Influencing factors and prevention measures of casing deformation in deep shale gas wells in Luzhou block,southern Sichuan Basin,SW China

Based on structural distribution and fault characteristics of the Luzhou block,southern Sichuan Basin,as well as microseismic,well logging and in-situ stress data,the casing deformation behaviors of deep shale gas wells are summarized,and the casing deformation mechanism and influencing factors are identified.Then,the risk assessment chart of casing deformation is plotted,and the measures for preventing and controlling casing deformation are proposed.Fracturing-activated fault slip is a main factor causing the casing deformation in deep shale gas wells in the Luzhou block.In the working area,the approximate fracture angle is primarily 10°-50°,accounting for 65.34%,and the critical pore pressure increment for fault-activation is 6.05-9.71 MPa.The casing deformation caused by geological factors can be prevented/controlled by avoiding the faults at risk and deploying wells in areas with low value of stress factor.The casing deformation caused by engineering factors can be prevented/controlled by:(1)keeping wells avoid faults with risks of activation and slippage,or deploying wells in areas far from the faulting center if such avoidance is impossible;(2)optimizing the wellbore parameters,for example,adjusting the wellbore orientation to reduce the shear force on casing to a certain extent and thus mitigate the casing deformation;(3)optimizing the casing program to ensure that the curvature radius of the curved section of horizontal well is greater than 200 m while the drilling rate of high-quality reservoirs is not impaired;(4)optimizing the fracturing parameters,for example,increasing the evasive distance,lowering the single-operation pressure,and increasing the stage length,which can help effectively reduce the risk of casing deformation.

Prediction models of burst strength degradation for casing with considerations of both wear and corrosion

Casing wear and casing corrosion are serious problems affecting casing integrity failure in deep and ultra-deep wells.This paper aims to predict the casing burst strength with considerations of both wear and corrosion.Firstly,the crescent wear shape is simplified into three categories according to common mathematical models.Then,based on the mechano-electrochemical(M-E)interaction,the prediction model of corrosion depth is built with worn depth as the initial condition,and the prediction models of burst strength of the worn casing and corroded casing are obtained.Secondly,the accuracy of different prediction models is validated by numerical simulation,and the main influence factors on casing strength are obtained.At last,the theoretical models are applied to an ultra-deep well in Northwest China,and the dangerous well sections caused by wear and corrosion are predicted,and the corrosion rate threshold to ensure the safety of casing is obtained.The results show that the existence of wear defects results in a stress concentration and enhanced M-E interaction on corrosion depth growth.The accuracy of different mathematical models is different:the slot ring model is most accurate for predicting corrosion depth,and the eccentric model is most accurate for predicting the burst strength of corroded casing.The burst strength of the casing will be overestimated by more than one-third if the M-E interaction is neglected,so the coupling effect of wear and corrosion should be sufficiently considered in casing integrity evaluation.

Uncertainty Analysis of the Residual Strength of Non-Uniformly Loaded Casingsin Deep Wells

An uncertainty analysis method is proposed for the assessment of the residual strength of a casing subjected to wear and non-uniform load in a deep well.The influence of casing residual stress,out-of-roundness and non-uniform load is considered.The distribution of multi-source parameters related to the residual anti extrusion strength and residual anti internal pressure strength of the casing after wear are determined using the probability theory.Considering the technical casing of X101 well in Xinjiang Oilfield as an example,it is shown that the randomness of casing wear depth,formation elastic modulus and formation Poisson’s ratio are the main factors that affect the uncertainty of residual strength.The wider the confidence interval is,the greater the uncertainty range is.Compared with the calculations resulting from the proposed uncertainty analysis method,the residual strength obtained by means of traditional single value calculation method is either larger or smaller,which leads to the conclusion that the residual strength should be considered in terms of a range of probabilities rather than a single value.

Numerical Analysis of Residual Strength in the Perforated Casing of Ultra Deep Wells

A three-dimensional model for the numerical simulation of casing-cement behavior is used to investigate residual strength in the perforated casing of ultra deep wells.The influence of the hole diameter,hole density and phase angle on the residual strength of the casing under non-uniform stress and fracturing conditions is revealed through the consideration of different perforation parameters.It is shown that the residual strength of the casing increases with the hole diameter and periodically changes with the hole density;the phase angle is the main factor that affects the residual strength of the perforated casing,and the perforation should be avoided in the direction of the minimum principal stress to reduce stress concentration at the perforation hole.Moreover,as shown by a companion orthogonal experiment,the descending order of influence of the different influential parameters is:phase angle,hole diameter,hole density and the thickness of casing.

Reshaping force for deformed casing repairing with hydraulic rolling reshaper and its influencing factors

Hydraulic rolling reshaper is an advanced reshaping tool to solve the problem of casing deformation,which has been widely used in recent years.When it is used for well repair operation,the reshaping force provided by ground devices is generally determined by experience.However,too large reshaping force may destroy the deformed casing,and too small reshaping force may also prolong the construction period and affect the repairing effect.In this paper,based on Hertz contact theory and elastic-plastic theory,combined with the process parameters of shaping,and considering the structural characteristics of the deformed casing and reshaper,we propose a mathematical model for calculating the reshaping force required for repairing deformed casing by hydraulic rolling reshaper.Meanwhile,the finite element model and numerical method of hydraulic rolling reshaper repairing deformed casing are established by using the finite element method,and the reliability of the mathematical model is verified by several examples.On this basis,the control variable method is used to investigate the influence of each parameter on the reshaping force,and the influence degree of each parameter is explored by orthogonal simulation test and Pearson correlation analysis.The research results not only provide an important theoretical basis for the prediction of reshaping force in on-site construction,but also provide a reference for the subsequent improvement of the shaping process.

Research on casing deformation prevention technology based on cementing slurry system optimization

The casing deformation prevention technology based on the optimization of cement slurry is proposed to reduce the casing deformation of shale oil and gas wells during hydraulic fracturing. In this paper, the fracture mechanism of hollow particles in cement sheath was firstly analyzed by discrete element method, and the effect of hollow particles in cement on casing deformation was investigated by laboratory experiment method. Finally, field test was carried out to verify the improvement effect of the casing deformation based on cement slurry modification. The results show that the formation displacement can be absorbed effectively by hollow particles inside the cement transferring the excessive deformation away from casing. The particles in the uncemented state provide deformation space during formation slipping. The casing with diameter of 139.7 mm could be passed through by bridge plug with the diameter of 99 mm when the mass ratio of particle/cement reaches 1:4. According to the field test feedback, the method based on optimization of cement slurry can effectively reduce the risk of casing deformation, and the recommended range of hollow microbeads content in the cement slurry is between 15% and 25%.

Analysis of mechanical strengths of extreme line casing joint considering geometric, material, and contact nonlinearities

To address the challenges associated with difficult casing running,limited annular space,and poor cementing quality in the completion of ultra-deep wells,the extreme line casing offers an effective solution over conventional casings.However,due to its smaller size,the joint strength of extreme line casing is reduced,which may cause failure when running in the hole.To address this issue,this study focuses on the CST-ZTΦ139.7 mm×7.72 mm extreme line casing and employs the elastic-plastic mechanics to establish a comprehensive analysis of the casing joint,taking into account the influence of geometric and material nonlinearities.A finite element model is developed to analyze the forces and deformations of the extreme line casing joint under axial tension and external collapse load.The model investigates the stress distribution of each thread tooth subjected to various tensile forces and external pressures.Additionally,the tensile strength and crushing strength of the extreme line casing joint are determined through both analytical and experimental approaches.The findings reveal that,under axial tensile load,the bearing surface of each thread tooth experiences uneven stress,with relatively high equivalent stress at the root of each thread tooth.The end thread teeth are valuable spots for failure.It is observed that the critical fracture axial load of thread decreases linearly with the increase of thread tooth sequence.Under external pressure,the circumferential stress is highest at the small end of the external thread,leading to yield deformation.The tensile strength of the joint obtained from the finite element model exhibits a relative error of less than 7%compared to the analytical and experimental values,proving the reliability of the finite element model.The tensile strength of the joint is 3091.9 k N.Moreover,in terms of anti-collapse capability,the joints demonstrate higher resistance to collapse compared to the casing body,which is consistent with the test results where the pipe body experiences collapse and failure while the joints remain intact during the experiment.The failure load of the casing body under external collapse pressure is 87.4 MPa.The present study provides a basic understanding of the mechanical strengths of extreme line casing joint.

Double casing warhead with sandwiched charge:The axial distribution of fragments velocities

The double casing warhead with sandwiched charge is a novel fragmentation warhead that can produce two groups of fragments with different velocity,and the previous work has presented a calculation formula to determine the maximum fragment velocity.The current work builds on the published formula to further develop a formula for calculating the axial distribution characteristics of the fragment velocity.For this type of warhead,the simulation of the dispersion characteristics of the detonation products at different positions shows that the detonation products at the ends have a much larger axial velocity than those in the middle,and the detonation products have a greater axial dispersion velocity when they are closer to the central axis.The loading process and the fragment velocity vary with the axial position for both casing layers,and the total velocity of the fragments is the vector sum of the radial velocity and the axial velocity.At the same axial position,the acceleration time of the inner casing is greater than that of the outer casing.For the same casing,the fragments generated at the ends have a longer acceleration time than the fragments from the middle.The proposed formula is validated with the X-ray radiography results of the four warheads previously tested experimentally and the 3D smoothedparticle hydrodynamics numerical simulation results of several series of new warheads with different configurations.The formula can accurately and reliably calculate the fragment velocity when the lengthto-diameter ratio of the charge is greater than 1.5 and the thickness of the casing is less than 20%its inner radius.This work thus provides a key reference for the theoretical analysis and the design of warheads with multiple casings.

A novel algorithm for evaluating cement azimuthal density based on perturbation theory in horizontal well

Cement density monitoring plays a vital role in evaluating the quality of cementing projects,which is of great significance to the development of oil and gas.However,the presence of inhomogeneous cement distribution and casing eccentricity in horizontal wells often complicates the accurate evaluation of cement azimuthal density.In this regard,this paper proposes an algorithm to calculate the cement azimuthal density in horizontal wells using a multi-detector gamma-ray detection system.The spatial dynamic response functions are simulated to obtain the influence of cement density on gamma-ray counts by the perturbation theory,and the contribution of cement density in six sectors to the gamma-ray recorded by different detectors is obtained by integrating the spatial dynamic response functions.Combined with the relationship between gamma-ray counts and cement density,a multi-parameter calculation equation system is established,and the regularized Newton iteration method is employed to invert casing eccentricity and cement azimuthal density.This approach ensures the stability of the inversion process while simultaneously achieving an accuracy of 0.05 g/cm^(3) for the cement azimuthal density.This accuracy level is ten times higher compared to density accuracy calculated using calibration equations.Overall,this algorithm enhances the accuracy of cement azimuthal density evaluation,provides valuable technical support for the monitoring of cement azimuthal density in the oil and gas industry.

Elimination of cracks in stainless steel casings via 3D printed sand molds with an internal topology structure

The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.

Myeloid sarcoma with maxillary gingival swell

BACKGROUND Myeloid sarcoma(MS),also referred to as granulocytic sarcoma or chloroma,is a rare type of extramedullary malignant tumor.MS comprises primitive granulocytic precursor cells that play a key role in the early stages of white blood cell development.Notably,the occurrence of this tumor in the gingiva is rare.CASE SUMMARY The present study reported the case of MS with gingival swelling in the maxillary region,with aleukemic presentation in a 32-year-old male patient.Following two courses of chemotherapy,computed tomography of the region demonstrated complete clearance of the tumor.At the 12-month follow-up appointment,the patient was in a stable condition with the absence of progression.The etiology,clinical features,diagnosis,and relevant treatment of MS are discussed in the present study.CONCLUSION Diagnosis of MS may be confirmed following histological and immunohistochemical examinations.

Mixed pancreatic ductal adenocarcinoma and well-differentiated neuroendocrine tumor:A case report

BACKGROUND Pancreatic mixed neuroendocrine-non-neuroendocrine neoplasms(MiNENs)are rare malignancies affecting the pancreas.The World Health Organization defines MiNENs as neoplasms composed of morphologically recognizable neuroendocrine and non-neuroendocrine components,each constituting 30%or more of the tumor volume.Adenocarcinoma-neuroendocrine carcinoma is the most frequent MiNEN combination.A well-differentiated neuroendocrine tumor(NET)component is rarely reported in MiNENs.CASE SUMMARY Here we report a rare case with intermingled components of ductal adenocarcinoma and grade 1 well-differentiated NET in the pancreas.The two tumors show distinct histology and significant differentiation discrepancy(poorly differentiated high grade adenocarcinoma and well-differentiated low grade NET),and also present as metastases in separate lymph nodes.Next generation sequencing of the two components demonstrates KRAS and TP53 mutations in the ductal adenocarcinoma,but no genetic alterations in the NET,suggesting divergent origins for these two components.Although tumors like this meet the diagnostic criteria for MiNEN,clinicians often find the diagnosis and staging confusing and impractical for clinical management.CONCLUSION Mixed NET/non-NET tumors with distinct histology and molecular profiles might be better classified as collision tumors rather than MiNENs.

Calculation analysis of sustained casing pressure in gas wells

Sustained casing pressure （SCP） in gas wells brings a serious threat to worker safety and environmental protection. According to geological conditions, wellbore structure and cement data of gas wells in the Sichuan-Chongqing region, China, the position, time, environmental condition and the value of SCP have been analyzed. On this basis, the shape of the pressure bleed-down plot and pressure buildup plot were diagnosed and the mechanism of SCP has been clarified. Based on generalized annular Darcy percolation theory and gas-liquid two-phase fluid dynamics theory, a coupled mathematical model of gas migration in a cemented annulus with a mud column above the cement has been developed. The volume of gas migrated in the annulus and the value of SCP changing with time in a gas well in Sichuan have been calculated by this model. Calculation results coincided well with the actual field data, which provide some reference for the following security evaluation and solution measures of SCP.

Multistring analysis of wellhead movement and uncemented casing strength in offshore oil and gas wells

This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include operating load during drilling and completion and the temperature field,pressure field and the end effect of pressure during gas production.The finite element method for multistring analysis is developed to simulate random contact between casings.The relevant finite element analysis scheme is also presented according to the actual procedures of drilling,completion and gas production.Finally,field cases are presented and analyzed using the proposed methods.These are four offshore wells in the South China Sea.The calculated wellhead growths during gas production are compared with measured values.The results show that the wellhead subsides during drilling and completion and grows up during gas production.The theoretical and finite element solutions for wellhead growth are in good agreement with measured values and the deviations of calculation are within 10％.The maximum von Mises stress on the uncemented intermediate casing occurs during the running of the oil tube.The maximum von Mises stress on the uncemented production casing,calculated with the theoretical method occurs at removing the blow-out-preventer （BOP） while that calculated with the finite element method occurs at gas production.Finite element solutions for von Mises stress are recommended and the uncemented casings of four wells satisfy strength requirements.

Effect of longwall-induced subsurface deformations on shale gas well casing stability under deep covers

This paper presents the results of a 2017 study conducted by the National Institute for Occupational Safety and Health(NIOSH), Pittsburgh Mining Research Division(PMRD), to evaluate the effects of longwall-induced subsurface deformations within a longwall abutment pillar under deep cover. The 2017 study was conducted in a southwestern Pennsylvania coal mine, which extracts 457 m-wide longwall panels under 361 m of cover. One 198 m-deep, in-place inclinometer monitoring well was drilled and installed over a 45 m by 84 m center abutment pillar. In addition to the monitoring well, surface subsidence measurements and underground coal pillar pressure measurements were conducted as the 457 m-wide longwall panel on the south side of the abutment pillar was being mined. Prior to the first longwall excavation, a number of simulations using FLAC3D^(TM) were conducted to estimate surface subsidence, increases in underground coal pillar pressure, and subsurface horizontal displacements in the monitoring well. Comparisons of the pre-mining FLAC3D simulation results and the surface, subsurface,and underground instrumentation results show that the measured in-place inclinometer casing deformations are in reasonable agreement with those predicted by the 3D finite difference models. The measured surface subsidence and pillar pressure are in excellent agreement with those predicted by the 3D models.Results from this 2017 research clearly indicate that, under deep cover, the measured horizontal displacements within the abutment pillar are approximately one order of magnitude smaller than those measured in a 2014 study under medium cover.

Heating of heavy oil by circulating hot water in closed double casing in ultra-deep wells

In heavy oil production,the loss of energy to ambient surroundings decreases the temperature of the heavy oil flowing upwards in a vertical wellbore,which increases the oil viscosity and the oil may not flow normally in the wellbore.Therefore,it is necessary to lower the heavy oil viscosity by heating methods to allow it to be lifted easily.Heating of heavy oil in an oil well is achieved by circulating hot water in annuli in the well（tubing-casing annulus,casing-casing annulus）.In this paper,based on heat transfer principles and fluid flow theory,a model is developed for produced fluids and hot water flowing in a vertical wellbore.The temperature and pressure of produced fluids and hot water in the wellbore are calculated and the effect of hot water on heavy oil temperature is analyzed.Calculated results show that the hot water circulating in the annuli may effectively heat the heavy oil in the tubing,so as to significantly reduce both oil viscosity and resistance to oil flow.

Thermal stresses analysis of casing string used in enhanced geothermal systems wells

In the enhanced geothermal systems wells, casing temperature variation produces casing thermal stresses, resulting in casing uplift or bucking. When the induced thermal stresses exceed casing material's yield strength, the casing deforms and collapses. The traditional casing design standard only considers the influence of temperature variation on casing material's yield strength. Actually, for commonly used grades of steel pipe, casing's material properties-such as yield strength, coefficient of thermal expansion, and modulus of elasticity change with temperature variation. In this paper, the modified thermal stress equation is given. Examples show that the allowable temperature of the material grade N80's casing is only 164 ℃, which is much lower than that of the traditional design standard. The effective method to improve the casing pipe's allowable temperature is pre-stressed cementing technology. Pre-stressed cementing includes pre-tension stress cementing and pre-pressure stress cementing. This paper focuses on the design method of full casing pre-tension stress cementing and the ground anchor full casing string pre-tension cementing construction process.

Erosion characteristics and simulation charts of sand fracturing casing perforation

Large-scale sand fracturing is a necessary means in the efficient exploitation of shale gas/oil.However,in the process of fracturing operation,the sand carrying fluid and proppant easily causes scouring and wear to production strings,especially the casing perforation system,which damage the wellbore integrity and deformation to affect the subsequent fracturing.For this problem,taking the actual construction conditions and perforation technology of an oilfield in western China as an example,the structural parameters of the downhole string were measured and the wall thickness reduction model of casing perforation suitable for large-displacement sand fracturing in horizontal well section was established.With software ANSYS-FLUENT,the casing perforation erosion under the conditions of different displacements,sand content and perforation sand-passing quantity in the process of sand fracturing was simulated and calculated.The influences of three parameters on perforation erosion and expansion were analyzed and the prediction chart of the influences of three main control factors on perforation erosion and expansion was established.The perforation erosion images after fracturing construction were obtained with the downhole eagle perforation logging technology.The logging chart results were compared with the downhole eagle perforation data.The error between the established numerical simulation calculation charts and the real logging data was about 5%,indicating that the simulation charts were the valuable reference.

Tooth arrangement design of retractable DTH hammer bit used for drilling while casing

Down-the-hole(DTH)hammer with casing while drilling(CWD)is a technology that has been proven to be able to alleviate many of the problems faced by complex formations.However,the drill bit is suffered from rapid wear,low drilling efficiency,and high energy consumption due to the unreasonable tooth arrangement and impact energy selection in drilling process,which affect the application effect of this technology.ABAQUS software was used for numerical simulation of rock breaking behavior under impact load with the single,three,and five teeth arrangement drill bit respectively,to improve the application effect and solve the aforementioned technical problems.Based on the calculated parameters of tooth arrangement,we designed a novel drill bit for hard rocks and provided a theoretical basis for the tooth arrangement of largediameter drill bits.

Variant of Wellen’s syndrome in type 1 diabetic patient: A case report

BACKGROUND Wellen’s syndrome is a form of acute coronary syndrome associated with proximal left anterior descending artery(LAD)stenosis and characteristic electro-cardiograph(ECG)patterns in pain free state.The abnormal ECG pattern is classified into type A(biphasic T waves)and type B(deeply inverted T waves),based on the T wave pattern seen in the pericodial chest leads.CASE SUMMARY We present the case of a 37-year-old male with history of type 1 diabetes mellitus(T1DM),gastroparesis,mild peripheral artery disease and right toe cellulitis on IV antibiotics who presented to the emergency department with nausea,vomiting and abdominal pain for 3 d and as a result couldn’t take his insulin.Noted to have fasting blood sugar 392 mg/dL.Admitted for diabetic gastroparesis.During the hospital course,the patient was asymptomatic and denied any chest pain.On admission,No ECG and troponin draws were performed.On day 2,the patient became hypoxic with oxygen saturation 80%on room air,intermittent mild right-sided chest pain which he attributed to vomiting from his gastroparesis.Initial ECG done was significant for Biphasic T wave changes in leads V2 and V3 and elevated high sensitivity troponin.Patient was transitioned to cardiac intensive care unit and cardiac catheterization performed with result significant for extensive coronary artery disease.CONCLUSION This case highlights an exceptional manifestation of Wellen's syndrome,wherein the right coronary artery and circumflex artery display a remarkable 100%constriction,alongside a proximal LAD stenosis of 90%-95%.Notably,this occurrence transpired in a patient grappling with extensive complications arising from T1DM.Moreover,it underscores the utmost significance of promptly recognizing the presence of Wellen's syndrome and swiftly initiating appropriate medical intervention.