套管参数对瞬变电磁测井响应的影响

瞬变电磁测井是一种利用套管井内的瞬变响应获取套管外地层电导率的有效方法,但是该方法受套管参数(电导率、磁导率、厚度)的影响很大.本文用频谱法分别在一维和三维三层介质套管井模型中求得了套管井内瞬变电磁响应的精确解,研究了套管对瞬变电磁响应的影响.在一维模型中,套管内表面的反射系数随套管电导率和厚度增加而增大,随磁导率的增加而减小;套管外表面的透射系数随套管电导率和厚度的增加而快速减小,然而其受磁导率的影响较小.在三维模型中,套管内表面的反射系数随套管电导率的增加而减小,随磁导率和套管厚度的增加而增大;套管外表面的透射系数则随套管电导率、磁导率和厚度的增加而减小.依据Doll电磁感应原理,用两个相邻井内深度点测量的瞬变电磁响应相减可以有效消除与地层电导率无关的无用信号.响应相减后的幅度与不同地层电导率的差在400 Hz以下的频率范围内呈线性关系.而0～100 Hz频率范围是瞬变电磁信号各频率分量的主要分布范围,因此用井内瞬变电磁方法对地层电导率进行测量具有可行性.     

弹性波数值模拟的延迟边界方法

在地震波场的波动方程数值模拟中,由于计算量的限制,必须加入人为的边界,使模拟计算可以在一定的空间范围内进行. 由于边界节点上的波场值不能像模拟区域内部的节点一样使用中心差分来计算,使其计算精度大大降低,从而产生边界反射. 为了消除边界反射,本文提出了延迟边界方法,根据弹性波在传播方向上等距离质点的等相位延迟性质和振幅衰减特性,由内部波场的时空分布,推算出边界波场的相位延迟的大小和振幅衰减系数,从而提高边界节点上的波场值计算精度,消除边界反射的产生.     

重磁场二维希尔伯特变换——直接解析信号解释方法

通过分析解析信号概念,指出目前重磁场解析信号事实上是重磁场梯度解析信号.在借助解析信号分量满足二维希尔伯特变换关系的基础上,提出重磁场直接解析信号的概念,并阐述重力异常及化极磁异常希尔伯特变换——直接解析信号的含义,并给出基于直接解析信号对位场增强的四种处理方法:直接解析信号模、水平分量模、改进Tilt angle和改...     

金属套管井中电磁测井响应的数值计算

分析了金属套管井中有限尺寸线圈的电磁响应特征,讨论了井眼泥浆参数、套管参数和不同线圈尺寸对电磁测井响应的影响,考察了金属套管中电磁测井对地层电阻率变化的灵敏度.径向非均匀介质的模拟计算表明,在套管井中井眼泥浆对电磁测井的影响较大,必须进行校正.在低频条件下,井间测量响应中金属套管与地层的电磁响应是非耦合的,两者可以分离.在套管参数一定时,套管响应与地层的响应的比值近似一个常数.电磁响应对地层电阻变化的灵敏度分析显示,井间电磁测量在储层研究尺度对地层电阻率变化响应灵敏,套管引起的衰减稳定.在其它参数相同的前提下,线圈直径的增大有助于有效电磁响应信号的增强,给大井间距测量提供了可能.不同磁导率金属套管的电磁响应分析表明,电磁测井中,采用非磁性或弱磁性套管要优于一般的铁磁性套管.     

基于Davis-Smith方法计算卫星磁强计零位补偿的误差特征研究

卫星所携带的磁通门磁强计会随时间发生零位漂移,因此需要对其进行补偿.基于行星际磁场的剪切阿尔芬波动特性,利用Davis-Smith方法可计算磁强计的零位磁场.本文利用数值模拟,分析了总磁场幅度B_T及压缩波动对Davis-Smith方法所产生零位补偿的误差特征.我们发现,B_T越大,零位补偿误差越大;且当压缩波动频率和剪切波动频率不同时,磁场各分量的零位补偿之间的比值与对应背景磁场的比值近似相等;压缩波动的幅度越小,零位补偿的误差趋于更小;此外,压缩波动的频率和初始相位等也会影响零位补偿的误差.这些误差特征可为提高零位补偿的可靠性提供重要的理论依据.     

小波域叠前地震资料衰减参数定性估计方法

叠前地震资料中,高频分量和低频分量随传播距离的衰减特性不同.本文给出了一种在小波域定性估计叠前地震资料衰减参数的方法.该方法利用连续小波变换提取共反射点道集的高、低频分量,以低频分量和高频分量之差定性反映地震波的衰减.通过累加不同偏移距的衰减,提高了估计的稳定性;采用幅度归一化方法,降低了信号幅值对衰减参数估计的影响.将本文提出方法与常用的基于叠后地震资料衰减估计方法用于某油田的地震资料处理,结果表明,本文方法得到的衰减估计结果能够更好地反映油气的空间展布.     

磁屏蔽室内磁性样品所产生干扰磁场的探讨

磁屏蔽室内岩石和各种沉积物样品所受的地磁场影响可以被有效地压制,然而磁性样品本身也会产生次级干扰磁场.本文通过理论模拟计算,定量评估了这种次级干扰磁场的影响.结果发现无论是单个还是聚集在一起的磁性样品,其产生的干扰磁场一般都低于磁屏蔽室的本底值(～300 nT).因此,弱磁性样品的相互影响可以忽略不计.这为进一步理解古...     

井间透射-反射波场分离方法及应用

近十几年来,井间地震在石油勘探领域发挥着重要作用.然而井间地震波极其复杂,给同相轴拾取、层析成像、偏移成像等工作带来了困难.因此,波场分离成为井间地震数据处理的一项重要内容.目前,不少学者研究了井间上下行波分离,纵横波分离等多种方法,但尚未出现相关文献研究透射波和反射波的分离方法.本文根据井间透射波和反射波在不同道集(共炮点集或共接收点集)中视速度极性的差异,首次提出了一种"透射.反射"波场分离方法.该方法首先在不同道集中利用τ-p变换进行视速度分离,得到反射上行波、反射下行波、透射上行波、透射下行波四个波场,然后选择对应的波场叠加,从而得到透射波和反射波.其中,透射波为井间层析成像提供了相对清晰的初至同相轴,尤其是横渡初至同相轴,以便进行到时提取;所得反射波为井中偏移成像提供了可靠的反射波数据,比人工切除透射波方法更为准确有效.本文通过理论模型试验和实际数据处理,证明了该方法的有效性和实用性.此外,在本文基础上,再进行纵横波分离处理可以得到更多的波场分量,为井间成像提供更有效的数据.     

CM4模型数据与台站实测数据的对比研究

本文利用第四代地磁场综合模型(Comprehensive Model 4,CM4),计算了1982—2002年隆尧地磁台站的磁层源磁场及其感应场、电离层源磁场及其感应场的地磁北向分量X、东向分量Y、垂直分量Z,分析了各场源磁场随时间的变化特征。磁层源磁场及其感应场呈现出11年和27天的周期性变化,有些年的27天周期性变化显著,有些年则不太显著;电离层源磁场及其感应场具有明显的季节变化,不同年相同季节的变化形态一致但幅度不同;日变化分析显示,磁静日和磁扰日期间的模型数据与台站实测数据变化一致性较好,相关性较高。     

1997年1月事件行星际扰动在三维背景太阳风中传播的数值模拟

利用一个三维的MHD模式,从数值预报的角度出发,以1997年1月事件的有关太阳观测为依据,构造比较符合物理实际的边值条件,通过三维数值模拟得到了稳定的比较接近真实的太阳风背景场.结果显示此次事件太阳风背景场的磁场关于赤道面不对称,有较明显的倾斜和扭曲,同时磁场较弱;等离子体各参量相对于事件的太阳源为东西和南北不对称结构.本文数值模拟了磁场南北分量Bθ的不同取法对背景场的影响,结果表明在源表面磁场有明显倾斜的情况下,内边界处磁场南北分量不宜假设为零.在此基础上,初步数值研究了行星际扰动在三维背景场中的传播过程,并与WIND卫星的观测进行了对比.     

Electromagnetic fields in a non-uniform steel-cased borehole

Since most oil wells are cased in steel, electromagnetic (EM) signals undergo severe attenuation as they diffuse across the casing. This paper examines an effect of non‐uniform casing properties on EM fields measured in a steel‐cased well embedded in a layered formation. We use a finite‐element method for computing secondary azimuthal electric fields in a cylindrically symmetric model, and analytically obtain primary fields for a homogeneous casing in a homogeneous whole space. Although steel casing largely masks EM signals induced into a layered formation, the induced signal is more pronounced in phase than in amplitude. The effect of casing non‐uniformity is quite large in measured fields but is highly localized. When electrical conductivity varies rapidly in the casing wall, the resulting EM fields also vary rapidly. A cross‐correlation function of these variations has strong peaks at two points, the interval between them being equal to the source–receiver distance. The high‐frequency coherent noise event caused by the non‐uniform casing can be greatly suppressed by low‐pass filtering to enhance EM signals indicating formation conductivity.     

含有倾斜薄裂缝孔隙地层中的井孔声场

应用三维交错网格应力-速度有限差分方法,数值模拟了含有倾斜裂缝孔隙介质地层中点声源所激发的井孔声场问题.为满足薄裂缝计算需求,开发了不均匀网格有限差分算法,提高了计算精度及计算速度.利用将孔隙介质方程参数取为流体极限的办法来处理裂缝中的流体,实现了流体-孔隙介质界面处的差分方程统一,使界面处的计算更加灵活方便.在验证了方法正确性的基础上,分别考察了单裂缝宽度、裂缝带宽度、裂缝倾斜角度以及孔隙介质渗透率等参数的变化对井轴上阵列波形的影响并进行了分析.结果表明,声波经过裂缝时可能产生反射横波及斯通利波,后者随裂缝宽度的减小而减小,而前者随裂缝宽度的改变,变化不大,在裂缝很小(20μm)时依然存在;裂缝带的宽度、密度越大,反射斯通利波越强;当裂缝(裂缝带)倾斜时,反射横波消失,但反射斯通利波受裂缝倾斜角度的影响较小;渗透率的改变对斯通利波的衰减影响较为明显.     

NUMERICAL MODELLING OF A NEW MULTI-FREQUENCY ELECTROMAGNETIC SYSTEM*

The amplitude of the horizontal magnetic field in the ground between two parallel wires, both carrying an alternating current in the same direction, is likely to have a saddle point if the separation between the wires is small and the frequency is low. The amplitude has a maximum in the vertical direction and a minimum in the horizontal. Rectangular geological structures in the ground which are centered between the wires have a varying effect on the magnetic fields at the surface. In general, the vertical magnetic field “crosses over” at the center of the structure. A shallow and flat lying conductor displays a broad flat type of profile when the horizontal magnetic field between the wires is measured. Changing the structure to a narrower but more conducting one at depth will provide a more pointed but still broad profile. The phase of the horizontal field is also increased. When the structure is a thin vertical dyke, the amplitude of the horizontal magnetic field anomaly due to the dyke rapidly decreases as the depth of the dyke is increased. The phase of the horizontal field is less sensitive to changes in depth of the dyke but is more sensitive to the conductivity ratio of the dyke and the half-space. The amplitude of the vertical magnetic field anomaly due to the dyke is only slightly influenced by conductivity contrast or the depth of the dyke. The phase of the vertical magnetic field, however, is strongly influenced by the conductivity contrast, particularly if the conductivity frequency product is greater than hundred. In essence, the field behaves like that of the conventional vertical loop source, but the fields are uniform over much larger areas. This suggests the possibility of using dip angle measurements for rapid reconnaissance.     

套管井贴壁声源激发的非轴对称声场的有限差分模拟及结果分析

套管井贴壁声波测井仪器在固井质量评价中的应用越来越广泛.本文利用三维交错网格高阶有限差分方法首次研究了贴壁声源在套管井中激发的非轴对称声场特征,给出了测井声源在贴壁固体弹性介质中激发时的数值模拟方法,模拟的全波波形与测井仪器在实际井中记录的波形吻合较好,这为利用数值模拟方式开发贴壁声波仪器的潜在应用奠定了基础.通过对套管井不同胶结状况下的数值模拟,得到了贴壁声源在套管井中激发的声场特征和传播规律,模拟结果显示加载声源的贴壁滑板的存在大大压制了套管中弯曲型Lamb波的幅度;套管中传播的拉伸波的幅度相对较强,其泄漏到水泥中的声波传播到水泥和地层界面时发生反射,反射波的幅度和相位特征携带了水泥环第二界面的胶结信息.数值计算结果为利用贴壁声源激发接收的波形实现水泥环第二界面井周不同角度上的胶结评价奠定了理论基础.     

基于黏弹滑移界面理论揭示套管中模式波的传播特征

目前固井质量评价主要是利用套管中模式波的幅度或衰减变化判断套管与水泥间的胶结状况.在超声测量频段（70~500 kHz）,现有声波测井仪器工作时在套管中激发的模式波类似薄板中的对称兰姆波（拉伸波）或反对称兰姆波（弯曲型兰姆波）.本文将黏弹滑移界面理论应用到套管和水泥的耦合界面,探讨了套管中的准兰姆波（包括拉伸波和弯曲型兰姆波）与套管后物质的耦合方式,拉伸波与套后物质主要以剪切刚度耦合,即便是0.01 mm的微环也会使得拉伸波的衰减明显降低,接近套后是流体时的响应特征;而弯曲型兰姆波与套管后物质主要以法向刚度耦合,这使得在套后胶结轻质水泥时弯曲型兰姆波对微环不敏感,在套后耦合常规水泥时微环的存在又会使得弯曲型兰姆波的衰减明显增强,衰减的增加说明其与套后物质的声耦合更紧密,也表明微环与常规水泥的等效声阻抗适当降低,更有利于弯曲型兰姆波传播时与套后介质实现法向刚度的匹配.拉伸波和弯曲型兰姆波对同一胶结状况的不同响应特征也为固井质量综合评价时区分不同的水泥胶结状况提供了可能.     

计算视复电阻率的新的近似公式

本文推导并评价了一个新的计算视复电阻率的近似公式,其视振幅表达式为|ρ_s（ω）|≈ρ_s（ω）|_{ρs（ω）=ρs（ω）|},视相位表达式为φ_s（ω）≈sum from i=1 to n（B_i（ω）φ_i（ω））,这里B_i（ω）是按各介质复电阻率振幅计算的稀释系数。此近似公式比迄今为止已发表过的同类近似公式都精确,可在频率域激电法数值模拟计算视复电阻率时应用。     

Reflection and transmission of inhomogeneous waves in a composite porous solid saturated by two immiscible fluids

This paper is concerned with reflection and transmission of a plane, elastic, and inhomogeneous wave striking obliquely at some discontinuity inside a porous medium composed of two distinct solids and saturated by two immiscible fluids. It is found that four P‐ and two SV‐waves are reflected, whereas four P‐ and two SV‐waves are transmitted at the interface. All reflected and transmitted waves are inhomogeneous in nature and specified with different directions of propagation and attenuation vectors. An expression for the Umov–Poynting energy flux vector is derived for the system. Continuity of energy flux along normal to the interface gives 12 required boundary conditions. Expressions of amplitude and energy ratios of various reflected and transmitted waves are derived. Variations in amplitude and energy coefficients of reflected and transmitted waves with angle of incidence are numerically studied for a porous matrix composed of shaley sandstone and clay, saturated with water and oil. The effects of change in oil saturation and volume fraction of clay are also observed on amplitude ratios. Numerical simulation reveals that the change in sign in the difference of capillary pressure across the interface causes jump in the values of amplitude ratios of all waves.     

频率域有限差分数值模拟地震波衰减和震电效应特征

地震波在地下含流体孔隙介质中传播时,会引起中观尺度的"局域流",进而产生地震波震电效应.基于Biot(1941)固结理论的准静态方程,在频率域中采用空间有限差分方法,正演模拟虚岩石物理岩样的地震波衰减和震电效应.与时间域虚岩石物理方法相比,该方法既可以直接求取任一频率下的地震波衰减和电势,便于应用于实际岩样的预测分析,也避免了讨论岩样外表面施加的力源函数表达式及时间剖分稳定性条件等问题.首先利用周期性层状介质模型验证了本文所描述方法的有效性,并进一步求取分析了周期性层状介质两种不同特征单元的渗流电流密度及电势,数值模拟结果表明由中观尺度"局域流"引起的震电效应电势振幅数量级在实验室测量范围之内,随后,分析研究了四种不同高渗介质占比值的地震衰减及震电效应特征.最后,将本文提出的震电效应数值计算方法推广至二维,并求取了二维斑块饱和模型的地震波衰减、速度频散、电势的振幅和相位角数值结果.     

套后介质声学性质对套管中三种模式波影响的对比分析

由于套管的厚度小于目前声波测井仪器工作频率下的波长,声波仪器工作时可在套管中激发Lamb波或SH模式波.目前评价水泥胶结质量的声波测井仪器主要是利用套管中的对称Lamb波(拉伸波,S0模式)或反对称Lamb波(泄漏弯曲波,A0模式)的相对幅度或衰减评价套管与水泥之间的胶结程度.Lamb波可看作是纵波和横波在套管边界的耦合形成的,在套管中还存在另一种非耦合的SH横波,偏振方向与套管轴向平行沿着周向传播.本文基于定向声源辐射技术,实现了对称Lamb波、反对称Lamb波的分波模拟技术,数值研究了套管后耦合不同声阻抗介质时,对称Lamb波、反对称Lamb波以及SH横波的测井响应,通过频散衰减曲线以及模式波的波形响应幅度的直观显示表明,由于套管中的SH波仅向固体水泥中辐射剪切波,这一传播特征与套管中的Lamb波相比可以极大提高套管-水泥界面胶结状况的测量灵敏度.Lamb波的固有缺陷是套管与两侧介质的较大声阻抗反差使得在井中测量套管后面水泥界面的灵敏度受到相当大的限制.     

Multichannel estimation of frequency-department Q from VSP data1

A Method of estimating attenauation from the first arrivals of VSP data is presented. The motivation is the desire to investigate the effects of scattering on wave propagation, and particularly the apparent attenuation and associated phase delay due to fine layering (the O'Doherty-Anstey effect). In order to take account of the frequency dependence of the predicted scattering attenuation, and to provide robust statistics for the estimates, a beam-forming method is used to measure the attenuation. This simularaneously estimates the slowness and polarization angle of the different wave modes, and results in attenuation measurements which are largely free of interference from reflected and mode-converted energy. By working in the frequency domain and measuring amplitude decay with depth, the frequency dependence of the attenuation is also accounted for. The beam-forming algorithm works in two passes, the first of which estimates slownesses and polarization angles over a small depth range, while the second uses the information from the first pass over a larger depth range to estimate attenuation. An approximate error analysis of the method shows that the standard variance of the estimated Q values is proportional to Q² and the data quality (measured by its spectral coherence), and inversely proportional to the square of the analysis depth range and the square of the frequency. Hence the depth resolution is traded against the stability of the results. The method is applied to a zero-offset three-component VSP. The data are of good quality, with a bandwidth ranging from 180 Hz in the shallow part to 100 Hz in the deepest part. Stable results were obtained using a 450 m depth range. Above about 50 Hz, there is little evidence of frequency dependence in the attenuation. There is a clear division in depth into layers of higher and lower attenuation, with values of Q typically between 50 and 200. Below 50 Hz, however, attenuation increases rapidly with decreasing frequency throughout the depth range, with values of Q of less than 10 at 15 Hz. This behaviour appears anomalous since on physical grounds we expect very high values of Q at low frequency, and we have no explanation for these observations.