Fatigue prediction method of drilling tool based on cycle accumulation, terminal and medium

Abstract

The invention particularly relates to a fatigue prediction method of a drilling tool based on cycle accumulation, a terminal and a medium. The fatigue prediction method comprises the steps that S10, the operated alternating stress amplitude and the operated cycle of the drilling tool in the using process are recorded; s20, the current in-use alternating stress amplitude and the in-use cycle of the drilling tool are obtained; and S30, according to the operated alternating stress amplitudes, the operated cycles, the in-use alternating stress amplitudes and the in-use cycles, the current remaining operation cycles of the drilling tool are obtained. According to the method, the operated alternating stress amplitude and the in-use alternating stress amplitude of the alternating stress amplitude are comprehensively considered, the situation that the alternating stress amplitude is complex and changeable can be well dealt with, and the accuracy of drilling tool fatigue prediction is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of drill string risk prediction, and particularly to a fatigue prediction method, a terminal and a medium for a drill string based on cycle accumulation. Background Art

[0002] In the process of exploiting resources such as oil and natural gas, drilling operation is a crucial link. As a key equipment for drilling, the drill string works in a complex and harsh downhole environment and bears various complex loads, resulting in easy fatigue damage of the drill string. According to statistics, more than 80% of the failures of the drill string belong to fatigue damage. The fatigue damage of the drill string is a very serious problem, which may lead to downhole accidents such as drill string fracture and stuck pipe, affecting the drilling progress, increasing costs, and threatening the safety of personnel.

[0003] For example, the fatigue life prediction method for the bottom hole assembly based on drill string dynamics disclosed in CN113065211A discloses a drill string fatigue prediction method, which predicts the drill string fatigue by means of dynamics and improves the effectiveness of drill string life prediction.

[0004] For example, a method for evaluating the risk of drill string fatigue failure disclosed in CN103967428B also discloses a drill string fatigue prediction method, which jointly determines the fatigue condition of the drill string through wellbore structure, drill string assembly structure and wellbore trajectory parameters, etc.

[0005] The prior arts all provide a single-dimensional fatigue prediction method, resulting in deviation in the accuracy of the drill string life prediction results obtained by the above technical solutions. In addition, the prior art CN113065211A mainly uses the dynamics method, which needs to comprehensively consider multiple mechanical factors such as system kinetic energy, system potential energy, system gravity and system centrifugal force, and the prediction method is relatively complex; while CN103967428B needs to consider wellbore structure, drill string assembly structure and actual wellbore trajectory parameters, and too many external factors are involved. Although the accuracy can be improved, the system complexity is greatly increased and the universality is not strong. Summary of the Invention

[0006] Aiming at the technical problems that single-parameter measurement in the prior art cannot be applied to complex alternating stress environments and the calculation process is complex, the present invention provides a fatigue prediction method, a terminal and a medium for a drill string based on cycle accumulation, which at least have the advantages of low implementation cost and high accuracy.

[0007] First Aspect

[0008] The present invention provides a fatigue prediction method for a drill string based on cycle accumulation, including:

[0009] S10. Record the already-operated alternating stress amplitude and its already-operated cycle number during the use of the drill string;

[0010] S20. Obtain the current in-use alternating stress amplitude of the drill string and its in-use cycle number.

[0011] S30. Based on the already-operated alternating stress amplitudes and the already-operated cycle numbers, as well as the in-use alternating stress amplitude and the in-use cycle number, obtain the remaining operating cycle number of the drill string currently.

[0012] Specifically, one of the main technical concepts of the present invention is that by comprehensively considering the already-operated alternating stress amplitude and the in-use alternating stress amplitude of the alternating stress amplitude, it can well handle the complex and changeable situation of the alternating stress amplitude, and improve the accuracy of drill string fatigue prediction.

[0013] Further, a fatigue prediction method for a drill string based on cycle number accumulation provided by the present invention includes:

[0014] S40. Monitor the change amplitude of the in-use alternating stress amplitude of the drill string. When its change amplitude is greater than a preset amplitude threshold, use the changed alternating stress amplitude as the new in-use alternating stress amplitude, and synchronously update steps S10 and S20, and then execute step S30 again.

[0015] Specifically, one of the other technical concepts of the present invention uses an iterative update method to handle the complex and changeable situation of the drill string stress amplitude affected by factors such as terrain, time, and drilling depth during use, so as to ensure the reliability of the drill string fatigue prediction method provided by the present invention.

[0016] It is worth explaining that the preset amplitude threshold is the maximum acceptable change amplitude when the alternating stress amplitude changes.

[0017] Further, a fatigue prediction method for a drill string based on cycle number accumulation provided by the present invention includes:

[0018] S50. According to the formula Obtain the cumulative damage value D of the drill string. When D≥preset life threshold, trigger a drill string alarm;

[0019] D i represents the damage value of the i-th already-operated alternating stress amplitude, n i represents the already-operated cycle number of the currently already-operated alternating stress amplitude, N i represents the operable cycle number of the currently already-operated alternating stress amplitude, k represents the cumulative number of already-operated alternating stress amplitudes and in-use alternating stress amplitudes, i∈[1,k], and i takes an integer.

[0020] Specifically, one of the main technical concepts of the present invention lies in combining cumulative damage to give early warnings to the drill tools, ensuring that the operating personnel are timely reminded to replace the drill tools before the fatigue risk arrives, thereby ensuring the safety of the drill tool fatigue prediction method provided by the present invention. It is worth explaining that the number of available operating cycles is determined according to the alternating stress amplitude, that is, given the already-operated alternating stress amplitude and the in-use alternating stress amplitude, the number of available operating cycles of the already-operated alternating stress amplitude and the number of available operating cycles of the in-use alternating stress amplitude can be known.

[0021] Optionally, the already-operated alternating stress amplitude is the arithmetic mean stress amplitude of its already-operated cycles.

[0022] Optionally, the in-use alternating stress amplitude is the arithmetic mean stress amplitude of its in-use cycles.

[0023] Further, through the stress probability density formula for the already-operated alternating stress amplitude and the in-use alternating stress amplitude, the maximum limit stress amplitude f(x) of the drill tool is obtained, and the minimum limit remaining operating cycles of the drill tool are obtained through the maximum limit stress amplitude;

[0024]

[0025] f(x) represents the maximum limit stress amplitude, m represents the shape parameter of the drill tool, λ represents the scale parameter, x represents the alternating stress amplitude, and γ represents the threshold value of the minimum alternating stress amplitude.

[0026] Specifically, another technical concept of the present invention lies in replacing the already-operated alternating stress amplitude and the in-use alternating stress amplitude with the maximum limit stress amplitude f(x) to obtain the minimum limit remaining operating cycles of the drill tool, and improving the reliability of the drill tool operation through the minimum limit remaining operating cycles.

[0027] Further, the value of m is used to adjust the distribution form of the stress probability density formula, including:

[0028] m < 1, so that the failure rate decreases with time;

[0029] m = 1, so that the failure rate is randomly distributed;

[0030] m > 1, so that the failure rate increases with time.

[0031] Specifically, another technical concept of the present invention lies in using the value of m to adapt to different drill tool situations, so that the prediction result of the maximum limit stress amplitude is more accurate and reliable, and further improving the accuracy of the drill tool fatigue prediction of the present invention.

[0032] In some alternative embodiments, according to the cumulative damage value, the current comprehensive fracture risk coefficient C of the drill tool is obtained risk ;

[0033]

[0034] C risk represents the comprehensive fracture risk coefficient, K I represents the alternating stress intensity factor at the crack tip Y represents the geometric correction factor, σ represents the far - field nominal stress, a represents the half - length of the crack, a c represents the critical half - length of the crack β represents the crack damage factor, and there is a positive - correlation linear relationship between the crack of the drill string and the cumulative damage value

[0035] Specifically, another technical concept of the present invention lies in using the comprehensive fracture risk coefficient to evaluate the fracture risk of the drill string, so as to make up for the deficiency of evaluating the fracture risk of the drill string through the cumulative damage value, thereby improving the reliability of the present invention

[0036] In some embodiments, according to the frequency - domain analysis method, the frequency components of the alternating stress are identified to obtain the operating alternating stress amplitude

[0037] Second aspect

[0038] The present invention provides a terminal for implementing a fatigue prediction method of a drill string based on weekly accumulation as provided in any possible embodiment of the first aspect. The technical effects provided by the second aspect can be understood with reference to the first aspect

[0039] Third aspect

[0040] The present invention provides a computer - readable storage medium in which a computer program is stored. When the computer program runs on a processor, it implements a method for downhole judgment based on drilling fluid as provided in any possible embodiment of the first aspect. The technical effects provided by the third aspect can be understood with reference to the first aspect

[0041] In summary, the present invention provides a fatigue prediction method, a terminal and a storage medium for a drill string based on weekly accumulation, and at least has the following advantages

[0042] 1. The present invention comprehensively considers the operating alternating stress amplitude and the in - use alternating stress amplitude of the alternating stress amplitude, can well cope with the complex and changeable situation of the alternating stress amplitude, and improves the accuracy of drill string fatigue prediction

[0043] 2. The present invention uses an iterative update method to cope with the complex and changeable situation of the stress amplitude of the drill string affected by factors such as terrain, time, and drilling depth during use, thereby ensuring the reliability of the drill string fatigue prediction method provided by the present invention

[0044] 3. The present invention combines cumulative damage to give early warnings for the drilling tools, ensuring that the operating personnel are timely reminded to replace the drilling tools before the fatigue risk arrives, and thus ensuring the safety of the drilling tool fatigue prediction method provided by the present invention.

[0045] 4. The present invention uses the maximum limit stress amplitude f(x) to replace the already-operated alternating stress amplitude and the in-use alternating stress amplitude, and obtains the remaining operating cycles of the minimum limit of the drilling tool. By means of the remaining operating cycles of the minimum limit, the operating reliability of the drilling tool is improved. At the same time, the present invention also uses the value of m to adapt to different drilling tool situations, so that the prediction result of the maximum limit stress amplitude is more accurate and reliable, and thus the accuracy of the drilling tool fatigue prediction of the present invention is improved.

[0046] 5. The present invention uses the comprehensive fracture risk coefficient to evaluate the fracture risk of the drilling tool to make up for the deficiency of evaluating the fracture risk of the drilling tool through the cumulative damage value, thereby improving the reliability of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will be further described in detail below in conjunction with the drawings and preferred embodiments. However, those skilled in the art will understand that these drawings are only drawn for the purpose of explaining the preferred embodiments and should not be used as a limitation on the scope of the present invention. In addition, unless otherwise specified, the drawings only schematically show the composition or structure of the described object and may include exaggerated displays, and the drawings are not necessarily drawn to scale.

[0048] Figure 1 Schematic flow chart of a method for predicting the fatigue of a drilling tool based on cycle accumulation provided by an embodiment of the present invention;

[0049] Figure 2 Schematic flow chart of a method for predicting the fatigue of a drilling tool based on cycle accumulation provided by another embodiment of the present invention;

[0050] Figure 3 Drilling tool fatigue prediction curve graph with cycle accumulation provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The following will be described in detail with reference to the attached Figures 1 to 3 , the present invention will be described in detail.

[0052] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] The main technical concept of the present invention lies in using the method of determining the accumulated alternating stress amplitude damage to solve the technical problem of prediction deviation caused by the complex and variable alternating stress amplitude, and improving the accuracy of drill string fatigue prediction.

[0054] Further, please refer to Figure 1 The figure shows a schematic flow chart of a drill string fatigue prediction method based on weekly accumulation provided by an embodiment of the present invention.

[0055] Embodiment 1

[0056] A drill string fatigue prediction method based on weekly accumulation provided by the present invention includes the following steps: S10, recording the already-operated alternating stress amplitude and its already-operated number of weeks during the use of the drill string; S20, obtaining the currently-used alternating stress amplitude and its currently-used number of weeks of the drill string; S30, obtaining the remaining operating number of weeks of the drill string according to each of the already-operated alternating stress amplitudes and the already-operated number of weeks, and the currently-used alternating stress amplitude and the currently-used number of weeks. It should be explained that step S10 is used to record the generated alternating stress amplitude and the number of weeks the drill string operates under this alternating stress amplitude, step S20 is used to record the current alternating stress amplitude and the number of weeks the drill string operates under this alternating stress amplitude, and step S30 is used to comprehensively consider the damage already caused to the drill string by the recorded alternating stress amplitudes, so as to obtain the number of cycles that can be cycled under the current alternating stress amplitude, thereby realizing the prediction of drill string fatigue, and having the advantages of accurate and reliable prediction results.

[0057] Further, please refer to Figure 2 The figure shows a schematic flow chart of a drill string fatigue prediction method based on weekly accumulation provided by another embodiment of the present invention.

[0058] Embodiment 2

[0059] On the basis of Embodiment 1, the present invention, through S40, monitors the change amplitude of the currently-used alternating stress amplitude of the drill string. When its change amplitude is greater than the preset amplitude threshold, the changed alternating stress amplitude is used as the new currently-used alternating stress amplitude, and steps S10 and S20 are synchronously updated, and step S30 is executed again. It should be explained that the alternating stress amplitude of the drill string is not constant during operation, especially under complex working conditions, the amplitude of the alternating stress amplitude changes frequently. At this time, through step S40, the change in the alternating stress amplitude caused by the fluctuation can be compensated, so as to ensure the accuracy and reliability of predicting the drill string fatigue through step S30.

[0060] Optionally, the preset amplitude threshold is 5%-10%. If the change amplitude of the alternating stress amplitude exceeds 5%-10%, it is determined as the new currently-used alternating stress amplitude.

[0061] Optionally, the operating alternating stress amplitude is the arithmetic mean stress amplitude of its operating cycles.

[0062] Optionally, the in-use alternating stress amplitude is the arithmetic mean stress amplitude of its operating cycles.

[0063] Optionally, the frequency components of the alternating stress are identified according to the frequency domain analysis method to obtain the operating alternating stress amplitude.

[0064] Optionally, the frequency components of the alternating stress are identified according to the frequency domain analysis method to obtain the in-use alternating stress amplitude.

[0065] It should be noted that the peak value and valley value of the alternating stress can be obtained through the frequency components, and the difference between the two is the alternating stress amplitude.

[0066] Furthermore, on the basis of Embodiment 2, the present invention includes S50. According to the formula the cumulative damage value D of the drill string is obtained. When D≥the preset life threshold, a drill string alarm is triggered; D i represents the damage value of the i-th operating alternating stress amplitude, n i represents the operating cycles of the current operating alternating stress amplitude, N i represents the operable cycles of the current operating alternating stress amplitude, k represents the cumulative number of the operating alternating stress amplitude and the in-use alternating stress amplitude, i∈[1,k], and i is an integer.

[0067] Optionally, the preset life threshold is 0.9 - 1. When D is greater than 0.9 - 1, it is determined that the current drill string is approaching the fatigue limit point, and the drill string should be replaced in time to avoid greater harm caused by the failure of the drill string.

[0068] Exemplarily:

[0069] The drill string has operated for 700,000 cycles at an alternating stress amplitude of 10 kpsi, 1,000,000 cycles at an alternating stress amplitude of 30 kpsi, and the current alternating stress amplitude is 12 kpsi and it has operated for 300,000 cycles. It is known that it can operate for 20,000,000 cycles at an alternating stress amplitude of 10 kpsi, 17,000,000 cycles at an alternating stress amplitude of 30 kpsi, and 19,000,000 cycles at an alternating stress amplitude of 12 kpsi. Then the remaining operating cycles are:

[0070] (1 - 700000 / 20000000 - 1000000 / 17000000 - 300000 / 19000000) * 19000000 = 16917352

[0071] That is, the drill string can still operate for 169,173,352 cycles under the current alternating stress amplitude of 12 kpsi.

[0072] At this time, D = 700,000 / 20,000,000 + 1,000,000 / 17,000,000 + 300,000 / 19,000,000 = 0.1096, which is far from the preset life threshold, and the fracture risk coefficient of this drill string is relatively low.

[0073] Exemplarily, the drill string has operated for 15,000,000 cycles under an alternating stress amplitude of 10 kpsi, has operated for 2,000,000 cycles under an alternating stress amplitude of 30 kpsi, the current alternating stress amplitude is 12 kpsi, and it has operated for 1,000,000 cycles. It is known that it can operate for 20,000,000 cycles under an alternating stress amplitude of 10 kpsi, can operate for 17,000,000 cycles under an alternating stress amplitude of 30 kpsi, and can operate for 19,000,000 cycles under an alternating stress amplitude of 12 kpsi. Then

[0074] D = 15,000,000 / 20,000,000 + 2,000,000 / 17,000,000 + 1,000,000 / 19,000,000 = 0.92;

[0075] If the preset life threshold is 0.9, the current D is greater than the preset life threshold, the current drill string has reached the fatigue warning value, and the fracture risk is extremely high. It is recommended to replace the drill string.

[0076] Example 3

[0077] Based on Example 1 or Example 2, the maximum limit stress amplitude f(x) of the drill string is obtained through the stress probability density formula for the already-operated alternating stress amplitude and the in-use alternating stress amplitude, and the minimum limit remaining operation cycles of the drill string are obtained through the maximum limit stress amplitude. f(x) represents the maximum limit stress amplitude, m represents the shape parameter of the drill string, λ represents the scale parameter, x represents the alternating stress amplitude, and γ represents the threshold value of the minimum alternating stress amplitude. Among them, the calculation method of the remaining operating cycles of the minimum limit is to obtain the maximum limit stress amplitude of the alternating stress amplitude that has been operated and the maximum limit stress amplitude of the alternating stress amplitude in use through the stress probability density formula, and then substitute them into steps S10 - S30 to obtain the remaining operating cycles of the minimum limit. It is worth explaining that although the alternating stress amplitude of the drill string can be obtained through sampling, in the actual use of the drill string, generally the most fatigue or the weakest part of the material will break first. Therefore, although the accurate remaining operating cycles of the drill string are obtained through cycle accumulation in the present invention, considering that the alternating stress amplitude in the calculation process cannot represent the alternating stress amplitude of the weakest part of the drill string, there is still a risk of premature fracture of the drill string when it reaches the critical limit of the drill string. Example 3 obtains the alternating stress amplitude of the weakest part of the drill string through the maximum limit stress amplitude formula, which can effectively solve the above technical problems and thus improve the reliability of the present invention.

[0078] Optionally, γ = 0 to correspond to the alternating stress starting from 0. If the alternating stress does not start from 0, then γ can take other values.

[0079] Optionally, the value of m is used to adjust the distribution form of the stress probability density formula, including: m < 1 to make the failure rate decrease with time; m = 1 to make the failure rate randomly distributed; m > 1 to make the failure rate increase with time.

[0080] It is worth explaining that m < 1 is used for drill strings dominated by material defects, m = 1 is used for conventional drill strings, and m > 1 is used for drill strings dominated by fatigue. By switching the selection of the above three m values, the calculation accuracy of the maximum limit stress amplitude f(x) can be effectively improved.

[0081] Optionally, the remaining operating cycles of the minimum limit and the cumulative damage value can be used independently or jointly.

[0082] Furthermore, when the remaining operating cycles of the minimum limit and the cumulative damage value are used jointly, the preset life threshold is confirmed by the quotient of the remaining operating cycles of the minimum limit and the remaining operating cycles.

[0083] Example 4

[0084] On the basis of Example 1 or Example 2, according to the cumulative damage value, obtain the current comprehensive fracture risk coefficient C of the drill string risk ; C risk represents the comprehensive fracture risk coefficient, K I represents the alternating stress intensity factor at the crack tip, Y represents the geometric correction factor, σ represents the far-field nominal stress, a represents the crack half-length, and a c represents the critical crack half-length, β represents the crack damage factor. The crack of the drill tool is linearly correlated with the cumulative damage value. It is worth explaining that although the present invention confirms the remaining operating cycles of the drill tool and the cumulative damage value warning through the alternating stress amplitude, it is still inevitable that there is a defect of only considering the accumulation of the alternating stress amplitude. Therefore, the comprehensive fracture risk coefficient is used to repair the above technical problems, where fenv is the environmental factor, which is used to take into account environmental corrosion, hydrogen embrittlement, etc., and K I , a, etc. are used to consider the cracks, thereby obtaining a comprehensive fracture risk coefficient based on the composite damage value D, thereby improving the reliability of the present invention.

[0085] Optional, Equivalent to D.

[0086] Optionally, the comprehensive fracture risk coefficient can be used in conjunction with the calculation of the remaining operating cycles, and the new remaining operating cycles are the quotient of the original remaining operating cycles and the comprehensive fracture risk coefficient, or, the comprehensive fracture risk coefficients in different value ranges correspond to a certain coefficient factor, and the new remaining operating cycles are the product of the original remaining operating cycles and the coefficient factor.

[0087] For further information, see Figure 3 Shown is a drill tool fatigue prediction curve diagram accumulated over cycles provided by an embodiment of the present invention.

[0088] Specifically, the drill tool has different operable cycles under different alternating stress amplitudes. Each alternating stress amplitude will consume the remaining operating cycles of the drill tool. When the remaining operating cycles are insufficient, it means that the drill tool has reached its fatigue limit.

[0089] Example 5

[0090] On the basis of Embodiments 1 to 4, the present invention provides a terminal, comprising a generating unit and a confirming unit;

[0091] The generation unit obtains all alternating stress amplitudes and operating cycles of the drilling tool during its use, and the alternating stress amplitudes and operating cycles of the drilling tool currently in use;

[0092] The confirmation unit is used to obtain the current remaining operation cycles of the drilling tool according to the operated alternating stress amplitudes and the operated cycles, as well as the in-use alternating stress amplitudes and the in-use cycles.

[0093] Optionally, the generating unit is used to monitor the change amplitude of the in-use alternating stress amplitude of the drilling tool, and when the change amplitude is greater than a preset amplitude threshold, the changed alternating stress amplitude is used as the new in-use alternating stress amplitude;

[0094] Optionally, the confirmation unit is configured to obtain the cumulative damage value D of the drill string according to the formula and trigger a drill string alarm when D ≥ a preset life threshold value.

[0095] Embodiment 6

[0096] Based on Embodiments 1 to 4, the present invention provides a storage medium. A computer program is stored in the computer-readable storage medium. When the computer program runs on a processor, it implements the method for downhole judgment based on drilling fluid provided in any possible embodiment provided in Embodiments 1 to 4.

[0097] The present invention has been introduced in detail above. Specific examples are used in the present invention to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the present invention and its core idea. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A fatigue prediction method for drilling tools based on weekly accumulation, characterized in that, Including: S10. Record the alternating stress amplitude and the number of operating cycles that the drill string has run during its use; S20. Obtain the current alternating stress amplitude and the number of operating cycles of the drill string in use; S30. Obtain the remaining operating cycles of the drill string currently based on the alternating stress amplitude and the number of operating cycles that have run, and the alternating stress amplitude and the number of operating cycles in use.

2. The fatigue prediction method of a drilling tool based on week - by - week accumulation as described in claim 1, wherein, The fatigue prediction method described above includes: S40. Monitor the change amplitude of the alternating stress amplitude in use of the drill string. When the change amplitude is greater than the preset amplitude threshold, use the changed alternating stress amplitude as the new alternating stress amplitude in use, and synchronously update steps S10 and S20, and then execute step S30 again.

3. The fatigue prediction method of a drill string based on weekly accumulation according to claim 1 or 2, characterized in that, The fatigue prediction method described above includes: S50. Obtain the cumulative damage value D of the drill string according to the formula and trigger a drill string alarm when D ≥ the preset life threshold value; D i represents the damage value of the alternating stress amplitude that has been run for the \(i\)th time n i represents the number of cycles that the alternating stress amplitude has been run currently, \(N\) i represents the number of cycles that the alternating stress amplitude can be run currently, \(k\) represents the cumulative number of the alternating stress amplitudes that have been run and are in use, \(i\in[1,k]\), and \(i\) takes integer values 4. The fatigue prediction method of a drilling tool based on weekly accumulation according to claim 3, characterized in that, The alternating stress amplitude that has run is the arithmetic mean stress amplitude of the number of operating cycles that have run.

5. The fatigue prediction method of a drill string based on weekly accumulation according to claim 4, wherein The alternating stress amplitude that has run and the alternating stress amplitude in use obtain the maximum limit stress amplitude f(x) of the drill string through the stress probability density formula, and obtain the minimum limit remaining operating cycles of the drill string through the maximum limit stress amplitude; f(x) represents the maximum limit stress amplitude, m represents the shape parameter of the drill string, λ represents the scale parameter, x represents the alternating stress amplitude, and γ represents the threshold of the minimum alternating stress amplitude.

6. The fatigue prediction method of a drilling tool based on weekly accumulation according to claim 5, characterized in that, The value of m described above is used to adjust the distribution form of the stress probability density formula, including: m < 1, so that the failure rate decreases with time; m = 1, so that the failure rate is randomly distributed; m > 1, so that the failure rate increases with time.

7. The fatigue prediction method of a drill string based on weekly accumulation according to claim 3, wherein Obtain the current comprehensive fracture risk coefficient C of the drill string according to the cumulative damage value risk ; C risk Denotes the comprehensive fracture risk coefficient, K I Denotes the alternating stress intensity factor at the crack tip Y denotes the geometric correction factor, σ denotes the far-field nominal stress, a denotes the half crack length, a c Denotes the critical half crack length β denotes the crack damage factor, and there is a positive linear correlation between the crack of the drill string and the cumulative damage value.

8. The fatigue prediction method of a drilling tool based on weekly accumulation according to claim 3, characterized in that, Identify the frequency components of the alternating stress according to the frequency domain analysis method to obtain the alternating stress amplitude that has run.

9. A terminal for implementing a fatigue prediction method of a drill string based on cycle accumulation as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, and when the computer program runs on a processor, it implements a method for downhole judgment based on drilling fluid as described in any one of claims 1-8.

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