Pipe String Research Articles

Study on Mechanical Calculation Method of Injection-production String in Changqing Gas Storage

on the basis of previous studies, According to the working conditions of injection and production wells in gas storage,this paper selects the mathematical model of the downhole string suitable for Changqing gas storage under the effects of piston, axial force, expansion, temperature and spiral bending. The mechanical analysis and calculation of injection-production string under simulated working condition and actual working condition are carried out by using corresponding mechanical analysis software, and the parameters such as the axial load, triaxial Factor of safety, minimum absolute triaxial Factor of safety, string elongation, string shortening are given, according to the calculation results, the safety strength of injection-production string is checked, and the load safety criterion for production and operation of string is given.Field Test and calculation of injection-production string are carried out. According to the actual test results, the deformation rule of the injection production string under the actual gas injection condition is summarized, and compared with the results calculated by the software, which verifies the accuracy of the calculating software and forms the method of the strength check of the injection and production string. It can provide effective evaluation means for the safe operation of injection and production string in gas storage. The safety failure of the injection and production pipe string is reduced, the safety and efficient operation of the gas storage is ensured.

Corrosion Analysis and Prevention of Tubing Nipples in Four Wells

A high-temperature and high-pressure gas field in an oil field requires the use of super 13 chromium material due to corrosive environments. In the recent production process, there have been four consecutive cases of corrosion, fracture, and perforation of tubing nipples, which have brought enormous economic losses to the oilfield. This article analyzes the failure causes of these four tubing nipples and proposes preventive measures. In this paper, the macroscopic morphology, chemical composition, mechanical properties, metallography, and microscopic morphology of four failed tubing nipples have been analyzed. Combined with the field service conditions and string structure of the tubing nipples, it is believed that the failure of the tubing nipples is mainly due to the connection of carbon steel and stainless steel materials, forming a typical galvanic corrosion galvanic cell. The geometric and environmental factors of the materials exacerbate this corrosion. Eventually, severe galvanic corrosion occurred on the inner surface of the tubing nipple, resulting in severe wall thinning or partial perforation, and four tubing nipples failed. The failed tubing nipples in Wells A, B, and C have erosion marks, which are caused by the action of high pressure and high flow rate fluids in the well; The inner surface of the tubing nipple in Well D is rusty yellow, mainly due to the corrosion of its inner wall caused by the acid fracturing fluid injected earlier. At the same time, the string structure of four wells shows that the tubing nipple is located at the variable diameter node of the string. When the fluid in the well flows from the large hole into the smaller hole, the fluid in the well will change there, and its flow rate and pressure will also increase, further exacerbating the erosion in this area. With the development of deep wells containing carbon dioxide in oil fields and the application of carbon dioxide injection secondary oil recovery technology, the use of 13Cr martensitic stainless steel is also increasing. In order to avoid the occurrence of similar accidents that will bring huge economic losses to the oil field, it is recommended that the material of the pipe string (including accessories) of such wells be confirmed using a portable direct reading spectrometer before entering the well.

Nanoarchitectonics and performance evaluation of a Fe3O4-stabilized Pickering emulsion-type differential pressure plugging agent

Abstract With the rapid growth of natural gas consumption capacity, the important role of gas storage in seasonal peak shaving and emergency response is gradually emerging. Long-term forced production and injection of gas storage will lead to problems such as wellhead equipment leakage and string seal failure. Replacing the string is not only costly but also takes a long time. Aiming at thread leakage caused by multiple rounds of forced production and injection in gas storage, a Pickering emulsion differential pressure plugging agent with a self-sealing function under a certain pressure difference was developed. We selected carboxyl nitrile latex with a self-polymerization function and modified the nano-stabilizer Fe3O4@SiO2. The Pickering differential pressure plugging agent with excellent plugging performance was prepared by the combination of modified particles and non-ionic emulsifier OP-10. The plugging test was carried out for the simulated oil pipe thread. When the leakage rate was 50 mL/min, no leakage occurred under a pressure of 20 MPa after plugging. The differential pressure plugging agent is expected to achieve plugging without moving the pipe string and rebuild the integrity of the wellbore.

Development of a Design Method for Casing and Tubing Strings under Complex Alternating Loads

With the escalating intricacy of downhole operational scenarios, encompassing frequent well cycling, acidification, multi-stage fracturing, steam injection, and intensive extraction, the efficacy of traditional casing-string-design methods rooted in strength considerations is progressively unveiling its limitations. Henceforth, it becomes imperative to establish string-design method standards that embrace the entirety of a well’s lifecycle, encompassing the phases of drilling, completion, fracturing, and production operations. Beginning with an analysis of the advantages and limitations of traditional casing-string-design methods, this paper introduces the features of strain and sealing design methods developed for the full lifecycle of the string. The strain design method, a departure from conventional design philosophies, enables the design concept of the controllable deformation of the pipe string. The sealing design method currently stands as the sole standard method for the design of tubing strings. Simultaneously, this paper proposes the establishment of a time dimension-based lifecycle pipe string-design method standard. This approach considers the trend of pipe strength degradation, effectively addressing the safety concerns related to pipe string design in production and operation.

The Effect of Clamping Force and Friction Coefficient on The Clamping Clamp

In order to study the influence of clamping force and friction coefficient on the stress distribution of drill pipe joint during the buckling process, the nonlinear contact problem and elastoplastic mechanical properties of Φ139.7mm × 9.17mm drill pipe were simulated by finite element analysis method in this paper, and the stress distribution and size of drill pipe joint during the buckling process were obtained. And the effect of clamping force and friction coefficient on the joint of drill pipe. It is found that the stress of drill pipe joint is mainly concentrated in the contact position of drill pipe and the stress value of drill pipe joint shows a trend of increasing. When the friction coefficient is 0.15 and the clamping force is 600KN, although there is stress concentration in the contact position between the clamp teeth and the drill pipe joint, it does not exceed the yield limit of the drill pipe joint, and no plastic deformation occurs. Through the simulation calculation, it is found that the maximum clamping force and the maximum torque are 1200KN and 81.9KN.m respectively. When the torque is fixed, the change of friction coefficient has a great influence on the maximum clamping force of drill pipe joint. With the increase of friction coefficient, the maximum clamping force of drill pipe joint decreases continuously, and the friction coefficient is inversely proportional to the maximum clamping force. The research in this paper enriches the understanding of the buckling process of punching pliers and provides a reference for the rational buckling of pipe string.

CARBON DIOXIDE STRESS CRACKING IN OIL PRODUCTION

The article describes stress corrosion cracking (SCC) of pipe string elements associated with exposure to carbon dioxide. SCC can occur in solutions containing H2S, CO2, ammonia, nitrates, chlorides, acids, alkalis, etc. The article shows two typical examples of stress corrosion cracking of high-carbon steels of tubular string elements (grades 40X13, 40XH) after operation in field environments whose well products do not contain hydrogen sulfide. The possible mechanism of carbon dioxide stress cracking was analyzed in comparison with carbonate stress corrosion cracking (Carbonate Stress Corrosion Cracking) described in the API 571-2020 standard. It is shown that an integral part of the mechanism of carbon dioxide stress cracking is the growth and development of cracks during hydrogen evolution in the cathodic reaction. The general metallurgical and operational characteristics of steel elements of tubular strings subjected to carbon dioxide stress cracking are given, which are in good agreement with the available foreign literature data. Based on the results of operation, it was confirmed that in «conventional» oilfield systems with carbon dioxide, equipment failures by the mechanism of carbon dioxide stress cracking are possible. Examination of the described failures included the following assessment methods: analysis of the accompanying documentation, visual-measuring control, micro-examinations by light microscopy and scanning electron microscopy, tests to determine the mechanical properties of the metal.Carbon dioxide stress cracking was observed in the presence of the following factors: carbon dioxide environment (in the absence of hydrogen sulfide); high concentration of carbon in steel (0.4 % wt.); increased hardness of steel (from 30.3 to 33.9 HRC); the presence of constant and alternating mechanical loads.

Design Optimization and Analysis of Tubing Head Spool for Surface Wellheads are used in the Oil and Gas Industry

The Tubing Head serves as the uppermost spool in a surface wellhead and is typically positioned above the production casing, which is the final string of pipe suspended within the well. It plays a vital role in various functions from well drilling to initial oil production. Tubing head spools have been employed in conventional surface wellheads for many years. However, the current design of the spool is characterized by its significant weight and bulkiness. While this design has proven its effectiveness in the field, there is a need for improvements in terms of size and shape. The primary objective of this study is to reduce the weight and modify the size and shape of the tubing head spool, specifically the 13-5/8”-10K Bottom X 7-1/16”-10K Top variant, utilizing Solidworks modelling and simulation techniques. By leveraging these tools, we aim to optimize the design, achieve weight reduction, and enhance the overall performance of the tubing head spool. The optimization process begins with a comprehensive analysis of the existing tubing head spool design to identify potential areas for improvement. This analysis includes evaluating the stress distribution, pressure containment capabilities, and material utilization of the spool. Various optimization techniques, such as finite element analysis (FEA) are employed to simulate and analyse different design scenarios. We successfully, achieved weight reduction of 5.16% in raw forging and 14.45% in finish part.

Study on mechanical behavior and fatigue life of defective ropes in HTHP gas well with high-sulfur content

As demand for energy increases, the number of “three-high” (high-pressure, high-yield, high-sulfur) gas Wells has doubled, the severe stress fluctuation of pipe string caused by downhole high-pressure environment leads to the failure of rope fracture is particularly prominent. It is easy to cause pipeline blockage and large amount of high-pressure toxic gas leakage caused by tool string accidental falling. Therefore, based on the theory of Love and elastoplastic contact theory, and considering the influence of Poisson’s ratio effect, this article establishes a calculation model for tensile fatigue of interaction between rope strands to study the influence of key structural parameters and breaking wire position on stress distribution and fatigue life of rope. The results show that: the core strand of the rope is the main force position, the overall stress shows the trend of decreasing with the increase of winding radius; when the rope is stretched, the axial deformation near the core of the rope is smaller than the deformation far from the core; under the same number of broken wires, the fatigue life of different ropes is related to the location of broken wires, the farther the location of broken wires from the core of the rope, the higher the fatigue life. The research work in this article provides theoretical guidance for the safe operation of ropes in “three-high” gas wells.

Experimental Investigation on the Penetrability Mechanism of Gel Slug During Well Completion Processes.

Reservoir formation damage is an essential problem which troubled oil and gas well production, a smart packer is a promising technology to maintain sustainable development for the oil and gas fields. Currently, the "gel valve" technology has been proved to be feasible with gel slug to seal casing and descend the completion pipe string, while the systemic performance of ideal gel is still not clear. In the underbalanced completion stage with the gel valve, the downward completion string needs to penetrate the gel slug to form an oil and gas passage in the wellbore. The penetration of rod string to gel is a dynamic process. The gel-casing structure often shows a time-dependent mechanical response, which is different from the static response. In the process of penetration, the interaction force between the rod and gel is not only related to the properties of the interface between gel and string but also affected by the moving speed, rod diameter, and thickness of the gel. The dynamic penetration experiment was carried out to determine the penetrating force varied with depth. The research showed that the force curve was mainly composed of three parts, the rising curve of elastic deformation, decline curve for the surface worn out, and another curve of the rod wear into. By changing the rod diameter, gel thickness, and penetration speed, the change rules of forces in each stage were further analyzed, which would provide a scientific basis for a well completion design with a gel valve.

UNIVERSAL HYDROGAS-DYNAMIC PATTERNS OF THE DRAINAGE ZONE OF OIL AND GAS WELLS

Large-scale experimental hydrogasodynamic studies of the flow of a two-phase gas-liquid mixture in a vertical pipeline were carried out. Based on the analysis of the results of these experimental studies, it was found that among the results obtained there are dependencies with theoretical bases by which theoretical hydrogasodynamic methods for studying multiphase flow in a vertical pipeline can be developed. The article provides a theoretical hydrogasodynamic study using dependencies describing a two-phase flow in a vertical pipeline of a round section, and it is confirmed by existing experiments. As a result of the gas-hydrodynamic study of pumping wells, in order to confirm the rational use of formation gas energy, a positive effect due to an increase in oil production rate and well process parameters, a relationship was established between well Q production rate, bottom-hole pressure of well P and production of formation gas V. Parameters can be modeled using three-term polynomials. During operation of wells in three modes (Qi, Vi or ∆Pi,Vi, where i = 1,2,3), processing of data obtained as a result of studies, indicators determined by existing research methods were obtained, and the technological mode ensuring layer-bylayer cooperation of the well system was selected.
 It is known that the motion of a two-phase flow of gas-liquid mixtures in a vertical pipe string is described on the basis of energy balance theory. The hydrogasodynamic characteristics of the drainage zone can be obtained in a real oil and gas well, as an experimental installation in the form of

Investigation of key problems of clustering perforation string running in horizontal well with unconventional oil-gas reservoirs

Currently, there are two main clustering perforation methods: coiled tubing-conveyed perforation (TCP) and cable-conveyed perforation (CCP). To improve the efficiency of CCP strings in wellbore pass-through capacity problems, considering wellbore geometry constraints, pipe string variable cross-section, flexible tool deformation, and other factors, the pass-through capacity analysis model of the perforating tool string was established and solved by geometric analysis and beam-column theory. Aiming at the running depth problem of a TCP string, considering the influence of the buckling effect, a model of coiled tubing running depth was established by the infinitesimal method. The field test data were used to verify the effectiveness of the two models. The effects of well trajectory, perforating string size, casing inner diameter, and coiled tubing size on the pass-through capacity of the CCP string and running depth of the TCP string were explored. The results indicate that with the increase of perforation string size or the reduction of casing inner diameter, the pass-through capacity of CCP string decreases; with the increase of coiled tubing specification, the running capacity of TCP string is improved. The work presented in this paper provides an effective analysis method and theoretical guidance for clustering perforation jobs in the field.

Experimental evaluation of the flow resistance of CO2 foam fracturing fluids and simulation prediction for fracture propagation

Shale gas fracturing requires huge amounts of water, but most well pads are located mainly in hilly areas where water is scarce. Water supply issues have limited the industrialization of shale gas development. CO2 foam fracturing fluids can meet the requirements for large-scale hydraulic fracturing of shale gas and relieve pressure on water resources. Friction calculations of CO2 foam fracturing fluids in conduit flow are key to the reliability of overall fracturing procedures, affecting fracture targeting and reservoir stimulation effects. Through the analysis of the experimental data of carbon dioxide foam fracturing fluid flow under the simulated reservoir conditions, the influence of pressure, temperature, shear rate, foam quality and other factors on the friction characteristics of CO2 foam fracturing fluid was obtained, and the mathematical calculation model of the friction coefficient of CO2 foam fracturing fluid was established, and the pipe string friction and bottom hole pressure during the fracturing process were obtained, Thus, the shape and extension behavior of hydraulic fractures in the process of carbon dioxide foam fracturing in shale reservoir are simulated and predicted, which provides a theoretical basis for effective evaluation of fracturing effect.

A numerical simulation study of the micro-mechanism of CO2 flow friction in fracturing pipe string

CO2 fracturing is a critical technique for carbon capture, utilization, and storage (CCUS). It has a crucial role in oil-gas development and combating climate change. However, the high flow friction severely affects the fracturing construction. The micro-mechanism of CO2 vertical flow friction in fracturing pipe string is unclear, and it is difficult to experimentally simulate the fracturing conditions. Computational Fluid Dynamics model is used to investigate the micro-mechanism of CO2 flow friction in fracturing conditions to reduce friction. A turbulence model was optimized to accurately calculate the friction of CO2 pipe flow. Subsequently, the relationships between the velocity profile, friction factor, and thickness of viscous sublayer of pure CO2 and thickened CO2 were analysed in fracturing pipe string, wherein the temperature and pressure were in the range of 253.15–343.15 K and 10–60 MPa, respectively. In this paper, the micro-mechanism of CO2 flow friction in fracturing pipe string was revealed and the situation of thickened CO2 was additionally considered, since the effect of the thickener has generally been ignored in previous numerical investigations. The results demonstrated that a uniform velocity profile reduced the friction factor. The temperature and pressure changed the relationship between the thickness of viscous sublayer and roughness, which caused the variation in the friction factor of pure CO2 and thickened CO2. The effect of roughness height on flow was different in the viscous sublayer and turbulent core region. A method was proposed to reduce the friction by optimizing the CO2 thickener and changing flow temperature and pressure.

Study on the mechanical variation law of the integrated water plugging operation string in horizontal wells

In order to study the force change law of the water plugging operation string in the complex wellbore, and to reduce the failure risk of the process string during the water plugging operation, this paper establishes the water plugging operation string based on the Euler-Bernoulli beam theory- The 3D full-well finite element model of the borehole wall was verified by field test data to verify the credibility of the numerical simulation model; according to the established finite element model, the force study of different types of tubing in complex horizontal wellbore was carried out, mainly for axial The force and the change law of the contact force between the pipe string and the well wall are analyzed, and finally, the force change law of the pipe string in different well sections is analyzed. The results show that the finite element model established in this paper has high simulation accuracy, and there is a large lateral contact force between the tubing and the inlet of the pitching section during the lifting process, and the contact between the pipe string and the borehole wall during the lowering process Mainly occurs at the entrance of the horizontal section. The research results provide theoretical guidance for the selection of tubing types and water plugging operations.

Failure analysis of S13Cr-110 telescopic tube used in an ultra-deep gas well

The failure reason and stress corrosion cracking mechanism of S13Cr-110 telescopic tube used in an ultra-deep gas well are discussed based on physical and chemical properties, operating conditions and construction processes. The results show that: stress corrosion cracking occurred in S13Cr-110 telescopic tube during acid fracturing, the crack initiated from the bottom of the corrosion pit in the inner wall of the telescopic tube and the crack propagation mode is inter-granular cracking. The reason for cracking is that S13Cr-110, the telescopic tube material, is exposed to high-chlorine-containing acid environment for a long time in the acid fracturing process, and the corrosion inhibitor used at the temperature of ultra-deep well has poor corrosion inhibition effect, resulting in inter-granular crack originated from the bottom of the corrosion pit on the inner wall of the telescopic tube. During the subsequent acidizing operations, the telescopic tube sustained a high circumferential tensile stress, stress corrosion occurs, and the stress corrosion cracks expand rapidly. It is suggested that the S13Cr-110 pipe string used in acidic environments with high chloride concentrations should be selected with appropriate corrosion inhibitor based on well depth and formation temperature.

Digital twin and contact analysis of ultra-long distance coiled tubing operation structures

Background: Coiled tubing operation is a high-quality operation method that considers both cost and efficiency in current oil and gas well operations. There is a significant difference between the calculation and prediction before operation and the actual operation. The reason is that the complex wellbore trajectory makes it difficult to evaluate the contact state between coiled tubing and wellbore, resulting in a significant error in the pipe string mechanics calculation and analysis. Methods: Aiming at the contact problem between coiled tubing and wellbore in the process of coiled tubing operation, the digital twin unit of coiled tubing and wellbore is established in this study. By constructing a feedback correction collision contact algorithm, the contact state of coiled tubing and casing under different three-dimensional trajectory models was simulated. Results: The research results show that the digital twin coiled tubing and contact algorithm can effectively predict the contact state of coiled tubing operations; the verification model shows that the contact algorithm can accurately analyze the contact state of different well trajectories. Conclusions: The digital twin of the coiled tubing operation structure and its contact algorithm can effectively solve the problem of deterministic friction state in the process of mechanical calculation of the tubing string, which has important guiding significance and engineering value for the mechanical calculation and operation safety analysis of coiled tubing operation.

Large-scale piezoelectric ultrasonic transducers with tubular near-period phononic crystal point defect structure

<sec>The coupling vibration of large-scale piezoelectric ultrasonic transducer will make the average value of the longitudinal displacement amplitude of its radiation surface small and the amplitude distribution uneven, which seriously affects the performance and reliability of the system. In order to improve the performance of large-scale ultrasonic vibration system, a two-dimensional hole/slot near-periodic phononic crystal structure is used to suppress the transverse vibration, but the structure will in turn affect the mechanical strength of the transducer while achieving the suppression of the transverse vibration. The working bandwidth and other performance parameters have adverse effects. Based on this, a new idea of optimizing the large-scale sandwich longitudinal vibration piezoelectric ceramic transducer by using the tubular near-periodic phononic crystal point defect structure is proposed. This method can not only use the point defect mode of the constructed solid/gas two-dimensional near-periodic phononic crystal structure to obtain extremely low energy loss, but also effectively improve the longitudinal displacement amplitude and amplitude distribution uniformity of the radiation surface of the system. The double annular holes in the pipe string structure can also be used to enhance the multiple scattering of sound waves, so that the transducer can also produce a band gap under the low conditions of the pipe string, effectively suppressing the transverse vibration, at the same time, significantly broadening the working bandwidth of the transducer system, enhancing the stability and mechanical strength of the system, and reducing the processing cost. Simulation results and experimental processing test results also prove the effectiveness of the optimization.</sec><sec>In order to find the best parameters for the performance of the large-scale longitudinal vibration piezoelectric ultrasonic transducer, in the paper the finite element analysis software is used to study the influence of the inner radius <i>r</i><sub>1</sub> of the pipe string, the width <i>r</i> of the pipe string ring, the radius <i>R</i> of the outermost air cylinder hole, and the height <i>h</i><sub>2</sub> of the pipe string at the longitudinal resonance frequency of the transducer performance, the longitudinal displacement amplitude distribution uniformity of the radiation surface, and the average longitudinal displacement amplitude. In the research is finally found the range of parameters that can make the performance of the transducer reach a relatively ideal state. The simulation results show that the tubular near-periodic phononic crystal point defect structure can improve the performance of large-scale longitudinal vibration piezoelectric ultrasonic transducer.</sec>

Numerical Analysis of Dynamical Effects Associated with a Plugging String in a Horizontal Well

The finite element method has been applied to simulate the dynamics of a water plugging string in a complex horizontal well of a low-permeability oilfield. The force associated with the pipe string and the packer has been determined under the sucking action of the oil well pump. Such analysis has been conducted for a real drilling well, taking into account the process of lifting, lowering, unblocking and water plugging. Comparison between field measured data and simulation data indicates that the model is reliable and accurate. The packer creep effect under different pressure differences has also been investigated in the framework of the same model.

A Model for the Determination of Semi-Circular Spot Corrosion Damage and Residual Strength in Oil Pipes

Pitting corrosion often occurs due to the presence of various corrosive substances, such as CO2 and H2S, in the pipe service environment. As a result of this process, the residual strength of oil pipes is reduced and this can compromise the integrity of the entire pipe string. In the present work, a model is introduced on the basis of the API579 standard to determine the so-called stress concentration coefficient. The model accounts for pitting corrosion shapes such as shallow semi-circles, semi-circles, and deep semi-circles. The relationship between the corrosion pit depth and opening diameter and the residual strength of the oil casing is obtained. The results show that the influence of the pit opening diameter on the stress concentration coefficient is smaller than that of the pit depth. For a constant pit opening diameter, the coefficient increases gradually with increasing the pit depth. The compressive strength and internal pressure strength of the carbon steel oil casing decrease accordingly. When the depth of the corrosion pit is relatively small, the growth of the coefficient is slower; when the depth of the corrosion pit increases to a certain value, the increase in stress concentration coefficient becomes obvious.

Experimental investigation of the shear bond strength between HGM cement and shallow formation in deepwater environments

Due to its low density and high strength, hollow glass micro-sphere (HGM) has become a popular additive to cement slurry in deepwater cementing. The shear bond strength (SBS) between the well cement and formation ensures the safety and integrity of oil and gas wells. We designed a simulation experiment to measure the SBS between HGM cement and shallow formations in deepwater environments. We studied the evolution of the tensile force when pulling a simulated pipe string and cement ring out of the soil layer with a constant force. The results suggest that the HGM content and size of the cement ring have no effect on the change in the tensile force over time. At the peak of the tension curve, the cement ring and soil begin to slip, causing the tensile force to decrease with time. We divided this curve into two sections, with the peak value as the dividing point. The first section is the accumulating section where the tension increases without displacement of the cement ring and the soil. The second section is the dynamic slip section. Additionally, we proposed the concepts of static SBS and dynamic shear bond coefficient. The static SBS is the strength at the pull-off position, and the dynamic shear bond coefficient is the cementation coefficient of the cement ring in the dynamic slip stage. We divided the cement ring into segments along its length, calculated the shear bond coefficient of the cement ring at different depths, and studied the variation in the dynamic shear bond coefficient with depth. The static SBS increases with decreasing HGM content and casing size, and the static SBS of the small casing is significantly greater than those of the middle casing and the large casing. The dynamic shear bond coefficient decreases after the occurrence of dynamic slip. This study provides important insights into the evolution of the cement-formation SBS, and the results can provide guidance for future cementing design.