Enhance liquid nitrogen fracturing performance on hot dry rock by cyclic injection

Producing complex fracture networks in a safe way plays a critical role in the hot dry rock (HDR) geothermal energy exploitation. However, conventional hydraulic fracturing (HF) generally produces high breakdown pressure and results only in single main fracture morphology. Furthermore, HF has also other problems such as the increased risk of seismic events and consuption of large amount of water. In this work, a new stimulation method based on cyclic soft stimulation (CSS) and liquid nitrogen (LN2) fracturing, known as cyclic LN2 fracturing is explored, which we believe has the potential to solve the above issues related to HF. The fracturing performances including breakdown pressure and fracture morphology on granites under true-triaxial stresses are investigated and compared with cyclic water fracturing. Cryo-scanning electron microscopy (Cryo-SEM) tests and X-ray computed tomography (CT) scanning tests were used for quantitative characterization of fracture parameters and to evaluate the cyclic LN2 fracturing performances. The results demonstrate that the cyclic LN2 fracturing results in reduced breakdown pressure, with between 21% and 67% lower pressure compared with using cyclic water fracturing. Cyclic LN2 fracturing tends to produce more complex and branched fractures, whereas cyclic water fracturing usually produces a single main fracture under a low number of cycles and pressure levels. Thermally-induced fractures mostly occur around the interfaces of different particles. This study shows the potential benefits of cyclic LN2 fracturing on HDR. It is expected to provide theoretical guidance for the cyclic LN2 fracturing application in HDR reservoirs.

Fabrication and sintering behavior of high-nitrogen nickel-free stainless steels by metal injection molding

High-nitrogen nickel-free stainless steels were fabricated by the metal injection molding technique using high nitrogen alloying powders and a mixture of three polymers as binders.Mixtures of metal powders and binders with various proportions were also investigated, and an optimum powder loading capacity was determined as 64vol%.Intact injection molded compacts were successfully obtained by regulating the processing parameters.The debinding process for molded compacts was optimized with a combination of thermo-gravimetric analysis and differential scanning calorimetry analysis.An optimum relative density and nitrogen content of the specimens are obtained at 1360℃,which are 97.8%and 0.79wt%,respectively.

Preparation of high nitrogen and nickel-free austenitic stainless steel by powder injection molding

High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding （PIM） technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintefing conditions are determined to be 1300℃,2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150℃for 90 rain and water quench, the 0.2% yield strength, ultimate tensile strength （UTS）, elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.

Nitrogen Injection in Molten Aluminum in a Tank Degasser

The injection of nitrogen in molten aluminum through a static impeller in a tank degassing unit is studied. Using basic principles of fluid mechanics, it is analyzed the influence of the nozzle diameter on the bubble diameter and the mean residence time of the bubbles in the molten aluminum. By means of transient isothermal 2D Computational Fluid Dynamics (CFD) simulations, the influence of the nitrogen volumetric flow rate on the phase distributions and the tank degasser dynamics is studied. Finally, an adiabatic CFD simulation is carried out in order to elucidate the changes in the molten aluminum temperature due to the injection of nitrogen at ambient temperature. This simulation shows that molten aluminum does not suffer drastic temperature reductions given that, in spite?that?the nitrogen is fed at ambient temperature, the mass of nitrogen is relatively small compared with the mass of aluminum.

Study on numerical simulation of spontaneous combustion prevention mechanism by nitrogen injection in goaf

Based on heterogeneous and porous medium seepage of air leakage-diffusionequation, as well as, gas and porous medium synthesis heat transferring equation, aspontaneous combustion non-steady numerical model of nitrogen injection goaf was established, which can be solved by upwind finite element numerical simulation method simultaneously. Taking the working face for example; air leakage seepage, nitrogen flow and gas distribution can be described in visual display in nitrogen injection goaf and the oxygen (O_2), carbon monoxide (CO) concentration and temperature distribution, as well as, their change were described in theory during the coal left behind combustion in goaf, which above reveals the complex mechanics course (mechanism) of seepage, diffusion and oxidation heat releasing during coal spontaneous combustion and its restraining. During the calculation, the effect factors of gas springing out and working face advancing were considered fully, and the spontaneous combustion course under different amount of trogen injection was simulated. The conclusions were obtained that under nitrogen injection condition, the high spontaneous combustion temperature area lean to the inlet air, but the shape becomes narrower, with the amount of nitrogen rising, the spontaneous combustion period becomes longer till to it does not happen. Meanwhile the nitrogen injection accelerates gas springing out in goaf. The result that turns out in theory simulation fits to practical nitrogen injection.

Calculation of the Gas Injection Rate and Pipe String Erosion in Nitrogen Drilling Systems

Detailed information is provided for the design and construction of nitrogen drilling in a coal seam.Two prototype wells are considered.The Guo model is used to calculate the required minimum gas injection rate,while the Finnie,Sommerfeld,and Tulsa models are exploited to estimate the ensuing erosion occurring in pipe strings.The calculated minimum gas injection rates are 67.4 m^(3)/min(with water)and 49.4 m^(3)/min(without water),and the actual field of use is 90–120 m^(3)/min.The difference between the calculated injection pressure and the field value is 6.5%–15.2%(formation with water)and 0.65%–7.32%(formation without water).The results show that the Guo model can more precisely represent the situation of the no water formation in the nitrogen drilling of a coal seam.The Finnie,Sommerfeld,and Tulsa models have different sensitivities to cutting densities,particle size,impact velocity and angle,and pipe string hardness.

RESEARCH THE CHANGE RULE OF OXIDATION ZONE WIDTH CAUSED BY NITROGEN INJECTION IN GOB

On the basis of heat transfer and chemical kinetics theory, both connections coal self ignite with oxygen concentration and range of oxidation zone with air leak intensity are analyzed, and calculating method is deduced to gain the lower limit of oxygen concentration and the range of oxidation zone. The change rule of correlative parameter is quantitatively researched between before nitrogen injection and after nitrogen injection in gob, such as oxygen concentration, oxidation zone width, etc. According to theoretical calculation, the relation position and flow of nitrogen injection with oxidation zone width is conformed, and computational formulas of the best flow and position of nitrogen injection are obtained. It offers a theoretic criterion for preventing and controlling float coal self ignite by nitrogen injection in gob.

注氮气机抽防腐防垢一体化管柱的研制与应用

针对塔河油田注氮气机抽井井筒及井下工具严重腐蚀结垢,易造成抽油泵卡泵、封隔器解封困难等井下故障的问题,在现有技术的基础上,优化改进结构、技术创新,研制了一种注氮气防腐防垢机抽一体化管柱。该管柱包括注气防垢杆式泵、防腐封隔器等关键工具,注气防垢杆式泵优化改进了柱塞和泵筒的结构,泵筒上部设计注气孔、下部设计封堵筒,柱塞下部设计密封堵头,注气时柱塞下部堵头将进油通道密封,能防止高压油液倒灌进入泵腔发生腐蚀结垢,消除柱塞下放失败的风险;防腐封隔器采用新型护肩式的胶筒组件及双“O”型圈、双向支撑密封结构、分级解封机构和分体式双向卡瓦锚定结构,提高封隔器胶筒的耐腐蚀性能、降低上提解封力和保证卡瓦锚定性能。经过理论校核和室内模拟试验均满足现场需求,现场应用表明,该管柱坐封、解封及注气均正常,转采成功率100%,满足开发需求,解决了注气腐蚀结垢卡泵和封隔器解封困难的工程难题,具有很高的推广价值。

平行升压防灭火技术在采煤工作面启封及回采中的应用

徐矿集团新疆赛尔能源有限责任公司六矿A_(3)煤层埋藏较浅,A_(3)015综采工作面属易自燃厚煤层工作面,因受采动影响造成地表出现裂隙,形成采空区漏风通道,大量新鲜空气通过地表裂隙迅速涌入采空区,为遗煤提供氧气,工作面回采期间存在采空区遗煤自燃隐患,采取注氮、均压等综合防灭火措施,控制采空区遗煤自燃,达到预期效果。

基于CFD的采空区三维流场分析及注氮参数优化研究

注氮是煤矿采空区发生自然发火征兆时常用的抑制措施,因其效果显著、安全可靠等特点被广泛应用于采空区灭火实践。注氮位置选取、注氮量的多少等直接影响注氮的效果及成本;采用数值模拟及现场实测相结合的方法,对注氮防灭火参数进行优化。以试验工作面为原型建立仿真物理模型,通过现场实测数据验证模型的有效性。在开展数值模拟试验的过程中,通过研究不同注氮位置、不同注氮流量等对采空区“三带”的影响,找到最优注氮参数,并进行了现场实测验证。研究结果表明,注氮口在进风侧距离工作面50 m处、注氮流量1 000 m~3/h时,注氮效果良好且成本最低。

朱集西煤矿自燃“三带”分布及注氮参数研究

为了研究朱集西煤矿11503综采工作面采空区自燃“三带”分布规律,在进、回风巷侧埋设束管对采空区内部氧气浓度变化规律进行现场实测,并采用数值模拟的方法研究不同注氮流量下自燃“三带”分布变化规律,确定合理的注氮流量。研究表明:增加注氮流量,采空区氧化带的分布范围和宽度会减小,当注氮流量增加至900 m^(3)/h以上时对减小氧化带宽度效果甚微,据此确定了合理的注氮流量900 m^(3)/h;通过计算得到11503工作面安全通风量为222 m^(3)/min。研究结果为该工作面的后续防灭火工作提供参考。

河口岸带氨氮原位快速分析方法研究

以自主研发的海水氨氮原位快速分析仪的现场可靠测量为目标,基于改进的靛酚蓝分光光度法建立了一种河口岸带氨氮的快速分析方法。论文基于正交实验分析,研究了不同盐度条件下,全自动快速测量最佳不完全显色反应时间,并确定了给定盐度范围内最佳不完全显色反应时间随盐度变化的规律。研究及分析结果表明,样品盐度为5‰的情况下,基于改进和优化后的靛酚蓝分光光度法,氨氮原位测量仪的检测耗时仅需要60s左右;样品盐度在0‰~25‰范围内,氨氮快速测量的最佳反应时间,随着盐度的增大而逐渐增加,样品盐度为25‰时,检测耗时为180s。光程长度为10cm、显色反应时间为60s时,盐度为5‰的氨氮样品检测下限为0.9945μmol·L^(-1),方法标准工作曲线R2大于0.99,证明改进后的靛酚蓝分光光度法可以满足河口岸带水体中氨氮的原位快速检测。将其应用于湛江湾水体中氨氮时间序列在线监测发现,监测期间氨氮浓度与水体盐度存在很好的负相关关系。与传统的人工检测和流动注射分析方法相比,自主研发的海水氨氮原位快速分析仪检测分析过程中样品和试剂消耗量极少(μL),反应时间短(盐度为5‰时60 s),可适用于河口岸带水体中氨氮的长时间序列原位及在线监测。

固溶处理对注射成形含氮双相不锈钢耐腐蚀性能的影响

将316L奥氏体不锈钢粉末和430铁素体不锈钢粉末制得的含氮双相不锈钢作为研究对象,在流动氩气保护下对含氮双相不锈钢进行固溶处理,固溶温度分别为1300、1320、1340℃。通过极化曲线和交流阻抗谱的检测,研究固溶处理温度对含氮双相不锈钢耐腐蚀性能的影响。结果表明:在流动氩气保护下1320℃固溶处理后,含氮双相不锈钢的耐点蚀性能比316L、430不锈钢好,自腐蚀电流密度、点蚀电位、电荷转移电阻分别为1.67×10^(-6)A·cm^(-2)、0.219 V、2.84×10^(3)Ω·cm^(2)。

基于压汞-低温液氮联孔与核磁共振分析的煤中孔径分布对比研究

煤中孔隙结构测量常用压汞法、低温液氮法和核磁共振法,因不同方法的原理和测试范围不同,导致结果无法统一使用,且压汞法中基质压缩效应会造成较大误差;为解决该问题,以沁水盆地晋城和长治矿区的3个高阶煤样为例,利用压汞、低温液氮吸附及核磁共振驰豫法分别测试煤样的孔隙结构,通过对压汞数据进行压缩性校正,与低温液氮数据在衔接孔径处拼接,对煤的孔隙结构进行了联合表征,并结合核磁共振对比分析了煤的孔径分布特征。结果表明:压汞数据校正后孔体积与低温液氮的结果更接近,偏差值在22.40%~38.51%;不同煤样采用联孔法进行孔隙结构分析的联孔位置在75~89 nm之间;联孔法煤样孔容积为0.00136~0.00458 cm^(3)/g,不同孔径孔容比例表现为过渡孔>大孔>中孔>微孔;与单一测试方法相比,联孔法与核磁共振法孔径分布更为接近,但同时也存在差异,联孔法表征的微孔、过渡孔、中孔和大孔平均分布比例分别为8.68%、45.58%、20.54%和25.20%,核磁法微孔、过渡孔、中孔和大孔平均分布比例分别为10.64%、64.21%、14.23%和10.92%,结果差异原因可能主要与压汞法、低温液氮法加压改变了煤的孔隙结构有关;通过核磁共振结果对比,联合校正后的压汞与低温液氮数据可提高煤中孔径分布测试结果的准确性。

全自动流动注射分光光度法测定锰厂排放水中的总氮

探讨了全自动流动注射分光光度法测定锰厂排放水质总氮含量的方法.在0~6.000 mg·L^(-1)浓度范围内呈线性关系,其回归方程为y=134.86x+116.7,相关系数R达到1.000 0,方法检出限为0.006 7 mg·L^(-1),加标回收率在98.6%~109%之间,实验结果表明线性关系良好,方法准确可靠.并采用全自动流动注射分光光度法和碱性过硫酸钾消解-紫外分光光度法对质控样品进行了对比测试,两种方法测定结果无显著差异,测定值均在标准值范围内.该法应用于电解锰厂排放废水水质总氮测定,具有操作简单、测试快速、准确度高、精密度好、检出限低的优点,能快速完成大批量样品测定.

稀燃缸内直喷氢内燃机NH_(3)-SCR后处理系统工作特性研究

氢内燃机具有零碳排放的特点,是实现低成本碳中和的重要手段。但是缸内燃烧的高温环境会生成大量的氮氧化物(NO_(x))排放,在日益严苛的排放法规要求下,利用选择性催化还原(SCR)NO_(x)的后处理技术是拓展氢内燃机大规模应用、不断提升其动力性和经济性的必要手段。首先通过试验验证了Cu基分子筛的NH_(3)-SCR后处理系统是一种高效的针对直喷氢内燃机的NO_(x)净化方案,接着使用简化反应机理对NH_(3)-SCR反应过程进行了建模仿真,并研究了反应温度、空速和氨氮比对氢内燃机边界下NH_(3)-SCR还原NO_(x)的影响。研究结果表明:在稀燃缸内直喷氢内燃机边界下,NH_(3)-SCR低温活性仍保持良好,后处理系统起燃温度(T_(50))为110℃,活性窗口(T 90)范围为150~425℃;在空速大于25000 h^(-1)时,NO_(x)转化效率都大于95%;当控制氨氮比为0.5,并保持反应温度在350~400℃时可保证最高的NO_(x)转化效率,实现直喷氢内燃机的近零NO_(x)排放。

膜进样质谱仪法在测量水体中过饱和溶解氮气的应用研究

高坝泄洪会导致水中溶解气体过饱和,使鱼类患气泡病甚至死亡。为探究大坝泄洪条件下,真实水体中的过饱和溶解氮的生成及其随泄洪条件的时空变化规律,利用膜进样质谱仪开展向家坝水电站泄洪条件下溶解氮的测量。结果表明,野外条件下采样运输过程中溶解气体的释放损失,导致膜进样质谱仪测量得到的溶解氮含量比通过利用总溶解气体和溶解氧的现场实测值计算得到的溶解氮含量低;利用质谱仪测量得到的溶解氮测值与总溶解气体测值之间同增的趋势性较好,但溶解氮测值与溶解氧测值之间相关关系较差。总结下来,向家坝电站泄洪导致坝下溶解氮、溶解氧和总溶解气体均达到过饱和,溶解气体饱和度在横向上基本均匀分布;受上游溪洛渡泄洪影响,向家坝坝前仍保持一定程度的溶解气体过饱和,并在垂向上表现出不均匀分布;泄洪生成的溶解气体饱和度随泄洪流量的增大而增大。为保证测量精度,建议原位开展测量,避免采样后长距离运输造成溶解气体的损失;在测量条件不满足的情况下,建议测量总溶解气体和溶解氧后进行溶解氮值换算。

东胜气田井筒O_(2)腐蚀评价与防护对策研究

膜分离制氮气举技术是东胜气田积液井、水淹井排出积液进而恢复产能的重要手段之一。但目前移动式膜分离制氮技术制取的氮气中O_(2)体积分数为5%左右,随着注入次数、注入量的增加,井筒管柱的O_(2)腐蚀问题愈发严重。该研究通过高温高压动态腐蚀试验明确了东胜气田腐蚀影响规律。试验表明:含O_(2)环境下,N80材质腐蚀速率稍大于P110材料;浸没程度对O_(2)腐蚀速率的影响为全浸没>半浸没>未浸没。据此优选抗O_(2)腐蚀缓蚀剂,室内评价试验表明:钼酸钠+葡萄糖酸钠型缓蚀剂缓蚀率达90%以上。现场3口试验井均取得了较好的缓蚀效果,最大缓蚀率达73.33%。

低瓦斯自燃采空区注氮工艺优化研究

为了分析注氮口埋深和注氮流量对采空区氧化带范围的影响,优化低瓦斯自燃煤层采空区注氮防灭火工艺,采用数值模拟和现场实测相结合的方法,分别模拟了未注氮,注氮流量为设计量且注氮口埋深为15 m、30 m、45 m、60 m和75 m,注氮口埋深为45 m且注氮流量为0.50倍、0.75倍、1.00倍、1.25倍、1.50倍和1.75倍设计量时采空区氧化带范围;现场实测了注氮口埋深为45 m且注氮流量为设计量时采空区氧化带范围。研究结果表明:随着注氮口埋深增加氧化带面积逐渐减小,注氮口埋深分别为15 m、30 m、45 m、60 m和75 m时,氧化带面积为未注氮时的100.8%、96.1%、90.5%、95.0%和79.1%;随着注氮流量增加,氧化带面积逐渐减小,注氮流量为0.50倍、0.75倍、1.00倍、1.25倍、1.50倍和1.75倍设计量时,氧化带面积为未注氮时的95.8%、93.4%、90.5%、87.1%、83.3%和79.2%;增加50%的注氮流量,氧化带面积减小7.9%,减少50%的注氮流量,氧化带面积增加5.9%。现场实测结果与数值模拟结果基本一致。对于9202工作面,合理的注氮口埋深为30~60 m,最佳注氮口埋深为45 m,注氮流量为设计量的1.00~1.50倍比较合适,最优注氮流量为设计量的1.25倍。