随钻声波测井隔声体刻槽影响的数值模拟研究*

针对随钻声波测井中钻铤波干扰以及刻槽后散射波问题,该文 利用时域有限差分法模拟钻铤波在随钻隔声体中的传播规律,首先考察在无限大流体中钻铤波在凹槽分界面处的散射特征,利用波场快照直观显示了钻铤波会有一部分能量在刻槽的固液界面转化为斯通利波。同时在有地层时分别对比了均匀内刻槽和外刻槽对钻铤波的衰减效果,发现在选择均匀内刻槽还是外刻槽时结果不仅与频率范围有关,而且与刻槽的深度也有关系。最后对比了槽宽较大的均匀凹槽隔声体和槽宽较小的渐变凹槽隔声体。可以得出结论,在设计随钻隔声体时,在10 kHz以下选择均匀外刻槽方式相对于内刻槽隔声效果会更好。随着刻槽槽深增加,外刻槽在10 kHz以下相比于内刻槽隔声性能优势更加明显。渐变刻槽在满足衰减钻铤波幅度要求的同时,散射波对后续地层波和斯通利波影响也更小。     

单极随钻声波测井换能器感知信号类型的研究

在假定钻铤是光滑的提前下,前人理论模拟了随钻测井的声压波形,但未发表关于理论波形与实验波形的比较的文章。为了认识测量信号所对应的力学类型及相应类型的钻铤波在钻铤内的分布,本文将理论模拟的随钻声波测井波形与实验波形进行对比。与前人单独考虑压电效应或井孔传播效应不同,本文模拟单极随钻声波测井响应时,将发射器、接收器、光滑钻铤和井孔结构作为一个整体,采用有限元法计算模拟了电压源激励下接收器纪录的声压信号和位移信号。将模拟的声压波形与电压信号进行比较,发现二者的钻铤波与斯通利波相对幅值相差较大,而模拟的径向位移波形更接近电压信号。进一步比较理论波形与小模型井内实验测量到的电压信号,证实电压信号更接近位移信号而与声压信号差异明显。这表明当钻铤光滑时,单极随钻声波测井换能器感知的主要是径向位移信号。研究还表明声压信号中的钻铤波能量主要集中在钻铤内壁,径向位移信号中的钻铤波能量主要集中在钻铤外壁。     

周期性非轴对称孔槽结构隔声性能数值模拟研究

设计了一种利用周期性非轴对称孔槽来消除钻铤模式波的隔声体结构,并采用三维有限元法对其隔声效果进行了数值模拟。结果表明:所提出的隔声体的隔声效果与孔槽圆弧的半径、孔槽间隔及孔槽的数目等有关;适当选取刻槽方式时,1 m长的隔声体对单极子源激发的钻铤波的衰减可达22 dB,但对偶极子源激发的挠曲波的衰减效果不明显。     

周期性轴对称凹槽结构隔声特性数值模拟

提出一种在钻铤上切割周期性轴对称凹槽方式构建隔声体,消除钻铤模式波的方法.结果表明,其隔声效果与凹槽深度H、长度L、凹槽数目N、凹槽截面形状以及钻铤壁厚有关.选择矩形截面凹槽、减小钻铤壁厚、增加凹槽深度都可有效提高隔声体的隔声效果,该结构最高可获得约36 dB的声衰减,基本满足随钻声波测井仪器对隔声效果要求.     

偶极随钻声波测井声压和径向位移响应的差异*

声波测井仪接收到的电信号通常是多个压电片响应的叠加,它主要是由声压还是径向位移响应转化而来,或是两种响应兼有目前未有定论。该文通过实轴积分法和复变函数法计算并对比分析随钻声波测井的声压和径向位移场,发现这两种响应特性有着显著的差异。首先,软地层的偶极随钻测井时,声压信号包含钻铤波和舒尔特波两个波群,而径向位移信号仅有钻铤波波群;其次,单极声源情况下,声压和径向位移信号的钻铤波能量分别集中在钻铤内、外壁,而偶极情况恰好相反,可见,钻铤按照单极情况的分析结果进行刻槽后,高频时的拖尾现象会影响偶极信号中舒尔特波对横波速度的反演。因此,阐明两类信号的差异对横波速度的反演和钻铤波的压制都具有重要意义。     

软地层随钻测井仪器偏心情况下低频四极子源 激发波场的数值分析*

为了探索测井仪器偏心对随钻低频四极子波场的影响,利用有限元法(多物理场耦合有限元软件包)对软地层井孔中随钻仪器偏心情况下低频四极子声源激发的波场进行了数值模拟。通过对随钻四极子测井波形的分析可知,当采用低频随钻四极子偏心声源激发时,测井波列中除传播速度与低速地层横波速度相当的地层四极子波模式外,还存在一个幅度非常低、传播速度略高于井孔流体中声速的模式波,该模式被对应钻铤弯曲波模式,且该模式波的幅度随着随钻四极子源偏离井孔中心距离的增大呈二次方规律增大,地层四极子模式波幅度呈三次方规律增加。     

圆弧片状声源向地层中辐射声场的有限差分模拟

提出了一种可用于随钻声波测井的非对称的圆弧片状声源,旨在发展一种能够在钻井过程中精确确定反射体位置的三维反射声波远探测方法。研究了在复杂的井孔条件(钻铤偏心、各向异性和不规则井孔形状)下,该声源向地层中辐射的声场的特征,进一步分析了不同井况条件对三维随钻远探测声波测井的影响。数值模拟结果表明,在圆形井孔、钻铤居中条件下,无论快速地层还是慢速地层,圆弧片状声源均能够向地层中定向辐射声波信号,其辐射指向性图主瓣3 dB角宽窄,旁瓣级低,方位分辨率较高,适用于随钻三维反射成像测井;井壁粗糙程度、地层各向异性等因素对声场特征影响不大,说明该方法适用于粗糙井壁和各向异性地层情况;钻铤偏心和井壁一侧的破坏对辐射声场的影响较大。对本文的模型而言,在破坏深度小于3 cm或者偏心距离小于2 cm时,声场仍有较好的方位特征,该方法仍然适用。而当破坏深度大于6 cm,声场指向性图出现多个幅值较大的角瓣,可能无法利用其确定反射体的方位。本文的研究结果为三维随钻反射声波仪的设计和研发提供了必备的理论基础。      

毫米波与太赫兹波在等离子体中传输特性

针对黑障区高速飞行器测控通信研究需求,在激波管设备上开展了Ka波段毫米波与太赫兹波在等离子体中传输特性的实验研究,获得了不同电子密度和碰撞频率的等离子体中传输衰减特性实验数据。采用辅助差分方程的时域有限差分（ADE-FDTD）方法对实验进行了数值模拟,数值模拟结果和实验结果有很好的一致性。实验结果和数值模拟结果均表明:太赫兹波信号在相同的实验等离子体中传输衰减比毫米波信号小得多,具有更强的穿透等离子体能力;毫米波与太赫兹波信号在等离子体中传输衰减量随着等离子体电子密度的增加而增加,二者的差值也增加;太赫兹波能够作为解决高密度等离子体中电磁波传输的有效技术手段。     

随钻核磁共振测井仪探测特性研究

随钻核磁共振测井是继电缆核磁共振测井之后的重要进步,具有直接探测原状地层孔隙度、束缚水、渗透率和流体饱和度等特点,受到广泛关注. 随钻核磁共振测井需要在更加恶劣的环境下作业,对探头尤其是对磁体有更高的要求. 该文研究随钻核磁共振测井的探测特性. 基于测量环境和工作方式,分析了随钻核磁共振测井静磁场设计中的特殊问题;利用有限元方法,分别模拟了MRIL-WD（哈里伯顿）、proVISION（斯伦贝谢）和MagTrak（贝克休斯） 3种随钻核磁共振测井仪的静磁场分布;根据数值模拟结果,提出可以抑制仪器随钻具运动（轴向转动、纵向钻进和径向振动）对测量的影响的随钻核磁共振测井静磁场方案,为自主随钻核磁共振测井仪器的设计、实现和优化提供了思路和注意事项.     

非均质各向异性地层中方位随钻电磁测井响应三维有限体积法数值模拟算法

方位随钻电磁测井是一种能够实时探测地层边界、实现地质导向与井眼成像的新型测井技术. 本文根据方位随钻电磁测井仪器的典型线圈系结构, 首先引入柱坐标系下非均质完全各向异性地层中电流源并矢Green函数, 并利用电磁场叠加原理给出倾斜发射线圈激发的电场以及倾斜接收线圈上感应电动势的计算公式; 然后应用电流源电场并矢Green函数的混合势克服非均质地层中电磁数值模拟的低感应数问题, 通过ρ 和z方向上Lebedev网格设法降低网格节点个数, 并且利用标准化算法确定柱坐标系下非均质单元上的等效电导率. 在此基础上, 用三维有限体积法建立柱坐标系电场混合势的离散方法, 得到一个交错网格上电场矢势和标势大型代数方程, 并用不完全LU分解以及稳定双共轭梯度法确定数值解. 最后, 通过数据模拟结果对算法的有效性进行检验, 并考察钻铤、线圈倾斜角度以及地层各向异性等参数对仪器响应的影响. 数值结果表明: 在柱坐标系下用三维有限体积法的数值模拟算法处理非均质各向异性层中方位随钻电磁测井响应可以得到很好的结果. 钻铤、电导率各向异性、层边界均对方位随钻电磁波测井响应产生较大的影响; 在电阻率较大的地层, 幅度比和相位差响应越小; 发射线圈和接收线圈同时倾斜时, 幅度比和相位差响应受地层的影响更灵敏.     

Leak noise propagation and attenuation in submerged plastic water pipes

Detection of water leaks in buried distribution pipes using acoustic methods is common practice in many countries. Correlation techniques are widely used in leak detection, and these have been extremely effective when attempting to locate leaks in metal pipes. However, a number of difficulties have been highlighted when trying to determine the position of leaks in plastic pipes. Of particular interest here is what happens to the leak noise when the pipe passes through an expanse of water, such as across a river or lake.In this paper, the low-frequency acoustic propagation and attenuation characteristics of a submerged plastic water pipe are investigated experimentally in the laboratory, supported by predictions from a theoretical model. It is found that, whilst the signal attenuation for a submerged pipe is increased relative to that for a similar in-vacuo pipe, energy does not, in fact, radiate into the water; furthermore, the attenuation is small compared with that for a pipe buried in soil.     

Generalized collar waves in acoustic logging while drilling

Tool waves, also named collar waves, propagating along the drill collars in acoustic logging while drilling(ALWD),strongly interfere with the needed P- and S-waves of a penetrated formation, which is a key issue in picking up formation P- and S-wave velocities. Previous studies on physical insulation for the collar waves designed on the collar between the source and the receiver sections did not bring to a satisfactory solution. In this paper, we investigate the propagation features of collar waves in different models. It is confirmed that there exists an indirect collar wave in the synthetic full waves due to the coupling between the drill collar and the borehole, even there is a perfect isolator between the source and the receiver.The direct collar waves propagating all along the tool and the indirect ones produced by echoes from the borehole wall are summarized as the generalized collar waves. Further analyses show that the indirect collar waves could be relatively strong in the full wave data. This is why the collar waves cannot be eliminated with satisfactory effect in many cases by designing the physical isolators carved on the tool.     

On the scattering of torsional elastic waves from axisymmetric defects in coated pipes

Long range ultrasonic testing is now a well established method for examining in-service degradation in pipelines. In order to protect pipelines from the surrounding environment it is common for viscoelastic coatings to be applied to the outer surface. These coatings are, however, known to impact on the ability of long range ultrasonic techniques to locate degradation, or defects, within a coated pipe. The coating dissipates sound energy travelling along the pipe, attenuating both the incident and reflected signals making responses from defects difficult to detect. This article aims to investigate the influence of a viscoelastic coating on the ability of long range ultrasonic testing to detect a defect in an axisymmetric pipe. The article focuses on understanding the behaviour of the fundamental torsional mode and quantifying the effect of bitumen coatings on reflection coefficients generated by axisymmetric defects. Reflection coefficients are measured experimentally for coated and uncoated pipes and compared to theoretical predictions generated using numerical mode matching and a hybrid finite element technique. Good agreement between prediction and measurement is observed for uncoated pipes, and it is shown that the theoretical methods presented here are fast and efficient making them suitable for studying long pipe runs. However, when studying coated pipes agreement between theory and prediction is observed to be poor for predictions based on those bulk acoustic properties currently reported in the literature for bitumen. Good agreement is observed only after conducting a parametric study to identify more appropriate values for the bulk acoustic properties. Furthermore, the reflection coefficients obtained for the fundamental torsional mode in a coated pipe show that significant sound attenuation is present over relatively short lengths of coating, thus quantifying those problems commonly encountered with the use of long range ultrasonic testing on coated pipes in the field.     

黏弹介质包裹的充液管道中低频轴对称波传播特性

研究埋地充液管道中低频轴对称波传播特性.将土壤考虑为黏弹介质,结合Kennard薄壳方程和Kelvin-Voigt线性黏弹性模型,引入土壤载荷矩阵,推导出土-管滑移情形下流体主导波和管壁压缩波的相速度表达式.通过数值模拟计算得到流体主导波和管壁压缩波的频散和衰减曲线并进行可靠性验证,分析两种波引起的管壁径向位移之比,讨...     

套管中弯曲型Lamb波数值仿真和物理模拟*

低密度水泥在低压易漏复杂井固井中的广泛应用使得声阻抗类测井方法难以准确、有效的评价固井质量。基于套管中传播的弯曲型Lamb对套后介质的声学参数和胶结状况的敏感性,本文通过理论计算和实验测量研究了不同频率下弯曲型Lamb 波衰减与水泥声学性质的关系,较低的工作频率会使得不同水泥阻抗下的衰减动态变化范围降低,且对水泥环第一界面的窜槽厚度也有很高的灵敏度;利用套管外胶结流体和固体时衰减率的差异,还可较好的区分套管外声阻抗接近的流体和固体;但弯曲型Lamb波的同一个衰减率值可与两个水泥声阻抗值相对应,因此需通过建立弯曲型Lamb波的衰减与水泥声阻抗的图版以提高低密度水泥固井质量评价的可信度。本文的计算分析结果对进一步应用弯曲型Lamb评价低密度水泥具有指导意义。     

On whistling of pipes with a corrugated segment: Experiment and theory

Corrugated pipes are commonly used because of their local rigidity combined with global flexibility. The flow through such a pipe can induce strong whistling tones, which is an environmental nuisance and can be a threat to the mechanical integrity of the system. This paper considers the use of a composite pipe: a shorter corrugated pipe segment embedded between smooth pipe segments. Such a pipe retains some flexibility, while the acoustical damping in the smooth pipe reduces whistling tones. Whistling is the result of coherent vortex shedding at the cavities in the wall. This vortex shedding is synchronized by longitudinal acoustic waves traveling along the pipe. The acoustic waves trigger the vortex shedding, which reinforces the acoustic field for a critical range of the Strouhal number values. A linear theory for plane wave propagation and the sound production is proposed, which allows a prediction of the Mach number at the threshold of whistling in such pipes. A semi-empirical approach is chosen to determine the sound source in this model. This source corresponds to a fluctuating force acting on the fluid as a consequence of the vortex shedding. The functional form of the Strouhal number dependency of the dimensionless sound source amplitude is based on numerical simulations. The magnitude of the source and the Strouhal number range in which it can drive whistling are determined by matching the model to results for a specific corrugated pipe segment length. This semi-empirical source model is then applied to composite pipes with different corrugated segment lengths. In addition, the effect of inlet acoustical convective losses due to flow separation is considered. The Mach number at the threshold of whistling is predicted within a factor 2.