An evaluation method and system for sealing attenuation of special threads of oil casings in a corrosive environment

Abstract

The application discloses a kind of corrosion environment under oil casing special thread sealing attenuation evaluation method and system, solve the current problem of the sealing performance attenuation prediction method of oil casing special thread under the comprehensive action of pressure, load and corrosion medium, provide quantitative attenuation prediction evaluation method, provide guidance for the selection and selection of oil casing special thread.It includes the following steps: based on the logging data and well logging data of the block to be evaluated in oil and gas field, obtain the block data information of the block to be evaluated;Acquire casing specification information of service casing;Finite element analysis is carried out on the special thread of service casing to obtain grid information;Based on the yield formula of tube body triaxial stress, the contact pressure generated on each grid at different load points is obtained;According to the obtained block data information, casing specification information, grid information and contact pressure, an attenuation evaluation model is constructed;Based on the attenuation evaluation model, the sealing performance attenuation result of special thread is obtained.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, specifically to a method and system for evaluating the attenuation of special thread seals in oil casing under corrosive environments. Background Technology

[0002] With the continuous development of natural gas exploration, the proportion of deep wells (depth > 3000 meters) and ultra-deep wells (depth > 6000 meters) in gas field development is constantly increasing. Deep and ultra-deep wells operate in complex environments, with downhole tubing facing the "three highs": high temperature (bottom hole temperature up to 180℃), high pressure (downhole pressure > 80MPa), and highly corrosive media. This results in the performance of downhole tubing being subjected to multiple tests of load, temperature, and corrosive media. Downhole tubing mainly consists of tubing strings and multi-layer casing strings. Tubing strings are responsible for transporting oil and gas resources from the formation to the surface, while casing strings are responsible for isolating the well from the formation. Both tubing strings and casing strings are composed of single tubing and casing connected by threads, and the sealing performance of the threaded connection is a prerequisite for ensuring the safe and stable production of oil and gas wells. Only when the casing string has good sealing performance can the oil and gas resources in the well bottom reservoir be stably transported to the surface without leakage downhole; only when the casing string has good sealing performance can non-oil and gas media in the formation not easily enter the wellbore and cause pollution.

[0003] Currently, special threads in oil casing and tubing are mainly divided into two categories: API threads conforming to API (American Petroleum Institute) standards and special threads developed independently by manufacturers. API threads lack a sealing structure and rely primarily on thread grease to fill the gaps formed after thread engagement to achieve sealing, resulting in relatively poor sealing performance. Special threads, on the other hand, are designed with a primary sealing structure and multi-stage auxiliary sealing structures, exhibiting excellent gas-tight performance. As oil and gas resources move towards deeper formations, traditional API oil casing and tubing can no longer meet the requirements of downhole conditions. Non-API special thread oil casing and tubing with higher gas-tightness is increasingly widely used in the exploitation of high-temperature and high-pressure oil and gas fields.

[0004] Current research on the sealing performance of special threads under downhole service conditions focuses on their performance under temperature, axial load (tension and compression), bending load, internal pressure, and external pressure. However, the corrosion conditions in deep and ultra-deep wells are quite harsh, mainly due to corrosive gases such as carbon dioxide and hydrogen sulfide contained in the fluid inside the tubing, formation water with high salinity and high Cl- content, completion fluid and kill fluid contained in the annulus formed by the tubing string and casing string, and residual acid flowback injected during acid fracturing. All of these factors can cause corrosion to the shoulders and sealing surfaces of the special threads in the tubing and casing. Once the threads corrode, their sealing capacity will decrease, resulting in a significant risk of leakage. However, there is currently limited research on the degradation of the sealing performance of special threads under the coupled effects of downhole loads and corrosive media. Furthermore, the test evaluation standards for the sealing performance of special threads only involve load, temperature, and pressure, without considering the influence of corrosive media. Additionally, there are no mature models for predicting the degree of sealing degradation. However, in deep and ultra-deep wells, corrosive media have a significant impact on the sealing performance of tubing and casing. If the degree of attenuation cannot be predicted, the selection and application of special threads for tubing and casing in oil and gas wells with high corrosive media content pose a considerable risk. The fact that this problem remains unresolved explains why leaks still occur after tubing and casing, which have passed testing and seal verification, are run into the well. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method and system for evaluating the sealing attenuation of special threads in oil casing under corrosive environments. It solves the problem of the lack of current methods for predicting the attenuation of sealing performance of special threads in oil casing under the combined effects of pressure, load and corrosive media, and provides a quantitative attenuation prediction and evaluation method, offering guidance for the selection and type selection of special threads in oil casing.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for evaluating the attenuation of special thread seals in oil casing under corrosive environments includes the following steps:

[0008] Based on well logging and well logging data of the oil and gas field blocks to be evaluated, obtain block data information of the blocks to be evaluated;

[0009] Collect and obtain casing specification information of in-service oil casing;

[0010] Finite element analysis was performed on the special threads of the in-service oil casing to obtain mesh information;

[0011] The contact pressure generated on each grid at different load points is obtained based on the triaxial stress yielding formula of the tube body.

[0012] A decay evaluation model is constructed based on the acquired block data, casing specifications, grid information, and contact pressure.

[0013] The attenuation results of special thread sealing performance are calculated based on the attenuation evaluation model.

[0014] Preferably, the block data information includes oil and gas pressure, CO2 / H2S partial pressure in the service casing, composition of the produced fluid, and pH analysis value.

[0015] Preferably, the casing specification information includes the outer diameter of the in-service oil casing and dimensional effect parameters.

[0016] Preferably, the grid information includes grid density and grid number.

[0017] Preferably, the step of obtaining the contact pressure generated on each grid at different load points based on the triaxial stress yield formula of the tube body specifically includes the following steps:

[0018] Draw the load envelope based on the triaxial stress yielding formula for the tube body;

[0019] By applying different axial loads, pressures, and temperatures, the contact pressure values ​​corresponding to different load points on each grid within the load envelope are obtained.

[0020] Preferably, the expression for the triaxial stress yield formula of the tube body is:

[0021] σ e =[σ r 2 +σ h 2 +(σ a +σ b ) 2 -σ r σ h -σ r (σ a +σ b )-σ h (σ a +σ b )+3τ ha 2 ] 1 / 2 ;

[0022] Where, σ e For the equivalent stress, σ r For the radial stress inside the pipe, σ h For the circumferential stress inside the pipe, σ a For axial stress, σ b For bending stress, τ ha It represents the circumferential torsional shear stress.

[0023] Preferably, the calculation model of the attenuation evaluation model is as follows:

[0024]

[0025] Where S is the attenuated sealing contact strength; σ i The sealing contact pressure on each unit grid on the special threaded sealing surface; Δl i Let n be the grid density, n be the number of grid cells, and i be 1-n.

[0026] P cr The partial pressure of CO2 / H2S gas inside the pipe; P oi denoted as ρ, where ρ is the total pressure of the medium inside the pipe; D is the outer diameter of the pipe body; B is a parameter related to the type of corrosive gas inside the pipe; r is a size effect parameter; m is the corrosion factor; and A is a parameter related to the pH value of the liquid inside the pipe.

[0027] Preferably, the size effect parameter r takes the following value:

[0028] When the outer diameter D of the tube is in the range of 60.32 to 114.3, r = 0.35;

[0029] When the outer diameter D of the tube is in the range of 127.00 to 339.72, r = 0.014;

[0030] When the outer diameter D of the tube is in the range of 355.6 to 508, r = -0.22.

[0031] Preferably, the parameter A related to the pH value of the liquid inside the pipe is:

[0032] When 0 < pH value of the liquid in the tube < 7, A = 15.326;

[0033] When the pH value of the liquid in the tube is ≥7, A = 12.189.

[0034] A system for evaluating the degradation of special thread seals in oil casing under corrosive environments includes:

[0035] The block data information acquisition module is used to acquire block data information of the blocks to be evaluated based on well logging and well logging data of the oil and gas field blocks to be evaluated.

[0036] The casing specification information acquisition module is used to collect and acquire the casing specification information of the oil casing in service;

[0037] The finite element analysis module is used to perform finite element analysis on the special threads of in-service oil casing to obtain mesh information;

[0038] The contact pressure calculation module is used to obtain the contact pressure generated on each grid at different load points based on the triaxial stress yield formula of the pipe body.

[0039] The attenuation evaluation model construction module is used to construct an attenuation evaluation model based on the acquired block data information, casing specification information, grid information, and contact pressure.

[0040] The attenuation evaluation module is used to calculate and obtain the attenuation results of special thread sealing performance based on the attenuation evaluation model.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] This invention provides a method for evaluating the sealing performance degradation of special threads in oil casing and tubing under corrosive environments. Specifically targeting the sealing performance of special threads in oil casing and tubing operating in CO2 / H2S humid environments, it utilizes oil and gas field logging data, well logging data, and relevant casing specifications of in-service oil casing and tubing. Finite element analysis is performed on the special threads of the oil casing and tubing to obtain contact pressure values ​​under different load conditions (axial load, pressure) within a mesh element. A degradation evaluation model is constructed using the obtained data. This model can accurately assess the degree of degradation in the sealing performance of oil casing and tubing caused by corrosion under different corrosive environments. Furthermore, all parameters in the model have clear physical meanings and value methods, providing significant reference value for selecting oil casing and tubing threads under corrosive operating conditions. Using the degradation evaluation method described in this invention can effectively reduce joint leakage accidents caused by corrosion. Attached Figure Description

[0043] Figure 1 This is a flowchart of the steps in the method for evaluating the attenuation of special thread seals in oil casing under corrosive environments as described in this invention.

[0044] Figure 2 This is a curve of the load envelope in an embodiment of the present invention. Detailed Implementation

[0045] The principles and features of the present invention will be further described in detail below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clearly illustrate the purpose of the embodiments of the present invention.

[0046] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or it can be in a centered component. When a component is said to be "connected to" another component, it can be directly connected to the other component or it may also be in a centered component. When a component is said to be "set to" another component, it can be directly set on the other component or it may also be in a centered component.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0048] This invention provides a method for evaluating the attenuation of special thread seals in oil casing under corrosive environments, such as... Figure 1 As shown, it includes the following steps:

[0049] Based on well logging and well logging data of the oil and gas field blocks to be evaluated, obtain block data information of the blocks to be evaluated;

[0050] Collect and obtain casing specification information of in-service oil casing;

[0051] Finite element analysis was performed on the special threads of the in-service oil casing to obtain mesh information;

[0052] The contact pressure generated on each grid at different load points is obtained based on the triaxial stress yielding formula of the tube body.

[0053] A decay evaluation model is constructed based on the acquired block data, casing specifications, grid information, and contact pressure.

[0054] The attenuation results of special thread sealing performance are calculated based on the attenuation evaluation model.

[0055] This invention designs a method for evaluating the sealing performance degradation of special threads in oil casing and tubing under corrosive environments. Targeting the sealing performance of special threads in oil casing and tubing operating in CO2 / H2S humid environments, it utilizes oil and gas field logging data, well logging data, and relevant casing specifications of in-service oil casing and tubing. Finite element analysis is performed on the special threads of the oil casing and tubing to obtain contact pressure values ​​under different load conditions (axial load, pressure) within a mesh element. Based on the obtained data, a degradation evaluation model is constructed. This model can accurately assess the degree of degradation in the sealing performance of oil casing and tubing caused by corrosion under different corrosive environments. Furthermore, all parameters in the model have clear physical meanings and value methods, providing significant reference value for the selection of oil casing and tubing threads under corrosive operating conditions. Using the degradation evaluation method described in this invention can effectively reduce joint leakage accidents caused by corrosion.

[0056] Specifically, the method for evaluating the attenuation of special thread seals in oil casing under corrosive environments, as described in this invention, includes the following steps in its implementation:

[0057] Step 1: Establish a decay evaluation model

[0058] Where S is the attenuated sealing contact strength, N / mm;

[0059] σ represents the sealing contact pressure on each unit grid on the special thread sealing surface, in MPa;

[0060] Δl i The grid density is mm / cell, n is the number of grid cells, and i is 1-n.

[0061] P cr The partial pressure of CO2 / H2S gas inside the pipe, in MPa;

[0062] P oi The total pressure of the medium inside the pipe, in MPa;

[0063] D is the outer diameter of the tube, in mm;

[0064] B is a parameter related to the type of corrosive gas inside the pipe; the parameter related to CO2 gas takes the value of B. CO2 =1.13, the parameter related to H2S gas takes the value of B. H2S =1.35;

[0065] r is the size effect parameter;

[0066] When the outer diameter D of the tube is in the range of (60.32~114.3) mm, r=0.35.

[0067] When the outer diameter D of the tube is in the range of (127.00~339.72) mm, r=0.014.

[0068] When the outer diameter D of the tube is in the range of (355.6~508) mm, r=-0.22;

[0069] m is the corrosion factor, with a value of 0.61;

[0070] A represents a parameter related to the pH value of the liquid inside the pipe, and N (mm). -(r+1) m -1 (lg(MPa 10 +MPa)) -1 When 0 < pH < 7, A = 15.326; when pH ≥ 7, A = 12.189.

[0071] Step 2: Collect well logging and well logging data of relevant blocks in the oil and gas field to obtain the results of oil and gas pressure, CO2 / H2S partial pressure, composition of produced fluid and pH analysis in the relevant oil and gas blocks.

[0072] Based on the collected data, set P in the attenuation evaluation model. cr The parameter values ​​of B, m, and A.

[0073] Step 3: Obtain the specifications of the in-service oil casing and set the parameter values ​​of D and r in the attenuation evaluation model.

[0074] Step 4: Perform finite element analysis on the special threads of the corresponding specification oil casing pipe, and determine the mesh density Δl from the obtained finite element analysis. i The number of grids, n, sets the parameter values ​​in the attenuation evaluation model.

[0075] Step 5: According to the triaxial stress yield formula for the tube: σ e =[σ r 2 +σ h 2 +(σ a +σ b ) 2 -σ r σ h -σ r (σ a +σ b )-σ h (σ a +σ b )+3τ ha 2 ] 1 / 2 Plot the load envelope (where the x-axis represents axial load and the y-axis represents pressure). Apply axial load, pressure, and temperature to the special thread according to the load envelope, and obtain the contact pressure generated on each grid at different load points (axial load, pressure), i.e., σ. i The value of σ is set in the attenuation evaluation model. i The parameter value.

[0076] In the formula, σ e For the equivalent stress, σ r For the radial stress inside the pipe, σ h For the circumferential stress inside the pipe, σ a For axial stress, σ b For bending stress, τ ha It represents the circumferential torsional shear stress.

[0077] Step 6: Based on the parameter values ​​obtained in the prediction model from Steps 2 to 5, substitute them into the prediction model in Step 1 to calculate the sealing performance degradation caused by the corrosive environment, i.e., the degraded sealing contact strength. Quantitatively determine the degree of degradation of the sealing performance of the special thread of the oil casing by the sealing contact strength S, and take corresponding measures based on the evaluation results.

[0078] This invention also provides a system for evaluating the attenuation of special thread seals in oil casing under corrosive environments, to implement the method for evaluating the attenuation of special thread seals in oil casing under corrosive environments described in this invention, comprising:

[0079] The block data information acquisition module is used to acquire block data information of the blocks to be evaluated based on well logging and well logging data of the oil and gas field blocks to be evaluated.

[0080] The casing specification information acquisition module is used to collect and acquire the casing specification information of the oil casing in service;

[0081] The finite element analysis module is used to perform finite element analysis on the special threads of in-service oil casing to obtain mesh information;

[0082] The contact pressure calculation module is used to obtain the contact pressure generated on each grid at different load points based on the triaxial stress yield formula of the pipe body.

[0083] The attenuation evaluation model construction module is used to construct an attenuation evaluation model based on the acquired block data information, casing specification information, grid information, and contact pressure.

[0084] The attenuation evaluation module is used to calculate and obtain the attenuation results of special thread sealing performance based on the attenuation evaluation model.

[0085] Example

[0086] This embodiment evaluates the impact of a CO2+-containing formation water service environment in an oilfield on the sealing performance of downhole tubing threaded joints.

[0087] Step 1: Select the attenuation evaluation model described in this invention:

[0088] Step 2: Based on the well logging data, well logging data, and produced fluid test report, the oil pressure in the well is determined to be 37 MPa, the CO2 partial pressure to be 2.4 MPa, and the formation water pH to be 7.4. Based on this, A = 12.189 and P in the model are set accordingly. cr =2.4, P oi =37MPa, B=1.13, m=0.61.

[0089] Step 3: The outer diameter of the tubing in this well is 88.9 mm. Based on this, set D = 88.9 and r = 0.35 in the model.

[0090] Step 4: Perform finite element analysis on the special threaded joint of the oil pipe, set the mesh density to 0.02 mm / element, and the number of meshes on the sealing surface of the special threaded joint to 120. Based on this, set Δl = 0.02 and n = 120 in the model.

[0091] Step 5: According to the triaxial stress yield formula σ of the tube body e =[σ r 2 +σ h 2 +(σa +σ b ) 2 -σ r σ h -σ r (σ a +σ b )-σ h (σ a +σ b )+3τ ha 2 ] 1 / 2 Draw the load envelope, where the horizontal axis represents the axial load and the vertical axis represents the pressure.

[0092] By applying axial load, pressure, and temperature to the special thread according to the load envelope, the contact pressure generated on each grid at different load points (axial load, pressure) is obtained, i.e., σ. i The value, such as Figure 2 As shown, the horizontal axis represents a single grid along the length of the sealing surface, with 0 representing the grid at the beginning of the sealing surface and 2.4 representing the grid at the end of the sealing surface. The vertical axis corresponding to each horizontal axis is the contact pressure value σ corresponding to that grid. i .

[0093] Step 6: Calculation Figure 2 The area under the curve is obtained The value is 1129 N / mm;

[0094] Calculate Alg(P) based on the values ​​obtained in steps 2-4. cr +B) m P oi D r The value is 724.8 N / mm;

[0095] Substituted into the attenuation evaluation model, the final calculation The value is 404.2 mm / N.

[0096] This shows that in a certain corrosive environment (such as the CO2+ formation water service environment described in this embodiment), the sealing strength of the thread is only 35% of that in a non-corrosive environment, with a large degree of attenuation and a significant risk of leakage. Based on the attenuation evaluation results, staff can take corresponding measures in a timely manner, such as replacing the oil casing with special threads or performing reinforcement treatment to prevent leakage from causing safety hazards.

[0097] The attenuation evaluation method described in this invention can also provide guidance for the selection and type selection of special threads for oil casing pipes. Based on the attenuation of the thread sealing performance under corrosive environment, replacements can be made to select special threads that are more suitable for the corrosive environment.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for evaluating the attenuation of special thread seals in oil casing under corrosive environments, characterized in that, The steps include the following: Based on well logging and well logging data of the oil and gas field blocks to be evaluated, block data information of the blocks to be evaluated is obtained; the block data information includes oil and gas pressure, CO2 / H2S partial pressure in the service casing, composition of produced fluid and pH analysis value. Collect and acquire casing specification information of in-service oil casing; the casing specification information includes the outer diameter and dimensional effect parameters of the in-service oil casing; Finite element analysis was performed on the special threads of the in-service oil casing to obtain mesh information; the mesh information included mesh density and mesh number. The contact pressure generated on each grid at different load points is obtained based on the triaxial stress yielding formula of the tube body. The method for obtaining the contact pressure generated on each grid at different load points based on the triaxial stress yielding formula of the tube body specifically includes the following steps: Draw the load envelope based on the triaxial stress yielding formula for the tube body; Under different axial loads, pressures, and temperatures, the contact pressure values ​​corresponding to different load points on each grid are obtained for each load envelope. The expression for the triaxial stress yielding formula of the tube body is: s e =[σ r 2 +s h 2 +(s a +s b ) 2 -s r s h -s r (s a +s b )-s h (s a +s b )+3τ ha 2 ] 1 / 2 ; Where, σ e For the equivalent stress, σ r For the radial stress inside the pipe, σ h For the circumferential stress inside the pipe, σ a For axial stress, σ b For bending stress, τ ha It is the circumferential torsional shear stress; A decay evaluation model is constructed based on the acquired block data, casing specifications, grid information, and contact pressure. The calculation model for the attenuation evaluation model is as follows: Where S is the attenuated sealing contact strength; σ i The sealing contact pressure on each unit grid on the special threaded sealing surface; Δl i Let n be the grid density, n be the number of grid cells, and i be 1-n. P cr The partial pressure of CO2 / H2S gas inside the pipe; P oi denoted as: Total pressure of the medium inside the pipe; D is the outer diameter of the pipe; B is a parameter related to the type of corrosive gas inside the pipe; r is a size effect parameter; m is the corrosion factor; A is a parameter related to the pH value of the liquid inside the pipe. The attenuation results of special thread sealing performance are calculated based on the attenuation evaluation model.

2. The method for evaluating the attenuation of special thread seals in oil casing under corrosive environments according to claim 1, characterized in that, The value of the size effect parameter r is: When the outer diameter D of the tube is in the range of 60.32 to 114.3, r = 0.35; When the outer diameter D of the tube is in the range of 127.00 to 339.72, r = 0.014; When the outer diameter D of the tube is in the range of 355.6 to 508, r = -0.

22.

3. The method for evaluating the attenuation of special thread seals in oil casing under corrosive environments according to claim 1, characterized in that, The parameter A, which is related to the pH value of the liquid inside the pipe, is taken as follows: When 0 < pH value of the liquid in the tube < 7, A = 15.326; When the pH value of the liquid in the tube is ≥7, A = 12.

189.

4. A system for evaluating the degradation of special thread seals in oil casing under corrosive environments, characterized in that, A method for evaluating the attenuation of special thread seals in oil casing under corrosive environments, based on any one of claims 1 to 3, includes: The block data information acquisition module is used to acquire block data information of the blocks to be evaluated based on well logging and well logging data of the oil and gas field blocks to be evaluated; The casing specification information acquisition module is used to collect and acquire the casing specification information of the oil casing in service; The finite element analysis module is used to perform finite element analysis on the special threads of in-service oil casing to obtain mesh information; The contact pressure calculation module is used to obtain the contact pressure generated on each grid at different load points based on the triaxial stress yield formula of the pipe body. The attenuation evaluation model construction module is used to construct an attenuation evaluation model based on the acquired block data information, casing specification information, grid information, and contact pressure. The attenuation evaluation module is used to calculate and obtain the attenuation results of special thread sealing performance based on the attenuation evaluation model.

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