Experimental investigation of shale breakdown pressure under liquid nitrogen pre-conditioning before nitrogen fracturing

Cryogenic fracturing with liquid nitrogen(LN_(2))offers the benefits of reducing the water consumption and adverse environmental impacts induced by water-based fracturing,as well as potentially enhancing the fracture complexity.We performed a series of laboratory experiments to explore the key mechanisms governing the breakdown pressures of shale during cryogenic fracturing.In this study,cylindrical shale samples were pre-conditioned by exposing a borehole to low-temperature LN_(2) for a certain time period,and then,the samples were fractured using gaseous N_(2) under triaxial stress and a high reservoir temperature.The effects of various key parameters on the breakdown pressure were investigated,including the duration of the low-temperature LN_(2) treatment,the confining pressure,the reservoir temperature,and the direction of the shale bedding relative to the borehole axis.The results demonstrate that the injection of low-temperature LN_(2) as a pre-fracturing fluid into a borehole can significantly reduce the breakdown pressure of the shale during subsequent nitrogen fracturing.This reduction in breakdown pressure can be further intensified by increasing the duration of the LN_(2) pre-conditioning.Without LN_(2) pre-conditioning,the breakdown pressure initially increases and then decreases with increasing reservoir temperature.When LN_(2) pre-conditioning is applied,the breakdown pressure keeps decreasing with increasing reservoir temperature.As the confining pressure increased,the breakdown pressure increased linearly in the tests with and without LN_(2) pre-conditioning.The experimental results demonstrate that LN_(2) preconditioning before N_(2) fracturing is a promising waterless fracturing technique that reduces the breakdown pressure and enhances the fracture complexity.

Synthesis and characterizations of boron and nitrogen co-doped high pressure and high temperature large single-crystal diamonds with increased mobility

We synthesized and investigated the boron-doped and boron/nitrogen co-doped large single-crystal diamonds grown under high pressure and high temperature(HPHT) conditions(5.9 GPa and 1290℃). The optical and electrical properties and surface characterization of the synthetic diamonds were observed and studied. Incorporation of nitrogen significantly changed the growth trace on surface of boron-containing diamonds. X-ray photoelectron spectroscopy(XPS) measurements showed good evident that nitrogen atoms successfully incorporate into the boron-rich diamond lattice and bond with carbon atoms. Raman spectra showed differences on the as-grown surfaces and interior between boron-doped and boron/nitrogen co-doped diamonds. Fourier transform infrared spectroscopy(FTIR) measurements indicated that the nitrogen incorporation significantly decreases the boron acceptor concentration in diamonds. Hall measurements at room temperature showed that the carriers concentration of the co-doped diamonds decreases, and the mobility increases obviously. The highest hole mobility of sample BNDD-1 reached 980 cm^(2)·V^(-1)·s^(-1), possible reasons were discussed in the paper.

Synthesis of large diamond crystals containing high-nitrogen concentration at high pressure and high temperature using Ni-based solvent by temperature gradient method

This paper reprots that with Ni-based catalyst/solvent and with a dopant of NAN3, large green single crystal diamonds with perfect shape are successfully synthesized by temperature gradient method under high pressure and high temperature in a China-type cubic anvil high-pressure apparatus （SPD-6 × 1200）, and the highest nitrogen concentration reaches approximately 121-1257 ppm calculated by infrared absorption spectra. The synthesis conditions are about 5.5 CPa and 1240-1300 ℃. The growth behaviour of diamond with high-nitrogen concentration is investigated in detail. The results show that, with increasing the content of NaN3 added in synthesis system, the width of synthesis temperature region for growth high-quality diamonds becomes narrower, and the morphology of diamond crystal is changed from cube-octahedral to octahedral at same temperature and pressure, the crystal growth rate is slowed down, nevertheless, the nitrogen concentration doped in synthetic diamond increases.

Electric and Spectroscopic Studies of Pulsed Corona Discharges in Nitrogen at Atmospheric Pressure

This paper is mainly dedicated to the experimental electric and spectroscopic analysis of positive corona discharges in the case of point to plane configuration, generated in nitrogen at atmospheric pressure. The maximum corona current (a few hundreds of mA), the average current (a few μA) and the average propagation velocity (a few 107 cm/s) are analyzed with the variation of the applied voltage (a few kV) and the gap distance (not exceeding 16 mm). By using an ICCD camera, the dynamics of the discharge during the propagation of primary and secondary streamers across the gap distance was analyzed. Spectroscopic study is emphasized in a spectral range from 200 nm up to 500 nm, to determine the important excited species present in the gaseous environment such as the second positive and the first negative systems (SPS and FNS respectively). The identification of the quenching NOγ emission bands is also emphasized.

Modeling, analysis, and screening of cyclic pressure pulsing with nitrogen in hydraulically fractured wells

Cyclic pressure pulsing with nitrogen is studied for hydraulically fractured wells in depleted reservoirs.A compositional simulation model is constructed to represent the hydraulic fractures through local-grid refinement.The process is analyzed from both operational and reservoir/hydraulic-fracture perspectives.Key sensitivity parameters for the operational component are chosen as the injection rate,lengths of injection and soaking periods and the economic rate limit to shut-in the well.For the reservoir/hydraulic fracturing components,reservoir permeability,hydraulic fracture permeability,effective thickness and half-length are used.These parameters are varied at five levels.A full-factorial experimental design is utilized to run 1250 cases.The study shows that within the ranges studied,the gas-injection process is applied successfully for a 20-year project period with net present values based on the incremental recoveries greater than zero.It is observed that the cycle rate limit,injection and soaking periods must be optimized to maximize the efficiency.The simulation results are used to develop a neural network based proxy model that can be used as a screening tool for the process.The proxy model is validated with blind-cases with a correlation coefficient of 0.96.

Producing ultra-high-speed nitrogen jets by arc heating in a low-pressure chamber

Pure nitrogen gas was heated with direct current arc, at input powers from several hundred Watt to over 5 kW, and then injected through a nozzle into a chamber at 1 or 10 Pa pressure, with the purpose of accelerating the gas to very high speed around 7 km/s. Various structures of the arc generator and gas expansion nozzle were examined. Results show that bypass exhausting of the boundary layer before it enters the nozzle divergent section can greatly increase flow speed of the jet, thus it might be possible to use nitrogen as a working gas in high speed gas dynamic test facilities.

Thermal Behavior,Sensitivity,Detonation Velocity and Pressure of a Nitrogen-Rich Compound

The nitrogen content of tetrazolo triazines is 68.9%.In this paper,tetrazolotriazines was synthetized.The TG-DSC test indicated its decomposition process in detail.The non-isothermal kinetic parameters were speculated by Kissinger and Ozawa methods.It revealed the mechanism function of thermal decomposition.The impact and friction sensitivity were tested.The detonation pressure and velocity were calculated.It has a wide range of potential applications as a kind of energetic material.

THE EFFECTS OF PULSE BIAS VOLTAGE AND N_2 PARTIAL PRESSURE ON TiAlN FILMS OF ARC ION PLATING (AIP)

Owing to the characteristics of arc ion plating(AIP) technique, the structure and composition of TiAlN films can be tailored by controlling of various parameters such as compositions of target materials, N2 partial pressure, substrate bias and so on. In this study, several titanium aluminum nitride films were deposited on 1Cr11Ni2W2MoV steel for compressor blade of areo-engine under different d.c pulse bias voltage and nitrogen partial pressure. The effects of substrate pulse bias and nitrogen partial pressure on the deposition rate, droplet formation, microstruture and elemental component of the films were investigated.

Diamond growth in a high temperature and high pressure Fe–Ni–C–Si system:Effect of synthesis pressure

Pressure is one of the necessary conditions for diamond growth.Exploring the influence of pressure on growth changes in silicon-doped diamonds is of great value for the production of high-quality diamonds.This work reports the morphology,impurity content and crystal quality characteristics of silicon-doped diamond crystals synthesized under different pressures.Fourier transform infrared spectroscopy shows that with the increase of pressure,the nitrogen content in the C-center inside the diamond crystal decreases.X-ray photoelectron spectroscopy test results show the presence of silicon in the diamond crystals synthesized by adding silicon powder.Raman spectroscopy data shows that the increase in pressure in the Fe-Ni-C-Si system shifts the Raman peak of diamonds from 1331.18 cm^(-1)to 1331.25 cm^(-1),resulting in a decrease in internal stress in the crystal.The half-peak width decreased from 5.41 cm^(-1)to 5.26 cm^(-1),and the crystallinity of the silicon-doped diamond crystals improved,resulting in improved quality.This work provides valuable data that can provide a reference for the synthesis of high-quality silicon-doped diamonds.

Influence of annealing treatment on as-grown Ib-type diamond crystal at a high temperature and high pressure

In this paper,we report on the influence of annealing treatment on as-grown Ib-type diamond crystal under high pressure and high temperature in a china-type cubic anvil high-pressure apparatus.Experiments are carried out at a pressure of 7.0 GPa and temperatures ranging from 1700 C to 1900 C for 1 h.Annealing treatment of the diamond crystal shows that the aggregation rate constant of nitrogen atoms in the as-grown Ib-type diamond crystal strongly depends on diamond morphology and annealing temperature.The aggregation rate constant of nitrogen remarkably increases with the increase of annealing temperature and its value in octahedral diamond is much higher than that in cubic diamond annealed at the same temperature.The colour of octahedral diamond crystal is obviously reduced from yellow to nearly colorless after annealing treatment for 1 h at 1900 C,which is induced by nitrogen aggregation in a diamond lattice.The extent of nitrogen aggregation in an annealed diamond could approach approximately 98% indicated from the infrared absorption spectra.The micro-Raman spectrum reveals that the annealing treatment can improve the crystalline quality of Ib-type diamond characterized by a half width at full maximum at first order Raman peak,and therefore the annealed diamond crystals exhibit nearly the same properties as the natural IaA-type diamond stones of high quality in the Raman measurements.

Multi-Pollutant Formation and Control in Pressurized Oxy-Combustion:SO_(x),NO_(x),Particulate Matter,and Mercury

Oxy-combustion is a promising carbon-capture technology,but atmospheric-pressure oxy-combustion has a relatively low net efficiency,limiting its application in power plants.In pressurized oxycombustion(POC),the boiler,air separation unit,flue gas recirculation unit,and CO_(2)purification and compression unit are all operated at elevated pressure;this makes the process more efficient,with many advantages over atmospheric pressure,such as low NO_(x)emissions,a smaller boiler size,and more.POC is also more promising for industrial application and has attracted widespread research interest in recent years.It can produce high-pressure CO_(2)with a purity of approximately 95%,which can be used directly for enhanced oil recovery or geo-sequestration.However,the pollutant emissions must meet the standards for carbon capture,storage,and utilization.Because of the high oxygen and moisture concentrations in POC,the formation of acids via the oxidation and solution of SO_(x)and NO_(x)can be increased,causing the corrosion of pipelines and equipment.Furthermore,particulate matter(PM)and mercury emissions can harm the environment and human health.The main distinction between pressurized and atmospheric-pressure oxy-combustion is the former’s elevated pressure;thus,the effect of this pressure on the pollutants emitted from POC—including SO_(x),NO_(x),PM,and mercury—must be understood,and effective control methodologies must be incorporated to control the formation of these pollutants.This paper reviews recent advances in research on SO_(x),NO_(x),PM,and mercury formation and control in POC systems that can aid in pollutant control in such systems.

合成气/氮氧化物的氧化特性实验与反应动力学研究

为明晰合成气与氮氧化物(NO_(x))之间的相互作用机制,采用高压流动反应器,在623~1273 K温度下,实验分析了不同压力(0.19,1.80 MPa)、不同NO_(x)初始摩尔分数(0,0.0925%,0.185%)工况下,典型煤制合成气掺混NO_(x)的氧化特性。基于6种已有的反应动力学模型开展模拟计算,并结合实验结果和计算得到的反应速率常数,更新了CRECK-2019模型。采用更新后的模型进一步开展反应动力学分析,揭示了合成气/NO_(x)氧化过程的关键反应。研究结果表明:升高压力对合成气的低温氧化存在促进作用,且促进作用随NO_(x)掺混量的增大而增强;掺混NO_(x)对0.19 MPa下合成气的低温氧化无明显影响,而对1.80 MPa下的低温氧化存在促进作用,且对不同压力下的中、高温氧化均存在抑制作用;反应H_(2)+NO_(2)=H+HONO对高压下合成气/NO_(x)的氧化有显著贡献,反应HNO+NO_(2)=HONO+NO、HNO+H=NO+H_(2)和HNO+OH=NO+H_(2)O严重影响着中高温下OH的生成。研究结果可为合成气燃气轮机开发与污染物排放控制提供理论支撑。

基于PID与模糊控制算法的高氮钢加压电渣炉熔速控制

为了提高氮钢加压电渣炉的熔速控制精度,文章设计了一种结合PID与模糊逻辑的控制系统,再利用粒子群优化算法进行了优化。结果表明,基于PID与模糊控制算法的高氮钢加压电渣炉熔速控制研究,不仅有效地提高了系统响应能力,还实现了系统的高精度控制。

氨燃烧过程中H_(2)NO中间体演化对氮氧化物NO_(x)生成的影响

氨(NH_3)是一种无碳富氢的燃料,可以实现燃烧过程中零碳排放。然而,氨中含有的N可能会被氧化生成氮氧污染物(NO_(x)),造成大气环境污染。为此,基于量子化学计算,该文从微观层面研究氨燃料燃烧过程中H_2NO中间体的演化过程,并分析其对NO_(x)生成的影响。理论计算结果表明,H_(2)NO是NO生成的重要中间体,通过氮氧化物分解基元反应生成NO,其活化能为93.53 kJ/mol;而H_(2)NO的脱氢产物HNO则是NO_(2)生成的关键中间体,通过氮氧化物氧化基元反应促成NO_(2)的生成,其活化能为43.73 kJ/mol。从量子化学角度来看,在氨燃烧过程中高温条件均使NO和NO_(2)生成反应的活化能和吉布斯自由能变不同程度地升高,而高压条件对其几乎没有产生影响。该研究可为降低氨燃烧过程中NO_(x)生成提供一定理论参考。

Different effect of NiMnCo or FeNiCo on the growth of type-Ⅱa large diamonds with Ti/Cu as nitrogen getter

In order to synthesize high-quality type-Ⅱa large diamond, the selection of catalyst is very important, in addition to the nitrogen getter. In this paper, type-IIa large diamonds are grown under high pressure and high temperature（HPHT） by using the temperature gradient method（TGM）, with adopting Ti/Cu as the nitrogen getter in Ni70Mn25Co5（abbreviated as NiMnCo） or Fe（55）Ni（29）Co（16）（abbreviated FeNiCo） catalyst. The values of nitrogen concentration（Nc） in both synthesized high-quality diamonds are less than 1 ppm, when Ti/Cu（1.6 wt%） is added in the FeNiCo or Ti/Cu（1.8 wt%） is added in the NiMnCo. The difference in solubility of nitrogen between both catalysts at HPHT is the basic reason for the different effect of Ti/Cu on eliminating nitrogen. The nitrogen-removal efficiency of Ti/Cu in the NiMnCo catalyst is less than in the FeNiCo catalyst. Additionally, a high-quality type-Ⅱa large diamond size of 5.0 mm is obtained by reducing the growth rate and keeping the nitrogen concentration of the diamond to be less than 1 ppm, when Ti/Cu（1.6 wt%） is added in the FeNiCo catalyst.

Effects of water application uniformity using a center pivot on winter wheat yield, water and nitrogen use efficiency in the North China Plain

In recent years, the use of fertigation technology with center pivot irrigation systems has increased rapidly in the North China Plain (NCP). The combined effects of water and nitrogen application uniformity on the grain yield, water use efficiency (WUE) and nitrogen use efficiency (NUE) have become a research hotspot. In this study, a two-year field experiment was conducted during the winter wheat growing season in 2016–2018 to evaluate the water application uniformity of a center pivot with two low pressure sprinklers (the R3000 sprinklers were installed in the first span, the corresponding treatment was RS;the D3000 sprinklers were installed in the second span, the corresponding treatment was DS) and a P85A impact sprinkler as the end gun (the corresponding treatment was EG), and to analyze its effects on grain yield, WUE and NUE. The results showed that the water application uniformity coefficients of R3000, D3000 and P85A along the radial direction of the pivot (CUH) were 87.5, 79.5 and 65%, respectively. While the uniformity coefficients along the traveling direction of the pivot (CUC) were all higher than 85%. The effects of water application uniformity of the R3000 and D3000 sprinklers on grain yield were not significant (P>0.05);however, the average grain yield of EG was significantly lower (P<0.05) than those of RS and DS, by 9.4 and 11.1% during two growing seasons, respectively. The coefficients of variation (CV) of the grain yield had a negative correlation with the uniformity coefficient. The CV of WUE was more strongly affected by the water application uniformity, compared with the WUE value, among the three treatments. The NUE of RS was higher than those of DS and EG by about 6.1 and 4.8%, respectively, but there were no significant differences in NUE among the three treatments during the two growing seasons. Although the CUH of the D3000 sprinklers was lower than that of the R3000, it had only limited effects on the grain yield, WUE and NUE. However, the cost of D3000 sprinklers is lower than that of R3000 sprinklers. Therefore, the D3000 sprinklers are recommended for winter wheat irrigation and fertigation in the NCP.

Synthesis of black phosphorus structured polymeric nitrogen

Since the discoveries of polymeric nitrogen, named cg-N (2004), LP-N (2014), HLP-N (2019), another polymorph named black phosphorus nitrogen (BP-N) was synthesized at high-pressure-high-temperature conditions. The narrow existing pressure region and similar synthesized pressure of BP-N compared with cg-N indicate that the stable energy and enthalpy of formation of these two structures are close to each other, which was confirmed by our theoretical calculation. In order to obtain the pressure region of BP-N phase, pure N2 and TiN/Pb + N2 precursors were used for laser-heating high pressure experiments in diamond anvil cell (DAC), and the phase identity was examined by Raman and XRD mapping. BP-N can be synthesized in the pressure range of 130 GPa to 140 GPa with the assistance of heating absorber. With the decrease of the pressure, BP-N can be quenched to ~ 40 GPa. The synthesizing pressure–temperature and the stable pressure region of BP-N are important for further exploration of BP-N and its kinetic and thermal dynamic relationship with other polymeric nitrogen, especially cg-N.

Yield of Ozone,Nitrite Nitrogen and Hydrogen Peroxide Versus Discharge Parameter Using APPJ Under Water

Discharge plasma in and in contact with water can be accompanied with ultraviolet radiation and electron impact, thus can generate hydroxyl radicals, ozone, nitrite nitrogen and hydrogen peroxide. In this paper, a non-equilibrium plasma processing system was established by means of an atmospheric pressure plasma jet immersed in water. The hydroxyl intensities and discharge energy waveforms were tested. The results show that the positive and negative discharge energy peaks were asymmetric, where the positive discharge energy peak was greater than the negative one. Meanwhile, the yield of ozone and nitrite nitrogen was enhanced with the increase of both the treatment time and the discharge energy. Moreover, the pH value of treated water was reduced rapidly and maintained at a lower level. The residual concentration of hydrogen peroxide in APPJ treated water was kept at a low level. Additionally, both the efficiency energy ratio of the yield of ozone and nitrite nitrogen and that of the removal of p-nitrophenol increased as a function of discharge energy and discharge voltage. The experimental results were fully analyzed and the chemical reaction equations and the physical processes of discharges in water were given.

Effects of Nitrogen Atmosphere on Microstructure and Mechanical Properties of Ti(C_(0.5)N_(0.5))-based Cermets

The traditional low-pressure sintering was optimized for the preparation of Ti(C_(0.5)N_(0.5))-WC-Mo_2 C-TaC-Co-Ni cermets. Nitrogen was introduced into sintering system during different stages and with different pressures. The morphology and mechanical properties of cermets were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), and measurements of transverse rupture strength(TRS), Vickers-hardness(HV) and fracture toughness(K_(IC)). The degree of denitrification is directly related to the amount of η phase. When nitrogen is introduced into the sintering system, the amount of observed η phase decreases. When nitrogen is introduced during solid-state sintering with appropriate pressure, the core-rim structure is well developed. And TRS and hardness get enhanced while toughness tends to be deteriorated with the nitrogen pressure increasing. When nitrogen is introduced after the sintering temperature reaches 1 350 ℃ or at higher pressures, the volume fraction of η phase increases. Sintered with a nitrogen pressure of 1.0 kPa during 1 200-1 350 ℃, the bulk materials possess enhanced mechanical properties, in which the TRS, HV, and K_(IC) are 1 966 MPa, 1 583 MPa, and 9.08 MPa·m^(1/2), respectively.

Effects of Nitrogen Application and Weed Interference on Performance of Some Tropical Maize Genotypes in Nigeria

Low soil nitrogen （N） and weed infestations are some of the major constraints to maize production in Nigeria. A split-split plot experiment in a randomized complete block design with three replicates was established at two sites with different agroecological zones, Ikenne （Typic Paleudalf） and Shika （Typic Tropaquept）, in Nigeria in 2002 and 2003 rainy seasons to investigate the responses of four maize genotypes （Oba super II, Low N pool C2, TZB-SR, and ACR 8328 BN C7） to N fertilizer applied at four rates, 0, 30, 60, and 90 kg N ha^-1, and three weed pressure treatments, no weed pressure （weekly weeding）, low weed pressure （inter-row weekly weeding）, and high weed pressure （no weeding throughout the growing season）. Growth and yield parameters of maize and weeds were taken at flowering and harvest. The results indicated that there was a significant reduction in maize leaf area, leaf area index, and photosynthetically active radiation due to weed interference at both sites. The application of nitrogen at 90 kg N ha^-1 significantly increased maize leaf area. Reductions in maize growth and yield at flowering and harvest were significant due to weed interference at both Ikenne and Shika, thus showing that the reductions in maize growth and yield due to weed interference were not ecological zone specific even though weed species and their seed banks may differ. Ameliorative management options could thus be the same in the two agroecological zones. Application of 90 kg N ha^-1 led to a significant increase in maize grain yield at Shika while there was no fertilizer effect at Ikenne on grain yield. There was no significant difference between 60 and 90 kg N ha^-1, suggesting that 60 kg N ha^-1 could be a possible replacement for the higher fertilizer rate at least for the identified maize genotypes. Low weed pressure treatment led to 26% and 35% reductions in maize grain yield at Ikenne and Shika, respectively, while 22% and 51% reductions, respectively, were observed due to high weed pressure. Generally, maize grain yield was higher at Ikenne than Shika. The maize genotypes Low N pool C2 and ACR 8328 PIN C7 performed better than the other genotypes at Ikenne while the maize genotype Oba super II had the best performance at harvest at Shika. Application of nitrogen increased weed biomass at flowering at Ikenne. The maize grain yield was highest in the N-efficient genotypes, Oba super II and Low N pool C2; the susceptible genotype TZB-SR had the least yield at Shika. There existed a negative and significant correlation between maize grain yield and weed biomass at both sites.