Flow field simulation of supercritical carbon dioxide jet: Comparison and sensitivity analysis

As a new jet technology developed in recent years, the supercritical carbon dioxide(SC-CO2) jet technology enjoys many advantages when applied in oil and gas explorations. In order to study the properties and parametric influences of the SC-CO2 jet, the flow fields of the SC-CO2 jet are simulated using the computational fluid dynamics method. The flow field of the SC-CO2 is compared with that of the water jet. The influences of several parameters on the flow field of the SC-CO2 jet are studied. It is indicated that like the water jet, the velocity and the pressure of the SC-CO2 jet could be converted to each other, and the SC-CO2 jet can generate a significant impact pressure on the wall, the SC-CO2 jet has a stronger impact pressure and a higher velocity than those of the water jet under the same conditions, the maximum velocity and the impact pressure of the SC-CO2 jet increase with the increase of the nozzle pressure drop, under the stimulation condition of this study, the influence of the SC-CO2 temperature on the impact pressure can be neglected in engineering applications, while the maximum velocity of the SC-CO2 jet increases with the increase of the fluid temperature. This paper theoretically explores the properties of the SC-CO2 jet flow field, and the results might provide a theoretical basis for the application of the SC-CO2 jet in oil and gas well drillings and fracturing stimulations.     

Experimental and numerical simulations of bottom hole temperature and pressure distributions of supercritical CO2 jet for well-drilling

The supercritical carbon dioxide （SC-CO2） drilling is a novel drilling technique developed in recent years. A detailed study of temperature and pressure distributions of the SC-CO2 jet on the bottom of a well is essensial to the SC-CO2 drilling. In this paper, the distributions of pressure and temperature on the bottom of the hole during the SC-CO2 jet drilling are simulated experimentally and numerically, and the impacts of the nozzle diameter, the jet length, and the inlet pressure of the SC-CO2 jet are analyzed. It is shown that, the bottom hole temperature and pressure increase with the increase of the nozzle diameter, and the bottom hole temperature reduces and the pressure increases first and then decreases with the increase of the jet length, indicating that the jet length has an optimum value. The increase of the inlet pressure can increase the temperature and pressure on the bottom, which has a positive effect on the drilling rate.     

Numerical simulation of the abrasive supercritical carbon dioxide jet: The flow field and the influencing factors

The supercritical carbon dioxide(SC-CO_2) jet can break rocks at higher penetration rates and lower threshold pressures than the water jet. The abrasive SC-CO_2 jet, formed by adding solid particles into the SC-CO_2 jet, is expected to achieve higher operation efficiency in eroding hard rocks and cutting metals. With the computational fluid dynamics numerical simulation method, the characteristics of the flow field of the abrasive SC-CO_2 jet are analyzed, as well as the main influencing factors. Results show that the two-phase axial velocities of the abrasive SC-CO_2 jet is much higher than those of the abrasive water jet, when the pressure difference across the jet nozzle is held constant at 20 MPa, the optimal standoff distance for the largest particle impact velocity is approximately 5 times of the jet nozzle diameter; the fluid temperature and the volume concentration of the abrasive particles have modest influences on the two-phase velocities, the ambient pressure has a negligible influence when the pressure difference is held constant. Therefore the abrasive SC-CO_2 jet is expected to assure more effective erosion and cutting performance. This work can provide guidance for subsequent lab experiments and promote practical applications.     

三重介质油藏斜井压力动态特征分析

针对裂缝与井筒连通,同时存在溶洞和裂缝、基岩和裂缝之间发生拟稳态窜流的三重介质,建立了这类三重介质油藏的斜井试井解释模型,采用汇源叠加等方法求得顶底封闭无限大三重介质油藏斜井在拉氏空间中的井底压力响应,绘制了相应的典型无因次压力曲线版图,分析了顶底封闭无限大三重介质油藏斜井的渗流规律,对其压力特征曲线进行了流动阶段的划分,并讨论了影响压力特征曲线的各种因素。所得的结果有利于提高对三重介质油藏斜井渗流规律的认识,为合理地运用斜井开发三重介质油藏提供理论依据。     

高温热采井水泥环缺陷对套管安全性的影响分析

针对水泥环缺陷导致套管承受非均匀载荷并引起套管失效的问题,建立了套管、含缺陷水泥环和地层耦合系统有限元计算模型。将温度场与应力场耦合,考虑套管强度降低,计算了水泥环缺陷形状、缺陷环向开度、缺陷深度及缺陷数量对套管安全的影响。应用塑性变形、剩余强度和安全系数来评价水泥环含缺陷井筒中套管的安全性,并分析了套管的失效模式。计算结果表明:完整井筒和水泥环含缺陷井筒中套管的屈服温度相差较大,水泥环缺陷环向开度和深度对套管安全的影响比较大。此研究为揭示套管失效机理提供了依据,对预防套损具有指导意义。     

水平井井筒内压力产量变化规律研究

对水平井生产系统进行分析,必然涉及到井筒中的流动问题,过去人们不考虑水平井井筒中的压降,这给水平井的生产系统分析带来较大的误差。本文考虑井筒摩擦和加速度对井筒压降的影响,同时考虑地层渗流和水平井筒流动,建立了水平井井筒流动与地层流动耦合的数学模型,以此获得了计算水平井井筒压降和产量分布的表达式,实例计算和分析了海上油藏一口水平井井筒的压力和产量变化规律。本文的研究为水平井的生产系统分析提供了理论基础。     

高喷灌浆技术在福安垸管涌治理中的应用

以福安垸为例,探讨高喷灌浆技术在管涌治理中的应用。在研究工程水文地质和工程地质的基础上,确定施工方案和质量控制措施,质检结果表明,高喷灌浆应用在老管涌险情治理中效果显著,供类似工程借鉴。     

高压喷射灌浆技术在下石陂水库除险加固中的应用

通过介绍高压喷射灌溉技术在下石陂水库除险加固中的成功应用,研究了此类病险水库的高喷灌浆防渗结构形式与工程布置,探讨了施工工艺和质量控制问题,供类似工程参考.     

超超临界机组汽水系统的设计特点分析

对邹县发电厂四期工程和系统状况进行了介绍,确定了主蒸汽系统和主给水系统管道的设计参数,选择了管道材料.对2×1000MW超超临界机组主蒸汽系统及主给水系统的主要设计特点进行了论述.     

高压旋喷灌浆技术在急水坝防渗加固中的应用

通过广西宾阳县露圩镇急水坝的高压旋喷灌浆施工,对土坝高压旋喷灌浆的布孔、灌浆、质量控制进行了论述,探讨高压旋喷灌浆技术在土坝防渗加固工程中的应用效果及前景。     

高喷灌浆技术在灵山县长安水库加固中的应用

介绍了灵山县长安水库高压喷射灌浆施工参数的确定过程及试验方法。论述了施工的工艺流程及各流程中的质量控制措施。     

IAPWS—IF97与IFC-67公式在超临界机组热力计算中的偏差分析

对IAPWS—IF97和IFC-67公式进行了简单对比。通过2种公式的计算偏差分析，说明了IAPWS—IF97公式在超临界600MW机组热力计算中应用的优势及推广的必要性。     

井筒环雾流传热模型及其在深水气井水合物生成风险分析中的应用

该文采用Hewitt流型判别法,表明深水含水气井测试时井筒内多为环雾流,考虑了气核与液膜间速度及热力学性质差异,建立了环雾流传热模型,与南海某深水气井实测数据对比,模型预测误差在5%以内。计算表明,忽略含水影响的气体单相模型在含水量大于0.1%时,泥线以上井筒压力和温度预测误差均超过10%,应用该研究建立的环雾流模型则可以得到更准确的结果。含水会使泥线以上一定范围内井段井筒温度显著降低,压力损失增大。产气量较低时,含水量对水合物生成风险基本无影响;产气量较高时,含水量会使得水合物生成区域下界下移,水合物生成区域增大,并使过冷度增大,更容易诱导水合物生成,水合物生成风险增大,需要增加水合物抑制剂用量,并加深注入位置。产水会使无水合物生成所对应的临界产气量增大,需要调整水合物抑制剂用量和注入位置。     

高压旋喷灌浆技术在钢板桩工程中的应用

洪湖钢板桩工程中在垂直铺塑与钢板桩两种工法联接处,采用高压旋喷桩墙形成封闭防渗体系。施工过程中,为保证质量,加强对中间关键环节的控制、检查,对出现的问题及时采取处理措施,有效地保证了工程质量。经开挖自检和钻孔检查,合格率100%,优良率75%,工程质量优良。施工结果表明,钢板桩和垂直铺塑接头处采用高压旋喷灌浆技术构筑防渗体是成功的。它具有效果好、速度快、质量有保证、经济适宜等特点,与其它工法相比具有明显的优势。     

超临界直流锅炉启动初期主汽温偏高原因分析

安徽华电宿州发电有限公司。1600MW超临界机组在调试启动过程中,多次出现主汽温偏高的问题,尤其以第1次并网带负荷最为频繁。其主要原因是燃烧热负荷小,总风量超过燃烧要求,投入的燃料量太多,给水流量偏大,减温水量设计不合理。对此,采取了降低启动点火时的给水流量,减少燃料的输入量,改善燃烧,增加燃烧热负荷,炉膛负压控制在-100Pa,锅炉总风量50～60万m^3／h,提高给水温度至100℃以上等措施,解决了启动初期主汽温偏高的问题,使各项参数均达到了设计要求。     

温度对碳纳米管束拉伸力学性能的影响:分子动力学研究(英文)

基于Tersoff势,采用分子动力学方法研究了碳纳米管束不同温度下的拉伸力学特征,对不同温度下碳纳米管束的力学特性进行了比较分析.结果表明,碳纳米管束的拉伸强度、断裂应变与杨氏模量都随着温度的增加而减小;拉伸强度和断裂应变随温度变化的趋势较为急剧,而杨氏模量随温度变化的趋势较为平缓;高温下的碳纳米管束的碳原子由于热震动导致碳管之间碳原子结键,从而导致碳纳米管束的各个力学特征急剧下降;同时碳管半径越小其拉伸强度越高,而碳纳米管束的拉伸强度约为单根碳纳米管的一半.     

水中游离二氧化碳与碳酸盐零共存现象研究

通过对水中游离二氧化碳和碳酸盐的滴定理论分析,并结合实际检测经验和数据,认为现行的SL83—94《中华人民共和国水利行业标准》中关于碳酸盐的测定方法中有值得商榷的地方,传统的数据处理方案也有不妥之处,并提出游离二氧化碳与碳酸盐零共存的概念,就指示剂的选择和数据处理等方面提出了自己的改进意见。     

前馈和积分分离在超临界机组协调控制的应用

介绍了静态前馈的线性关系和动态前馈控制技术。针对华电潍坊发电有限公司2×670MW超临界机组协调控制的特点,论述了超临界机组协调控制中的锅炉指令、燃料指令、给水指令和燃料发热量（BTU）校正的要点。分析了积分分离的应用效果。     

600MW超临界机组低压加热器正常疏水改造

介绍了某公司2×600MW超临界机组低压加热器疏水系统存在的问题,分析了某公司2×600MW超临界机组低压加热器正常疏水系统疏水不畅的原因,提出了改进措施及建议,在实际运行中取得了很好的效果。     

Simulation of gas kick with high HeS content in deep well

The phase transition, from asubcriticalstate to a gaseousstate, of the natural gas with high H₂S content and thesolubility of the H₂S component in the drilling fluid will make the multiphase flow behavior very different from the pure natural gas-drilling fluid two-phase flow under the gas kick condition in a deep well. With consideration of the phase transition and thesolubility of the H₂S component in the natural gas, a multiphase flow model is established. Thesimulation analysis results indicate that, for a typical case of a well depth of 4 325 m, the density of the 100%-H₂S natural gas can be 4 times higher than that of the 0%-H₂S natural gas, and thesolubility of the 100%-H₂S natural gas is 130 times higher than that of the 0%-H₂S natural gas. These will make the detection of the gas invasion more difficult. While the invasion gas moves up along the wellbore to a certain position, the phase transition and the release of the dissolved gas may cause a rapid volume expansion, increasing the blowout risk. The calculation results alsoshow that the risks of a gas kick can be reduced by increasing the wellhead back pressure.