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。     

Sediment greenhouse gases (methane and carbon dioxide) in the Lobo-Broa Reservoir, São Paulo State, Brazil: Concentrations and diffuse emission fluxes for carbon budget considerations

Carbon gases (methane, CH₄, and carbon dioxide, CO₂) were measured for the first time in sediments of the Lobo‐Broa Reservoir, near São Carlos in São Paulo State, Brazil. It is believed these are the first measurements of this kind in any of the many reservoirs located in Brazil. Even though the Lobo‐Broa Reservoir is classified as oligotrophic, the sediment gas concentrations were exceedingly high, ranging from 0.4–3 mmol L^?1 for CH₄ and 1–9 mmol L^?1 for CO₂. Both gases exceeded their in situ gas saturation values at these shallow water depths (7 m in central basin; 11 m at dam), resulting in numerous sediment bubbles. Organic matter was highly concentrated in the reservoir sediments, averaging 25.5% loss on ignition (LOI) (dam) to 26.9% LOI (central basin) for the 0–12 cm depth interval, with values as high as 29–30% LOI (12% organic carbon) in the surface 0–5 mm layer. The theoretical flux of dissolved pore water carbon gases to the sediment–water interface (SWI) averaged 3.4 mmol L^?1 m^?2 day^?1 CH₄ and 7.3 mmol L^?1 m^?2 day^?1 CO₂ for the surface 0–10 mm. From gas emission measurements at the water surface, it was calculated that 90% of CH₄ is consumed either at the SWI or in the water column, resulting in a loss of 0.31 mmol L^?1 m^?2 day^?1 of CH₄ to the atmosphere. However, only 20% of the total CO₂ gas transported across the water–atmosphere interface (36.3 mmol L^?1 m^?2 day^?1, or 1600 mg CO₂ m^?2 day^?1) was produced in the sediments. The remaining 80% of CO₂ probably comes from other carbon sources. With CH₄ oxidation in the aerobic water column, close to 30% of the carbon gas flux to the atmosphere could be accounted for by gas production of CO₂ and CH₄ in the sediments and their diffuse transport to the water column.     

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。     

夏季朱衣河二氧化碳分压分布特征及影响因素分析

为研究夏季三峡水库支流库湾-朱衣河的水体二氧化碳分压(p(CO_2))分布特征及影响因素,于2016年7月进行两次分层采样。根据水体的碳酸平衡原理和亨利公式计算水体p(CO_2)并利用水体中超额的二氧化碳分压(E_(p(CO_2)))和表观耗氧量(AOU)的比值(E_(p(CO_2))/AOU)表征生物好氧呼吸作用对p(CO_2)影响程度,研究结果为:上游表层水体的p(CO_2)变化范围大概在5.14~53.67 Pa,受使水体中H+减小的浮游植物光合作用影响较大,导致碳酸盐平衡向右移动,水体中CO_2极不饱和;5 m以下分层水体的p(CO_2)随着水深有变大的趋势,变化范围最低是26.04 Pa,最高是117.28 Pa,而?E_(p(CO_2))/?AOU值高达1.04~2.91,远高于评估上限值,其主要受外源碳汇入影响明显;河口的p(CO_2)大概为39.93 Pa,?E_(p(CO_2))/?AOU的值为0.64±0.01,受生物好氧呼吸作用影响显著;整体的p(CO_2)与温度(T)、pH、溶解氧(DO)、叶绿素ɑ(Chl-a)、硝氮(NO_3~-)存在显著的负相关关系,与浊度(TD)有显著的正相关性,与溶解有机碳(DOC)无显著相关性。     

First assessment of methane and carbon dioxide emissions from shallow and deep zones of boreal reservoirs upon ice break-up

Most studies dealing with greenhouse gas (GHG) emissions from large boreal reservoirs were conducted during the ice‐free period. In this paper, the potential methane (CH₄) and carbon dioxide emissions are estimated for two hydroelectric reservoirs, as well as for a small experimental reservoir from boreal latitudes (northern Quebec, Canada) at the ice break‐up event through diffusion (diffusive fluxes) and release of bubbles (bubbling fluxes). The results of this preliminary study suggest that the winter diffusive fluxes at the air–water interface of the sampled reservoirs represent < 7% of their cumulative carbon emissions during the ice‐free period. Furthermore, the release upon ice‐break of CH₄ bubbles accumulated under the ice cover during the winter could represent  2% of the summer carbon emissions from hydroelectric reservoirs in northern Quebec. The results presented herein suggest that the GHG emissions upon ice break‐up from the boreal reservoirs investigated are a small, but non‐negligible, component of their annual GHG emissions.     

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。     

某水源井四氯化碳污源调查及分析

通过对土壤四氯化碳含量的测试,研究了某水源井附近和某电器设备安装公司厂区土壤四氯化碳污染特征,明确了水源井地下水的污染源和污染途径,分析了土壤四氯化碳污染晕分布的控制因素。在该水源井及厂区附近的钻孔土样中均检出了连续分布的四氯化碳,最高浓度可达46.0 ng/g,在厂区内部四氯化碳主要分布在包气带中,而在厂区外围则主要分布在含水层中。该公司在历史上倾倒在地表的四氯化碳清洗剂,在厂区内通过垂直入渗进入含水层,而后受场地地下水流场的控制,沿地下水主要流向向厂区东部水源井水平运移。现状场地内不存在饱和浓度的四氯化碳污染团(DNAPL Poll)。土壤四氯化碳污染晕的分布主要受污染源的距离、岩性、水动力条件、四氯化碳的自然降解和水源井抽水等因素的控制。     

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.     

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。     

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。     

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。     

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。     

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。     

基于POD方法的圆型喷口射流速度场结构分析

大空间建筑中分层空调系统喷口送风射流运动卷吸会造成热量自上部非空调区向下部空调区转移,这是导致空调系统负荷增加的原因之一。本文搭建圆型喷口射流运动盐水模型实验台,利用粒子速度测量系统(PIV)提取喷口卷吸剪切层附近流场速度矢量场信息,借助特征正交分解方法(POD)剖析剪切层内的相干结构及其能量分布、竖向与横向速度特征值比例,为后期研究喷口卷吸运动引起的大空间对流转移热量提供实验与理论参考。