Method for predicting service life of coiled tubing under cooperation of plasticity and damage

Abstract

The method for predicting the service life of the coiled tubing under the cooperation of plasticity and damage is characterized in that the fatigue service life and the strain amplitude under the specific curvature radius are obtained through a full-size bending fatigue test, and the fatigue service life and the strain amplitude are substituted into a Manson-Coffin model to invert an unknown coefficient; the method comprises the following steps: determining mechanical parameters of a material in combination with a uniaxial tensile test, constructing a finite element mechanical model, carrying out finite element simulation on bending working conditions of a damaged coiled tubing on a roller and a guider, extracting strain amplitudes, and further establishing strain amplitude calculation models under different working conditions by adopting a Levenberg-Marquardt algorithm; coupling the model with a Manson-Coffin equation, and respectively constructing fatigue life prediction models of the roller and the guider; and on the basis of the Miner theory, three times of bending cycles with different curvatures in one trip are regarded as complete load cycles, an accumulated damage value is calculated, a correction coefficient is determined through low-cycle fatigue finite element simulation, a calculation model of the number of remaining trip times is established, and quantitative prediction of the remaining life is achieved. The method is suitable for the technical field of petroleum and natural gas drilling engineering.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well drilling and production engineering technology, specifically a method for predicting the life of coiled tubing under the combined effects of plasticity and damage. Background Technology

[0002] As global oil and gas exploration and development moves towards deeper, unconventional, and complex operating conditions, coiled tubing, as a core operating material in the oil and gas development field, is a key piece of equipment for solving complex development problems and ensuring increased oil and gas reserves and production. It can serve as an essential piece of equipment for unconventional oil and gas development, solving problems such as drilling and grinding bridge plugs and wellbore cleaning in long horizontal shale oil and gas wells. It can also serve as a technical support for increasing production in old wells and treating inefficient wells, enabling the removal of accumulated fluids in old wells and the repair of tubing strings to restore production capacity. Compared with traditional drill pipe operation technology, coiled tubing has the advantages of strong operational flexibility, high efficiency, and versatility. A single length can reach several kilometers and can be bent and coiled, enabling continuous tripping under pressure, adapting to complex well conditions. It also has faster tripping speed, smaller footprint, and lower energy consumption. It can also be attached to different tools to complete dozens of operations such as well workover, logging, and drilling. It has been widely used in shale oil and gas, deep wells, and ultra-deep wells.

[0003] However, due to its unique operating method, coiled tubing undergoes three bending-straightening cycles during a single trip to and from the well, with different radii of curvature for each bend: the first bend occurs when wound onto the drum, while the latter two bends occur during passage through the guide. This repeated bending-straightening process easily leads to material fatigue damage, resulting in fatigue failure. Simultaneously, coiled tubing typically operates in harsh environments with high temperatures, high pressures, and corrosive media, making it susceptible to corrosion and surface or localized damage. These damaged areas exhibit stress concentration effects, further exacerbating the initiation and propagation of fatigue cracks, significantly shortening the service life of the coiled tubing, increasing the risk of downhole accidents, and threatening operational safety. Therefore, there is an urgent need for a technical solution that can accurately predict the remaining life of coiled tubing to ensure operational safety and optimize equipment lifespan.

[0004] Furthermore, existing methods for predicting the life of coiled tubing typically only consider its fatigue life under a single constant bending radius condition, failing to accurately reflect the varied bending conditions experienced by the coiled tubing during tripping in and out of the well. This simplistic assumption can easily lead to misjudgments of the actual service life of the coiled tubing: on the one hand, it may overestimate its fatigue life, potentially causing safety accidents; on the other hand, it may underestimate its effective service life, resulting in unnecessary replacements and increased operating costs.

[0005] To overcome the shortcomings of existing technologies, this invention proposes a method for predicting the fatigue life of coiled tubing under the combined effects of plasticity and damage. This method considers both the impact of corrosion damage on the fatigue life of coiled tubing and the influence of changes in the radius of curvature during the tripping process. This enables high-precision prediction of the fatigue life of coiled tubing under the combined effects of plastic deformation and damage. Using the method provided by this invention, petroleum engineers can accurately assess the remaining service life of coiled tubing and make timely risk identification and maintenance decisions. Summary of the Invention

[0006] The purpose of this invention is to provide a method for predicting the life of coiled tubing under the combined effects of plasticity and damage, so as to achieve high-precision prediction of the fatigue life of coiled tubing under the combined effects of plastic deformation and damage. This method is applicable to the life prediction of coiled tubing of different steel grades under the service conditions of deep wells, ultra-deep wells and unconventional oil and gas wells.

[0007] To achieve the above objectives, the present invention provides a method for predicting the life of coiled tubing under the synergistic effects of plasticity and damage. The method is characterized by: firstly, conducting full-scale bending fatigue tests on the coiled tubing to obtain its fatigue life and corresponding strain amplitude at a specific radius of curvature; substituting the measured fatigue life and strain amplitude into the Manson-Coffin fatigue life model to invert and determine the fatigue ductility index and fatigue plasticity coefficient in the model; secondly, performing uniaxial tensile tests on the coiled tubing material to determine its basic mechanical parameters, and constructing a mechanical constitutive model of the coiled tubing in finite element simulation software based on the obtained parameters; thirdly, performing finite element simulations on the mechanical behavior of damaged coiled tubing under bending conditions to obtain strain amplitude data when bending on rollers and guides, respectively; and finally, using the Levenberg-Marquardt optimization algorithm to establish strain amplitude calculation models suitable for different bending conditions; subsequently, combining the strain amplitude calculation model with the Manson-Coffin fatigue life model to establish fatigue life calculation models for the coiled tubing under bending conditions on rollers and guides, respectively; and finally, based on Miner... The linear cumulative damage theory considers the three bending cycles with different radii of curvature experienced by coiled tubing during a single well trip as a complete load cycle. Based on this, the cumulative damage value is calculated, and a correction factor is introduced. This correction factor is determined through low-cycle fatigue finite element simulation, establishing a model for calculating the remaining number of well trips that coiled tubing can be run through. By substituting relevant parameters of the coiled tubing, a quantitative prediction of the service life of the coiled tubing can be achieved. The specific technical solution adopted is as follows.

[0008] Step 1: Obtain the service pressure of the coiled tubing in the field P Pipe diameter D Wall thickness t Drum radius Rg and guide radius R d Ultrasonic testing was conducted on the coiled tubing on site to determine the depth of corrosion pits. H axial length L Z Circumferential length L H .

[0009] Step 2: Take coiled tubing of the same steel grade and manufacturer as the coiled tubing used on site, and divide it into two groups, A and B.

[0010] Step 3: Process the coiled tubing of Group A obtained in Step 2 into standard tensile test specimens, and cut the coiled tubing of Group B into two 1500mm long sections.

[0011] Step 4: Conduct a tensile test using the standard tensile test specimen obtained in Step 3 to measure the elastic modulus of the coiled tubing. E Poisson's ratio e And stress-strain constitutive relations.

[0012] Step 5: Conduct full-scale bending fatigue tests on the coiled tubing segments obtained in Step 3 under different bending radii to determine the fatigue life of the coiled tubing. N f The strain amplitude was measured using strain gauges during the experiment. e a .

[0013] Step Six: Based on the fatigue life of the coiled tubing measured in Step Five N f strain amplitude e a The Manson-Coffin fatigue life model was calculated. fatigue ductility index c Fatigue plasticity coefficient .

[0014] Step 7: Based on the fatigue ductility index obtained in Step 6 c Fatigue plasticity coefficient The Manson-Coffin fatigue life model for coiled tubing was obtained. N f = f1( e a ).

[0015] Step 8: Based on the coiled tubing diameter obtained in Step 1 D Wall thickness t Drum radius R gand guide radius R d A three-dimensional geometric model was established to simulate the bending mechanical behavior of coiled tubing with damage defects.

[0016] Step 9: Use the elastic modulus of the coiled tubing measured in Step 4. E Poisson's ratio e The stress-strain constitutive relationship and the three-dimensional geometric model established in step eight are used to establish a bending mechanical model of a coiled tubing with damage defects.

[0017] Step 10: Based on the mechanical model established in Step 9, conduct finite element simulations of the mechanical behavior of coiled tubing with the same damage defects bending at different radii of curvature under different internal pressures, and obtain the strain amplitude generated when coiled tubing with the same damage defects bends under different internal pressures.

[0018] Step 11: Based on the mechanical model established in Step 9, conduct finite element simulation of the mechanical behavior of continuous tubing with different depths of corrosion pits bending with different radii of curvature under the same internal pressure, and obtain the strain amplitude generated when continuous tubing with different depths of corrosion pits bends under the same internal pressure.

[0019] Step 12: Based on the mechanical model established in Step 9, conduct finite element simulation of the mechanical behavior of continuous tubing with corrosion pits of different axial lengths bending with different radii of curvature under the same internal pressure, and obtain the strain amplitude generated when continuous tubing with corrosion pits of different axial lengths bending under the same internal pressure.

[0020] Step 13: Based on the mechanical model established in Step 9, conduct finite element simulation of the mechanical behavior of continuous tubing with different circumferential length corrosion pits under the same internal pressure and bending with different radii of curvature, and obtain the strain amplitude generated when continuous tubing with different circumferential length corrosion pits bends under the same internal pressure.

[0021] Step Fourteen: Based on the strain amplitude data obtained in Steps Ten, Eleven, Twelve, and Thirteen, the Levenberg-Marquardt optimization algorithm is used to establish strain amplitude calculation models for coiled tubing bending on a drum. e ag = f2( P , H , L Z , L H ) and the strain amplitude calculation model when the coiled tubing bends on the guide. e ad = f3( P , H , L Z , L H).

[0022] Step 15: Apply the strain amplitude calculation model obtained in Step 14. e ag = f2( P , H , L Z , L H ), e ad = f3( P , H , L Z , L H Substitute these values ​​into the Manson-Coffin fatigue life model of the coiled tubing obtained in step seven. N f = f1( e a A fatigue life calculation model for coiled tubing bending on a drum was obtained. N fg = f4( P , H , L Z , L H And a fatigue life calculation model for bending on the guide. N fd = f5( P , H , L Z , L H ).

[0023] Step Sixteen: When tripping a well with coiled tubing, one bend is required on the drum and two bends on the guide tube. This is based on Miner's damage theory, with a correction factor introduced. α , β The formula for calculating the number of well runs is as follows: .

[0024] Step 17: Based on the bending mechanical model of the coiled tubing with damage defects established in Step 9, conduct two sets of low-cycle fatigue finite element simulations to obtain the number of well runs. N 1 , N 2 The service pressures of the two models are respectively P 1 , P 2 The depths of the corrosion pits are respectively H1 , H 2 The axial lengths are respectively L Z1 , L Z2 The circumferential lengths are respectively L H1 , L H2 .

[0025] Step 18: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require the full context.] P 1 , P 2 , H 1 , H 2 , L Z1 , L Z2 , L H1 , L H2 Substitute the values ​​into the fatigue life calculation model for the coiled tubing bending on the drum established in step 15. N fg = f4( P , H , L Z , L H ) and fatigue life calculation model when bending on the guide N fd = f5( P , H , L Z , L H ), thus obtaining the corresponding fatigue life. N fg1 , N fg2 , N fd1 , N fd2 .

[0026] Step 19: Based on the number of well runs obtained in Step 17 N 1 , N 2 and the result obtained in step eighteen N fg1 , N fg2 , N fd1 , Nfd2 The correction coefficients were obtained using an analytical method. α , β The formula for calculating the number of well runs obtained in step sixteen is further expressed as follows: .

[0027] Step 20: Use the coiled tubing service pressure obtained in Step 1 P Depth of corrosion pits H axial length L Z Circumferential length L H Substitute the fatigue life calculation model of the coiled tubing bending on the drum established in step 15 into the model. N fg = f4( P , H , L Z , L H The fatigue life of the coiled tubing when it bends on the drum is calculated. N fg .

[0028] Step 21: Use the coiled tubing service pressure obtained in Step 1 P Depth of corrosion pits H axial length L Z Circumferential length L H Substitute the fatigue life calculation model of the coiled tubing bending on the guide established in step 15 into the input model. N fd = f5( P , H , L Z, L H The fatigue life of the coiled tubing when it bends on the guide was calculated. N fd .

[0029] Step 22: Calculate the results in Step 20. N fg and the result calculated in step twenty-one N fd Substituting the formula for calculating the number of well runs obtained in step nineteen, the number of well runs that can be run with coiled tubing can be calculated. N This enables the prediction of the remaining life of coiled tubing.

[0030] The advantages of this invention are:

[0031] Taking into account the impact of damage and the different bending radii during the tripping of coiled tubing on fatigue life, this method enables high-precision prediction of the fatigue life of coiled tubing under the combined effects of plastic deformation and damage. Attached Figure Description

[0032] Figure 1 This is a technical roadmap for the present invention.

[0033] Figure 2 This is the stress-strain curve for a coiled tubing.

[0034] Figure 3 A mechanical model of bending of a coiled tubing with damage defects. Detailed Implementation

[0035] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail with reference to the accompanying drawings, but this should not be construed as limiting the scope of implementation of the present invention.

[0036] This invention proposes a method for predicting the life of coiled tubing under the combined effects of plasticity and damage. The method mainly includes the following steps.

[0037] Step 1: Obtain the service pressure of the coiled tubing in the field P = 60MPa, measured pipe diameter D = 60.3mm, wall thickness t =4.4mm, roller radius R g = 1145mm, guide radius R d = 2286mm, ultrasonic testing was conducted on the coiled tubing in the field to determine the depth of the corrosion pit. H = 0.3mm, axial length L Z = 6mm, circumferential length L H = 4mm.

[0038] Step 2: Take coiled tubing of the same steel grade and manufacturer as the coiled tubing used on site, and divide it into two groups, A and B.

[0039] Step 3: Process the coiled tubing of Group A obtained in Step 2 into standard tensile test specimens, and cut the coiled tubing of Group B into two 1500mm long pipe segments, which are designated as pipe segments 1# and 2# respectively.

[0040] Step 4: Conduct a tensile test using the standard tensile test specimen obtained in Step 3 to measure the elastic modulus of the coiled tubing. E = 189.1 GPa, Poisson's ratio e= 0.3, Stress-strain constitutive relations are as follows: Figure 2 As shown.

[0041] Step 5: Conduct full-scale bending fatigue tests on pipe sections #1 and #2 obtained in Step 3, with bending radii of curvature of 1219 mm and 1829 mm respectively. The fatigue lives of pipe sections #1 and #2 were measured to be... N f1 = 347 times N f2 = 679 times, strain amplitudes were respectively e a1 = 0.0208、 e a2 = 0.0139.

[0042] Step Six: Take the measurements obtained in Step Five N f1 = 347 times N f2 = 679 times e a1 = 0.0208、 e a2 = 0.0139 Substituted into the Manson-Coffin fatigue life model In the process, the fatigue ductility index was calculated. c = -0.6043, fatigue plasticity coefficient = 0.5418.

[0043] Step 7: Based on the fatigue ductility index obtained in Step 6 c Fatigue plasticity coefficient The Manson-Coffin fatigue life model for coiled tubing was obtained. .

[0044] Step 8: Based on the coiled tubing diameter obtained in Step 1 D Wall thickness t Drum radius R g and guide radius R d A three-dimensional geometric model was established to simulate the bending mechanical behavior of coiled tubing with damage defects.

[0045] Step 9: Use the elastic modulus of the coiled tubing measured in Step 4. E Poisson's ratio e The stress-strain constitutive relation and the three-dimensional geometric model established in step seven are used to establish a bending mechanical model of a coiled tubing with damage defects, as shown in the attached figure. Figure 3 As shown.

[0046] Step 10: Based on the mechanical model established in Step 9, conduct internal pressure analysis. P = 0, 15, 30, 45, 60 MPa, Corrosion pit depth of coiled tubing H = 0.6mm, axial length of corrosion pit L Z = 5mm, axial length of corrosion pit L H = 5mm, radius of curvature R Finite element simulation of bending mechanical behavior at 1145mm and 2286mm was performed. The strain amplitudes generated by bending of continuous tubing with the same damage defects under different internal pressures are shown in the table below. Step 11: Based on the mechanical model established in Step 9, conduct internal pressure analysis. P = 30MPa, depth of corrosion pit in coiled tubing H = 0.3, 0.6, 0.9, 1.2, 1.5 mm, axial length of corrosion pit L Z = 5mm, axial length of corrosion pit L H = 5mm, radius of curvature R Finite element simulation of bending mechanical behavior at 1145mm and 2286mm was performed, and the strain amplitude generated by bending of continuous tubing with different depths of corrosion pits under the same internal pressure is shown in the table below. Step 12: Based on the mechanical model established in Step 9, conduct internal pressure analysis. P = 30MPa, depth of corrosion pit in coiled tubing H = 0.6mm, axial length of corrosion pit L Z = 5, 10, 15, 20, 25 mm, axial length of corrosion pit L H = 5mm, radius of curvature R Finite element simulation of bending mechanical behavior at 1145mm and 2286mm was performed. The strain amplitude of continuous tubing with corrosion pits of different axial lengths under the same internal pressure during bending is shown in the table below. Step Thirteen: Based on the mechanical model established in Step Nine, conduct internal pressure analysis. P = 30MPa, depth of corrosion pit in coiled tubing H = 0.6mm, axial length of corrosion pit L Z = 5mm, axial length of corrosion pitL H = 5, 10, 15, 20, 25 mm, radius of curvature R Finite element simulation of bending mechanical behavior at 1145mm and 2286mm was performed. The strain amplitude of continuous tubing with different circumferential length corrosion pits under the same internal pressure during bending is shown in the table below. Step Fourteen: Based on the strain amplitude data obtained in Steps Ten, Eleven, Twelve, and Thirteen, the Levenberg-Marquardt optimization algorithm is used to establish a strain amplitude calculation model for coiled tubing bending on a drum. Calculation model for strain amplitude of coiled tubing bending on guide tube .

[0047] Step 15: Apply the strain amplitude calculation model obtained in Step 14. e ag = f2( P , H , L Z , L H ), e ad = f3( P , H , L Z , L H Substitute these values ​​into the Manson-Coffin fatigue life model of the coiled tubing obtained in step seven. N f = f1( e a ), thus obtaining a fatigue life calculation model for coiled tubing bending on a drum. And a fatigue life calculation model for coiled tubing bending on a guide. .

[0048] Step Sixteen: When tripping a well with coiled tubing, one bend is required on the drum and two bends on the guide tube. This is based on Miner's damage theory, with a correction factor introduced. α , β The formula for calculating the number of well runs is as follows: .

[0049] Step 17: Based on the bending mechanical model of the damaged coiled tubing established in Step 9, conduct two sets of low-cycle fatigue finite element simulations to obtain the number of well runs. N 1 = 29、 N2 = 34, where the service pressures of the two models are respectively P 1 =60MPa P 2 = 60MPa corrosion pit depths are respectively H 1 = 0.3mm, H 2 = 0.15mm, axial lengths are respectively L Z1 = 6mm L Z2 = 7mm, circumferential lengths are respectively L H1 = 5mm L H2 = 5mm.

[0050] Step 18: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require the full context.] P 1 , P 2 , H 1 , H 2 , L Z1 , L Z2 , L H1 , L H2 Substitute the values ​​into the fatigue life calculation model for the coiled tubing bending on the drum established in step 15. N fg = f4( P , H , L Z , L H ) and fatigue life calculation model when bending on the guide N fd = f5( P , H , L Z , L H ), thus obtaining the corresponding fatigue life. N fg1 = 41 times N fg2 = 49 times N fd1 = 147 times Nfd2 = 184 times.

[0051] Step 19: Based on the number of well runs obtained in Step 17 N 1 = 27、 N 2 = 33 and the result obtained in step eighteen N fd1 , N fd2 , N fg1 , N fg2 The correction coefficients were obtained using a nonlinear fitting method. α = 0.99、 β = 0.92, the formula for calculating the number of well runs obtained in step sixteen is further expressed as: .

[0052] Step 20: Use the coiled tubing service pressure obtained in Step 1 P Depth of corrosion pits H axial length L Z Circumferential length L H Substitute the fatigue life calculation model of the coiled tubing bending on the drum established in step 15 into the model. N fg = f4( P , H , L Z , L H The fatigue life of the coiled tubing when it bends on the drum is calculated. N fg = 36 times.

[0053] Step 21: Use the coiled tubing service pressure obtained in Step 1 P Depth of corrosion pits H axial length L Z Circumferential length L H Substitute the fatigue life calculation model of the coiled tubing bending on the guide established in step 15 into the input model. N fd = f5( P , H , L Z , L H The fatigue life of the coiled tubing when it bends on the guide was calculated. Nfd = 266 times.

[0054] Step 22: Calculate the fatigue life of the coiled tubing under bending conditions on the drum, as obtained in Step 20. N fg And the fatigue life of the coiled tubing under bending on the guide, calculated in step twenty-one. N fd ,Will N fg , N fd Substituting the formula for calculating the number of well runs obtained in step nineteen, the number of well runs that can be run with coiled tubing can be calculated. N = 29 trips.

[0055] This invention proposes a method for predicting the fatigue life of coiled tubing under the combined effects of plasticity and damage. This method considers both the impact of damage on the fatigue life of coiled tubing and the influence of different bending radii during the tripping process. This enables high-precision prediction of the fatigue life of coiled tubing under the combined effects of plastic deformation and damage. Using the method provided by this invention, petroleum engineers can accurately assess the remaining service life of coiled tubing and make timely risk identification and maintenance decisions.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting the life of coiled tubing under the combined effects of plasticity and damage, characterized in that, The method mainly includes the following steps: (a) Obtain the service pressure, geometry, and corrosion pit geometry parameters of the coiled tubing in the field; (b) Tensile tests and full-scale bending fatigue tests were conducted on coiled tubing of the same manufacturer and steel grade to obtain its mechanical property parameters and Manson-Coffin fatigue life model; (c) Based on the geometric dimensions of step (a) and the mechanical performance parameters of step (b), establish a bending mechanical model of a coiled tubing with damage defects. (d) Based on the mechanical model in step (c), perform finite element simulation to construct strain amplitude calculation models for bending on the roller and guide respectively, and combine them with the fatigue life model in step (b) to obtain the corresponding fatigue life calculation model. (e) Based on Miner's damage theory and combined with the fatigue life calculation model in step (d), establish a formula for calculating the number of well runs, and determine the correction coefficient through finite element simulation; (f) Substitute the field parameters obtained in step (a) into the corrected calculation formula to obtain the number of runs that can be run into the well with coiled tubing, and complete the prediction of remaining life.

2. The method for predicting the life of coiled tubing under the synergistic effects of plasticity and damage according to claim 1, characterized in that, The geometric dimensions mentioned in step (a) include pipe diameter, wall thickness, roller radius, and guide radius; the geometric parameters of the corrosion pit include corrosion pit depth, axial length, and circumferential length.

3. The method for predicting the life of coiled tubing under the synergistic effects of plasticity and damage according to claim 1, characterized in that, The mechanical performance parameters mentioned in step (b) include elastic modulus, Poisson's ratio, and stress-strain constitutive relation; the Manson-Coffin fatigue life model is... Its fatigue ductility index c and fatigue plasticity coefficient Fatigue life measured by full-scale bending fatigue test and strain amplitude Calculated.

4. The method for predicting the life of coiled tubing under the synergistic effects of plasticity and damage according to claim 1, characterized in that, The strain amplitude calculation model described in step (d) is as follows: when bending on the drum When bending on the guide ;in P Due to service pressure, H This represents the depth of the corrosion pit. L Z axial length L H The circumferential length is given; this model was obtained by fitting the finite element simulation data using the Levenberg-Marquardt optimization algorithm.

5. The method for predicting the life of coiled tubing under the synergistic effects of plasticity and damage according to claim 1, characterized in that, The fatigue life calculation model described in step (d) is as follows: when bending on the roller... When bending on the guide .

6. The method for predicting the life of coiled tubing under the synergistic effects of plasticity and damage according to claim 1, characterized in that, The formula for calculating the number of well runs mentioned in step (e) is as follows: ,in α , β The correction factor is obtained by substituting the number of well runs obtained from at least two sets of finite element simulations and the fatigue life calculated in step (d) into the formula and solving it analytically.

Images