分形油藏非牛顿幂律流体低速非达西不稳定渗流的组合数学模型

结合分形理论与渗流理论,对分形油藏非牛顿幂律流体低速非达西不稳定渗流的试井分析问题的数学模型进行了推导.该分形油藏模型由内域为非牛顿幂律流体低速非达西渗流,外域为非牛顿幂律流体达西渗流的同心圆域组成.在考虑井筒储存、表皮效应影响下,建立了该油藏的不稳定渗流有效井径组合数学模型,在3种外边界条件下求出了两个区域内压力在Laplace空间的解析解,应用Stehfest数值反演方法求得井底的无因次压力,分析了井底压力动态特征和参数影响.非牛顿幂律流体的幂律指数、分形参数均对典型曲线产生较大的影响,呈现出与牛顿流体和均质油藏明显不同的特征.这对非均质油藏非牛顿流体的不稳定试井分析及研究其非线性渗流特征均十分重要.     

考虑渗透率张量的非均质油藏有限元数值模拟方法

针对具有混合边界的非均质油藏,考虑全张量形式的渗透率,建立弹性微可压缩单相流体不稳定渗流问题的数学模型.根据变分原理,将压力微分方程的边值问题转化为泛函的极值问题,建立渗流模型的有限元方程.针对典型的均质和非均质渗流问题进行模拟计算,得到油藏内压力动态分布曲线,并分析曲线特征.研究表明,有限元法计算精度很高,适用于求解利用渗透率张量表征的非均质油藏渗流问题.为非均质油藏的开发和精细油藏数值模拟提供了理论依据.     

部分射开压裂直井渗流压力动态分析

建立符合非均质油藏部分射开地层实际的物理模型和三维各向异性矩形油藏的不稳定渗流数学模型,考虑不渗透顶、底边界和定压顶、底边界等边界条件的组合,通过无因次量纲变换、拉普拉斯变换、傅里叶余弦变换和分离变量等方法,得到拉普拉斯域的解析解,利用斯蒂芬森数值反演方法,得出实数域的压力数值解.绘制压力动态曲线,并进行敏感性分析.计算结果与数值模拟基本吻合,证实方法的可靠性.敏感性分析表明:压力动态曲线可分为早期线性流、中期径向流、晚期球形流、边界控制流四个流动期.裂缝长度主要影响早期线性流,渗透率各向异性主要影响中期径向流,储层射开程度和裂缝方位主要影响晚期球形流,边界条件和油藏宽度主要影响边界控制流.该方法可以确定最优射开程度、垂向渗透率等参数,为油藏工程分析和压裂工艺设计提供指导.     

分形复合油藏非牛顿幂律流体不稳定渗流的数学模型

对不稳定渗流的数学模型进行了推导并建立了分形复合油藏不稳定渗流模型.在无限大地层、有界定压、有界封闭三种外边界条件下分别求出了它们在Laplace空间的解析解.对于两区的特殊情况,分析了井底压力动态特征和参数影响,制作了典型曲线.非牛顿幂律流体的幂律指数,分形参数均对典型曲线产生较大的影响,呈现出与牛顿流体和均质油藏明显不同的特征.这对于非均质油藏非牛顿流体的不稳定试井分析和研究非线性渗流特征都是十分重要的.     

压敏三重介质油藏压力响应特征

建立由基岩系统、裂缝系统和溶洞系统组成,并考虑溶洞渗透率随压降的增加呈指数减小的压敏三重介质油藏试井解释模型,采用隐式差分格式对考虑井筒储存和污染效应的情况进行了求解.研究表明:无因次渗透率模数导致压力及压力导数明显增大,窜流系数影响窜流阶段出现的早晚,弹性储容比影响压力导数曲线"凹陷"的宽度和深度,外边界条件的影响则和普通三重介质明显不同,表皮系数主要影响全部压力和压力导数早期的"凸起",而无因次渗透率模数则主要影响压力和压力导数的后期.     

聚合物驱两相流试井参数敏感性

考虑油水两相、生产历史、油藏平面非均质性、井筒储存和表皮效应等因素,建立了生产历史阶段聚合物驱数学模型和不稳定试井阶段的流线模型,用流管法对解释模型进行了数值求解.研究表明:随着油水粘度比的增大,压力及压力导数曲线向上平移,随着生产时间的增加,储层的有效渗透率降低,当高渗透条带沿主流线方向分布时,注水井压降导数曲线反映不出油水前缘的影响,而随着聚合物注入浓度的增大,压力导数曲线下凹出现的越来越早.     

利用显微红外光谱技术表征非均质油气储层裂缝特征——以任丘潜山蓟县系雾迷山组碳酸盐岩储层为例

油气储层裂缝既是重要的储油空间,又是油气运移的主要通道,因此,裂缝表征非常重要。然而储层岩石具有强烈的非均质性,如何精确表征非均质储层裂缝是需要亟待解决的问题。利用显微红外光谱技术可以对矿物分子的光谱曲线进行分析,得到不同的峰值特征,精确获得岩石介质成分、裂缝的大小、裂缝充填物特性等。以任丘潜山型碳酸盐岩非均质储层为例,基于显微红外光谱技术,通过分析岩心光片显微红外成像光谱图和不同特征区域的光谱曲线,获得了目标样品岩石介质的物化特性和空间分布特征,预测了裂缝可能发育的区域, 并分析了裂缝的有效性。结果表明,岩心样品主要介质为白云岩;储层裂缝中含有烃类有机物和盐水包裹体,它们主要赋存于白云岩介质中;裂缝充填物中盐水包裹体所占比例为51.7%,烷烃有机物所占比例为26.0%,裂缝发育从岩心样品左上方区域延伸至右下方区域,表明该延伸区域可能是流体运移的通道;盐水包裹体会阻碍油气的运移,导致裂缝的渗透率降低;实验测得岩石裂缝宽度为1~1.5 mm,属于大裂缝,油气可以顺利通过,因此,裂缝的有效性好。研究表明利用显微红外光谱成像技术表征非均质储层裂缝特征是切实可行的,为非均质油气储层精确表征提供了一种新方法。     

分形低渗透缝洞型油藏非线性渗流规律

引入分形理论,建立考虑低速非达西效应的分形三重介质缝洞型油藏数学模型,通过Laplace变换及Stehfest数值反演方法求出井底压力,借助Matlab编程绘制压力动态曲线,划分渗流阶段,分析渗流规律,进行非线性参数敏感性分析.最后结合实际算例,验证模型的正确性.结果表明：分形三重介质油藏渗流过程分为早期纯井储,过渡流,缝洞窜流,拟径向流,基质与溶洞、裂缝窜流及总体径向流6个渗流阶段;低速非达西效应对渗流的影响随时间的推移逐渐增大;启动压力梯度越大,总径向流阶段压力动态曲线上翘幅度越大;分形系数影响整个渗流过程,随着分形系数的增大,裂缝迂曲程度随之增大,致使渗流阻力增加,引起压力动态曲线整体上移幅度增大.     

新型填料湿化器热力性能实验研究

湿化器是湿空气透平(HAT)循环的关键部件。本文对加压条件下采用新型SiC泡沫陶瓷填料的湿化器的热力性能进行了实验研究,分析了操作压力、水气比等参数对湿化过程的影响。在此基础上,通过归纳实验数据,建立了能够预报湿化器变工况性能的无因次关联式。研究表明,随湿化器内操作压力增加,出口空气含湿量及气液两相间传热量减小,出口空气温度增加。随水气比增加,填料传质单元高度减小,气侧体积传质系数和气侧体积传热系数均提高。     

利用核磁共振录井技术定量评价储层的分选性

储层分选性是反应储层物性、 均质程度及沉积环境好坏的重要标志. 分选系数一般是通过实验室的粒度分析（粒度分选）或压汞试验（孔喉分选）来得到,利用核磁共振评价储层孔喉分选性多是通过建立T_2g与常规分选系数之间的关系公式来得到. 在深入研究常规分选系数计算原理的基础上,结合T₂谱累积曲线对储层分选性的反应,提出了2种不依附于实验室分析、可由单个样品来定量评价储层分选性的新方法,并且取得了与其他方法较为一致的评价结果. 该项研究打破了录井不能定量评价储层分选性的局面,对于快速指导油气勘探开发具有十分重要的意义.     

实际闭式中冷回热布雷顿循环新析

用有限时间热力学方法分析了变温热源条件下实际闭式中冷回热布雷顿循环的性能,导出了无因次功率及效率的解析式。由数值计算,分析了循环最优功率和最优效率时的最佳中间压比分配,并研究了中冷度等一些主要循环参数对性能的影响,发现了不管有无回热,中冷都可以提高循环效率这一新结果。     

分形裂缝性页岩气藏多段压裂水平井瞬态压力特征

基于分形理论和连续性假设,考虑页岩气吸附解吸、基质-裂缝窜流等机制,建立分形裂缝性页岩气藏多段压裂水平井试井解释模型,并通过拉氏变换、点源函数及压降叠加原理等方法得到模型的解.绘制无因次压力随时间变化的双对数曲线,研究分形裂缝性页岩气藏多段压裂水平井的压力特征,分析分形指数、分形维数等参数对压力动态的影响.结果表明：分形裂缝性页岩气藏多段压裂水平井的压力动态可划分为7个流动阶段;分形指数越大或分形维数越小,晚期径向流直线段的斜率越大;其它参数对水平井的压力动态也有一定的影响.     

Four-Objective Optimizations for an Improved Irreversible Closed Modified Simple Brayton Cycle

An improved irreversible closed modified simple Brayton cycle model with one isothermal heating process is established in this paper by using finite time thermodynamics. The heat reservoirs are variable-temperature ones. The irreversible losses in the compressor, turbine, and heat exchangers are considered. Firstly, the cycle performance is optimized by taking four performance indicators, including the dimensionless power output, thermal efficiency, dimensionless power density, and dimensionless ecological function, as the optimization objectives. The impacts of the irreversible losses on the optimization results are analyzed. The results indicate that four objective functions increase as the compressor and turbine efficiencies increase. The influences of the latter efficiency on the cycle performances are more significant than those of the former efficiency. Then, the NSGA-II algorithm is applied for multi-objective optimization, and three different decision methods are used to select the optimal solution from the Pareto frontier. The results show that the dimensionless power density and dimensionless ecological function compromise dimensionless power output and thermal efficiency. The corresponding deviation index of the Shannon Entropy method is equal to the corresponding deviation index of the maximum ecological function.     

A FREQUENCY-DOMAIN METHOD OF STRUCTURAL DAMAGE IDENTIFICATION FORMULATED FROM THE DYNAMIC STIFFNESS EQUATION OF MOTION

This paper introduces a frequency-domain method of structural damage identification. It is formulated in a general form from the dynamic stiffness equation of motion for a structure and then applied to a beam structure. Only the dynamic stiffness matrix for the intact state appears in the final form of the damage identification algorithm as the structure model. The appealing features of the present damage identification method are: (1) it requires only the frequency response functions experimentally measured from the damaged structure as the input data, and (2) it can locate and quantify many local damages at the same time. The feasibility of the present damage identification method is tested through some numerically simulated damage identification analyses and then experimental verification is conducted for a cantilevered beam with damage caused by introducing three slots.     

长脉冲激光作用下薄膜表面鼓包的形成机理

 在光学薄膜的激光损伤实验中，可以在显微镜下观测到激光辐照引起的尺寸较大、形状对称性很好的鼓包。从杂质气化的角度，应用弹性力学的球壳受压膨胀模型，分析薄膜表面鼓包的形成机制，同时得到了相应情况下薄膜的损伤机制。结果表明，半径越大杂质在激光辐照下越容易引起薄膜破坏，填埋得越浅的杂质也越容易引起薄膜破坏。杂质诱导破坏机制下，薄膜的裂纹首先出现在杂质附近的薄膜基体中。在薄膜中出现裂纹的临界状态时，半径越大、填埋得越深的杂质所引起的鼓包尺寸越大、高度越高。这种热力耦合模型，弥补了现有理论的不足，进一步完善了现有理论。     

Modeling and analysis of stick-slip and bit bounce in oil well drillstrings equipped with drag bits

Rotary drilling systems equipped with drag bits or fixed cutter bits (also called PDC), used for drilling deep boreholes for the production and the exploration of oil and natural gas, often suffer from severe vibrations. These vibrations are detrimental to the bit and the drillstring causing different failures of equipment (e.g., twist-off, abrasive wear of tubulars, bit damage), and inefficiencies in the drilling operation (reduction of the rate of penetration (ROP)). Despite extensive research conducted in the last several decades, there is still a need to develop a consistent model that adequately captures all phenomena related to drillstring vibrations such as nonlinear cutting and friction forces at the bit/rock formation interface, drive system characteristics and coupling between various motions. In this work, a physically consistent nonlinear model for the axial and torsional motions of a rotating drillstring equipped with a drag bit is proposed. A more realistic cutting and contact model is used to represent bit/rock formation interaction at the bit. The dynamics of both drive systems for rotary and translational motions of the drillstring, including the hoisting system are also considered. In this model, the rotational and translational motions of the bit are obtained as a result of the overall dynamic behavior rather than prescribed functions or constants. The dynamic behavior predicted by the proposed model qualitatively agree well with field observations and published theoretical results. The effects of various operational parameters on the dynamic behavior are investigated with the objective of achieving a smooth and efficient drilling. The results show that with proper choice of operational parameters, it may be possible to minimize the effects of stick-slip and bit-bounce and increase the ROP. Therefore, it is expected that the results will help reduce the time spent in drilling process and costs incurred due to severe vibrations and consequent damage to equipment.     

Mechanism study of sidewall damage in deep silicon etch

The formation and etch mechanism of sidewall damage in deep silicon etch using standard Bosch process have been investigated in this work for the first time. The sidewall damage occurs at a certain depth where the sidewall is not sufficiently protected from lateral etch during long-time ion bombardment, and further, we demonstrate that the formation of sidewall damage is not only related to passivation film on the trench sidewall, but also closely relies on ion-enhanced etch mechanism. In addition, it is found that the starting depth of sidewall damage is almost inversely proportional to etch pressure and ion incidence angle, which can be attributed to a broader ion angular distribution (IAD) at higher chamber pressure. Then, a quantitative etch model based on IAD function has been also proposed to investigate the dependence of the starting depth of sidewall damage on ion incidence angle. Finally, by optimizing process parameters, high-quality etch profile without any observable sidewall damage has been successfully achieved at etch pressure of 60 mTorr.