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%.

Research on the solid particle erosion wear of pipe steel for hydraulic fracturing based on experiments and numerical simulations

Erosion wear is a common failure mode in the oil and gas industry.In the hydraulic fracturing,the fracturing pipes are not only in high-pressure working environment,but also suffer from the impact of the high-speed solid particles in the fracturing fluid.Beneath such complex conditions,the vulnerable components of the pipe system are prone to perforation or even burst accidents,which has become one of the most serious risks at the fracturing site.Unfortunately,it is not yet fully understood the erosion mechanism of pipe steel for hydraulic fracturing.Therefore,this article provides a detailed analysis of the erosion behavior of fracturing pipes under complex working conditions based on experiments and numerical simulations.Firstly,we conducted erosion experiments on AISI 4135 steel for fracturing pipes to investigate the erosion characteristics of the material.The effects of impact angle,flow velocity and applied stress on erosion wear were comprehensively considered.Then a particle impact dynamic model of erosion wear was developed based on the experimental parameters,and the evolution process of particle erosion under different impact angles,impact velocities and applied stress was analyzed.By combining the erosion characteristics,the micro-structure of the eroded area,and the micro-mechanics of erosion damage,the erosion mechanism of pipe steel under fracturing conditions was studied in detail for the first time.Under high-pressure operating conditions,it was demonstrated through experiments and numerical simulations that the size of the micro-defects in the eroded area increased as the applied stress increased,resulting in more severe erosion wear of fracturing pipes.

Corrosion behavior of the expandable tubular in formation water

The corrosion behavior of expandable tubular materials was investigated in simulated downhole formation water environments using a series of electrochemical techniques. The corrosion morphologies in the real downhole environment after three months of application were also observed by stereology microscopy and scanning electron microscopy （SEM）. The results show that, compared with the unex- panded sample, the area of ferfite increases dramatically after a 7.09% expansion. The expanded material shows a higher corrosion current in the polarization curve and a lower corrosion resistance in the electrochemical impedance spectroscopy （EIS） plot at every studied tempera- ture. The determined critical pitting temperatures （CPT） before and after expansion are 87.5℃and 79.2℃, respectively. SEM observations demonstrate stress corrosion cracks, and CO2 corrosion and H2S corrosion also occur in the downhole environment. Due to additional defects generated during the plastic deformation, the corrosion performance of the expanded tubing deteriorates.

A hybrid machine learning optimization algorithm for multivariable pore pressure prediction

Pore pressure is essential data in drilling design,and its accurate prediction is necessary to ensure drilling safety and improve drilling efficiency.Traditional methods for predicting pore pressure are limited when forming particular structures and lithology.In this paper,a machine learning algorithm and effective stress theorem are used to establish the transformation model between rock physical parameters and pore pressure.This study collects data from three wells.Well 1 had 881 data sets for model training,and Wells 2 and 3 had 538 and 464 data sets for model testing.In this paper,support vector machine(SVM),random forest(RF),extreme gradient boosting(XGB),and multilayer perceptron(MLP)are selected as the machine learning algorithms for pore pressure modeling.In addition,this paper uses the grey wolf optimization(GWO)algorithm,particle swarm optimization(PSO)algorithm,sparrow search algorithm(SSA),and bat algorithm(BA)to establish a hybrid machine learning optimization algorithm,and proposes an improved grey wolf optimization(IGWO)algorithm.The IGWO-MLP model obtained the minimum root mean square error(RMSE)by using the 5-fold cross-validation method for the training data.For the pore pressure data in Well 2 and Well 3,the coefficients of determination(R^(2))of SVM,RF,XGB,and MLP are 0.9930 and 0.9446,0.9943 and 0.9472,0.9945 and 0.9488,0.9949 and 0.9574.MLP achieves optimal performance on both training and test data,and the MLP model shows a high degree of generalization.It indicates that the IGWO-MLP is an excellent predictor of pore pressure and can be used to predict pore pressure.

Hot Deformation Behavior of Ti-6Al-4V-0.5Ni-0.5Nb Titanium Alloy

Characterization of hot deformation behavior of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy was investigated through isothermal compression at various temperatures from 750 to 1050℃and strain rate from 0.01 to 10 s^(-1).The isothermal compression experiment results showed that the peak stress of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy decreased with the temperature increasing and the strain rate decreasing.The softening mechanism was dynamic recovery below T_(β)and changed to dynamic recrystallization above T_(β).The arrheniustype relationship was used to calculate the constitutive equation of Ti-6Al-4V-0.5Ni-0.5Nb alloy in two-phase regions.It was found that the apparent activation energies were 427.095 kJ·mol^(-1)in theα+βphase region and 205.451 kJ·mol^(-1)in theβphase region,respectively.On the basis of dynamic materials model,the processing map is generated,which shows that the highest peak efficiency of power dissipation of 56%occurs at about 1050℃/0.01 s^(-1).It can be found in the processing maps that the strain had significant effect on the peak region of power dissipation efficiency of Ti-6Al-4V-0.5Ni-0.5Nb alloy.Furthermore,optimized hot working regions were investigated and validated through microstructure observation.The optimum thermo mechanical process condition for hot working of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy was suggested to be in the temperature range of 950-1000℃with a strain rate of 0.01-0.1 s^(-1).

Efficiency enhancement to 24.62%in inverted perovskite solar cells through poly(ionic liquid)bulk modification

Small-molecule ionic liquids(ILs)are frequently employed as efficient bulk phase modifiers for perovskite materials.However,their inherent characteristics,such as high volatility and ion migration properties,pose challenges in addressing the stability issues associated with perovskite solar cells(PSCs).In this study,we design a poly(IL)with multiple active sites,named poly[4-styrenesulfonyl(trifluoromethylsulfonyl)imide]pyri-dine(P[STFSI][PPyri]),as an efficient additive of perovskite materials.The S=O in the sulfonyl group chelates with uncoordinated Pb^(2+)and forms hydrogen bonds with the organic cations in the perovskite,suppressing the volatilization of the organic cations.The N+in pyridine can fix halide ions through electrostatic interaction with I-and Br-ions to prevent halide ion migration.P[STFSI][PPyri]demonstrates the ability to passivate defects and suppress nonradiative recombination in PSCs.Additionally,it facilitates the fixation of organic and halide ions,thereby enhancing the device’s stability and photoelectric performance.Consequently,the introduction of P[STFSI][PPyri]as a dopant in the devices resulted in an excellent efficiency of 24.62%,demonstrating outstanding long-term operational stability,with the encapsulated device maintaining 87.6%of its initial effi-ciency even after 1500 h of continuous maximum power point tracking.This strategy highlights the promising potential of poly(IL)as an effective additive for PSCs,providing a combination of high performance and stabil-ity.

A study of hydrate plug formation in a subsea natural gas pipeline using a novel high-pressure flow loop

The natural gas pipeline from Platform QKI8-1 in the southwest of Bohai Bay to the onshore processing facility is a subsea wet gas pipeline exposed to high pressure and low temperature for a long distance. Blockages in the pipeline occur occasionally. To maintain the natural gas flow in the pipeline, we proposed a method for analyzing blockages and ascribed them to the hydrate formation and agglomeration. A new high-pressure flow loop was developed to investigate hydrate plug formation and hydrate particle size, using a mixture of diesel oil, water, and natural gas as experimental fluids. The influences of pressure and initial flow rate were also studied. Experimental results indicated that when the flow rate was below 850 kg/h, gas hydrates would form and then plug the pipeline, even at a low water content （10%） of a water/oil emulsion. Furthermore, some practical suggestions were made for daily management of the subsea pipeline.

Effect of microstructure on the low temperature toughness of high strength pipeline steels

Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.

Impact of Improving Design Factor over 0.72 on the Safety and Reliability of Gas Pipelines and Feasibility Justification

Many years experience of the operation of high stress (>72% specified minimum yield strength, SMYS) gas pipelines and statistical analysis results of pipeline incidents showed that the operating pipelines at stress levels over 72% SMYS have not presented problems in USA and Canada, and design factor does not control incidents or the safety of pipelines. Enhancing pipeline safety management level is most important for decreasing incident rate. The application history of higher design factors in the U.S and Canada was reviewed. And the effect of higher factors to the critical flaw size, puncture resistance, change of reliability with time, risk level and the arrest toughness requirements of pipeline were analyzed here. The comparison of pipeline failure rates and risk levels between two design factors (0.72 and 0.8) has shown that a change in design factor from 0.72 to 0.8 would bring little effect on failure rates and risk levels. On the basis of the analysis result, the application feasibility of design factor of 0.8 in China was discussed and the related suggestions were proposed. When an operator wishes to apply design factor 0.8 to gas pipeline, the following process is recommended: stress level of line pipe hydro test should be up to 100% SMYS, reliability and risk assessment at the design feasibility or conceptual stage should be conducted, Charpy impact energy should meet the need of pipeline crack arrest; and establish and execute risk based integrity management plan. The technology of pipeline steel metallurgy, line pipe fabrication and pipeline construction, and line pipe quality control level in China achieved tremendous progresses, and line pipe product standards and property indexes have come up to international advanced level. Furthermore, pipeline safety management has improved greatly in China. Consequently, the research for the feasibility of application of design factor of 0.8 in China has fundamental basis.

Microstructures and wear resistance of chromium coatings on P110 steel fabricated by pack cementation

In order to obtain a high-performance surface on P110 steel that can meet the requirements in oil/gas field environment, the chromium coatings were fabricated by pack cementation. The chromium coatings differed in with/without the addition of La2O3. Scanning electron microscope （SEM）, energy dispersive X-ray spectrometer （EDS）, X-ray diffractometer （XRD） and microhardness tester were employed to investigate the surface morphologies, surface element distributions, microstructures, phase constitutions and microhardness of the coatings. Friction-wear tests of the P110 steel substrate and the coatings were conducted in air at ambient temperature and humidity. The results show that ＇uniform and continuous coatings are formed on P110 steel regardless of adding La2O3 or not. The chromium coatings consist of Cr23C6, Cr7C3, and （Cr, Fe）7C3. The La2O3-added chromium coating is more beneficial in terms of surface morphology, microstructure, thickness and microharduess as compared with the coating without adding La2O3. Chromizing treatment significantly improves the surface hardness and wear resistance of the P110 steel. The wear resistance of the tested samples can be sorted in the following sequence： La2O3-coating 〉 no RE-coating 〉bare P110 steel.

Welding of 2205 duplex stainless steel natural gas pipeline

There are abundant natural gas resources in western China, but many oil and gas fields are rich in chloridion, sulfureted hydrogen, carbon dioxide and other corrosive medium, which have strong corrosivity to pipeline. One gas field possesses abundant natural gas with great pressure, and the chloridion concentration in the water separated from gas is about 10% , so the medium has great corrosivity. In order to ensure the safety of the pipeline, about 13 km length pipeline and the internal pipes of a gas treatment plant that purifies gas about 12 billion cubic meter a year are made of 2205 duplex stainless steel （2205 DSS ） . 2205 DSS has many characteristics in welding with complex welding process; and because of high quality requirements for the construction of natural gas pipeline and restriction of on-site conditions, the site welding is very difficult. Around the engineering application, a large number of experimental researches have been carried out on the material microstructure, properties and weldability. Finally welded joints which conform to the requirements of standard are obtained, contributing to the first large-scale application of this material in the field of oil and gas pipelines. Considering the engineering application and the latest research development, the welding and key factors affecting the joint properties of 2205 DSS pipes are summarized and analyzed.

An unequal fracturing stage spacing optimization model for hydraulic fracturing that considers cementing interface integrity

Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in this paper,by considering the integrity of the wellbore interface,a fracture propagation model was established based on displacement discontinuity method and the competition mechanism of multifracture joint expansion,leading to the proposal of an unequal stage spacing optimization model.The results show that in the first stage,the interfacial fractures spread symmetrically along the axis of the central point during that stage,while in the second and subsequent stages,the interfacial fractures of each cluster extend asymmetrically along the left and right sides.There are two kinds of interface connectivity behaviour:in one,the existing fractures first extend and connect within the stage,and in the other,the fractures first extend in the direction close to the previous stage,with the specific behaviour depending on the combined effect of stress shadow and flow competition during hydraulic fracture expansion.The stage spacing is positively correlated with the number of fractures and Young’s modulus of the cement and formation and is negatively correlated with the cluster spacing and horizontal principal stress difference.The sensitivity is the strongest when the Young’s modulus of the cement sheath is 10-20 GPa,and the sensitivity of the horizontal principal stress difference is the weakest.

Corrosion Behavior of Cu/Ni Coatings on Ti-6Al-4V Alloy after Diffused Treatment

To improve the low thermal conductivities and poor wear resistances of TC4(Ti-6Al-4V)alloy,the most widely used titanium alloy,the surface of TC4 alloys is modified by electroplating deposition of Ni and Cu layers,and then heat-treated to increase the diffusivity at the interface.In this paper,the corrosion behavior of Cu/Ni coatings on TC4 alloy at different heat treatment processes was investigated in 3.5 wt%Na Cl by the electrochemical analysis,and the microstructure and composition of corrosion products was carried out to reveal the corrosion resistance mechanism of Cu/Ni coatings.It was found that the corrosion resistance was significantly influenced by heat treatment temperature.With the increasing diffusion treatment temperature from 500 to 700℃,the corrosion potential positively shifted from-330.87 to-201.14 m V,and the corrosion current density decreased from 4.02×10^-3 to 0.514×10^-3 m A/cm^2.However,when heat treatment temperature increased to 800℃,the corrosion potential negatively shifted to-207.21 m V,and the current density increased to 1.62×10^-3 m A/cm^2.The diffusion behavior of Ti,Ni and Cu elements occurred and small amounts of Ni and Ti elements appeared on the specimen surface under different heat treatment temperature.Especially heattreated at 700℃,the smaller pore size,dense Cu2O film,and highly stable Ti O and Ni O oxide layer were formed,which dramatically enhanced the corrosion resistance of Cu/Ni coatings.Finally,a novel model of corrosion resistance was proposed based on the analysis mentioned above.

Key technologies and practice for gas field storage facility construction of complex geological conditions in China

In view of complex geological characteristics and alternating loading conditions associated with cyclic large amount of gas injection and withdrawal in underground gas storage(UGS) of China, a series of key gas storage construction technologies were established, mainly including UGS site selection and evaluation, key index design, well drilling and completion, surface engineering and operational risk warning and assessment, etc. The effect of field application was discussed and summarized. Firstly, trap dynamic sealing capacity evaluation technology for conversion of UGS from the fault depleted or partially depleted gas reservoirs. A key index design method mainly based on the effective gas storage capacity design for water flooded heterogeneous gas reservoirs was proposed. To effectively guide the engineering construction of UGS, the safe well drilling, high quality cementing and high pressure and large flow surface injection and production engineering optimization suitable for long-term alternate loading condition and ultra-deep and ultra-low temperature formation were developed. The core surface equipment like high pressure gas injection compressor can be manufactured by our own. Last, the full-system operational risk warning and assessment technology for UGS was set up. The above 5 key technologies have been utilized in site selection, development scheme design, engineering construction and annual operations of 6 UGS groups, e.g. the Hutubi UGS in Xinjiang. To date, designed main indexes are highly consistent with actural performance, the 6 UGS groups have the load capacity of over 7.5 billion cubic meters of working gas volume and all the storage facilities have been running efficiently and safely.

Sequential Growth of Cs_(3)Bi_(2)I_(9)/BiVO_(4)Direct Z-Scheme Heterojunction for Visible-Light-Driven Photocatalytic CO_(2)Reduction

The high exciton binding energy and lack of a positive oxidation band potential restrict the photocatalytic CO_(2)reduction efficiency of lead-free Bi-based halide perovskites Cs_(3)Bi_(2)X_(9)(X=Br,I).In this study,a sequential growth method is presented to prepare a visible-light-driven(λ>420 nm)Z-scheme heterojunction photocatalyst composed of BiVO_(4)nanocrystals decorated on a Cs_(3)Bi_(2)I_(9)nanosheet for photocatalytic CO_(2)reduction coupled with water oxidation.The Cs_(3)Bi_(2)I_(9)/BiVO_(4)Z-scheme heterojunction photocatalyst is stable in the gas-solid photocatalytic CO_(2)reduction system,demonstrating a high visible-light-driven photocatalytic CO_(2)-to-CO production rate of 17.5μmol/(g·h),which is approximately three times that of pristine Cs_(3)Bi_(2)I_(9).The high efficiency of the Cs_(3)Bi_(2)I_(9)/BiVO_(4)heterojunction was attributed to the improved charge separation in Cs_(3)Bi_(2)I_(9).Moreover,the Z-scheme charge-transfer pathway preserves the negative reduction potential of Cs_(3)Bi_(2)I_(9)and the positive oxidation potential of BiVO_()4.This study off ers solid evidence of constructing Z-scheme heterojunctions to improve the photocatalytic performance of lead-free halide perovskites and would inspire more ideas for developing leadfree halide perovskite photocatalysts.

Discussion on New Evaluation Technology of Non-Metallic Composite Continuous Pipe for Oil and Gas Field

In view of the serious lack and lag of the test and evaluation technology of non-metallic composite continuous pipe, and focusing on the characteristics of the application of non-metallic composite continuous pipe in oil field, this paper discusses a series of new full-scale test and evaluation technologies for accurately evaluating the product quality and practical application performance of non-metallic composite continuous pipe, which effectively solves the major technical problem that the new products of non-metallic pipe cannot be accurately evaluated. Based on the characteristics of the application of non-metallic composite continuous pipe in oil field, a series of new full-scale test evaluation technologies which can accurately evaluate the product quality and practical application performance of non-metallic pipe are designed through a large number of tests. The test and evaluation technology can accurately evaluate the key performance of high and low pressure cycle, high and low temperature cycle, gas permeability resistance, minimum bending radius etc. It provides a scientific evaluation basis for the standardized application of non-metallic continuous pipe and a reliable quality control method for the selection of products in oil field.

Microstructure and properties of HAZ for X100 pipeline steel

In general, the weld thermal cycle results in significant changes in microstructure and mechanical properties of the weld heat affected zone （ HAZ）. The microstructure, microhardness and low temperature impact toughness of HAZfor X100 pipeline steel were studied by means of welding thermal simulation. Influence of cooling time on the microstructure and properties in coarse-grained heat affected zone （CGHAZ） was investigated. The results illustrated that polygonal ferrite and a small amount of granular bainite were obtained when the cooling time ts/5 is larger than 1 500 s. Mainly granular bainite was formed when the cooling time t8/5 is in the range of 1500 s to 100 s. Bainite ferrite was observed when the cooling time is smaller than 60 s. Martensite appeared in the CGHAZ with the 20 s cooling time. The value of microhardness in the CGHAZ was higher than that of base metal （ BM） when the cooling time ts/s is smaller than 100 s. The CVN absorbed energy in the CGHAZ was higher than the value of BM when the cooling time t8/5 is smaller than 30 s.

The anti-Temperature-vibration properties of viscoelastic anticorrosive tape

Viscoelastic anticorrosive tape is extensively used for repairing anticorrosive layers on compressor outlet pipelines in the oil and gas industry.However,there is no relevant research on the coupling effect of temperature and vibration on the performance of viscoelastic anticorrosive tape.In this paper,acceleration tests of temperature and vibration coupling conditions were conducted to investigate the performance of viscoelastic anticorrosive tape.After temperature and vibration treatment,the specimens showed wide variance in thickness,and the adhesion and chemical soaking resistance of the tape was reduced.However,the viscoelastic anticorrosive tape still showed high adhesion.According to theoretical calculations,the tested viscoelastic body can repair pipes with a maximum diameter of 903 mm.Therefore,this viscoelastic anticorrosive tape is suitable for the compressor outlets of buried pipelines with diameters smaller than 903 mm.The research in this paper provides a method and basis for the selection of repairing materials for the anticorrosion coatings of compressor outlet pipelines.

Discussion on the Key Properties of Fiberglass Tubing Used in Oilfield

CNPC implements the call of energy conservation and emission reduction, and promotes the application of new energy conservation and emission reduction technologies and new products to achieve production and reduce pollution. As China’s oilfields enter the period of high water cut development, corrosion problem and scale formation ordinary steel tubing are becoming more and more serious in oilfield application, which influence and restrict the production and development and bring about energy waste. FRP tubing has been widely used in oil and gas fields because of its excellent corrosion resistance, small friction coefficient and less wear. With the gradual popularization of FRP tubing in oilfields, failure cases also show a growing trend as threaded release, leakage, fracture and so on, which affect the normal production of oilfields. In this paper, a series of key performance properties affecting service performance of high-pressure FRP tubing are tested which took from common failure cases. The key properties of FRP tubing, such as unloading, anti-collapse, short-term failure pressure at high ambient temperature and high ambient temperature axial tension, are tested in the research. The article provides a scientific basis for applicability evaluation of FRP tubing. This research has important significance for energy saving, decreasing pollution and safe operation of tubing pipes. Several suggestions are put forward on material selection and design of FRP tubing.

Investigation of the Corrosion and Passive Behavior of HP-13Cr Stainless Steel in Formate Annulus Protection Fluid

The corrosion and passive behavior of HP-13Cr stainless steel(HP-13Cr SS)in formate annulus protection fluid was investigated.HP-13Cr SS exhibited good passive behavior in clean formate annulus protection fluid,which was attributed to a thinner and more dense passive film mainly composed of Cr_(2)O_(3).In the formation water solution,the passive film was composed of metastable Cr(OH)3,which was explained by the isoelectric point theory,resulting in the deterioration of the passive behavior of HP-13Cr SS.When the formation water penetrated the formate annulus protection fluid,a large number of loose FeCO_(3)particles formed in the corrosion scales,thus HP-13Cr SS suffered severe corrosion.Therefore,avoiding formation water penetrating the formate annulus protection fluid is conducive to improving the service life of HP-13Cr SS oil tubes in extremely aggressive environment.