地震绕射波弱信号U-net网络提取方法

绕射波携带大量小尺度非均匀地质体信息,对于提高地震勘探分辨率具有重要意义.绕射波能量远小于反射波,在地震记录中常被强反射波掩盖,因此分离并单独成像绕射波,为探测小尺度非均匀地质体的关键问题.传统绕射波分离方法受限于理论模型假设,对陡倾角反射波去除效果不佳,且易对绕射波造成损伤.基于经典编码-解码框架下的U-net网络和注意力机制,本文提出了一种绕射波智能分离方法,通过编码器自动提取地震数据中的绕射波特征,再由解码器恢复绕射波,从而隐性去除反射波.该方法作为端到端的机器学习,训练后的U-net网络可自适应地分离绕射波.本文通过数值模拟数据与实际数据构建训练数据集,利用训练后的U-net网络分离绕射波,并将结果偏移成像.数值模型测试和实际资料应用表明,融合了注意力机制的U-net网络能够有效压制反射波能量,保留绕射波动力学特征,克服了传统绕射波分离方法难以去除陡倾角反射的局限性,其提取的绕射波弱信号特征较为完整,能够进一步提高地震成像分辨率,在小尺度断裂刻画上具有优势.     

局部倾角滤波和预测反演联合分离绕射波

地震绕射波源于介质非连续性,从地震记录中将绕射波分离出来并进行成像,其结果对研究诸如碳酸盐岩缝洞储层这类复杂非均质储层具有重要意义.对炮集记录进行平面波分解,在地层倾角不大的假设下,反射波和绕射波同相轴在平面波分解剖面上存在较大的倾角差异.基于此,我们提出分步进行绕射波分离的方法:(1)利用局部倾角滤波方法将绕射波的较大倾角信息成分分离出来,此时,余下的部分包含有反射波和残留的低倾角绕射波信息;(2)利用频率-空间域预测反演方法从上述含有反射波和残留的低倾角绕射波信息中分离出残留绕射波成分;(3)将两次分离的绕射波信息相加得到最终的绕射波估计.用该方法能够得到相对完整的绕射波信息,有效地克服了靠单一的倾角差异进行绕射波分离时明显损失低倾角信息,从而影响绕射波成像结果横向分辨率这一问题.理论与实际资料试算验证了该方法的有效性.     

利用最小二乘自适应滤波实现绕射波分离

尺度目标体的绕射波能量较弱,常被能量较强的反射波淹没,与反射波一起成像难度较大.因而,实现绕射波成像的核心问题之一为绕射波与反射波分离.通常建立反射波模型的方法有Radon变换等域变换类方法,但该类方法在减去反射波能量上存在问题.为更彻底实现压制反射波目的,本文引入自适应滤波方法,该方法较简单的减去法能更好预测反射波能量.实际资料应用效果表明,最小二乘自适应滤波方法能更好突显单炮记录上绕射波特征,得到的叠加剖面中反射波去除更为彻底干净,偏移剖面中小断层、断点、尖灭点等小尺度地质体成像清晰.     

地震勘探中的边缘绕射波及其动力学识别方法

深层、小尺度岩性体的高分辨率探测已超出常规的反射波地震勘探能力,而绕射波成像技术具有高分辨率.综述国内外绕射波的研究现状,本文将发展已久却未受到高度重视的几何绕射理论引入到勘探地震中,从物理直观性上阐述了边缘绕射波的运动学和动力学特征,详细分析了沉积不连续、透镜体和正断层产生的边缘绕射问题.目前主要依据走时差异识别边缘...     

基于倾角-偏移距域道集的绕射波成像

地震绕射波是地下非连续性地质体的地震响应,绕射波成像对地下断层、尖灭和小尺度绕射体的识别具有重要的意义.在倾角域共成像点道集中,反射波同相轴表现为一条下凸曲线,能量主要集中在菲涅耳带内,绕射波能量则比较发散.由于倾角域菲涅耳带随偏移距变化而存在差异,因此本文提出一种在倾角-偏移距域道集中精确估计菲涅耳带的方法,在各偏移距的倾角域共成像点道集中实现菲涅耳带的精确切除,从而压制反射波.在倾角-偏移距域道集中还可以分别实现绕射波增强,绕射波同相轴相位校正,因此能量弱的绕射波可以清晰地成像.在倾角域共成像点道集中,反射波同相轴的最低点对应于菲涅耳带估计所用的倾角,因此本文提出一种在倾角域共成像点道集中直接自动拾取倾角场的方法.理论与实际资料试算验证了本文绕射波成像方法的有效性.     

平面波预测滤波分离绕射波方法研究（英文）

常规地震资料处理通常将地震波场当作反射波处理,绕射波的存在会降低处理成果的分辨率,因此将其当做干扰噪音进行压制。然而,绕射波往往包含了非常重要的地质信息(裂缝、溶洞、断层等特殊构造),即使偏移将绕射波归位,因为绕射波能量较弱也会被反射同相轴遮盖。将反射波和绕射波进行分离并单独成像处理,将提高绕射目标构造的成像精度。根据在平面波域反射波拟线性、绕射波拟双曲的形态差异,本文利用平面波预测滤波技术对平面波炮记录进行波场分离。首先,采用平面波解构滤波器估算地震同相轴的局部倾角,利用局部倾角信息预测并提取反射波,然后从全波场中减去反射波,间接分离出绕射波,对绕射波成像可获得高分辨率的绕射目标体成像结果。通过对2D SEG盐丘模型进行波场分离与成像,分析表明:本文采用的平面波预测滤波技术解决了平面波解构滤波的极性反转问题,保持了绕射波原有的相位信息,保证了波场分离后的绕射波场保真度,成像结果表明用平面波预测滤波方法提取的绕射波进行偏移可改善非均质目标体的成像精度。     

绕射波逆时偏移成像方法研究

地震剖面中的绕射点反应地下断层、尖灭、溶洞等不连续体的位置信息,因此绕射波对于实现小尺度构造的精细成像具有重要意义.基于逆时偏移的绕射波成像方案包括乘法成像条件法和倾角域拾取法.乘法成像条件利用正\负倾角构造剖面相乘实现绕射点的定位,倾角域拾取法则根据绕射波能量在角度域的特征进行拾取.其中,通过Hilbert变换和伴随...     

基于斜率分析的倾角域绕射波分离及成像研究（英文）

碳酸盐岩缝洞型储层所含缝、洞尺度差异大、岩性和速度变化剧烈,造成复杂的绕射响应特征。部分缝洞体尺度小产生的绕射能量较弱,在成像剖面上被连续反射层掩盖,而难以识别。基于此,本文发展了一种倾角域道集的绕射波成像方法,提高对成像剖面上小尺度绕射构造的分辨能力。借助高斯束偏移技术抽取倾角域成像点道集,根据在倾角域道集上绕射同相轴拟线性、反射能量拟抛物的几何形态差异,基于斜率分析方法实现波场分离,并采用汉宁窗函数提高绕射波分离效果,将分离后的绕射波倾角域道集水平叠加得到绕射波成像结果。理论分析和数值模型测试结果表明:在窗函数的基础上,应用基于斜率分析的波场分离方法得到的绕射波倾角域道集能够更好的压制噪声,叠加后的绕射波成像剖面中绕射构造更加清晰。     

潜山裂缝型油气藏绕射波属性预测方法

潜山裂缝型油气藏的勘探重点之一是裂缝发育区域的预测,本文发展了应用绕射波属性数据进行裂缝分布描述的方法,并提出利用主成分分析方法,结合绕射信息及敏感属性提取,给出裂缝预测的工作流程。模型试算表明绕射波场能够较好地反映构造裂缝的分布规律。将该方法应用于裂缝型油藏精细描述中,绕射波分析方法能够更为精细、全面地描述潜山裂缝型油气藏中裂缝的分布规律。      

基于机器学习的时间反转散射体检测方法

地下小尺度散射体的检测和识别对于提高地震勘探的分辨率具有重要意义,目前业界普遍采用绕射波分离及成像方法检测地下散射体,而绕射波成像的质量主要取决于绕射波和反射波波场分离的程度.本文将被动源震源定位问题中常用的时间反转原理引入到地下散射体检测中,首先通过分析被动源和主动源模型反传波场的聚焦状态,验证了时间反转原理应用于地下散射体检测中的可行性;并引入机器学习中的朴素贝叶斯分类算法,给出适用于时间反转散射体检测的分类算法框架,计算模型中每个点成为散射体的概率,最终检测出地下散射体最有可能存在的位置.散射体模型和Sigsbee2a模型的试算结果证实了本文方法在不需对反射波和绕射波分离的情况下,即可实现对地下散射体的检测和定位,同时由于考虑了多次散射的影响,检测结果能准确反映地下散射体的位置.     

On the synchronism in the events within the core and on the surface of the earth: the changes in the organic world and in the polarity of the geomagnetic field in the phanerozoic

The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes in the organic world.     

On the gravimetric undulations of the geoid and the deflections of the vertical

Summary The author mentions the aims of the World-wide gravity project he established in the Ohio State University in Columbus, in 1950. He outlines the practical procedure of the gravimetric computations of the undulationsN and the vertical deflection components and and emphasizes that only by the global international cooperation and additional gravity observations at sea carried out during the last decade it has been possible to gather to Columbus the needed gravity material. Since there exist still large gravimetrically unsurveyed areas it is of vital significance to study what gravity anomalies are best to be used for these regions. The given figures concerning the accuracy of theN, and , estimated theoretically and obtained in practice, indicate that in the gravimetrically well surveyed parts of the world like in Europe and the United States we can get gravimetrically on basis of existing gravity material theN-values with accuracy of about 5–10 meters, and and with the accuracy of about 1. The geoid undulationsN are already computed in Columbus for more than 6000 points of the northern hemisphere. The sample maps show the interesting geoid of Europe and vicinity between the latitudes 60° and 30° and longitude 5° W and 30° E, drafted on basis of more than 1000N-values computed at the corners of 1°×1° squares. It is interesting to realize that the geoid undulations in all this area are positive, the extreme values being between 40 and 50 meters. The geophysical significance of the geoid maps of this kind is pointed out.     

On the maintenance of the axisymmetric part of the flow in the atmosphere

Summary The maintenance of the axisymmetric component of the flow in the atmosphere is investigated by means of a steady-state, quasi-geostrophic formulation of the meteorological equations. It is shown that the meridional variations in the time-averaged axisymmetric variables can be expressed as the sum of three contributions, one being due to the eddy heat transport, another to the eddy momentum transport, and a third to the convective-radiative equilibrium temperature which enters the problem through the specification of a Newtonian form of diabatic heating. The contributions by the large scale eddies are evaluated through the use of observed values for the eddy heat and momentum transports.The contributions from each of the three forcing mechanisms to the temperature and zonal wind fields are invstigated individually and found to be of about equal importance. The sum of the three contributions are also presented for the temperature, the zonal wind, the stream function associated with the mean meridional circulation and the corresponding vertical motion. Although the results fail to reproduce the main observed features of the lower stratosphere, they are found to be in good agreement with observations in the middle latitude troposphere. At any pressure level, for example, the computed mean zonal wind has a jet-like profile and the axis of the jet is found to slope to the south with height, as observed in the atmosphere.Based in part on a thesis submitted by the first author as partial fulfillment of the requirements for the Ph.D. degree at the University of Michigan. — Publication No. 194 from the Department of Meteorology and Oceanography, The University of Michigan.     

太平洋中部地磁台11年周期变化的研究

综合APIA、HONOLULU、PAMATAI 3个地磁台三分量的11年周期变化的形态后,可定性地提出该变化源于内场。如内源为核幔边界的电涡流,则其中心点应位于3台之间。     

Comparison Between the Nutations of the Planet Mars and the Nutations of the Earth

The nutations of the planets Mars andEarth are investigated and compared. Alarge number of interior structureparameters are involved in the nutationcomputations. The comparison between the observations and the computationsprovides several constraints on these parmeters andtherefore allows a better understanding of the physics of the interior of theplanet. For the Earth, the high precision of the observations of the nutationshas led to a very good determination of interior properties of the planet. ForMars, observations of nutations are not yet available, and we review how theamplitude of the Martian nutations depends on the hypotheses consideredfor its interior. Although Mars is very similar to the Earth, its interior is not well known;for example, we don't knowif its core is liquid or solid. Only if the core is liquid,the Free Core Nutation (FCN) normal mode exists and can alter the nutationswhich are close to the resonance. From the observed geoids, it is known thatboth planets are not in hydrostatic equilibrium. The departure is larger forMars than for the Earth, and consequently, the implication of considering a convective mantle instead of a mantle in hydrostatic equilibrium described byClairaut's equation for the initial equilibrium state of the planet is largeron the Martian nutations than on the Earth nutations. The consequences of theuncertainty in the core dimensions are also examined and shown to be of a veryhigh influence for Mars if the core is liquid, due to the potential changes inthe FCN resonance. The influence of the presence of an inner core, which isknown to exist for the Earth, could be more important for Mars than for theEarth if the inner core is large. Due to the presence of Tharsis on Mars, thetriaxiality of this planet has, additionally, larger effects than on Earth.     

Magnetic stratigraphy of the Ordovician in the lower reach of the Kotuy River: the age of the Bysy-Yuryakh stratum and the rate of geomagnetic reversals on the eve of the superchron

Until recently, the existing data prevented the geophysicists from accurately dating the Bysy-Yuryakh stratum, which outcrops in the middle reach of the Kotuy River, constraining the time of its formation to a wide interval from the end of the Late Cambrian to the beginning of the Silurian. The obtained paleomagnetic data unambiguously correlate the Bysy-Yuryakh stratum to the Nyaian regional stage and constrain its formation, at least a considerable part of it, by the Tremadocian. This result perfectly agrees with the data on the Bysy-Yuryakh conodonts studied in this work and yields a spectacular example of the successful application of paleomagnetic studies in solving important tasks of stratigraphy and, correspondingly, petroleum geology. Within the Bysy-Yuryakh stratum, we revealed a large normal-polarity interval corresponding to the long (>1 Ma) period when the geomagnetic reversals were absent. This result, in combination with the data for the Tremadocian and Middle–Upper Cambrian sequences of the other regions, indicates that (1) the rate of occurrence of the geomagnetic reversals on the eve of the Ordovician Moyero superchron of reversed polarity was at most one reversal per Ma; (2) the superchron does not switch on instantaneously but is preceded by a certain gradual change in the operation conditions of the dynamo mechanism which, inter alia, manifests itself by the reduction of the frequency of geomagnetic reversals with the approach of the superchron. This finding supports the views according to which a process preparing the establishment of the superchrons takes place at the core–mantle boundary.     

On the variation in the geomagnetic dipole over the geological history of the Earth

The global database on the paleointensity, containing determinations of the virtual dipole moment (VDM) for a stable (normal) regime of the geomagnetic field in a time interval of up to 3.5 Ga, is supplemented by new VDM determinations and analyzed. The field generation process started no later than 3–3.5 Ga (earlier data are absent) at the stage of the Earth’s core formation. Since that time, the dipole value has differed from its present value by no more than an order of magnitude, and the deviations that have already been detected tend toward smaller values. The distribution of VDM values in the time interval 0–400 Ma is bimodal, which apparently reflects the presence of two different generation levels of the geomagnetic field distinguished by a relatively large value (close to the present field value) and a relatively small value (approximately half as large as the present value). The total duration of decreased VDM values appreciably exceeds that of increased VDM values (179.1 and 28.6 Myr, respectively). On the whole, data on the paleointensity do not contradict the hypothesis about the dipole nature of the field over the last 400 Myr; however, the number of determinations at high paleolatitudes is too small to draw decisive conclusions on the validity (or invalidity) of the dipole field approximation based solely on paleointensity data.     

Structure of the poleward wall of the trough and the inclination of the geomagnetic field above the EISCAT radar

A special high-resolution routine of the EISCAT radar has been used to investigate the structure and development of the poleward wall of a deep trough in electron density. The feature was tracked by the radar during a 7-hour period under very quiet geomagnetic conditions. The field-aligned nature of the structure enabled an estimate to be made of the inclination of the geomagnetic field above EISCAT that was in good agreement with the current model. Observations of narrow field-aligned enhancements in electron temperature demonstrated that the wall of this trough is a dynamic feature, reforming regularly as the electron density responds on a time scale of tens of minutes to energy input from soft-particle precipitation.