Method and device for evaluating safety of tubular column of lifting system of electric submersible screw pump

Abstract

The invention discloses a method and a device for evaluating safety of a pipe column of an electric submersible screw pump lifting system. The method comprises the following steps: constructing a well depth track and a well curvature model according to well bore data and well track data; according to the well depth track and the borehole curvature model, the stress of a tubular column of the electric submersible screw pump lifting system under different working conditions is analyzed and determined in combination with the stress of the electric submersible screw pump unit; the working conditions comprise well lifting, pump lowering and unit operation processes; establishing a tubular column stress model of the electric submersible screw pump lifting system according to the stress of the tubular column of the electric submersible screw pump lifting system under different working conditions; determining the maximum stress intensity on the cross section of the tubular column based on the tubular column stress model of the electric submersible screw pump lifting system; and according to the maximum stress strength on the cross section of the tubular column, determining the strength safety coefficient of the tubular column by using a tubular column strength safety coefficient formula.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pipe string safety evaluation, and in particular to a method and device for evaluating the safety of a pipe string of an ESP (electrical submersible pump) lifting system. BACKGROUND

[0002] With the development of oil and gas resource development towards deep wells, ultra-deep wells and super-deep wells, deep well lifting as a key link in the process of oil and gas resource development directly affects the cost and benefit of the development. The ESP (electrical submersible pump) unit is an important part of the oil production system, and its safety and mechanical properties play a crucial role in the stability and safety of the whole system. In the actual deep well and ultra-deep well lifting process, the dynamics analysis of the ESP unit is crucial. The ESP unit may bear huge load and pressure in the conditions of well tripping, pump tripping and unit operation, and may cause vibration and damage of the unit, and even failure.

[0003] Therefore, it is necessary to provide a safety evaluation method to solve the problem of system pipe string safety evaluation of deep well ESP lifting process in the background technology, and to avoid the problems of ESP unit not tripping down, not running stably for a long time and not tripping out in the actual oil production process. SUMMARY

[0004] The present application provides a method and device for evaluating the safety of a pipe string of an ESP (electrical submersible pump) lifting system. The present application analyzes the stress of the pipe string of the ESP lifting system under different conditions, calculates the minimum safety factor, and combines the analysis of the maximum passing length and the curvature of the unit to realize the safety evaluation under the conditions of well tripping, pump tripping and unit operation, so as to improve the efficiency and safety of deep well ESP lifting.

[0005] In a first aspect, the present application provides a method for evaluating the safety of a pipe string of an ESP (electrical submersible pump) lifting system, the method comprising:

[0006] constructing a well depth trajectory and a borehole curvature model according to well data and borehole trajectory data;

[0007] determining the stress of the pipe string of the ESP lifting system under different conditions according to the well depth trajectory and the borehole curvature model, in combination with the stress analysis of the ESP unit; the conditions include well tripping, pump tripping and unit operation process;

[0008] establishing a pipe string stress model of the ESP lifting system according to the stress of the pipe string of the ESP lifting system under different conditions;

[0009] determining the maximum stress intensity on the cross section of the pipe string based on the pipe string stress model of the ESP lifting system;

[0010] The pipe string strength safety factor is determined according to the maximum stress intensity on the pipe string cross section by using a pipe string strength safety factor formula.

[0011] Optionally, the pipe string stress model of the ESP pump lifting system is composed of tensile or compressive stress generated by axial force, bending stress generated by wellbore bending, bending stress generated by helical buckling, shear stress generated by torque, and radial and circumferential stress generated by internal and external pressure.

[0012] Optionally, the tensile or compressive stress generated by axial force is:

[0013]

[0014] In the above formula, σ t is the tensile or compressive stress generated by axial force, A r is the cross-sectional area of the pipe string, and F is the axial force.

[0015] The bending stress generated by wellbore bending is:

[0016] σ b = Ekr s

[0017] In the above formula, σ b is the bending stress generated by wellbore bending, E is the elastic modulus, k is the curvature, and r s is the radius of any point on the pipe string cylinder wall.

[0018] The bending stress generated by helical buckling is:

[0019]

[0020] In the above formula, σ bc is the bending stress generated by helical buckling, r is the radial gap between the pipe string and the casing, F1 is the axial pressure acting on the oil pipe, r s is the radius of any point on the pipe string cylinder wall, and I is the moment of inertia of the cross section.

[0021] The shear stress generated by torque is:

[0022]

[0023] In the above formula, τ is the shear stress generated by buckling additional torque, M t is the buckling additional torque, J is the polar moment of inertia of the pipe string cross section, and r s is the radius of any point on the pipe string cylinder wall.

[0024] The radial and circumferential stress generated by internal and external pressure is:

[0025]

[0026] In the above formula, σ r is the radial stress, σ θ is the circumferential stress, r o is the outer radius of the pipe string, r i is the inner radius of the pipe string, r s is the radius of any point on the inner wall of the pipe string, and r i < r s < r o .

[0027] Optionally, the pipe string stress model based on the ESP lifting system determines the maximum stress intensity on the pipe string cross section, comprising:

[0028] Different stress sections are divided according to different working conditions and different well sections; the stress sections include: a tension section, a compression section without spiral buckling, and a compression section with spiral buckling;

[0029] The pipe string stress intensity of different stress sections is calculated based on the pipe string stress model of the ESP lifting system;

[0030] The pipe string stress intensity of each stress section is sorted to determine the maximum stress intensity on the pipe string cross section.

[0031] Optionally, the pipe string stress intensity of different stress sections includes:

[0032] The pipe string stress intensity of the tension section:

[0033]

[0034] The pipe string stress intensity of the compression section without spiral buckling:

[0035]

[0036] The pipe string stress intensity of the compression section with spiral buckling:

[0037]

[0038] In the above formula, σ r is the radial stress, σ θ is the circumferential stress, σ t is the tensile or compressive stress generated by the axial force, σ b is the bending stress generated by the wellbore bending, and σ bc is the bending stress generated by the spiral buckling.

[0039] Optionally, the pipe string strength safety factor formula is:

[0040]

[0041] In the above formula, n is the safety factor, σ s is the yield limit of the pipe string material, σ imax is the maximum stress intensity on the pipe string cross section.

[0042] Optionally, after determining the pipe string strength safety factor using the pipe string strength safety factor formula according to the maximum stress intensity on the pipe string cross section, the method further comprises:

[0043] determining the electrical submersible pump unit and the pipe string threaded joint connection strength according to the relevant parameters of the electrical submersible pump unit and the pipe string threaded joint;

[0044] determining the maximum through-hole curvature of the electrical submersible pump and the pipe string threaded joint according to the safety factor and the threaded stress concentration factor in combination with the axial force;

[0045] wherein the electrical submersible pump unit and the pipe string threaded joint connection strength is:

[0046] P j = f ymn {π[(D4-2h s ) 2 -d 2 ] / 4};

[0047] In the above formula, P j is the electrical submersible pump unit and the pipe string threaded joint connection strength, f ymn is the specified minimum tensile strength of the threaded joint, D4 is the large end diameter of the pipe body, h s is the tooth profile height, and d is the inner diameter of the pipe body.

[0048] The maximum through-hole curvature of the electrical submersible pump and the pipe string threaded joint is:

[0049]

[0050] In the above formula, C mp is the maximum through-hole curvature of the electrical submersible pump unit and the pipe string threaded joint, Pe is the effective axial force, D0 is the outer diameter of the electrical submersible pump system pipe string, A is the cross-sectional area of the electrical submersible pump system pipe string, and K is the comprehensive coefficient.

[0051] Optionally, after determining the pipe string strength safety factor using the pipe string strength safety factor formula according to the maximum stress intensity on the pipe string cross section, the method further comprises:

[0052] calculating the maximum through length of the pipe string under different wellbore curvatures using a length calculation formula;

[0053] wherein the length calculation formula is:

[0054]

[0055] In the above formula, L m is the maximum passing length of the pipe string under a certain hole curvature, R is the radius of curvature, D w is the hole diameter, and D is the outer diameter of the pipe string.

[0056] In a second aspect, the embodiments of the present application further provide a device for evaluating the safety of the pipe string of the ESP lifting system, the device comprising: a memory and a processor; the memory is configured to store a program for evaluating the safety of the pipe string of the ESP lifting system, and the processor is configured to read and execute the program for evaluating the safety of the pipe string of the ESP lifting system, and execute the method of any one of the above embodiments.

[0057] In a third aspect, the embodiments of the present application further provide a computer readable storage medium, and the computer readable storage medium stores a data processing program, and the data processing program is configured to execute the method for evaluating the safety of the pipe string of the ESP lifting system by the processor.

[0058] Compared with the related art, the present application provides a method and device for evaluating the safety of the pipe string of the ESP lifting system, and the method comprises the following steps: constructing a well depth trajectory and a wellbore curvature model according to well data and wellbore trajectory data; determining the stress of the pipe string of the ESP lifting system under different working conditions according to the well depth trajectory and the wellbore curvature model in combination with the force analysis of the ESP unit; the working conditions include: well tripping, pump lowering and unit operation process; establishing a pipe string stress model of the ESP lifting system according to the stress of the pipe string of the ESP lifting system under different working conditions; determining the maximum stress intensity on the pipe string cross section based on the pipe string stress model of the ESP lifting system; and determining the pipe string strength safety factor according to the maximum stress intensity on the pipe string cross section by using the pipe string strength safety factor formula. By constructing the mechanical models under the three working conditions of well tripping, pump lowering and unit operation, the minimum safety factor is calculated, and the maximum passing length and the curvature of the unit are analyzed, so that the safety evaluation under the three working conditions of well tripping, pump lowering and unit operation is realized, and the efficiency and safety of the deep well ESP lifting are improved.

[0059] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. Other advantages of the present application can be realized and obtained by means of the solutions described in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0060] The accompanying drawings are included to provide a further understanding of the technical solutions of the present application, and constitute a part of the specification, and are used together with the embodiments of the present application to explain the technical solutions of the present application, and do not constitute a limitation to the technical solutions of the present application.

[0061] Figure 1 A flow chart of a method for evaluating safety of an ESP pump lifting system string according to an embodiment of the present application;

[0062] Figure 2 A schematic diagram of a device for evaluating safety of an ESP pump lifting system string according to an embodiment of the present application;

[0063] Figure 3 A flow chart of a method for evaluating safety of an ESP pump lifting system string according to some example embodiments;

[0064] Figure 4 A schematic diagram of a force analysis of a micro-element section of an ESP pump unit string according to some example embodiments;

[0065] Figure 5 A schematic diagram of a "hard card" of an ESP pump unit according to some example embodiments. DETAILED DESCRIPTION

[0066] A number of embodiments of the application have been described. Such description is illustrative only and is not restrictive; many other embodiments will become apparent to those skilled in the art, in view of the foregoing description. Although many of the features and aspects of the disclosed embodiments are described in the singular, for the sake of clarity, it should be understood that each of the features and aspects of the disclosed embodiments can be combined with any or all of the other features and aspects of the disclosed embodiments. The various embodiments can be implemented in hardware, software or a combination thereof. The various embodiments can be implemented in one or more computer systems or other processing systems.

[0067] The present application includes and contemplates combinations of features and elements known to those of ordinary skill in the art. The embodiments, features and elements disclosed herein can also be combined with any conventional features or elements to form unique inventive solutions that are within the scope of the claims. Any feature or element of any embodiment can also be combined with features or elements from other inventive solutions to form another unique inventive solution that is within the scope of the claims. Therefore, it is to be understood that any feature shown and / or discussed in the present application can be implemented alone or in any appropriate combination. Embodiments are, therefore, not to be limited to anything discussed in the present application, except as set forth in the claims and their equivalents. Additionally, modifications and alterations will occur to others upon reading and understanding the detailed description, and it is intended to include all such modifications and alterations insofar as they come within the scope of the claims. Further, it will be understood that the application is not limited on the details of the embodiments described herein, and the methodology can be practiced by other suitable methods.

[0068] Furthermore, in describing representative embodiments, the specification can have presented the method and / or process as a particular sequence of steps. However, to the extent that the method or process depends on the particular order of steps, this description should not be construed as limiting since other steps can be performed in other sequences and / or omitted from the method or process. Therefore, the particular order of steps presented in the specification should not be construed as a limitation on the claims. Furthermore, the claims should not be limited to the steps of the method and / or process in the order in which they are written, as other sequences of steps can be performed and / or steps can be omitted in other orders and still remain within the scope of the claims.

[0069] The embodiments of the present application provide a method for evaluating the safety of a pipe string of an ESP lifting system, as shown in the accompanying drawings, the method comprises steps S100-S140: Figure 1

[0070] S100: constructing a well depth trajectory and a borehole curvature model according to well depth data and borehole trajectory data;

[0071] S110: determining the stress of the pipe string of the ESP lifting system under different working conditions according to the well depth trajectory and the borehole curvature model, in combination with force analysis of the ESP unit;

[0072] S120: establishing a pipe string stress model of the ESP lifting system according to the stress of the pipe string of the ESP lifting system under different working conditions;

[0073] S130: determining the maximum stress intensity on the pipe string cross section based on the pipe string stress model of the ESP lifting system;

[0074] S140: determining the pipe string strength safety factor by using a pipe string strength safety factor formula according to the maximum stress intensity on the pipe string cross section.

[0075] In an exemplary embodiment, the working conditions include: well tripping, pump lowering and unit running.

[0076] In an exemplary embodiment, the pipe string stress model of the ESP lifting system is composed of tensile or compressive stress generated by axial force, bending stress generated by borehole bending, bending stress generated by helical buckling, shear stress generated by torque and radial and circumferential stress generated by internal and external pressure.

[0077] I. In the pipe string stress model of the present ESP lifting system, the tensile or compressive stress generated by axial force is:

[0078]

[0079] In the above formula, σ t ​A = F / A r F = A x σ

[0080] B = σ

[0081] σ b = Ekr s

[0082] σ b = Ekr s

[0083] C = τ

[0084]

[0085] τ = Pa x M bc s

[0086] D = σ

[0087]

[0088] τ = Pa x M t 4 s

[0089] E = σ

[0090]

[0091] σ r = F / A θ = F / A o = r i = r s = r i = r s = r o ​​​​​​, m; p i pressure inside the tubular string, p o pressure outside the tubular string.

[0092] In an example embodiment, determining the maximum stress intensity on the tubular string cross section based on the tubular string stress model comprises:

[0093] Step 1, calculating the stress intensity of different stress sections of the tubular string respectively;

[0094] According to different working conditions and different well sections, different stress sections are divided, which can be divided into tension section, compression section without spiral buckling and compression section with spiral buckling.

[0095] Step 2, sorting the stress intensity of each section of the tubular string to determine the maximum stress intensity on the tubular string cross section.

[0096] Step 3, the stress state of the electric submersible screw pump unit lifting tubular string is relatively complex, and the stress intensity is analyzed by using the sectional method.

[0097] In an example embodiment, the stress intensity of each stress section of the tubular string is calculated respectively, which comprises:

[0098] The stress intensity of the tension section of the tubular string is:

[0099]

[0100] The stress intensity of the compression section without spiral buckling of the tubular string is:

[0101]

[0102] The stress intensity of the compression section with spiral buckling of the tubular string is:

[0103]

[0104] In the above formula, σ r is the radial stress, σ θ is the circumferential stress, σ t is the tensile or compressive stress generated by the axial force, σ b is the bending stress generated by the wellbore bending, and σ bc is the bending stress generated by the spiral buckling.

[0105] In an example embodiment, the tubular string strength safety factor formula is:

[0106]

[0107] In the above formula, n is the safety factor, σ s is the yield limit of the tubular string material, which is a known parameter determined according to the tubular string material, and σ imaxThe maximum stress intensity on the pipe string cross section.

[0108] In an exemplary embodiment, after determining the pipe string strength safety factor according to the maximum stress intensity on the pipe string cross section using the pipe string strength safety factor formula, the method further comprises:

[0109] Step 1, determining the electrical submersible screw pump unit and its pipe string threaded joint connection strength according to the electrical submersible screw pump unit and its pipe string threaded joint self parameters; wherein the pipe string threaded joint self parameters include threaded tooth type, threaded tooth number, effective threaded length, material, etc.

[0110] Step 2, determining the maximum wellbore curvature passed by the electrical submersible screw pump and its pipe string threaded joint according to the safety factor and the threaded stress concentration factor, combined with the axial force.

[0111] Wherein, the electrical submersible screw pump unit and its pipe string threaded joint connection strength:

[0112] P j = f ymn {π[(D4-2h s ) 2 -d 2 ] / 4};

[0113] P j is the threaded connection tensile strength, f ymn is the specified minimum tensile strength of the threaded joint, D4 is the large end diameter of the pipe body, hs is the tooth height, and d is the inner diameter of the pipe body.

[0114] The maximum wellbore curvature passed by the electrical submersible screw pump and its pipe string threaded joint is:

[0115]

[0116] In the above formula, C m p is the maximum wellbore curvature passed by the electrical submersible screw pump unit and its pipe string threaded joint, P e is the effective axial force, D0 is the outer diameter of the electrical submersible screw pump system pipe string, A is the cross-sectional area of the electrical submersible screw pump system pipe string, and K is a coefficient considering safety factor and threaded stress concentration and other factors.

[0117] In an exemplary embodiment, after determining the pipe string strength safety factor according to the maximum stress intensity on the pipe string cross section using the pipe string strength safety factor formula, the method further comprises:

[0118] First step, regarding the electrical submersible screw pump unit as a rigid body, calculating the maximum pipe string passing length under different wellbore curvatures;

[0119] Since the included angle between the curved part and the straight part of the pipe string has multiple values, i.e. has different wellbore curvatures, such asFigure 5 Therefore, to calculate the maximum passing length of the pipe string under different wellbore curvature conditions, the maximum passing length calculation model is:

[0120]

[0121] In the above formula, L m is the maximum passing length of the unit under a certain wellbore curvature, m; R is the radius of curvature, m; D w is the wellbore diameter, m; and D is the outer diameter of the pipe string, m.

[0122] Secondly, according to the maximum passing curvature of the unit, the corresponding maximum passing length can be calculated.

[0123] The maximum length calculation formula of the pipe string uses the radius of curvature, which is the inverse of the curvature, that is, the maximum length of the unit designed under a given wellbore curvature, which can ensure the safety of the unit during the tripping process.

[0124] In this embodiment, after the safety factor is calculated, and it is determined that the safety factor is greater than 1.6, it is indicated that the pipe string will not cause a safety accident due to exceeding the yield limit during the tripping process. In the case that the safety factor of the pipe string is greater than 1.6, the maximum passing curvature of the unit is further calculated, and the maximum passing length is calculated under the maximum passing curvature. That is, in this deviated well case, if the safety factor of the pipe string is greater than 1.6 and the length is less than the maximum passing length, it is theoretically safe. That is, the total length of the screw pump unit (including the length of the screw pump, the length of the connector, the length of the protector, the length of the permanent magnet direct drive motor, the length of the carrier sensor, etc.) is less than the maximum passing length, which can ensure the normal tripping process.

[0125] The method for evaluating the safety of the pipe string of the electric submersible screw pump lifting system implemented in this embodiment has the following technical effects:

[0126] 1. The temperature effect, expansion effect, coupling effect, pipe string load, stress intensity, buckling law, friction and drag, centralizer, maximum passing length and maximum passing curvature of the pipe string, and other factors are comprehensively considered to construct the mechanical model of the tripping, pump lowering and unit operation conditions.

[0127] 2. According to the established mechanical model of the electric submersible screw pump lifting system under the tripping, pump lowering and unit operation conditions, the safety factor can be accurately calculated, and the pipe string safety can be more accurately evaluated to ensure the safety of deep well operation.

[0128] Secondly, the embodiment of the present application also provides a device for evaluating the safety of the pipe string of the electric submersible screw pump lifting system, which comprises Figure 2As shown, the device includes a memory 210 and a processor 220; the memory is used to store a program for evaluating the safety of the electric submersible screw pump lifting system string, and the processor is used to read and execute the program for evaluating the safety of the electric submersible screw pump lifting system string, and execute the method described in any of the above embodiments.

[0129] Thirdly, embodiments of the present invention also provide a computer-readable storage medium storing a data processing program, wherein the data processing program is executed by a processor as described in any of the above embodiments, a method for evaluating the safety of the tubing of an electric submersible screw pump lifting system.

[0130] Example 1

[0131] This example demonstrates the process of establishing a tubular stress model for an electric submersible screw pump lifting system, such as... Figure 3 As shown, the specific process is as follows:

[0132] Step 1: Analyze the forces acting on the electric submersible screw pump unit;

[0133] An electric submersible screw pump unit consists of several components. The exact weight of some components is known, while the weight of others needs to be estimated based on the weights of other components. The weight of the electric submersible screw pump unit can be expressed as:

[0134] F g =(M p +2M f )g

[0135] In the formula: F g The unit is the weight of the generator set, expressed in N; M p The total weight of the unit is in kg; M f The weight of the upright body is expressed in kg; g is the acceleration due to gravity.

[0136] The electric submersible screw pump unit experiences buoyancy. The buoyancy force on the electric submersible screw pump unit in the well fluid can be expressed as:

[0137] F f =ρ1g(A p L p +2A f L f )

[0138] In the formula: F f The buoyancy force acting on the generator unit is expressed in N (Newtons); A p The average cross-sectional area of ​​the unit, in meters. 2 L p A is the length of the unit, in meters; f The cross-sectional area of ​​the straightening body is expressed in meters (m²). 2 L fρ1 is the length of the unit, in meters; ρ1 is the density of the downhole fluid, in kilograms per cubic meter of water. 3 .

[0139] The relative motion between the electric submersible screw pump unit and the casing wall generates frictional resistance, which can be calculated using the formula for solid contact friction:

[0140] F m =f[(M p +2M f )g-ρ1g(A p L p +2A f L f )+F ef cosα

[0141] In the formula: F m F represents the frictional force between the generator set and the bushing, expressed in N; f is the coefficient of friction between the generator set and the bushing; F ef The lateral contact force generated by borehole bending, measured in N; M p The total weight of the unit is in kg; M f The weight of the body being straightened is expressed in kg; A p The average cross-sectional area of ​​the unit is m. 2 L p A is the length of the unit, in meters; f Let m be the cross-sectional area of ​​the uprighting body. 2 L f The length of the unit is in meters (m).

[0142] In this embodiment, the axial force of the electric submersible screw pump mainly consists of three parts:

[0143] F b =F c +F f +F p

[0144] In the formula: F c Fa is the axial load on the bushing during liquid flow within the screw pump's sealing cavity, expressed in N; Ff is the reaction force along the screw axis caused by the collision between the screw face and the bushing face, expressed in N; Fa p This refers to the axial force generated by the difference in liquid level between the discharge and input ends of the screw pump, expressed in N.

[0145] Step 2: Analyze the stress on the tubing of the electric submersible screw pump lifting system under three different working conditions during well tripping, pump running-in, and unit operation.

[0146] like Figure 4As shown in Figure a, the force analysis of the micro-element segment of the tubing under the lower pump condition yields the mechanical equilibrium equations for the micro-element segment of the electric submersible screw pump system under the lower pump condition:

[0147]

[0148] f rt =fF n

[0149] F n =(q r -f r cosα+F nb

[0150] In the formula: F x(i) and F x(i+1) These represent the axial forces at the lower and upper ends of the tubing segment during pump lowering, respectively, in N; α is the average well inclination angle, in °; F n F represents the total contact force between the tubing segment and the casing, expressed in N / m. nb q represents the additional contact force caused by the buckling deformation of a small segment of the tubular column, expressed in N / m. r f is the weight per unit length of the tubular string, expressed in N. r ρ is the buoyancy force per unit length of the tubing, in N / m; f is the coefficient of friction between the unit and the casing; f mz1 f is the viscous resistance of the well fluid per unit tubing string, expressed in N; 1s f is the local resistance per unit length of the coupling, expressed in N / m; rt This represents the frictional resistance per unit length between the tubing and the casing wall, expressed in N / m.

[0151] like Figure 4 As shown in Figure b, the force analysis of the micro-segment of the tubing string under well tripping conditions yields the mechanical equilibrium equations for the micro-segment of the tubing string under well tripping conditions:

[0152]

[0153] f rt =fF n

[0154] F n =(q r -f r cosα

[0155] In the formula: F s(i) and F s(i+1) These are the axial forces at the lower and upper ends of the tubing segment during well tripping, respectively, in N.

[0156] like Figure 4As shown in the c diagram in the force analysis of the unit operation condition pipe column microelement section, the mechanical equilibrium equation of the electric submersible screw pump system pipe column microelement section under the unit operation condition is obtained:

[0157] F r(i+1) F r(i) F r F ) F ls F mzl F

[0158] F r(i) F r(i+1) F

[0159] Step 3, combined with the force analysis analyzed in step 2, the mechanical model of the electric submersible screw pump lifting system under the pump working condition, the mechanical model of the electric submersible screw pump lifting system under the unit operation condition and the mechanical model of the electric submersible screw pump lifting system under the well lifting condition are established respectively;

[0160] Step 4, stress analysis is performed on the mechanical model under each working condition respectively;

[0161] The pipe column stress calculation model is composed of the stress borne by any point on the pipe column of the electric submersible screw pump unit lifting pipe column, including the tensile (compressive) stress generated by the axial force, the bending stress generated by the wellbore bending, the bending stress generated by the spiral bending, the shear stress generated by the torque (additional torque generated by the spiral bending) and the radial and circumferential stress generated by the internal and external pressure. Based on the pipe column stress, including axial stress, pipe column bending stress, pipe column spiral bending stress and pipe column internal and external stress, the fourth strength theory is used for calculation when the pipe column stress intensity is calculated.

[0162] Step 5, the pipe column safety evaluation method of the electric submersible screw pump lifting system.

[0163] Example Two

[0164] The example provides a pipe column safety evaluation method of an electric submersible screw pump lifting system, and the specific implementation process is as follows:

[0165] The safety evaluation method specifically includes: wellbore trajectory model establishment, force analysis of the electric submersible screw pump unit, force analysis of the pipe column during the lifting system pipe column well lifting, pump lowering and unit operation process, pipe column mechanical property analysis, pipe column stress calculation model, safety factor calculation model, maximum passing length calculation model and maximum passing curvature calculation model.

[0166] Step 1, wellbore trajectory model establishment;

[0167] Combined with the existing wellbore data, the wellbore trajectory data is obtained, and the well depth trajectory and wellbore curvature model are constructed.

[0168] Step 2: Based on the stress analysis of the tubing during the well start-up, pump running, and unit operation of the lifting system, establish a tubing stress calculation model.

[0169] Step 3: Using the segmented method and combined with the stress calculation model of the tubing, calculate the stress intensity of the tubing at different stress sections.

[0170] Step 4: Determine the maximum stress intensity on the cross-section of the tubular column, and calculate the safety factor using the safety factor calculation model.

[0171] Step 5: The maximum wellbore curvature through which the electric submersible screw pump and its tubing threaded joint pass;

[0172] Based on the parameters of the electric submersible screw pump unit and its tubing threaded joint, considering the safety factor and thread stress concentration factor, and taking into account the axial force, the maximum wellbore curvature that the electric submersible screw pump and its tubing threaded joint can pass through is calculated.

[0173] Step 6: Based on the maximum passing curvature of the unit calculated in Step 5, the corresponding maximum passing length can be calculated.

[0174] Step 7: Based on the calculated safety factor, maximum passing curvature, and maximum passing length, combined with the well depth parameters, wellbore trajectory, and electric submersible screw pump unit parameters, a comprehensive safety evaluation is conducted under three operating conditions: well start-up, pump running-down, and unit operation.

[0175] In this embodiment, after calculating the safety factor, and determining that the safety factor is greater than 1.6, it indicates that the tubing string will not experience a safety accident due to exceeding the yield limit during the tripping process. With a safety factor greater than 1.6, the maximum curvature of the tripping unit is further calculated, and the maximum passage length is calculated under the maximum curvature condition. That is, in this deviated well configuration, if the tubing string's own safety factor is greater than 1.6 and its length is less than the maximum passage length, it is theoretically safe. In other words, a normal tripping process can be guaranteed when the total length of the screw pump unit (including the screw pump length, connector length, protector length, permanent magnet direct drive motor length, carrier sensor length, etc.) is less than the maximum passage length.

[0176] The method comprehensively considers temperature effect, expansion effect, coupling effect, pipe string load, stress intensity, buckling law, friction and drag, centralizer, maximum passing length of pipe string and maximum passing curvature of pipe string, and builds a mechanical model of well tripping, pump lowering and unit operation conditions, and through solving the mechanical models of the three conditions, the axial load, friction resistance, pipe string deformation, pipe string stress, minimum safety factor, maximum passing length and curvature of the unit of the deep well electric submersible screw pump lifting system are analyzed, and the actual calculation results are combined with the well depth parameters, well trajectory and electric submersible screw pump unit parameters to realize the safety evaluation under the three conditions of well tripping, pump lowering and unit operation.

[0177] Those of ordinary skill in the art will understand that all or some of the steps in the methods disclosed above, the functions of the modules / units in the systems and devices, can be implemented by software, firmware, hardware, or any appropriate combination thereof. In hardware implementation, the division between the functional modules / units referred to in the above description can not necessarily correspond to the division between physical components; for example, one physical component can have multiple functions, or one function or step can be performed by several physical components working together. Some or all of the components can be implemented as software executed by a processor, such as a digital signal processor or a microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on computer-readable media, which can include computer storage media (or non-transitory media) and communication media (or transitory media). As is well known to those of ordinary skill in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by a computer. Furthermore, it is common knowledge to those of ordinary skill in the art that communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and can include any information delivery media.

Claims

1. A method of evaluating the safety of an ESP pump-lift system string, characterized by, The method comprises: constructing a well depth trajectory and a borehole curvature model according to well depth data and borehole trajectory data; determining the stress of the pipe string of the ESP lifting system under different working conditions according to the well depth trajectory and the borehole curvature model in combination with force analysis of the ESP unit; the working conditions include: well tripping, pump running and unit operation; establishing a pipe string stress model of the ESP lifting system according to the stress of the pipe string of the ESP lifting system under different working conditions; determining the maximum stress intensity on the pipe string cross section based on the pipe string stress model of the ESP lifting system; determining the pipe string strength safety factor by using the pipe string strength safety factor formula according to the maximum stress intensity on the pipe string cross section.

2. The method of evaluating the safety of an ESP pump-lift system string according to claim 1, wherein, The pipe string stress model of the ESP lifting system is composed of tensile or compressive stress generated by axial force, bending stress generated by borehole bending, bending stress generated by helical buckling, shear stress generated by torque and radial and circumferential stress generated by internal and external pressure.

3. The method for evaluating the safety of the pipe string of the ESP lifting system according to claim 2, wherein, the tensile or compressive stress generated by the axial force is: In the above equation, σ t is the tensile or compressive stress resulting from the axial force, A r is the cross-sectional area of the pipe string, and F is the axial force. the bending stress generated by the borehole bending is: σ b = Ekr s In the above equation, σ b is the bending stress due to wellbore curvature, E is the modulus of elasticity, and k is the curvature. the bending stress generated by the helical buckling is: In the above equation, σ bc is the bending stress due to helical buckling, r is the radial gap between the tubing string and the casing, F1 is the axial pressure acting on the tubing, and I is the moment of inertia of the cross section. the shear stress generated by the torque is: In the above formula, τ is the shear stress generated by buckling additional torque, M is the buckling additional torque, and J is the polar moment of inertia of the pipe string cross section; the radial and circumferential stress generated by the internal and external pressure is: In the above equation, σ r is the radial stress, σ θ is the circumferential stress, r o is the outer radius of the string, r i is the inner radius of the string, r s is the radius of any point on the string wall, and r i < r s < r o .

4. The method for evaluating the safety of the pipe string of the ESP lifting system according to claim 1, wherein, the determination of the maximum stress intensity on the pipe string cross section based on the pipe string stress model of the ESP lifting system comprises: dividing different stress sections according to different working conditions and different well sections; the stress sections include: a tensile section, a compressive section without helical buckling and a compressive section with helical buckling; calculating the pipe string stress intensity of different stress sections based on the pipe string stress model of the ESP lifting system; sorting the pipe string stress intensity of each stress section to determine the maximum stress intensity on the pipe string cross section.

5. The method of evaluating the safety of an ESP pump-lift system string according to claim 4, wherein, The pipe string stress intensity of different stress sections includes: the pipe string stress intensity of the tensile section, the pipe string stress intensity of the compressive section without helical buckling and the pipe string stress intensity of the compressive section with helical buckling; wherein the pipe string stress intensity of the tensile section is: the pipe string stress intensity of the compressive section without helical buckling is: the pipe string stress intensity of the compressive section with helical buckling is: In the above equation, σ r is the radial stress, σ θ is the circumferential stress, σ t is the tensile or compressive stress due to axial force, σ b is the bending stress due to wellbore curvature, and σ bc is the bending stress due to helical buckling.

6. The method for evaluating the safety of the pipe string of the ESP lifting system according to claim 1, wherein, the pipe string strength safety factor formula is: In the above equation, n is the safety factor, σ s is the yield limit of the pipe column material, σ imax is the maximum stress intensity on the pipe column cross section.

7. The method of evaluating the safety of an ESP pump lift system string according to claim 1, wherein, after the determination of the pipe string strength safety factor by using the pipe string strength safety factor formula according to the maximum stress intensity on the pipe string cross section, the method further comprises: determining the connection strength of the ESP unit and the pipe string threaded joint according to the relevant parameters of the ESP unit and the pipe string threaded joint; determining the maximum borehole curvature passed by the ESP and the pipe string threaded joint according to the safety factor and the threaded stress concentration factor in combination with the axial force; wherein the connection strength of the ESP unit and the pipe string threaded joint is: P j = f ymn { π [ (D4- 2h s ) 2 - d 2 ] / 4} ; In the above formula, P j is the connection strength of the electric submersible screw pump unit and the pipe string threaded joint, f ymn is the specified minimum tensile strength of the threaded joint, D4 is the large end diameter of the pipe body, h s is the tooth profile height, and d is the inner diameter of the pipe body. The maximum passing hole curvature of the ESP and its string threaded joint is: In the above formula, C mp is the maximum through-hole curvature of the electric submersible screw pump and its string threaded joint, P e is the effective axial force, D0 is the outer diameter of the electric submersible screw pump system string, A is the cross-sectional area of the electric submersible screw pump system string, and K is the comprehensive coefficient.

8. The method of evaluating the safety of an ESP pump-lift system string according to claim 7, wherein, After the string strength safety factor is determined according to the maximum stress intensity on the string cross section by using the string strength safety factor formula, the method further comprises: The maximum passing length of the string under different hole curvatures is calculated by using a length calculation formula; The length calculation formula is: In the above formula, L m is the maximum passing length of the pipe string under a certain hole curvature, R is the radius of curvature, D w is the hole diameter, and D is the outer diameter of the pipe string.

9. An apparatus for evaluating the safety of a ESP pump-lift system string, characterized in that, The device comprises a memory and a processor; the memory is used to save a program for evaluating the safety of the ESP lifting system string, and the processor is used to read and execute the program for evaluating the safety of the ESP lifting system string and execute the method of any one of claims 1-8. 10.A computer readable storage medium, wherein a data processing program is stored on the computer readable storage medium, and the data processing program is executed by a processor to execute the method for evaluating the safety of the ESP lifting system string according to any one of claims 1-8.

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