triaxial stress checking model of a technical casing pipe; and performs safety evaluation on the tailpipe hanger by using the prediction model of the pressure gradient of the outer wall of the pipe string varying with internal pressure and the triaxial stress checking model of the technical casing pipe. The application breaks through to realize quantitative evaluation on the safety of the tailpipe hanger according to the ground stress and the internal pressure of the wellbore in time, and has guiding significance for actual production.

Description

Technical Field

[0001] This invention relates to the field of high-temperature and high-pressure deep well production technology, and in particular to a quantitative safety evaluation method for tailpipe hangers. Background Technology

[0002] In well operations, well depth significantly impacts operational requirements. Tail-end suspension cementing is typically employed in deep well operations. Using a tail-end hanger for cementing reduces the weight of casing run into the well during deep well runs, improves the load on the drilling rig's hoisting system during casing run-in, reduces the flow resistance of the cement slurry, and promotes safer operations. Tail-end reconnection can resolve drilling operations affected by upper casing wear. Tail-end suspension cementing also reduces casing usage, saving drilling costs. Furthermore, for well operations in areas with extremely high formation pressure (up to 153 MPa) and high shut-in pressure (up to 118 MPa), according to the requirements of high-temperature, high-pressure well integrity design, guidelines, and management regulations, the tail-end hanger, as a key component of the well barrier, has a significant impact on well testing, fracturing, and well control safety during operations such as well testing and fracturing.

[0003] In practical applications of tailpipe hangers in deep and ultra-deep high-temperature wells, especially under complex conditions after cementing of ultra-deep tailpipe hangers, the actual external wall pressure of the hydraulic cylinder and its safety analysis and evaluation are crucial for safe production. However, currently, field engineers or tailpipe hanger designers can only estimate the pressure on the hanger's external wall after cementing based on experience, such as directly calculating the external pressure based on formation pressure transmitted to the hydraulic cylinder or directly calculating the external pressure based on brine density and liquid column pressure. This leads to inaccurate pressure calculations and makes it difficult to guarantee safety. Currently, there is no readily available safety evaluation method for tailpipe hangers, necessitating targeted research in this area.

[0004] Improving the structure of the tailpipe suspension itself can enhance its safety to some extent. However, due to the lack of practical application verification and the lack of accurate evaluation of the tailpipe suspension's safety, it is impossible to predict and detect unsafe conditions of the tailpipe suspension in a timely manner.

[0005] The existing technology has the following shortcomings:

[0006] 1. Technicians rely on experience to make estimations, and there is a lack of methods for evaluating the safety of tailpipe suspensions;

[0007] 2. Improvements to the tailpipe suspension's own structure cannot avoid the problem of lacking a safety assessment of the tailpipe suspension, making it impossible to predict and detect unsafe conditions of the tailpipe suspension in a timely manner. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a quantitative safety evaluation method for tailpipe hangers, comprising the following steps: establishing a finite element mechanical solid model of the tailpipe hanger's location, wherein the finite element mechanical solid model, starting from the cross-section where the tailpipe hanger is located and proceeding inward, consists of the cross-section formation, cement sheath, technical casing, liquid, hydraulic cylinder, and central pipe; the technical casing includes: a hydraulic cylinder located in the middle, a return sleeve connected to the upper part of the hydraulic cylinder, and a tailpipe connected to the lower part of the hydraulic cylinder; converting the finite element mechanical solid model of the tailpipe hanger's location into a finite element mechanical mesh model; performing finite element simulation on the pressure gradient of the outer wall of the tailpipe hanger and its return sleeve; establishing a predictive model for the change of pressure gradient on the outer wall of the tubing string with internal pressure; establishing a triaxial stress verification model for the technical casing; and using the predictive model for the change of pressure gradient on the outer wall of the tubing string with internal pressure and the triaxial stress verification model for the technical casing to conduct a safety evaluation of the tailpipe hanger. This invention achieves a breakthrough in realizing timely and quantitative evaluation of the safety of tailpipe hangers based on ground stress and wellbore pressure, which has guiding significance for actual production.

[0009] This invention provides a quantitative safety evaluation method for tailpipe suspension devices, comprising the following steps:

[0010] A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder.

[0011] Convert the finite element solid model of the tailpipe hanger location into a finite element mesh model.

[0012] In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation.

[0013] Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model;

[0014] Establish a triaxial stress verification model for the technical sleeve;

[0015] A predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger.

[0016] Preferably, the finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return cylinder specifically includes: establishing a finite element simulation calculation model of the external ground stress of the hanger cylinder or return cylinder using plane strain, and applying the maximum and minimum ground stress of the stratum to the finite element simulation calculation model of the external ground stress of the hanger cylinder or return cylinder.

[0017] Preferably, the finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return sleeve further includes: establishing a finite element simulation calculation model of the external ground stress of the tailpipe using plane strain, and applying the maximum and minimum ground stress of the stratum to the finite element simulation calculation model of the external ground stress of the tailpipe.

[0018] Preferably, the finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return tube further includes: calculating and saving the pressure distribution at each contact interface, and dividing the pressure on the contact surface of the innermost hydraulic cylinder or the outer wall of the return tube by the well depth to obtain the pressure gradient data.

[0019] Preferably, based on the established finite element mechanical mesh model, combined with the geostress and rock mechanical parameters, formation rock, cement sheath and technical casing mechanical parameters, as well as the geostress and wellbore pressure at the calculated location, the pressure distribution at each contact interface is obtained.

[0020] Preferably, a predictive model is established for the pressure gradient on the outer wall of the tubing as a function of internal pressure, specifically including:

[0021] Based on the location of the tailpipe hanger, formation pressure, maximum horizontal stress gradient, minimum horizontal stress gradient, in-tubing fracturing fluid density under extreme conditions, and tubing back pressure required for the fracturing plate, the in-situ stress at the hanger location and the pressure P inside the wellbore and hydraulic cylinder are obtained. i ;

[0022] An internal pressure P is applied to the wellbore and the hydraulic cylinder in the mesh model of the finite element mechanical solid model. i and formation pressure P out P out Take the maximum horizontal ground stress;

[0023] The suspended weight T of the tailpipe in the cement slurry is calculated using the following formula:

[0024] T=(ρ s -ρ m A s L

[0025] in,

[0026] ρ s Density of steel;

[0027] ρ m Density of cementing mud;

[0028] A s This refers to the cross-sectional area of ​​the tailpipe.

[0029] L is the length of the tailpipe;

[0030] Apply a corresponding preload to the central tube; the preload is determined based on the suspended weight.

[0031] Continuously change the pressure P inside the wellbore i Obtain the corresponding contact pressure on each path;

[0032] The relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure under different working conditions was obtained.

[0033] Preferably, after obtaining the relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure on the inner wall under different working conditions, the following steps are also included:

[0034] The average value of the external pressure along the path with the thinnest cylinder wall, which varies with the internal pressure, is taken as the cylinder's external wall pressure. This yields the pressure P of the wellbore's internal pressure and the cylinder's external wall pressure. o The relationship is as follows:

[0035] P o =0.618Pi + 30.5

[0036] Obtain the internal pressure P of the wellbore i Pressure P on the outer wall of the central tube oc The relationship is as follows:

[0037] P oc =0.322Pi + 43.6

[0038] In the calculation process, the Drucker-Prager failure criterion is used to determine whether the cement sheath and the profiled formation rock have failed. The expression is as follows:

[0039]

[0040] In the formula,

[0041] α and k are both material parameters;

[0042] f represents the micro-element strength of the rock in the cross-section, in MPa;

[0043]

[0044]

[0045] I1=σ1+σ2+σ3

[0046]

[0047] In the formula,

[0048] The friction angle of the material;

[0049] C represents the cohesive force of the material;

[0050] σ1, σ2, and σ3 are the maximum principal stress, intermediate principal stress, and minimum principal stress, respectively;

[0051] I1 is the first invariant of stress;

[0052] J2 is the second invariant of stress deviator.

[0053] Preferably, the establishment of the triaxial stress verification model for the technical sleeve specifically includes:

[0054] The three axes include: Z-axis, r-axis, and circumferential axis; the positive direction of the Z-axis is downward along the center of the wellbore, the positive direction of the r-axis is outward along the radial direction of the wellbore, and the circumferential axis is θ.

[0055] Based on the Lame formula for tubular structures in elasticity theory, the axial stress σ of the technical casing is established. z Radial stress σ r and circumferential stress σ θ The calculation model is as follows:

[0056]

[0057]

[0058]

[0059] in,

[0060] P o The external extrusion force (MPa) of the technical casing;

[0061] P i The internal pressure (MPa) of the technical casing;

[0062] r o The outer radius of the technical sleeve (mm);

[0063] r i The inner radius of the technical sleeve (mm);

[0064] r is any radius (mm) of the technical sleeve;

[0065] δ θ Let r be the circumferential stress (MPa) at any radius r of the technical sleeve;

[0066] δ Z Let r be the axial stress (MPa) at any radius r of the technical sleeve;

[0067] δ r Let r be the radial stress (MPa) at any radius r of the technical sleeve;

[0068] F a For axial load (N).

[0069] Preferably, the safety evaluation of the tailpipe hanger is conducted using a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure and a triaxial stress verification model of the technical casing, specifically including:

[0070] The pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube were calculated based on a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure.

[0071] Based on the calculated pressure on the outer wall of the hydraulic cylinder and the outer wall of the central tube, the axial stress σ at any radius r of the sleeve is used. z Radial stress σ r and circumferential stress σ θ The computational model calculates the triaxial stress of the technical sleeve;

[0072] The safety of the tailpipe suspension is evaluated based on triaxial stress and triaxial stress safety factor.

[0073] Preferably, the safety evaluation of the tailpipe hanger is conducted using a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure and a triaxial stress verification model of the technical casing, specifically including:

[0074] Based on the pressure inside the wellbore and the pressure on the outer wall of the hydraulic cylinder P o The relationship between the two formulas is used to calculate the pressure P on the outer wall of the hydraulic cylinder when the internal pressure Pi of the wellbore is given. o ;

[0075] According to the wellbore internal pressure P i Pressure P on the outer wall of the central tube oc The relationship between the two formulas is used to calculate the pressure P on the outer wall of the central tube when the internal pressure Pi of the wellbore is given. oc ;

[0076] The axial stress σ of the casing is adopted. z Radial stress σ r and circumferential stress σ θ The calculation model calculates the radial stress, circumferential stress, and axial stress of the casing.

[0077] According to the Von-Mises yield strength criterion of the fourth strength theory, determine whether the triaxial stress of the technical sleeve satisfies the following formula and the safety factor S3 of the triaxial stress is ≥1.25. If all conditions are met, the tailpipe hanger is in a safe state; otherwise, the tailpipe hanger is in a dangerous state.

[0078]

[0079]

[0080] In the formula,

[0081] σ VME The triaxial stress (MPa) of the technical sleeve;

[0082] Y p The yield strength (MPa) of the pipe material for the technical casing;

[0083] S3 is the safety factor for triaxial stress.

[0084] Preferably, the conversion of the finite element solid model of the tailpipe suspension location into a finite element mesh model specifically includes:

[0085] The finite element mechanical solid model uses 8-node elements to divide the structural mesh, and contact finite elements are used between different material interfaces to establish 5 sets of contact pair element models.

[0086] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0087] (1) This invention adopts the finite element method theory of elastoplastic contact problem and the principle and method of nonlinear contact problem of discontinuous medium to establish a finite element mechanical solid model of the position of the tailpipe hanger in ultra-deep high temperature and high pressure well. On this basis, a general prediction model of the pressure gradient of the outer wall of the pipe string as a function of the internal pressure is established, so as to realize the timely quantitative evaluation of the safety of the hanger based on the ground stress and the pressure inside the well.

[0088] (2) This invention establishes a general prediction model of the pressure gradient of the outer wall of the tubing string as a function of internal pressure by finite element simulation of the pressure gradient of the tailpipe hanger and its return sleeve, and forms a set of calculation formulas that break through technical bottlenecks. This facilitates triaxial stress verification and safety evaluation of the hanger cylinder, return sleeve and tailpipe, and also facilitates the formulation of wellhead limit pressure, providing a reliable guidance method for the standard evaluation of tailpipe hangers in ultra-deep wells. Attached Figure Description

[0089] Figure 1 This is a flowchart of a quantitative safety evaluation method for tailpipe hangers according to an embodiment of the present invention;

[0090] Figure 2 This is a flowchart of a quantitative safety evaluation method for tailpipe hangers according to another embodiment of the present invention;

[0091] Figure 3 A finite element mechanical solid model of the cross-section of the tailpipe hanger location, established for an embodiment of the present invention; σ in the figure m This is ground stress;

[0092] Figure 4 (a) and (b) are schematic diagrams of the solid model of the downhole hydraulic cylinder and return sleeve established according to an embodiment of the present invention; P in the figure in For internal pressure, P out Formation pressure;

[0093] Figure 5 This is a schematic diagram of the well shaft structure of the tailpipe hanger according to an embodiment of the present invention;

[0094] Figure 6 This is a 1 / 4 scale structural diagram of the finite element mechanical solid model of the tailpipe hanger location according to an embodiment of the present invention (the tailpipe hanger is a double-layered tube column); in the figure, σ H The maximum ground stress (MPa); σ h The minimum ground stress (MPa) is shown; the arrow on the left indicates the casing pressure.

[0095] Figure 7 (a) and (b) are, respectively, the finite element mechanical solid model and mesh model of the tailpipe hanger location established according to an embodiment of the present invention; in the figure, σ H The maximum ground stress (MPa); σ h Minimum ground stress (MPa); P i The internal pressure of the casing (MPa);

[0096] Figure 8 This is a schematic diagram of the distribution of in-situ stress and wellbore pressure transmitted to various interfaces, obtained according to an embodiment of the present invention; in the figure, R1, R2, R3, R4 and R5 are the radii of the inner wall of the cement sheath, the inner wall of the technical casing, the outer wall of the technical casing, the inner wall of the hydraulic cylinder, the inner wall of the central tube and the outer wall of the central tube, respectively, and n1, n2, n3 and n4 represent the interface level. Detailed Implementation

[0097] The following is in conjunction with the appendix Figure 1-8 The specific embodiments of the present invention will be described in detail below.

[0098] This invention provides a quantitative safety evaluation method for tailpipe suspension devices, comprising the following steps:

[0099] A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder.

[0100] Convert the finite element solid model of the tailpipe hanger location into a finite element mesh model.

[0101] In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation.

[0102] Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model;

[0103] Establish a triaxial stress verification model for the technical sleeve;

[0104] A predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger.

[0105] According to a specific embodiment of the present invention, the finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return cylinder specifically includes: establishing a finite element simulation calculation model of the external ground stress of the hanger cylinder or return cylinder using plane strain, and applying the maximum and minimum ground stress of the stratum to the finite element simulation calculation model of the external ground stress of the hanger cylinder or return cylinder.

[0106] According to a specific embodiment of the present invention, the finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return sleeve further includes: establishing a finite element simulation calculation model of the external ground stress of the tailpipe using plane strain, and applying the maximum and minimum ground stress of the stratum to the finite element simulation calculation model of the external ground stress of the tailpipe.

[0107] According to a specific embodiment of the present invention, the finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return tube further includes: calculating and saving the pressure distribution at each contact interface, and dividing the pressure on the contact surface of the innermost hydraulic cylinder or the outer wall of the return tube by the well depth to obtain the pressure gradient data.

[0108] According to a specific embodiment of the present invention, based on the established finite element mechanical mesh model, combined with the geostress and rock mechanical parameters, formation rock, cement sheath and technical casing mechanical parameters, as well as the geostress and wellbore pressure at the calculated location, the pressure distribution of each contact interface is obtained.

[0109] According to a specific embodiment of the present invention, a predictive model for the change of pressure gradient on the outer wall of the tubing as a function of internal pressure is established, specifically including:

[0110] Based on the location of the tailpipe hanger, formation pressure, maximum horizontal stress gradient, minimum horizontal stress gradient, in-tubing fracturing fluid density under extreme conditions, and tubing back pressure required for the fracturing plate, the in-situ stress at the hanger location and the pressure P inside the wellbore and hydraulic cylinder are obtained. i ;

[0111] An internal pressure P is applied to the wellbore and the hydraulic cylinder in the mesh model of the finite element mechanical solid model. i and formation pressure P out P out Take the maximum horizontal ground stress;

[0112] The suspended weight T of the tailpipe in the cement slurry is calculated using the following formula:

[0113] T=(ρs -ρ m A s L

[0114] in,

[0115] ρ s Density of steel;

[0116] ρ m Density of cementing mud;

[0117] A s This refers to the cross-sectional area of ​​the tailpipe.

[0118] L is the length of the tailpipe;

[0119] Apply a corresponding preload to the central tube; the preload is determined based on the suspended weight.

[0120] Continuously change the pressure P inside the wellbore i Obtain the corresponding contact pressure on each path;

[0121] The relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure under different working conditions was obtained.

[0122] According to a specific embodiment of the present invention, after obtaining the relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure on the inner wall under different working conditions, the following steps are further included:

[0123] The average value of the external pressure along the path with the thinnest cylinder wall, which varies with the internal pressure, is taken as the cylinder's external wall pressure. This yields the pressure P of the wellbore's internal pressure and the cylinder's external wall pressure. o The relationship is as follows:

[0124] P o =0.618Pi + 30.5

[0125] Obtain the internal pressure P of the wellbore i Pressure P on the outer wall of the central tube oc The relationship is as follows:

[0126] P oc =0.322Pi + 43.6

[0127] In the calculation process, the Drucker-Prager failure criterion is used to determine whether the cement sheath and the profiled formation rock have failed. The expression is as follows:

[0128]

[0129] In the formula,

[0130] α and k are both material parameters;

[0131] f represents the micro-element strength of the rock in the cross-section, in MPa;

[0132]

[0133]

[0134] I1=σ1+σ2+σ3

[0135]

[0136] In the formula,

[0137] The friction angle of the material;

[0138] C represents the cohesive force of the material;

[0139] σ1, σ2, and σ3 are the maximum principal stress, intermediate principal stress, and minimum principal stress, respectively;

[0140] I1 is the first invariant of stress;

[0141] J2 is the second invariant of stress deviator.

[0142] According to a specific embodiment of the present invention, the establishment of the triaxial stress verification model for the technical sleeve specifically includes:

[0143] The three axes include: Z-axis, r-axis, and circumferential axis; the positive direction of the Z-axis is downward along the center of the wellbore, the positive direction of the r-axis is outward along the radial direction of the wellbore, and the circumferential axis is θ.

[0144] Based on the Lame formula for tubular structures in elasticity theory, the axial stress σ of the technical casing is established. z Radial stress σ r and circumferential stress σ θ The calculation model is as follows:

[0145]

[0146]

[0147]

[0148] in,

[0149] P o The external extrusion force (MPa) of the technical casing;

[0150] P i The internal pressure (MPa) of the technical casing;

[0151] r o The outer radius of the technical sleeve (mm);

[0152] ri The inner radius of the technical sleeve (mm);

[0153] r is any radius (mm) of the technical sleeve;

[0154] δ θ Let r be the circumferential stress (MPa) at any radius r of the technical sleeve;

[0155] δ Z Let r be the axial stress (MPa) at any radius r of the technical sleeve;

[0156] δ r Let r be the radial stress (MPa) at any radius r of the technical sleeve;

[0157] F a For axial load (N).

[0158] According to a specific embodiment of the present invention, the safety evaluation of the tailpipe hanger is carried out using a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure and a triaxial stress verification model of the technical casing, specifically including:

[0159] The pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube were calculated based on a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure.

[0160] Based on the calculated pressure on the outer wall of the hydraulic cylinder and the outer wall of the central tube, the axial stress σ at any radius r of the sleeve is used. z Radial stress σ r and circumferential stress σ θ The computational model calculates the triaxial stress of the technical sleeve;

[0161] The safety of the tailpipe suspension is evaluated based on triaxial stress and triaxial stress safety factor.

[0162] According to a specific embodiment of the present invention, the safety evaluation of the tailpipe hanger is carried out using a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure and a triaxial stress verification model of the technical casing, specifically including:

[0163] Based on the pressure inside the wellbore and the pressure on the outer wall of the hydraulic cylinder P o The relationship between the two formulas is used to calculate the pressure P on the outer wall of the hydraulic cylinder when the internal pressure Pi of the wellbore is given. o ;

[0164] According to the wellbore internal pressure P i Pressure P on the outer wall of the central tube oc The relationship between the two formulas is used to calculate the pressure P on the outer wall of the central tube when the internal pressure Pi of the wellbore is given. oc ;

[0165] The axial stress σ of the casing is adopted. z Radial stress σr and circumferential stress σ θ The calculation model calculates the radial stress, circumferential stress, and axial stress of the casing.

[0166] According to the Von-Mises yield strength criterion of the fourth strength theory, determine whether the triaxial stress of the technical sleeve satisfies the following formula and the safety factor S3 of the triaxial stress is ≥1.25. If all conditions are met, the tailpipe hanger is in a safe state; otherwise, the tailpipe hanger is in a dangerous state.

[0167]

[0168]

[0169] In the formula,

[0170] σ VME The triaxial stress (MPa) of the technical sleeve;

[0171] Y p The yield strength (MPa) of the pipe material for the technical casing;

[0172] S3 is the safety factor for triaxial stress.

[0173] According to a specific embodiment of the present invention, the conversion of the finite element solid model of the location of the tailpipe hanger into a finite element mesh model specifically includes:

[0174] The finite element mechanical solid model uses 8-node elements to divide the structural mesh, and contact finite elements are used between different material interfaces to establish 5 sets of contact pair element models.

[0175] Example 1

[0176] According to a specific embodiment of the present invention, the quantitative safety evaluation method for tailpipe hangers of the present invention will be described in detail below.

[0177] This invention provides a quantitative safety evaluation method for tailpipe suspension devices, comprising the following steps:

[0178] A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder.

[0179] Convert the finite element solid model of the tailpipe hanger location into a finite element mesh model.

[0180] In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation.

[0181] Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model;

[0182] Establish a triaxial stress verification model for the technical sleeve;

[0183] A predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger.

[0184] Example 2

[0185] According to a specific embodiment of the present invention, the quantitative safety evaluation method for tailpipe hangers of the present invention will be described in detail below.

[0186] This invention provides a quantitative safety evaluation method for tailpipe suspension devices, comprising the following steps:

[0187] A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder.

[0188] Convert the finite element solid model of the tailpipe hanger location into a finite element mesh model.

[0189] In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation.

[0190] Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model;

[0191] Establish a triaxial stress verification model for the technical sleeve;

[0192] A predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger.

[0193] The finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return sleeve specifically includes:

[0194] A finite element simulation model of the external ground stress of the suspension cylinder or return tube is established using plane strain, and the maximum and minimum ground stresses of the strata are applied to the finite element simulation model of the external ground stress of the suspension cylinder or return tube.

[0195] A finite element simulation model of the external geostress of the tailpipe was established using plane strain, and the maximum and minimum geostress of the strata were applied to the finite element simulation model of the external geostress of the tailpipe.

[0196] Based on the established finite element mechanical mesh model, combined with the geostress and rock mechanical parameters, formation rock, cement sheath and technical casing mechanical parameters, as well as the geostress and wellbore pressure at the calculation location, the pressure distribution of each contact interface is obtained.

[0197] Save the pressure distribution at each contact interface, and divide the pressure on the outer wall contact surface of the innermost liquid cylinder or return cylinder by the well depth to obtain pressure gradient data.

[0198] Example 3

[0199] According to a specific embodiment of the present invention, the quantitative safety evaluation method for tailpipe hangers of the present invention will be described in detail below.

[0200] This invention provides a quantitative safety evaluation method for tailpipe suspension devices, comprising the following steps:

[0201] A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder.

[0202] Convert the finite element solid model of the tailpipe hanger location into a finite element mesh model.

[0203] In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation.

[0204] Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model;

[0205] Establish a triaxial stress verification model for the technical sleeve;

[0206] A predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger.

[0207] A predictive model for the pressure gradient on the outer wall of the tubing as a function of internal pressure is established, specifically including:

[0208] Based on the location of the tailpipe hanger, formation pressure, maximum horizontal stress gradient, minimum horizontal stress gradient, in-tubing fracturing fluid density under extreme conditions, and tubing back pressure required for the fracturing plate, the in-situ stress at the hanger location and the pressure P inside the wellbore and hydraulic cylinder are obtained. i ;

[0209] An internal pressure P is applied to the wellbore and the hydraulic cylinder in the mesh model of the finite element mechanical solid model. i and formation pressure P out P out Take the maximum horizontal ground stress;

[0210] The suspended weight T of the tailpipe in the cement slurry is calculated using the following formula:

[0211] T=(ρ s -ρ m A s L

[0212] in,

[0213] ρ s Density of steel;

[0214] ρ m Density of cementing mud;

[0215] A s This refers to the cross-sectional area of ​​the tailpipe.

[0216] L is the length of the tailpipe;

[0217] Apply a corresponding preload to the central tube; the preload is determined based on the suspended weight.

[0218] Continuously change the pressure P inside the wellbore i Obtain the corresponding contact pressure on each path;

[0219] The relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure under different working conditions was obtained.

[0220] The average value of the external pressure along the path with the thinnest cylinder wall, which varies with the internal pressure, is taken as the cylinder's external wall pressure. This yields the pressure P of the wellbore's internal pressure and the cylinder's external wall pressure. o The relationship is as follows:

[0221] P o =0.618Pi + 30.5

[0222] Obtain the internal pressure P of the wellbore i Pressure P on the outer wall of the central tube oc The relationship is as follows:

[0223] P oc =0.322Pi + 43.6

[0224] In the calculation process, the Drucker-Prager failure criterion is used to determine whether the cement sheath and the profiled formation rock have failed. The expression is as follows:

[0225]

[0226] In the formula,

[0227] α and k are both material parameters;

[0228] f represents the micro-element strength of the rock in the cross-section, in MPa;

[0229]

[0230]

[0231] I1=σ1+σ2+σ3

[0232]

[0233] In the formula,

[0234] The friction angle of the material;

[0235] C represents the cohesive force of the material;

[0236] σ1, σ2, and σ3 are the maximum principal stress, intermediate principal stress, and minimum principal stress, respectively;

[0237] I1 is the first invariant of stress;

[0238] J2 is the second invariant of stress deviator.

[0239] The triaxial stress verification model for establishing the technical sleeve specifically includes:

[0240] The three axes include: Z-axis, r-axis, and circumferential axis; the positive direction of the Z-axis is downward along the center of the wellbore, the positive direction of the r-axis is outward along the radial direction of the wellbore, and the circumferential axis is θ.

[0241] Based on the Lame formula for tubular structures in elasticity theory, the axial stress σ of the technical casing is established. z Radial stress σ r and circumferential stress σ θ The calculation model is as follows:

[0242]

[0243]

[0244]

[0245] in,

[0246] P o The external extrusion force (MPa) of the technical casing;

[0247] P iThe internal pressure (MPa) of the technical casing;

[0248] r o The outer radius of the technical sleeve (mm);

[0249] r i The inner radius of the technical sleeve (mm);

[0250] r is any radius (mm) of the technical sleeve;

[0251] δ θ Let r be the circumferential stress (MPa) at any radius r of the technical sleeve;

[0252] δ Z Let r be the axial stress (MPa) at any radius r of the technical sleeve;

[0253] δ r Let r be the radial stress (MPa) at any radius r of the technical sleeve;

[0254] F a For axial load (N).

[0255] The safety evaluation of the tailpipe hanger is conducted using a predictive model of the pressure gradient on the outer wall of the tubing as a function of internal pressure and a triaxial stress verification model of the technical casing. Specifically, this includes:

[0256] The pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube were calculated based on a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure.

[0257] Based on the calculated pressure on the outer wall of the hydraulic cylinder and the outer wall of the central tube, the axial stress σ at any radius r of the sleeve is used. z Radial stress σ r and circumferential stress σ θ The computational model calculates the triaxial stress of the technical sleeve;

[0258] The safety of the tailpipe suspension is evaluated based on triaxial stress and triaxial stress safety factor.

[0259] Example 4

[0260] According to a specific embodiment of the present invention, the quantitative safety evaluation method for tailpipe hangers of the present invention will be described in detail below.

[0261] This invention provides a quantitative safety evaluation method for tailpipe suspension devices, comprising the following steps:

[0262] A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder.

[0263] Convert the finite element solid model of the tailpipe hanger location into a finite element mesh model.

[0264] In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation.

[0265] Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model;

[0266] Establish a triaxial stress verification model for the technical sleeve;

[0267] A predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger.

[0268] A predictive model for the pressure gradient on the outer wall of the tubing as a function of internal pressure is established, specifically including:

[0269] Based on the location of the tailpipe hanger, formation pressure, maximum horizontal stress gradient, minimum horizontal stress gradient, in-tubing fracturing fluid density under extreme conditions, and tubing back pressure required for the fracturing plate, the in-situ stress at the hanger location and the pressure P inside the wellbore and hydraulic cylinder are obtained. i ;

[0270] An internal pressure P is applied to the wellbore and the hydraulic cylinder in the mesh model of the finite element mechanical solid model. i and formation pressure P out P out Take the maximum horizontal ground stress;

[0271] The suspended weight T of the tailpipe in the cement slurry is calculated using the following formula:

[0272] T=(ρ s -ρ m A s L

[0273] in,

[0274] ρ s Density of steel;

[0275] ρ m Density of cementing mud;

[0276] A s This refers to the cross-sectional area of ​​the tailpipe.

[0277] L is the length of the tailpipe;

[0278] Apply a corresponding preload to the central tube; the preload is determined based on the suspended weight.

[0279] Continuously change the pressure P inside the wellbore i Obtain the corresponding contact pressure on each path;

[0280] The relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure under different working conditions was obtained.

[0281] The average value of the external pressure along the path with the thinnest cylinder wall, which varies with the internal pressure, is taken as the cylinder's external wall pressure. This yields the pressure P of the wellbore's internal pressure and the cylinder's external wall pressure. o The relationship is as follows:

[0282] P o =0.618Pi + 30.5

[0283] Obtain the internal pressure P of the wellbore i Pressure P on the outer wall of the central tube oc The relationship is as follows:

[0284] P oc =0.322Pi + 43.6

[0285] In the calculation process, the Drucker-Prager failure criterion is used to determine whether the cement sheath and the profiled formation rock have failed. The expression is as follows:

[0286]

[0287] In the formula,

[0288] α and k are both material parameters;

[0289] f represents the micro-element strength of the rock in the cross-section, in MPa;

[0290]

[0291]

[0292] I1=σ1+σ2+σ3

[0293]

[0294] In the formula,

[0295] The friction angle of the material;

[0296] C represents the cohesive force of the material;

[0297] σ1, σ2, and σ3 are the maximum principal stress, intermediate principal stress, and minimum principal stress, respectively;

[0298] I1 is the first invariant of stress;

[0299] J2 is the second invariant of stress deviator.

[0300] The triaxial stress verification model for establishing the technical sleeve specifically includes:

[0301] The three axes include: Z-axis, r-axis, and circumferential axis; the positive direction of the Z-axis is downward along the center of the wellbore, the positive direction of the r-axis is outward along the radial direction of the wellbore, and the circumferential axis is θ.

[0302] Based on the Lame formula for tubular structures in elasticity theory, the axial stress σ of the technical casing is established. z Radial stress σ r and circumferential stress σ θ The calculation model is as follows:

[0303]

[0304]

[0305]

[0306] in,

[0307] P o The external extrusion force (MPa) of the technical casing;

[0308] P i The internal pressure (MPa) of the technical casing;

[0309] r o The outer radius of the technical sleeve (mm);

[0310] r i The inner radius of the technical sleeve (mm);

[0311] r is any radius (mm) of the technical sleeve;

[0312] δ θ Let r be the circumferential stress (MPa) at any radius r of the technical sleeve;

[0313] δ Z Let r be the axial stress (MPa) at any radius r of the technical sleeve;

[0314] δ r Let r be the radial stress (MPa) at any radius r of the technical sleeve;

[0315] F a For axial load (N).

[0316] The safety evaluation of the tailpipe hanger is conducted using a predictive model of the pressure gradient on the outer wall of the tubing as a function of internal pressure and a triaxial stress verification model of the technical casing. Specifically, this includes:

[0317] Based on the pressure inside the wellbore and the pressure on the outer wall of the hydraulic cylinder P o The relationship between the two formulas is used to calculate the pressure P on the outer wall of the hydraulic cylinder when the internal pressure Pi of the wellbore is given. o ;

[0318] According to the wellbore internal pressure P i Pressure P on the outer wall of the central tube oc The relationship between the two formulas is used to calculate the pressure P on the outer wall of the central tube when the internal pressure Pi of the wellbore is given. oc ;

[0319] The axial stress σ of the casing is adopted. z Radial stress σ r and circumferential stress σ θ The calculation model calculates the radial stress, circumferential stress, and axial stress of the casing.

[0320] According to the Von-Mises yield strength criterion of the fourth strength theory, determine whether the triaxial stress of the technical sleeve satisfies the following formula and the safety factor S3 of the triaxial stress is ≥1.25. If all conditions are met, the tailpipe hanger is in a safe state; otherwise, the tailpipe hanger is in a dangerous state.

[0321]

[0322]

[0323] In the formula,

[0324] σ VME The triaxial stress (MPa) of the technical sleeve;

[0325] Y p The yield strength (MPa) of the pipe material for the technical casing;

[0326] S3 is the safety factor for triaxial stress.

[0327] Example 5

[0328] According to a specific embodiment of the present invention, the quantitative safety evaluation method for tailpipe hangers of the present invention will be described in detail below.

[0329] This invention provides a quantitative safety evaluation method for tailpipe suspension devices, comprising the following steps:

[0330] A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder.

[0331] The finite element mechanical solid model of the tailpipe hanger location is converted into a finite element mechanical mesh model. The finite element mechanical solid model uses 8-node elements to divide the structural mesh, and contact finite elements are used between different material interfaces to establish 5 sets of contact pair element models.

[0332] In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation.

[0333] Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model;

[0334] Establish a triaxial stress verification model for the technical sleeve;

[0335] A predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger.

[0336] The finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return sleeve specifically includes:

[0337] A finite element simulation model of the external ground stress of the suspension cylinder or return tube is established using plane strain, and the maximum and minimum ground stresses of the strata are applied to the finite element simulation model of the external ground stress of the suspension cylinder or return tube.

[0338] A finite element simulation model of the external geostress of the tailpipe was established using plane strain, and the maximum and minimum geostress of the strata were applied to the finite element simulation model of the external geostress of the tailpipe.

[0339] Based on the established finite element mechanical mesh model, combined with the geostress and rock mechanical parameters, formation rock, cement sheath and technical casing mechanical parameters, as well as the geostress and wellbore pressure at the calculation location, the pressure distribution of each contact interface is obtained.

[0340] Save the pressure distribution at each contact interface, and divide the pressure on the outer wall contact surface of the innermost liquid cylinder or return cylinder by the well depth to obtain pressure gradient data.

[0341] A predictive model for the pressure gradient on the outer wall of the tubing as a function of internal pressure is established, specifically including:

[0342] Based on the location of the tailpipe hanger, formation pressure, maximum horizontal stress gradient, minimum horizontal stress gradient, in-tubing fracturing fluid density under extreme conditions, and tubing back pressure required for the fracturing plate, the in-situ stress at the hanger location and the pressure P inside the wellbore and hydraulic cylinder are obtained. i ;

[0343] An internal pressure P is applied to the wellbore and the hydraulic cylinder in the mesh model of the finite element mechanical solid model. i and formation pressure P out P out Take the maximum horizontal ground stress;

[0344] The suspended weight T of the tailpipe in the cement slurry is calculated using the following formula:

[0345] T=(ρ s -ρ m A s L

[0346] in,

[0347] ρ s Density of steel;

[0348] ρ m Density of cementing mud;

[0349] A s This refers to the cross-sectional area of ​​the tailpipe.

[0350] L is the length of the tailpipe;

[0351] Apply a corresponding preload to the central tube; the preload is determined based on the suspended weight.

[0352] Continuously change the pressure P inside the wellbore i Obtain the corresponding contact pressure on each path;

[0353] The relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure under different working conditions was obtained.

[0354] The average value of the external pressure along the path with the thinnest cylinder wall, which varies with the internal pressure, is taken as the cylinder's external wall pressure. This yields the pressure P of the wellbore's internal pressure and the cylinder's external wall pressure. o The relationship is as follows:

[0355] P o =0.618Pi + 30.5

[0356] Obtain the internal pressure P of the wellbore i Pressure P on the outer wall of the central tube oc The relationship is as follows:

[0357] P oc =0.322Pi + 43.6

[0358] In the calculation process, the Drucker-Prager failure criterion is used to determine whether the cement sheath and the profiled formation rock have failed. The expression is as follows:

[0359]

[0360] In the formula,

[0361] α and k are both material parameters;

[0362] f represents the micro-element strength of the rock in the cross-section, in MPa;

[0363]

[0364]

[0365] I1=σ1+σ2+σ3

[0366]

[0367] In the formula,

[0368] The friction angle of the material;

[0369] C represents the cohesive force of the material;

[0370] σ1, σ2, and σ3 are the maximum principal stress, intermediate principal stress, and minimum principal stress, respectively;

[0371] I1 is the first invariant of stress;

[0372] J2 is the second invariant of stress deviator.

[0373] The triaxial stress verification model for establishing the technical sleeve specifically includes:

[0374] The three axes include: Z-axis, r-axis, and circumferential axis; the positive direction of the Z-axis is downward along the center of the wellbore, the positive direction of the r-axis is outward along the radial direction of the wellbore, and the circumferential axis is θ.

[0375] Based on the Lame formula for tubular structures in elasticity theory, the axial stress σ of the technical casing is established. z Radial stress σ r and circumferential stress σ θ The calculation model is as follows:

[0376]

[0377]

[0378]

[0379] in,

[0380] P o The external extrusion force (MPa) of the technical casing;

[0381] P i The internal pressure (MPa) of the technical casing;

[0382] r o The outer radius of the technical sleeve (mm);

[0383] r i The inner radius of the technical sleeve (mm);

[0384] r is any radius (mm) of the technical sleeve;

[0385] δ θ Let r be the circumferential stress (MPa) at any radius r of the technical sleeve;

[0386] δ Z Let r be the axial stress (MPa) at any radius r of the technical sleeve;

[0387] δ r Let r be the radial stress (MPa) at any radius r of the technical sleeve;

[0388] F a For axial load (N).

[0389] The safety evaluation of the tailpipe hanger is conducted using a predictive model of the pressure gradient on the outer wall of the tubing as a function of internal pressure and a triaxial stress verification model of the technical casing. Specifically, this includes:

[0390] Based on the pressure inside the wellbore and the pressure on the outer wall of the hydraulic cylinder P o The relationship between the two formulas is used to calculate the pressure P on the outer wall of the hydraulic cylinder when the internal pressure Pi of the wellbore is given. o ;

[0391] According to the wellbore internal pressure P i Pressure P on the outer wall of the central tube oc The relationship between the two formulas is used to calculate the pressure P on the outer wall of the central tube when the internal pressure Pi of the wellbore is given. oc ;

[0392] The axial stress σ of the casing is adopted. z Radial stress σ r and circumferential stress σ θ The calculation model calculates the radial stress, circumferential stress, and axial stress of the casing.

[0393] According to the Von-Mises yield strength criterion of the fourth strength theory, determine whether the triaxial stress of the technical sleeve satisfies the following formula and the safety factor S3 of the triaxial stress is ≥1.25. If all conditions are met, the tailpipe hanger is in a safe state; otherwise, the tailpipe hanger is in a dangerous state.

[0394]

[0395]

[0396] In the formula,

[0397] σ VME The triaxial stress (MPa) of the technical sleeve;

[0398] Y p The yield strength (MPa) of the pipe material for the technical casing;

[0399] S3 is the safety factor for triaxial stress.

[0400] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A quantitative safety evaluation method for tailpipe suspension devices, characterized in that, Includes the following steps: A finite element mechanical solid model of the location of the tailpipe hanger is established. The finite element mechanical solid model consists of the following elements from the cross section where the tailpipe hanger is located inward: cross section strata, cement sheath, technical sleeve, liquid, liquid cylinder and central tube. The technical sleeve includes: liquid cylinder located in the middle, return sleeve connected to the upper part of the liquid cylinder and tailpipe connected to the lower part of the liquid cylinder. Convert the finite element solid model of the tailpipe hanger location into a finite element mesh model. In the finite element mechanical mesh model, the pressure gradient of the tailpipe hanger and the outer wall of its return cylinder is simulated by finite element simulation. Establish a predictive model for the variation of pressure gradient on the outer wall of a tubular column with internal pressure in a finite element mechanical mesh model; Establish a triaxial stress verification model for the technical sleeve; A prediction model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure was used, along with a triaxial stress verification model of the technical casing, to evaluate the safety of the tailpipe hanger. A predictive model for the pressure gradient on the outer wall of the tubing as a function of internal pressure is established, specifically including: According to the position of the liner hanger, formation pressure, maximum horizontal stress gradient, minimum horizontal stress gradient, fracturing fluid density in the pipe under the limit working condition and the required tubing back pressure of the fracturing rupture disc, the ground stress at the position of the hanger and the pressure P in the wellbore and the liquid cylinder are obtained i ; An internal pressure P is applied to the wellbore and the hydraulic cylinder in the mesh model of the finite element mechanical solid model. i and formation pressure P out P out Take the maximum horizontal ground stress; The suspended weight T of the tailpipe in the cement slurry is calculated using the following formula: in, Density of steel; Density of cementing mud; This refers to the cross-sectional area of ​​the tailpipe. L This refers to the length of the tailpipe. Apply a corresponding preload to the central tube; the preload is determined based on the suspended weight. Continuously change the pressure P inside the wellbore i Obtain the corresponding contact pressure on each path; The relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube and the pressure under different working conditions was obtained. After obtaining the relationship between the pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube under different working conditions, the following steps are also included: The average value of the external pressure along the path with the thinnest cylinder wall, which varies with the internal pressure, is taken as the cylinder's external wall pressure. This yields the pressure P of the wellbore's internal pressure and the cylinder's external wall pressure. o The relationship is as follows: Obtain the internal pressure P of the wellbore i Pressure P on the outer wall of the central tube oc The relationship is as follows: In the calculation process, the Drucker-Prager failure criterion is used to determine whether the cement sheath and the profiled formation rock have failed. The expression is as follows: In the formula, α and k All are material parameters; f The strength of the rock element in the cross-section is expressed in MPa. In the formula, The friction angle of the material; C represents the cohesive force of the material; , , These are the maximum principal stress, intermediate principal stress, and minimum principal stress, respectively. I 1 is the first invariant of stress; J 2 is the second invariant of stress deviator.

2. The quantitative safety evaluation method for tailpipe hangers according to claim 1, characterized in that, The finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return cylinder specifically includes: establishing a finite element simulation model of the external ground stress of the hanger cylinder or return cylinder using plane strain, and applying the maximum and minimum ground stress of the stratum to the finite element simulation model of the external ground stress of the hanger cylinder or return cylinder.

3. The quantitative safety evaluation method for tailpipe hangers according to claim 2, characterized in that, The finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return sleeve also includes: establishing a finite element simulation calculation model of the external geostress of the tailpipe using plane strain, and applying the maximum and minimum geostress of the stratum to the finite element simulation calculation model of the external geostress of the tailpipe.

4. The quantitative safety evaluation method for tailpipe hangers according to claim 3, characterized in that, Finite element simulation of the pressure gradient on the outer wall of the tailpipe hanger and its return tube also includes: calculating and saving the pressure distribution at each contact interface, and dividing the pressure on the contact surface of the innermost hydraulic cylinder or the outer wall of the return tube by the well depth to obtain the pressure gradient data.

5. The quantitative safety evaluation method for tailpipe hangers according to claim 4, characterized in that, Based on the established finite element mechanical mesh model, combined with the geostress and rock mechanical parameters, formation rock, cement sheath and technical casing mechanical parameters, as well as the geostress and wellbore pressure at the calculated location, the pressure distribution at each contact interface is obtained.

6. The quantitative safety evaluation method for tailpipe hangers according to claim 1, characterized in that, The triaxial stress verification model for establishing the technical sleeve specifically includes: The three axes include: Z-axis, r-axis, and circumferential axis; the positive direction of the Z-axis is downward along the center of the wellbore, the positive direction of the r-axis is outward along the radial direction of the wellbore, and the circumferential axis is θ. Based on the Lame formula for tubular structures in elasticity theory, the axial stress of the technical casing is established. Radial stress and circumferential stress The calculation model is as follows: in, P o The external extrusion force of the technical casing is expressed in MPa. P i The internal pressure of the technical casing is expressed in MPa. r o The outer radius of the technical sleeve is expressed in mm. r i The inner radius of the technical sleeve is in mm. r The radius of the technical sleeve is arbitrary, in mm; δ θ Let r be the circumferential stress at any radius r of the technical sleeve, in MPa. δ Z Let r be the axial stress at any radius r of the technical sleeve, in MPa. δ r The radial stress at any radius r of the technical sleeve is expressed in MPa. F a This is the axial load, measured in N.

7. The quantitative safety evaluation method for tailpipe hangers according to claim 6, characterized in that, The safety evaluation of the tailpipe hanger is conducted using a predictive model of the pressure gradient on the outer wall of the tubing as a function of internal pressure and a triaxial stress verification model of the technical casing. Specifically, this includes: The pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube were calculated based on a predictive model of the pressure gradient on the outer wall of the tubing as a function of the internal pressure. Based on the calculated pressure on the outer wall of the hydraulic cylinder and the pressure on the outer wall of the central tube, the axial stress at any radius r of the sleeve is used. Radial stress and circumferential stress The computational model calculates the triaxial stress of the technical sleeve; The safety of the tailpipe suspension is evaluated based on triaxial stress and triaxial stress safety factor.

8. The quantitative safety evaluation method for tailpipe hangers according to claim 7, characterized in that, The safety evaluation of the tailpipe hanger is conducted using a predictive model of the pressure gradient on the outer wall of the tubing as a function of internal pressure and a triaxial stress verification model of the technical casing. Specifically, this includes: Based on the pressure inside the wellbore and the pressure on the outer wall of the hydraulic cylinder P o The relationship between the two formulas is used to calculate the pressure P on the outer wall of the hydraulic cylinder when the internal pressure Pi of the wellbore is given. o ; According to the wellbore internal pressure P i Pressure P on the outer wall of the central tube oc The relationship between the two formulas is used to calculate the pressure P on the outer wall of the central tube when the internal pressure Pi of the wellbore is given. oc ; Axial stress of the casing using technology Radial stress and circumferential stress The calculation model calculates the radial stress, circumferential stress, and axial stress of the casing. Based on the Von-Mises yield strength criterion of the fourth strength theory, determine whether the triaxial stress of the technical sleeve satisfies the following formula and the safety factor of the triaxial stress. S If 3 ≥ 1.25, the tailpipe suspension is in a safe state; otherwise, the tailpipe suspension is in a dangerous state. In the formula, σ VME The triaxial stress of the technical sleeve is expressed in MPa. Y p The yield strength of the pipe material for the technical casing is expressed in MPa. S 3 is the safety factor for triaxial stress.

9. The quantitative safety evaluation method for tailpipe hangers according to claim 5, characterized in that, The process of converting the finite element solid model of the tailpipe hanger location into a finite element mesh model specifically includes: The finite element mechanical solid model uses 8-node elements to divide the structural mesh, and contact finite elements are used between different material interfaces to establish 5 sets of contact pair element models.

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