Ultra-deep well pipe column safety analysis method based on high temperature and high pressure prediction

Abstract

The invention relates to an ultra-deep well string safety analysis method based on high-temperature and high-pressure prediction, and the method comprises the steps: employing a three-dimensional space modeling theory to carry out well track prediction according to well track parameters; establishing a wellbore temperature and pressure prediction model according to a wellbore trajectory prediction result; forming a tubular column axial deformation and stress analysis module according to the wellbore temperature and pressure prediction model; according to a tubular column axial deformation and stress analysis module, combining the determined tubular column safety coefficient, and adopting a tubular column safety coefficient calculation method to check the strength of the tubular column; and performing safety and reliability evaluation on the ultra-deep well pipe column according to a pipe column strength checking result. According to the ultra-deep well pipe column safety analysis method based on high temperature and high pressure prediction, the stress and deformation of the pipe column when the ultra-deep well pipe column is influenced by high temperature and high pressure can be scientifically calculated, the strength of the pipe column is checked, the calculation result is checked and corrected in test operation practice, and high scientificity is achieved.

Description

Technical Field

[0001] The present invention relates to the field of safety and reliability in the field of petroleum and natural gas in the energy industry, and in particular to a safety analysis method for ultra-deep well pipes based on high temperature and high pressure prediction. Background Art

[0002] With the continuous increase in energy demand and the extension of oil and gas exploration and development, deep and ultra-deep oil and gas have become important alternative energy sources. Generally speaking, deep and ultra-deep oil and gas have the characteristics of high temperature and high pressure. For ultra-deep wells, the working environment of the downhole tubing is very harsh. At the same time, the stress and deformation of the tubing are complex and changeable, resulting in frequent downhole accidents such as tubing fracture and packer failure, which seriously restricts the safe and economic development of ultra-deep wells. Compared with normal temperature and pressure wells, the stress of ultra-deep well tubing has the following characteristics: in ultra-deep wells, the distribution of wellbore temperature and pressure at different production rates is quite different, and the distribution is nonlinear; with the increase of well depth, the sensitivity of the stress and deformation of the downhole tubing to factors such as temperature, pressure, viscous friction and friction between oil casing and casing also increases; changes in temperature and pressure will cause a large additional load on the downhole tubing, which will significantly affect its stress and deformation, and even cause the failure of downhole tools such as packers. There is still no complete evaluation method for the safety status of ultra-deep well strings, which are mainly affected by three major forces: axial tension, external extrusion and internal pressure. So far, the testing of ultra-deep, high-temperature and high-pressure wells in China has not yet formed a complete and effective test design and construction model and specification due to the limitations of equipment, conditions and experience. On-site mainly uses the casing string design method to design and verify the oil pipe string. There is still little research on the safety of such ultra-deep well strings at home and abroad, especially the problems of force analysis and strength verification under various working conditions.

[0003] The present invention fully considers the characteristics of ultra-deep wells and ultra-deep well tubular safety testing technologies at home and abroad, studies the structural composition of the ultra-deep well testing system, and performs force analysis and calculation on the temperature effect, expansion effect, buckling effect, piston effect and flow effect that cause axial force deformation of the tubular according to the test requirements and purposes, and establishes a tubular axial deformation calculation model to evaluate the safety of the downhole tubular, providing a basis for the reasonable configuration of the tubular combination and the reasonable selection of production operation parameters, and compiles a set of application software system integrating tubular mechanics calculation, deformation analysis, safety verification, stability analysis, tubular design, data management and other functions. Summary of the invention

[0004] The purpose of the present invention is to provide an ultra-deep well string safety analysis method based on high temperature and high pressure prediction to solve the problems mentioned in the background technology.

[0005] The present invention provides a method for ultra-deep well string safety analysis based on high temperature and high pressure prediction, comprising:

[0006] S1. Based on the trajectory parameters of the drilled wellbore, the wellbore trajectory is predicted using the three-dimensional space modeling theory;

[0007] S2. Based on the prediction results of the wellbore trajectory, the law of fluid flow in the wellbore, differential method and numerical method are used to analyze the law of temperature change of gas in the wellbore with depth, and a wellbore temperature and pressure prediction model is established;

[0008] S3. Based on the wellbore temperature and pressure prediction model and the basic effects affecting the deformation of the tubing string, a differential equation for the bending of the completion tubing string is constructed to form an axial deformation and force analysis module for the tubing string;

[0009] S4. According to the pipe string axial deformation and stress analysis module, combined with the determined pipe string safety factor, the pipe string safety factor calculation method is used to check the pipe string strength;

[0010] S5. Based on the results of the string strength verification, a curve of the axial force and axial safety factor changing with the well depth is drawn through computer simulation to carry out a reliability assessment of the safety of the ultra-deep well string.

[0011] Preferably, the method of predicting the wellbore trajectory using three-dimensional space modeling theory based on the wellbore trajectory parameters includes:

[0012] S1.1, based on the small rectangle simulation modeling, obtain the three-dimensional data of the formation;

[0013] S1.2. Based on the three-dimensional data of the stratum, the stereoscopic display technology is used to improve the visual reality effect, and the stratum stereogram is obtained through perspective projection;

[0014] S1.3. According to the formation stereogram, a wellbore trajectory model is established through a spatial arc model, a cylindrical spiral model, and a natural curve model.

[0015] Preferably, the method of analyzing the law of temperature variation of gas in the wellbore with depth by using the flow law of fluid in the wellbore, differential method and numerical method according to the wellbore trajectory prediction result to establish the wellbore temperature and pressure prediction model comprises:

[0016] S2.1. Calculate the total fluid pressure gradient based on the parameters of the drilled wellbore trajectory and the flow law of the fluid in the wellbore;

[0017] S2.2. Based on the decomposed total pressure gradient, the wellbore is divided into several small sections using the idea of ​​the differential element method, so as to calculate the pressure at the outlet of each section;

[0018] S2.3. According to the energy conservation equation for stable gas flow, the radial heat transfer from the wellbore to the surrounding formation and the radial change rate of the gas enthalpy are analyzed to obtain the ordinary differential calculation equation for the gas temperature;

[0019] S2.4. Based on the ordinary differential equation of gas temperature, using the idea of ​​differential element method, the wellbore is divided into several small sections to obtain the temperature at the outlet of each section;

[0020] S2.5. Based on the pressure and temperature at the outlet of each section, a numerical method is used to combine the trial and error method with the iteration method to establish a coupling model of the temperature field and pressure field, and further obtain the temperature and pressure distribution of the entire wellbore.

[0021] Preferably, the total fluid pressure gradient expression in S2.1 is as follows:

[0022]

[0023] Among them, α represents the acceleration direction; h represents the gravity direction; f represents the friction direction; p represents the pressure, MPa; z represents the length of the oil cylinder, m.

[0024] Preferably, the pressure expression at each outlet of S2.2 is as follows:

[0025]

[0026] in, represents (5×10 -9 Q st / d ii 2 ) 2 ; C2 represents 3484.48γ; C3 represents Z g T / P; P in Indicates the pressure at the inlet; g indicates the acceleration due to gravity, m / s 2 ;d ii Indicates the inner diameter of the oil pipe, m; Q st Indicates the output under standard conditions, m 3 / d;Z g represents the gas compressibility factor; T represents the temperature, K.

[0027] Preferably, the ordinary differential calculation equation for the gas temperature in S2.3 is expressed as follows:

[0028]

[0029] Among them, T f Indicates fluid temperature, °C; T e represents the formation temperature, °C; v represents the flow velocity, m / s; C p represents specific heat at constant pressure; C J represents the Joule-Thomson coefficient.

[0030] Preferably, the expression of each outlet temperature in S2.4 is as follows:

[0031]

[0032] Among them, T eout Indicates the outlet formation temperature, °C; z in Indicates the length of the inlet oil cylinder; z out Indicates the length of the outlet oil cylinder; g T represents geothermal gradient, ℃ / m; d represents pipe diameter; T fin Indicates the inlet fluid temperature.

[0033] Preferably, the wellbore temperature and pressure prediction model is combined with the basic effects affecting the deformation of the tubing string to construct a completion tubing string bending differential equation to form a tubing string axial deformation and force analysis module, which includes:

[0034] S3.1. Based on the wellbore temperature and pressure prediction model, the basic effect principle of pipe string deformation is used to simulate the deformation results of a single pipe string, and the composite pipe string is segmented in combination with the actual structure and fluid conditions of the pipe string;

[0035] S3.2. For the composite pipe string segmentation, numerical integration and iteration techniques are used, combined with boundary conditions and force balance differential equations, to solve the variation law of the pipe string load along the axial direction, and obtain the stress distribution and axial deformation of the pipe string;

[0036] S3.3. According to the stress distribution and axial deformation of the tubing, the buckling of the gas well tubing is analyzed, the differential equation of the completion tubing bending is established, the critical sinusoidal buckling load and critical helical buckling load of the completion tubing in the inclined well are analyzed, and the stress process of the tubing is calculated.

[0037] Preferably, the pipe string strength verification is performed according to the pipe string axial deformation and stress analysis module, in combination with the determined pipe string safety factor, using a pipe string safety factor calculation method, including:

[0038] S4.1. Based on the pipe string axial deformation and stress analysis module, combined with the determined pipe string safety factor, the fourth strength theory is used to check the pipe string strength;

[0039] S4.2. Based on the fourth strength theory and the three-dimensional stress calculation formula, the expression of the equivalent stress of the ultra-deep well string is as follows:

[0040]

[0041] Among them, σ a represents axial stress, Pa; σ θ represents the circumferential stress, Pa; σ r represents radial stress, Pa;

[0042] S4.3. Based on the expression of equivalent stress and the allowable stress of the ultra-deep well string, the safety factor of each section is calculated to obtain the result of the string strength check.

[0043] Preferably, the process of drawing a curve of axial force and axial safety factor along the well depth based on the string strength verification result by computer simulation to carry out reliability assessment of the safety of the ultra-deep well string includes:

[0044] S5.1. Based on the results of the string strength verification, the curves of the axial force and the shaft safety factor along the well depth are drawn through computer simulation to conduct safety assessment and analysis;

[0045] S5.2. Draw the curve of axial force and axial safety factor along the well depth according to computer simulation, compare it with the given safety factor, evaluate whether the ultra-deep well string is safe under the working condition, and give the evaluation result;

[0046] S5.3. Comprehensively consider the evaluation results of S5.1 and S5.2 to determine the safety status of the ultra-deep well string.

[0047] The present invention proposes a new ultra-deep well string safety analysis method based on high temperature and high pressure prediction. The present invention vividly simulates the wellbore trajectory prediction, and accordingly establishes a wellbore temperature and pressure prediction model, and performs deformation and force analysis of the string based on the temperature and pressure prediction model. At the same time, combined with the specific string safety factor, the string strength is checked. On this basis, a comprehensive ultra-deep well string safety analysis method based on high temperature and high pressure prediction is formed, which provides an accurate and reasonable research method for analyzing string safety and strength verification, and provides an important reference for the research of similar problems in the engineering field.

[0048] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic flow chart of a method for ultra-deep well string safety analysis based on high temperature and high pressure prediction provided by an embodiment of the present invention;

[0050] Figure 2 A three-dimensional curve diagram of wellbore trajectory prediction in an embodiment of the present invention;

[0051] Figure 3 A model diagram of a pipe string in an embodiment of the present invention;

[0052] Figure 4 It is a schematic diagram of the coupling process of the wellbore pressure field and temperature field in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] Example

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Reference Figure 1-Figure 4 The embodiment of the present invention provides a method for ultra-deep well string safety analysis based on high temperature and high pressure prediction, comprising steps S1 to S5, wherein:

[0056] In step S1, the wellbore trajectory is predicted using three-dimensional space modeling theory according to the parameters of the drilled wellbore trajectory;

[0057] In step S2, based on the wellbore trajectory prediction results, the law of fluid flow in the wellbore, differential method and numerical method are used to analyze the law of temperature change of gas in the wellbore with depth, and a wellbore temperature and pressure prediction model is established;

[0058] In step S3, based on the wellbore temperature and pressure prediction model and combined with the basic effects affecting the deformation of the tubing string, a completion tubing string bending differential equation is constructed to form a tubing string axial deformation and force analysis module;

[0059] In step S4, according to the pipe string axial deformation and force analysis module, combined with the determined pipe string safety factor, a pipe string safety factor calculation method is used to perform pipe string strength verification;

[0060] In step S5, based on the string strength verification result, a curve of the axial force and the axial safety factor along the well depth is drawn through computer simulation to carry out a reliability assessment of the safety of the ultra-deep well string.

[0061] In this embodiment, first, the borehole trajectory is predicted based on the parameters of the drilled wellbore trajectory using the three-dimensional space modeling theory; then, based on the wellbore trajectory prediction results, the pressure at the outlet of each section is calculated using the flow law of the fluid in the wellbore and the idea of ​​the differential element method; based on the energy conservation equation when the gas is flowing steadily, the radial heat transfer from the wellbore to the surrounding formation and the radial rate of change of the enthalpy of the gas are analyzed to obtain the ordinary differential calculation equation of the gas temperature; based on the ordinary differential equation of the gas temperature, the wellbore is divided into several small sections using the idea of ​​the differential element method to obtain the temperature at the outlet of each section; based on the pressure and temperature at the outlet of each section, the trial and error method is combined with the iteration method to establish the coupled temperature field and pressure field. Combined model, further obtain the temperature and pressure distribution of the entire wellbore; then, according to the wellbore temperature and pressure prediction model, combined with the basic effects affecting the deformation of the tubing string, the axial deformation of the tubing string is obtained, and then the buckling of the gas well tubing string is analyzed, and the completion tubing string bending differential equation is established to analyze the critical sinusoidal buckling load and critical spiral buckling load of the completion tubing string in the ultra-deep well; then, according to the tubing string axial deformation and force analysis module, combined with the determined tubing string safety factor, the fourth strength theory is used to check the tubing string strength; finally, according to the tubing string strength verification result, the curve of the axial force and axial safety factor along the well depth is drawn through computer simulation, and a safety assessment analysis is performed to form a reliability assessment result. In summary, the present invention vividly simulates the prediction of the wellbore trajectory, and accordingly establishes a wellbore temperature and pressure prediction model, performs deformation and force analysis of the tubing string based on the temperature and pressure prediction model, and at the same time, combines the specific tubing string safety factor to perform the strength verification of the tubing string. The above process constitutes a complete set of ultra-deep well tubing string safety analysis methods based on high temperature and high pressure prediction.

[0062] Step S1, based on the parameters of the drilled wellbore trajectory, the wellbore trajectory is predicted using the three-dimensional space modeling theory. The specific method is as follows:

[0063] (1) Based on the parameters of the drilled wellbore trajectory, the wellbore trajectory is predicted using the three-dimensional space modeling theory; taking the formation as an example: the three-dimensional shape of the formation is a curved surface, which needs to be simulated by many small rectangles, so the formation data is grid data. The grid spacing is set to a fixed size, so that the X, Y coordinates of any grid vertex on the surface can be known by knowing only the X, Y coordinates of the starting point (upper left corner or lower left corner) and the grid spacing. Therefore, only the depth Z coordinate of each grid vertex needs to be saved. The formation data can be processed into three-dimensional formation data using a processed three-dimensional data volume file, or directly read from the development database.

[0064] (2) Connect the upper left vertex of each grid with the lower right vertex to divide the entire grid into two triangles, calculate the face vectors of all triangles adjacent to the vertex, and then average all the face vectors adjacent to the vertex to obtain the normal vector of the point. Calculate the normal vectors of each vertex on the stratum surface, and then perform a three-dimensional display. At the same time, stereoscopic display technology is used to produce two pictures of the same scene. One is for the left eye and the other is for the right eye. Improve the visual reality and enhance the realism of the user's interaction with the virtual environment. Design a light point and the range it covers to simulate various scenarios in daily life, and use perspective projection to achieve the effect of smallness in the distance and largeness in the near.

[0065] (3) Establish a wellbore trajectory model based on the spatial arc model, cylindrical spiral model, and natural curve model.

[0066] 1.1 Space arc model

[0067]

[0068] in,

[0069]

[0070] cosε=cosα1cosα2+sinα1sinα2cos(θ2-θ1)

[0071] 1.2 Cylindrical helical model

[0072]

[0073] in,

[0074]

[0075] 1.3 Natural curve model

[0076]

[0077] in,

[0078]

[0079] c H =f S (α1,α2)

[0080]

[0081] Step S2, based on the wellbore trajectory prediction described in step S1, establish a wellbore temperature and pressure prediction model, the specific method is as follows:

[0082] (1) According to the parameters of the drilled wellbore trajectory, it is assumed that the gas is in a one-dimensional stable flow in the wellbore; at any cross section in the wellbore, all characteristic parameters of the gas are uniform; the heat transfer from the tubing to the second interface (the contact surface between the cement sheath and the formation) is a one-dimensional stable heat transfer, and the heat transfer from the second interface to the formation around the wellbore is a one-dimensional unsteady heat transfer; the heat loss in the wellbore and the formation is radial, and the heat transfer along the depth direction is not considered; the vertical formation temperature changes linearly, and the geothermal gradient is known; the tubing is anchored and the packer is set; the casing and oil pipe are concentric. Based on the flow law of the fluid in the wellbore, the total pressure gradient of the fluid is decomposed into three parts: acceleration pressure gradient, gravity pressure gradient, and friction pressure gradient.

[0083]

[0084] Among them, α represents the acceleration direction; h represents the gravity direction; f represents the friction direction; p represents the pressure, MPa; z represents the length of the oil cylinder, m.

[0085] According to the decomposed total pressure gradient, the acceleration pressure gradient, gravity pressure gradient and friction pressure gradient are analyzed respectively, and then the gas density is solved by combining the state equation to obtain the differential equation of pressure.

[0086]

[0087] Based on the idea of ​​the differential element method, the wellbore is divided into several small sections, and then the Dranchuk, Purris and Robinson methods are used for the gas compressibility factor. At the same time, the pressure drop caused by the change in fluid kinetic energy is taken into account to calculate the pressure at the outlet of each section.

[0088]

[0089] in, represents (5×10 -9 Q st / d ii 2 ) 2 ; C2 represents 3484.48γ; C3 represents Z g T / P; P in Indicates the pressure at the inlet; g indicates the acceleration due to gravity, m / s 2 ;d ii Indicates the inner diameter of the oil pipe, m; Q st Indicates the output under standard conditions, m 3 / d;Z g represents the gas compressibility factor; T represents the temperature, K.

[0090] (2) According to the energy conservation equation for steady gas flow

[0091]

[0092] The radial heat transfer from the wellbore to the surrounding formation (dq / dz) and the radial rate of change of the gas enthalpy (dh / dz) are analyzed, the thermophysical parameters Cp and CJ are calculated, and the ordinary differential calculation equation of the gas temperature is obtained.

[0093]

[0094] Among them, T f Indicates fluid temperature, °C; T e represents the formation temperature, °C; ν represents the flow velocity, m / s; C p represents specific heat at constant pressure; C J represents the Joule-Thomson coefficient.

[0095] According to the ordinary differential equation of gas temperature and based on the idea of ​​differential element method, the wellbore is divided into several small sections, and the heat generated by the friction between the pipe wall and the gas is considered at the same time, so as to obtain the temperature at the outlet of each section.

[0096]

[0097] Among them, T eout Indicates the outlet formation temperature, °C; z in Indicates the length of the inlet oil cylinder; z out Indicates the length of the outlet oil cylinder; g T represents geothermal gradient, ℃ / m; d represents pipe diameter; T fin Indicates the inlet fluid temperature.

[0098] (3) According to the pressure and temperature at the outlet of each section, the coupled field of temperature and pressure is established by combining the trial and error method with the iteration method. The steps are as follows:

[0099] ① Taking the bottom hole pressure (or wellhead pressure) as the starting point, the well is divided into several sections according to the well depth. Before starting the calculation, determine the parameters such as gas production, well depth, bottom hole temperature, bottom hole pressure, tubing diameter and geothermal gradient. The entire tubing is divided into sections, and the length of each section is Dz, which depends on the accuracy requirements and is generally less than 5% of the entire pipe length.

[0100] ② Calculate the rough value of the temperature at the outlet of the first section.

[0101]

[0102] ③ Based on the rough value of the temperature at the outlet of the first section calculated in step ②, substitute it into formula (2-3) to calculate and obtain the pressure and gas flow rate at the outlet of the first section.

[0103] ④Substitute the pressure and gas flow rate at the first section outlet calculated in step ③ into formula (2-8) to recalculate the precise value of the temperature at the first section outlet.

[0104] ⑤Judge the precise value of the temperature at the outlet of the first section calculated in step ④ to see whether it meets the accuracy requirement. If not, return this precise value as a rough value to step ③ and repeat the calculation. Continue to the next step until the accuracy requirement is met.

[0105] ⑥Use the precise values ​​of the temperature, pressure and gas flow rate at the outlet of the first section calculated previously as the temperature, pressure and gas flow rate at the inlet of the second section, repeat steps ② to ⑤, and you can calculate the temperature and pressure at the outlet of the second section.

[0106] ⑦ By iterative calculation using this method, the pressure and temperature distribution of the entire wellbore can be obtained, such as Figure 4 .

[0107] Step S3, based on the wellbore temperature and pressure prediction model described in step S2, a pipe string axial deformation and force analysis module is formed, and the specific method is as follows:

[0108] (1) Considering the deadweight of the tubing, Hooke's law is used to calculate the degree of deformation of the tubing affected by its deadweight. Under working conditions, the tubing will produce temperature effects, piston effects, expansion effects and spiral bending effects due to changes in temperature and pressure. These effects can be used to calculate the total deformation of a single tubing. A single tubing refers to tubing of the same size, with one fluid in the tubing and one fluid in the annular space. Composite tubing includes one or more of the following: more than one tubing size; more than one casing size; more than two fluids in the tubing and casing. The composite tubing is divided into sections according to the actual structure of the tubing and the fluid conditions in the well.

[0109] (2) For the composite pipe string segmentation, mathematical methods such as numerical integration and iteration techniques are used, combined with boundary conditions and force balance differential equations, to solve the variation law of the pipe string load along the axial direction and obtain the total deformation of the pipe string. Taking the temperature effect as an example:

[0110] Calculation of a single string:

[0111] ΔF1=104.4WΔT (3-1)

[0112] ΔL1=1.59×10 -5 ×LΔT (3-2)

[0113] Where, ΔL1 is the change in length of the tubing string caused by temperature effect, m;

[0114] Calculation of composite pipe string:

[0115] If the composite string has n sections, the generalized formula for length change is:

[0116]

[0117] (3) Through mechanical analysis, the axial deformation law of the downhole tubing and the working stress of the tubing under different working conditions are studied, and the tubing force model is established. Then, the buckling analysis of the gas well tubing is carried out, and the static equilibrium method is used to establish the bending differential equation of the completion tubing.

[0118] The buckling equation of the tubing string in a slanted wellbore is obtained:

[0119]

[0120] The buckling equation of the pipe string in the vertical wellbore is obtained:

[0121]

[0122] And the buckling equation of the tubing string in a horizontal wellbore:

[0123]

[0124] The critical sinusoidal buckling load and critical helical buckling load of the completion string in the inclined vertical well are analyzed. Based on the above data and the actual operating conditions of the gas well string system, the force process of the string is calculated by numerical simulation method, and the data is preliminarily processed based on the calculation results.

[0125] Step S4, according to the pipe string axial deformation and force analysis module described in step S3, combined with the determined pipe string safety factor, adopt the pipe string safety factor calculation method to perform pipe string strength verification, the specific method is as follows:

[0126] (1) According to the fourth strength theory, considering that the downhole tubing in ultra-deep wells works under a three-dimensional complex stress state, a triaxial strength verification method is given:

[0127] The formula of axial stress of pipe string is:

[0128]

[0129] Radial stress formula:

[0130]

[0131] Circumferential stress:

[0132]

[0133] Among them, F a is the axial force of the dangerous section, and r is the radius of any point on the dangerous section. According to formulas (4-1)(4-2)(4-3), a large amount of data can be calculated by computer to obtain the three-dimensional stress of the ultra-deep well string at different well depths.

[0134] (2) Based on the axial stress, radial stress and circumferential stress of the pipe string, the expression of equivalent stress is obtained:

[0135]

[0136] Among them, σ a represents axial stress, Pa; σ θ represents the circumferential stress, Pa; σ r Represents radial stress, Pa; based on the axial stress, radial stress and circumferential stress of the pipe string obtained by computer processing of data, the equivalent stress of the pipe string at different depths can be calculated.

[0137] (3) Based on the expression of equivalent stress, the safety factor of each section can be expressed as:

[0138]

[0139] where k s is the triaxial stress safety factor, and the allowable stress of the gas well string is σ. The result of strength verification is obtained through analysis.

[0140] Step S5, based on the string strength verification result described in step S4, the reliability assessment of the safety of the ultra-deep well string is carried out, and the specific method is as follows:

[0141] (1) Based on the results of the triaxial strength verification, a large amount of data is processed by computer to draw the curves of the axial force variation along the well depth and the curve of the safety factor variation along the well depth.

[0142] (2) Based on the curve of the axial force changing with the well depth, the turning point in the figure is analyzed to evaluate whether the tubing will break due to excessive axial force at that point; based on the curve of the safety factor changing with the well depth, the safety factor of the ultra-deep well tubing at different depths is compared with the set safety factor to determine whether the tubing is in a safe state.

[0143] (3) Taking these two evaluation results into consideration, it can be basically concluded whether the ultra-deep well string is in a safe state.

[0144] Therefore, the present invention adopts the above-mentioned ultra-deep well string safety analysis method based on high temperature and high pressure prediction, fully considers the characteristics of ultra-deep wells and ultra-deep well string safety testing technology at home and abroad, studies the structural composition of the ultra-deep well test system, and scientifically calculates the composite force and motion changes of the downhole string when it is affected by pressure and other factors according to the test requirements and purposes, and analyzes and calculates the temperature effect, expansion effect, buckling effect, piston effect and flow effect that cause the axial force deformation of the string, and establishes a string axial deformation calculation model to evaluate the safety of the downhole string, providing a basis for the reasonable configuration of the string combination and the reasonable selection of production operation parameters, and compiles a set of application software system integrating string mechanical calculation, deformation analysis, safety verification, stability analysis, string design, data management and other functions. The software is of great significance to the safe operation and production of ultra-deep wells, and plays a guiding role in the safety testing of ultra-deep well strings.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for ultra-deep well string safety analysis based on high temperature and high pressure prediction, characterized in that: include: S1. Based on the trajectory parameters of the drilled wellbore, the wellbore trajectory is predicted using the three-dimensional space modeling theory; S2. Based on the prediction results of the wellbore trajectory, the law of fluid flow in the wellbore, differential method and numerical method are used to analyze the law of temperature change of gas in the wellbore with depth, and a wellbore temperature and pressure prediction model is established; S3. Based on the wellbore temperature and pressure prediction model and the basic effects affecting the deformation of the tubing string, a completion tubing string bending differential equation is constructed to form a tubing string axial deformation and force analysis module; S4. According to the pipe string axial deformation and stress analysis module, combined with the determined pipe string safety factor, the pipe string safety factor calculation method is used to check the pipe string strength; S5. Based on the results of the string strength verification, a curve of the axial force and axial safety factor changing along the well depth is drawn through computer simulation to carry out a reliability assessment of the safety of the ultra-deep well string.

2. The ultra-deep well string safety analysis method based on high temperature and high pressure prediction according to claim 1 is characterized in that: The method of predicting the wellbore trajectory using the three-dimensional space modeling theory according to the wellbore trajectory parameters includes: S1.1, based on the small rectangle simulation modeling, obtain the three-dimensional data of the formation; S1.

2. Based on the three-dimensional data of the stratum, a stereoscopic display technology is used to improve the visual reality effect, and a three-dimensional stratum map is obtained through perspective projection; S1.

3. According to the formation stereogram, a wellbore trajectory model is established through a spatial arc model, a cylindrical spiral model, and a natural curve model.

3. The method for ultra-deep well string safety analysis based on high temperature and high pressure prediction according to claim 2 is characterized in that: The method of analyzing the law of temperature change of gas in the wellbore with depth based on the prediction result of the wellbore trajectory, using the flow law of the fluid in the wellbore, differential method and numerical method, and establishing the wellbore temperature and pressure prediction model includes: S2.

1. Calculate the total fluid pressure gradient based on the parameters of the drilled wellbore trajectory and the flow law of the fluid in the wellbore; S2.

2. Based on the decomposed total pressure gradient, the wellbore is divided into several small sections using the idea of ​​the differential element method, so as to calculate the pressure at the outlet of each section; S2.

3. According to the energy conservation equation for stable gas flow, the radial heat transfer from the wellbore to the surrounding formation and the radial change rate of the gas enthalpy are analyzed to obtain the ordinary differential calculation equation for the gas temperature; S2.

4. Based on the ordinary differential equation of gas temperature, using the idea of ​​differential element method, the wellbore is divided into several small sections to obtain the temperature at the outlet of each section; S2.

5. Based on the pressure and temperature at the outlet of each section, a numerical method is used to combine the trial and error method with the iteration method to establish a coupling model of the temperature field and pressure field, and further obtain the temperature and pressure distribution of the entire wellbore.

4. The method for ultra-deep well string safety analysis based on high temperature and high pressure prediction according to claim 3 is characterized in that: The total fluid pressure gradient expression in S2.1 is as follows: Among them, α represents the acceleration direction; h represents the gravity direction; f represents the friction direction; p represents the pressure; and z represents the length of the oil cylinder.

5. The method for ultra-deep well string safety analysis based on high temperature and high pressure prediction according to claim 3 is characterized in that: The pressure expression at the outlet of each section in S2.2 is as follows: in, represents (5×10 -9 Q st / d ii 2)2; C2 represents 3484.48γ; C3 represents Z g T / P; P in represents the pressure at the inlet; g represents the acceleration due to gravity; d ii Indicates the inner diameter of the oil pipe; Q st Indicates the output under standard conditions; Z g represents the gas compressibility factor; T represents the temperature.

6. The method for ultra-deep well string safety analysis based on high temperature and high pressure prediction according to claim 3 is characterized in that: The ordinary differential equation for gas temperature in S2.3 is as follows: Among them, T f Indicates fluid temperature; T e represents the formation temperature; v represents the flow velocity; C p represents specific heat at constant pressure; C J represents the Joule-Thomson coefficient.

7. The method for ultra-deep well string safety analysis based on high temperature and high pressure prediction according to claim 3 is characterized in that: The expression for the outlet temperature of each section in S2.4 is as follows: Among them, T eout Indicates the outlet formation temperature; z in Indicates the length of the inlet oil cylinder; z out Indicates the length of the outlet oil cylinder; g T represents geothermal gradient; d represents pipe diameter; T fin Indicates the inlet fluid temperature.

8. The method for ultra-deep well string safety analysis based on high temperature and high pressure prediction according to claim 3 is characterized in that: The wellbore temperature and pressure prediction model is combined with the basic effects that affect the deformation of the tubing string to construct a completion tubing string bending differential equation to form a tubing string axial deformation and force analysis module, including: S3.

1. Based on the wellbore temperature and pressure prediction model, the basic effect principle of pipe string deformation is used to simulate the deformation results of a single pipe string, and the composite pipe string is segmented in combination with the actual structure and fluid conditions of the pipe string; S3.

2. For the composite pipe string segmentation, numerical integration and iterative technology mathematical methods are used, combined with boundary conditions and force balance differential equations, to solve the variation law of the pipe string load along the axial direction, and obtain the stress distribution and axial deformation of the pipe string; S3.

3. According to the stress distribution and axial deformation of the tubing, the buckling of the gas well tubing is analyzed, the differential equation of the completion tubing bending is established, the critical sinusoidal buckling load and critical helical buckling load of the completion tubing in the inclined well are analyzed, and the stress process of the tubing is calculated.

9. The method for ultra-deep well string safety analysis based on high temperature and high pressure prediction according to claim 8, characterized in that: The pipe string strength check is performed according to the pipe string axial deformation and stress analysis module, in combination with the determined pipe string safety factor, using the pipe string safety factor calculation method, including: S4.

1. Based on the pipe string axial deformation and stress analysis module, combined with the determined pipe string safety factor, the fourth strength theory is used to check the pipe string strength; S4.

2. Based on the fourth strength theory and the three-dimensional stress calculation formula, the expression of the equivalent stress of the ultra-deep well string is obtained as follows: Among them, σ a represents the axial stress; σ θ represents the circumferential stress; σ r represents radial stress; S4.

3. Based on the expression of equivalent stress and the allowable stress of the ultra-deep well string, the safety factor of each section is calculated to obtain the result of the string strength check.

10. The ultra-deep well string safety analysis method based on high temperature and high pressure prediction according to claim 9, characterized in that: According to the string strength verification result, the curve of axial force and axial safety factor along the well depth is drawn through computer simulation, and the reliability assessment of the safety of the ultra-deep well string is carried out, including: S5.

1. Based on the results of the string strength verification, the curves of the axial force and the shaft safety factor along the well depth are drawn through computer simulation to conduct safety assessment and analysis; S5.

2. Draw the curve of axial force and axial safety factor along the well depth according to computer simulation, compare it with the given safety factor, evaluate whether the ultra-deep well string is safe under the working conditions, and give the evaluation results; S5.3: The safety status of the ultra-deep well string is obtained by combining the evaluation results of S5.1 and S5.2.

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