A method for analyzing the reliability of a coiled tubing drilling cement sheath quality

Abstract

This invention discloses a method for reliability analysis of cement sheath quality in coiled tubing drilling, relating to the field of construction technology. The steps of this invention are as follows: S1: Identify the damage forms and characteristics of the cement sheath; S2: Test the impact of cement sheath loss on the external load of the casing; S3: Test the casing performance using different parameters; S4: Calculate the external load and strength data of the casing; S5: Calculate reliability data, test the failure morphology of the cement sheath after fracturing under high-pressure formation fluid and fracturing conditions, test the sealing integrity of the perforated section under fracturing operation conditions, and observe the cement sheath crack propagation morphology and microcrack propagation characteristics around the perforation channel using CT scanning. This invention, through method improvements, facilitates the visual observation of cement sheath failure morphology; evaluates the cement sheath sealing performance under different operating conditions; and analyzes the impact of different cement sheath damage degrees on the casing stress state.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology, and in particular relates to a method for analyzing the reliability of cement sheath quality in coiled tubing drilling. Background Technology

[0002] Deep well casing strings face a more complex service environment, which can be divided into geological loads and engineering loads. These include high temperature and high pressure, saline layers, formation creep, fault displacement, sand production impact, in-situ stress, reservoir compaction, steep formations, wellbore structure, acid fracturing, staged stimulation, high-pressure water injection, etc. However, the impact of cementing quality has also attracted attention.

[0003] After the casing is solidified by a cement ring, a cement ring-casing pressure-bearing carrier is formed, which is a commonly used method in finite element simulation studies of casing damage. However, the cement ring and casing are not ideal concentric and fully filled media, which leads to changes in the pressure-bearing carrier, including pressure channel crossflow, poor interface bonding quality, eccentricity, and local missing parts.

[0004] Engineering operations can also affect the integrity of the cement sheath, which in turn can lead to changes in the pressure-bearing capacity of the cement sheath-casing pressure carrier. Current research has confirmed that pressure cyclic loading and changes in wellbore pressure can cause cement sheath failure, but the damage modes of cement sheath caused by perforation operations and fracturing still need further research.

[0005] The traditional maximum load method for casing design is used to calculate and verify the safety factor (the ratio of casing load to casing strength). Although it takes into account working conditions such as annular pressure, there are still shortcomings: ① The cement ring-casing is not considered as a pressure-bearing carrier; ② The external load calculation is relatively simple and does not take into account the uncertainty of casing strength.

[0006] The strength and load of the casing vary with time, depth, and operating conditions, and are factors that need to be considered in the safety and reliability assessment of the casing: uniform strength, partial factor, random distribution, weighting factor, etc.; operating conditions mainly refer to drilling, completion, and production, while cementing quality mainly discusses stress concentration phenomena.

[0007] The main forms of cement sheath damage include local missing parts, eccentricity, and flow channels induced by seal integrity failure. The causes are related to cementing operation technology, wellbore quality, cement slurry performance, and temperature and pressure corrosion environment. Damage characteristics include characteristic parameters and cement sheath parameters. At the same time, the impact load generated by perforation, high formation pressure fluids, and fracturing operations can also cause cement sheath damage. The forms and characteristics of damage need to be further clarified. Summary of the Invention

[0008] The purpose of this invention is to provide a method for analyzing the reliability of cement sheath quality in coiled tubing drilling, so as to solve the problems mentioned in the background art.

[0009] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0010] This invention relates to a method for reliability analysis of cement sheath quality in coiled tubing drilling, the steps of which are as follows:

[0011] S1: Identify the forms and characteristics of cement sheath cementing quality damage;

[0012] S2: Test the impact of missing cement ring on the external load of the casing;

[0013] S3: Test the performance of the bushing by varying the parameters;

[0014] S4: Calculate the external load data and strength data of the casing;

[0015] S5: Calculate reliability data.

[0016] Furthermore, the failure morphology of the cement sheath after fracturing was tested under high-pressure fluid conditions and fracturing conditions.

[0017] Furthermore, the sealing integrity of the perforated section under fracturing operation conditions was tested, and the propagation morphology of the cement sheath cracks and the propagation characteristics of microcracks around the perforation channels were observed by CT scanning.

[0018] Furthermore, based on the Abaqus finite element software, a three-dimensional formation-cement sheath-casing model of cementing quality damage was established.

[0019] Furthermore, the external load data of the casing is calculated as follows:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026] Calculation of casing strength data:

[0027]

[0028] In the above formula, A is the area of ​​the fitted graph, mm²; w is the width of the fitted graph, mm; α is the angle of the missing cement ring; α c y0 is the average missing angle; y0 is the casing strength, MPa; σ n s1 is the casing stress, MPa; s2 is the non-uniform external load, MPa; ky k is a dimensionless correction coefficient related to the missing angle. θ k is a dimensionless correction coefficient related to the eccentricity angle. a The correction factor related to eccentricity is dimensionless; t z k is a dimensionless coefficient related to the thickness of the cement ring. p p is a dimensionless coefficient related to pore pressure and annular pressure. p s0 is the pore pressure or annular pressure, MPa; s1 is the equivalent stress of the casing under non-uniform stress, MPa; s1 is the non-uniform load, MPa; ξ is the material difference coefficient, dimensionless; λ is the stiffness ratio, dimensionless; υ s σ is the Poisson's ratio of the formation, which is dimensionless; H The maximum ground stress is expressed in MPa; σ h Minimum in-situ stress, MPa; m is the ratio of the inner and outer diameters of the cement ring, dimensionless; υ is the Poisson's ratio of the casing; E is the elastic modulus of the casing, GPa; E s The elastic modulus of the formation is expressed in GPa and m. c E is the ratio of the inner and outer diameters of the casing, dimensionless. c υ is the elastic modulus of cement ring, in GPa; c Y is the Poisson's ratio of the cement ring, dimensionless; p The casing yield strength is given by T in MPa. y The tensile strength of the casing is kN; r o The outer diameter of the casing is in mm; r i The inner diameter of the sleeve is in mm.

[0029] Furthermore, according to and The safety and reliability data of the casing after the cement ring is missing are derived as follows:

[0030]

[0031] In the formula, R(Z) represents the reliability; ρ c The density of the cement paste is expressed in kg / m³.

[0032] The present invention has the following beneficial effects:

[0033] This invention, through method improvements, enables easy observation of the failure morphology of the cement ring; evaluation of the sealing performance of the cement ring under different working conditions; and analysis of the influence of different cement ring damage degrees on the stress state of the casing. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the testing device structure of the present invention;

[0036] Figure 2 This is a schematic diagram of the internal structure of the simulated wellbore.

[0037] Figure 3 This is a schematic diagram of a CT scan for the present invention;

[0038] Figure 4 This is a schematic diagram of the model of the present invention;

[0039] Figure 5 This is a schematic diagram of the sleeve stress of the present invention;

[0040] Figure 6 This is a schematic diagram illustrating the variation of the outer diameter of the sleeve in this invention;

[0041] Figure 7 This is a schematic diagram illustrating the change in the elastic modulus of the present invention;

[0042] Figure 8 This is a schematic diagram illustrating the change in residual stress in this invention;

[0043] Figure 9 This is a schematic diagram illustrating the change in sleeve eccentricity according to the present invention;

[0044] Figure 10 This is a schematic diagram illustrating the variation of the sleeve eccentricity according to the present invention;

[0045] Figure 11 This is a schematic diagram illustrating the missing angle variation of the present invention;

[0046] Figure 12 This is a schematic diagram illustrating the variation in missing thickness according to the present invention;

[0047] Figure 13 This is a schematic diagram illustrating the analysis of the present invention;

[0048] Figure 14 This is a schematic diagram of the output stress distribution of the present invention;

[0049] Figure 15 This is a schematic diagram of the safety factor distribution of the present invention;

[0050] Figure 16 This is a schematic diagram of the sleeve stress of the present invention;

[0051] Figure 17 This is a schematic diagram illustrating the failure probability and safety factor of the present invention;

[0052] Figure 18 This is a schematic diagram showing the failure probability and safety factor of the present invention under different annular pressures / pore pressures;

[0053] Figure 19 This is a schematic diagram illustrating the failure probability and safety factor for different missing thicknesses in this invention;

[0054] Figure 20 This is a schematic diagram showing the missing angle of the cement ring in this invention;

[0055] Figure 21 This is a schematic diagram showing the missing thickness of the cement ring in this invention;

[0056] Figure 22 This is a schematic diagram of the sleeve eccentricity angle of the present invention;

[0057] Figure 23 This is a schematic diagram of the pore pressure at the missing part of the present invention;

[0058] Figure 24 This is a schematic diagram of the parameter variation coefficients of the present invention. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Please see Figures 1-24 As shown, this invention is a method for analyzing the reliability of cement sheath quality in continuous tubing drilling.

[0061] 1. The forms and characteristics of cement sheath cementing quality damage were identified, and fracturing simulation experiments were conducted.

[0062] Fracturing damage test: Under high-pressure fluid and fracturing conditions, observe the failure morphology of the cement sheath after fracturing, and analyze the crack propagation morphology of the cement sheath and the microcrack propagation characteristics around the perforation channel.

[0063] Experimental Testing Apparatus: The wellbore sealing integrity evaluation simulation device mainly consists of five parts: a simulated wellbore, a data acquisition system, a strain measurement system, a pressure control system, and a temperature control system. Through different operating methods, this simulation device can achieve the following functions: cement slurry curing under heated and pressurized conditions; monitoring changes in casing condition; visually observing the failure morphology of the cement sheath; and evaluating the sealing performance of the cement sheath under different working conditions (reference). Figure 1 ).

[0064] Fracturing damage test: Based on the size of the wellbore sealing integrity evaluation simulation device, a test experiment on the sealing integrity of the perforated section under fracturing operation conditions was conducted. The propagation morphology of the cement sheath fractures and the microcrack propagation characteristics around the perforation channels were observed using CT scanning. The specific procedure is as follows.

[0065] ① Preparation of the perforated section of the wellbore

[0066] A 2mm radius hole is pre-drilled in the middle of a Φ35mm steel pipe to simulate the perforated section casing after actual perforation operations.

[0067] A 5mm long paraffin column with an outer diameter of 2mm was prepared and inserted into the casing hole. After curing, the paraffin was removed. A plastic plate was used to simulate the initial micro-annulus at the cementing interface caused by perforation.

[0068] Simulated wellbore assembly and cement ring curing. Curing in a curing autoclave for 7 days.

[0069] ②Seal integrity test of the perforated section of the wellbore

[0070] First, the initial cement ring was tested for sealing performance under a confining pressure of 15 MPa for 10 minutes.

[0071] If the pressure on the upper part of the cement ring changes from 0 MPa during the loading process, it indicates that the cement ring has failed. At this time, the pressure inside the casing is the failure pressure of the cement ring.

[0072] Disassemble the simulated wellbore, remove the damaged cement sheath, and observe its failure pattern (reference). Figure 2 ).

[0073] There are both radial cracks extending along the shaft axis and circumferential cracks at the borehole, and the boreholes will be connected by radial or circumferential cracks to form a connected network of cracks.

[0074] Following hydraulic fracturing, the failure morphology of the cement sheath is predominantly radial cracks that extend axially. Due to the influence of steel casing artifacts, micro-annular gaps are difficult to extract and visualize on CT scans (see reference). Figure 3 ).

[0075] 2. Simulation of the impact of missing cement sheath on the external load of the casing

[0076] Model building:

[0077] A three-dimensional numerical simulation model of the formation-cement sheath-casing system, considering cementing quality damage, was established using Abaqus finite element software. This model can analyze the influence of different cement sheath damage levels on the casing stress state.

[0078] Model assumptions:

[0079] Considering that the casing, cement sheath, and formation are homogeneous materials with isotropic physical properties;

[0080] Ignore the ellipticity and wall thickness uniformity of the sleeve;

[0081] The simplified geometry of the radial crack in the cement ring is a cuboid.

[0082] The simplified geometry of the missing cement ring is a sector-shaped prism.

[0083] Boundary conditions:

[0084] The displacements of a single surface perpendicular to the x and y axes in the outer boundary of the model are fixed in the x and y directions, and the displacements of the two surfaces perpendicular to the z axis in the z direction are fixed.

[0085] External stress is applied to the horizontally unfixed displacement surface, and corresponding pressure is applied to the inner wall of the casing and the exposed outer wall of the casing due to the absence of cement sheath.

[0086] The interfaces between the formation, casing, and cement sheath are bonded together (see reference). Figure 4 and Figure 5 ).

[0087] ① Set a fixed direction displacement for the outer boundary in the software to simulate the formation stress state and prevent the calculation from failing to converge.

[0088] ② Model mesh. Tetrahedral meshes are used to facilitate mesh generation, and seeding is applied at the boundaries of the casing, cement sheath, and formation end face to ensure smooth mesh transition.

[0089] ② Taking into account the wellbore structure and specific casing failure scenarios of wells such as Yangta 5-5, YM46-H3, YD103H, and YM352-1H, the model's geometric dimensions were designed. A three-dimensional model of casing-cement sheath-formation was established for 95 / 8″ casing, with a wellbore size of 12 1 / 4″. The overall length, width, and height of the model are 5m, 5m, and 0.7m, respectively.

[0090] Calculated range: ① Pore pressure range: 82.32-102.9 MPa. During the preparation test for production, the casing pressure increased (0↑45.64 MPa). It was suspected on site that the 95 / 8″ casing was leaking and high-pressure brine (2.18) entered the annulus at 4792m.

[0091] ② Annular pressure range: 60-70MPa. Local defects in the cement ring create a sealed space containing liquid. The heat released during the hydration of the cement ring and the heat transfer during the production process lead to localized temperature rise and high pressure. The pressure increase is related to the temperature increase and can reach 60-70MPa.

[0092] ③ Set the physical property parameters and boundary conditions, and perform calculations using static analysis steps. The calculation results focus on Von Mises Stress, considering the casing steel grade as TP140V or BG140V, with a yield strength of 1000MPa.

[0093] 3. Random distribution of parameters

[0094] (1) Distribution of casing strength parameters

[0095] By statistically analyzing the destructive testing data and production quality control data of the casing, and fitting the data using a nonlinear formula, the distribution law of the casing strength parameters was obtained. The results show that the statistical laws for parameters such as outer diameter, wall thickness, elastic modulus, Poisson's ratio, residual stress, and yield strength fit the normal distribution well, exhibiting a significant and strong correlation (reference). Figures 6-8 ).

[0096] (2) Distribution of casing load parameters

[0097] Based on statistical analysis of cementing amplitude logging, sonic variable density logging, and cement bond logging with human-controlled imaging data, the distribution and fitting curves of cement sheath eccentricity, eccentricity, missing angle, and missing thickness were obtained. The distribution patterns of cementing quality parameters at different well depths all fit well with normal distributions and are all significantly strongly correlated (reference). Figures 9-12 ).

[0098] Table 1. Types of Casing Parameter Distribution

[0099]

[0100]

[0101] The external load parameters acting on the casing, such as maximum ground stress, minimum ground stress, and internal pressure, have a certain degree of randomness. The elastic parameters and strength parameters of the formation and cement sheath also have a certain degree of randomness. These uncertainties will inevitably have a certain impact on the reliability and safety of the casing.

[0102] Using the structural parameters and performance parameters of the casing, the elastic parameters of the cement sheath and formation, and the load on the casing during operation as input parameters, the safety and reliability of the casing when there are defects in the cementing quality are studied.

[0103] (3) Sensitivity analysis of random distribution parameters (refer to) Figure 13 )

[0104] Correlation analysis

[0105] A Latin hypercube sampling design was used to divide the 20 input parameters into design points and perform parallel parameter design, generating a total of 283 original samples. The influence between the random variables and the output variables was quantified to obtain correlation coefficients, and parameter sensitivity analysis was conducted. The results show that missing thickness, internal pressure, missing angle, eccentricity, and pore pressure eccentricity angle have a significant impact on casing safety, with correlation coefficients all above 0.5.

[0106] 4. Casing External Load and Strength Model

[0107] Casing external load model

[0108]

[0109]

[0110]

[0111]

[0112]

[0113]

[0114] Casing strength model:

[0115]

[0116] In the above formula, A is the area of ​​the fitted figure, mm²; w is the width of the fitted figure, mm; α is the angle of the missing cement ring, °; α c y0 is the average missing angle, °; y0 is the casing strength, MPa; σ n s1 is the casing stress, MPa; s2 is the non-uniform external load, MPa; k y k is a dimensionless correction coefficient related to the missing angle. θ k is a dimensionless correction coefficient related to the eccentricity angle. a The correction factor related to eccentricity is dimensionless; t z k is a dimensionless coefficient related to the thickness of the cement ring. p p is a dimensionless coefficient related to pore pressure and annular pressure. p s0 is the pore pressure or annular pressure, MPa; s1 is the equivalent stress of the casing under non-uniform stress, MPa; s1 is the non-uniform load, MPa; ξ is the material difference coefficient, dimensionless; λ is the stiffness ratio, dimensionless; υ s σ is the Poisson's ratio of the formation, which is dimensionless; H The maximum ground stress is expressed in MPa; σ hMinimum in-situ stress, MPa; m is the ratio of the inner and outer diameters of the cement ring, dimensionless; υ is the Poisson's ratio of the casing; E is the elastic modulus of the casing, GPa; E s The elastic modulus of the formation is expressed in GPa and m. c E is the ratio of the inner and outer diameters of the casing, dimensionless. c υ is the elastic modulus of cement ring, in GPa; c Y is the Poisson's ratio of the cement ring, dimensionless; p The casing yield strength is given by T in MPa. y The tensile strength of the casing is kN; r o The outer diameter of the casing is in mm; r i The inner diameter of the casing is in mm;

[0117] Nonlinear fitting was performed on the equivalent stress variation law of the missing casing to correct the maximum radial stress formula of the casing-cement sheath-formation stress distribution under non-uniform stress, and a corrected mechanical model of external load on the casing with missing cement sheath under non-uniform stress was established.

[0118] 5. Reliability Calculation Method

[0119] Based on reliability theory, and according to equations (1) and (2), the safety and reliability model of the casing after the cement ring is missing is derived:

[0120]

[0121] R(Z) represents reliability; ρ c The density of cement paste is expressed in kg / m³.

[0122] (1) Reliability calculation:

[0123] By inputting the structural parameters, performance parameters, and external load parameters of the bushing, the distribution of the equivalent stress and safety factor of the bushing is obtained. Based on the stress-strength interference theory, the relationship between reliability, safety factor, and equivalent stress is derived.

[0124] With a constant eccentricity, the probability of casing failure increases with increasing casing stress, meaning the casing reliability decreases. Under the same safety factor, a larger eccentricity leads to a higher probability of failure, meaning an increased eccentricity reduces casing reliability (reference). Figures 13-19 ).

[0125] When the annular pressure / pore pressure at the missing point exceeds 90 MPa, with a constant safety factor, the probability of casing failure increases with increasing pressure, meaning casing reliability decreases. When the annular pressure / pore pressure is constant, the probability of casing failure increases with increasing casing stress, also meaning casing reliability decreases. With a constant external load on the casing, the thickness of the missing part has a relatively small impact; however, as the missing part thickness increases, the safety factor decreases and the probability of failure increases. A failure probability of 0.5 corresponds to a safety factor of approximately 1.4.

[0126] (2) Analysis of the impact of parameter variation coefficient on the safety and reliability of the casing (reference) Figures 20-24 )

[0127] The distribution of cementing quality parameters in different well sections is random. As the coefficient of variation of each parameter increases, the average reliability of the casing decreases and the reliability range widens. That is, while the reliability of the casing decreases, the accuracy of the casing safety calculation method also decreases. Therefore, obtaining high-precision cementing quality detection data is crucial.

[0128] The order of influence of each sensitivity parameter on reliability is as follows: cement sheath missing thickness > cement sheath missing angle > casing eccentricity angle > casing eccentricity > pore pressure > internal pressure, which is basically consistent with the correlation analysis of the parameters.

[0129] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0130] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for reliability analysis of cement sheath quality in coiled tubing drilling, characterized in that, The steps are as follows: S1: Identify the forms and characteristics of cement sheath cementing quality damage; S2: Test the impact of missing cement ring on the external load of the casing; S3: Test the performance of the bushing by varying the parameters; S4: Calculate the external load data and strength data of the casing; S5: Calculate reliability data; The external load data for the casing are calculated as follows: Calculation of casing strength data: In the above formula, The area of ​​the fitted figure is measured in mm². The width of the fitted graph, in mm; This is the missing corner of the cement ring; The average missing angle; The strength of the casing is expressed in MPa. For casing stress, MPa; For non-uniform external load, MPa; The correction coefficient related to the missing angle is dimensionless. The correction factor related to the eccentricity angle is dimensionless. The correction factor related to the eccentricity is dimensionless. A dimensionless coefficient relating to the thickness of the cement ring; A dimensionless coefficient related to pore pressure and annular pressure; Pore ​​pressure or annular pressure, MPa; The equivalent stress of the casing under non-uniform stress is expressed in MPa. The material difference coefficient is dimensionless. The stiffness ratio is dimensionless. Poisson's ratio of the stratigraphic unit is dimensionless. The maximum ground stress is expressed in MPa. Minimum ground stress, MPa; The ratio of the inner and outer diameters of the cement ring is dimensionless. The casing's Poisson's ratio; The elastic modulus of the casing is given in GPa. Here is the formation elastic modulus, in GPa; The ratio of the inner and outer diameters of the casing is dimensionless. The elastic modulus of the cement ring is given in GPa. The Poisson's ratio of the cement ring is dimensionless. The sleeve yield strength is given by MPa. The tensile strength of the casing is kN; The outer diameter of the casing is in mm; The inner diameter of the sleeve is in mm.

2. The method for reliability analysis of cement sheath quality in coiled tubing drilling according to claim 1, characterized in that, The failure mode of the cement sheath after fracturing was tested under high-pressure fluid and fracturing conditions in the formation.

3. The method for reliability analysis of cement sheath quality in coiled tubing drilling according to claim 2, characterized in that, The sealing integrity of the perforated section under fracturing operation conditions was tested, and the propagation morphology of the cement sheath fracture and the propagation characteristics of microcracks around the perforation channel were observed by CT scanning.

4. The method for reliability analysis of cement sheath quality in coiled tubing drilling according to claim 1, characterized in that, Based on the Abaqus finite element software, a three-dimensional formation-cement sheath-casing model of cementing quality damage was established.

5. The method for reliability analysis of cement sheath quality in coiled tubing drilling according to claim 1, characterized in that, according to and The safety and reliability data of the casing after the cement ring is missing were obtained: In the formula, For reliability; The density of cement paste is kg / m³. 3 .

Images