Genetic algorithm in seismic waveform inversion and its application in deep seismic sounding data interpretation

A genetic algorithm of body waveform inversion is presented for better understanding of crustal and upper mantle structures with deep seismic sounding （DSS） waveform data. General reflection and transmission synthetic seismogram algorithm, which is capable of calculating the response of thin alternating high and low velocity layers, is applied as a solution for forward modeling, and the genetic algorithm is used to find the optimal solution of the inverse problem. Numerical tests suggest that the method has the capability of resolving low-velocity layers, thin alternating high and low velocity layers, and noise suppression. Waveform inversion using P-wave records from Zeku, Xiahe and Lintao shots in the seismic wide-angle reflection/refraction survey along northeastern Qinghai-Xizang （Tibeteau） Plateau has revealed fine structures of the bottom of the upper crust and alternating layers in the middle/lower crust and topmost upper mantle.

Crustal velocity structure of central Gansu Province from regional seismic waveform inversion using firework algorithm

The firework algorithm（FWA） is a novel swarm intelligence-based method recently proposed for the optimization of multi-parameter, nonlinear functions. Numerical waveform inversion experiments using a synthetic model show that the FWA performs well in both solution quality and efficiency. We apply the FWA in this study to crustal velocity structure inversion using regional seismic waveform data of central Gansu on the northeastern margin of the Qinghai-Tibet plateau. Seismograms recorded from the moment magnitude（MW） 5.4 Minxian earthquake enable obtaining an average crustal velocity model for this region. We initially carried out a series of FWA robustness tests in regional waveform inversion at the same earthquake and station positions across the study region,inverting two velocity structure models, with and without a low-velocity crustal layer; the accuracy of our average inversion results and their standard deviations reveal the advantages of the FWA for the inversion of regional seismic waveforms. We applied the FWA across our study area using three component waveform data recorded by nine broadband permanent seismic stations with epicentral distances ranging between 146 and 437 km. These inversion results show that the average thickness of the crust in this region is 46.75 km, while thicknesses of the sedimentary layer, and the upper, middle, and lower crust are 3.15,15.69, 13.08, and 14.83 km, respectively. Results also show that the P-wave velocities of these layers and the upper mantle are 4.47, 6.07, 6.12, 6.87, and 8.18 km/s,respectively.

A method of seismic meme inversion and its application

Under the condition of thin interbeds with great lateral changes in terrestrial basins,a seismic meme inversion method is established based on the analysis of seismic sedimentology technology.The relationship between seismic waveform and high-frequency well logs is established through dynamic clustering of seismic waveform to improve the vertical and horizontal resolution of inversion results;meanwhile,by constructing the Bayesian inversion framework of different seismic facies,the real facies controlled inversion is realized.The forward model verification results show that the seismic meme inversion can realize precise prediction of 3 m thick thin interbeds,proving the rationality and high precision of the method.The application in the Daqing placanticline shows that the seismic meme inversion could identify 2 m thin interbeds,and the coincidence rates of inversion results and drilling data were more than 80%.The seismic meme inversion method can improve the accuracy of reservoir prediction and provides a useful mean for thin interbeds prediction in terrestrial basins.

Full moment tensor inversion constrained by doublecouple focal mechanism for induced seismicity

In this study,we propose a new method to determine full moment tensor solution for induced seismicity.This method generalizes the full waveform matching algorithm we have developed to determine the double-couple(DC)focal mechanism based on the neighbourhood algorithm.One major difference between the new method and the former one is that we adopt a new misfit function to constrain the candidate moment tensor solutions with respect to a reference DC solution in addition to other misfit terms characterizing the waveform matching.Through synthetic tests using a real passive seismic survey geometry,the results show the new constraint can help better recover the DC components of inverted moment tensors.We further investigate how errors in the velocity model and source location affect the moment tensor solution.The synthetic test results indicate that the constrained inversion is robust in recovering both the DC and non-DC components.We also test the proposed method on several real induced events in an oil/gas field in Oman using the same observation system as synthetic tests.While it is found that the full moment tensor solutions without using the DC constraints have much larger non-DC components than solutions with the DC constraints,both solutions are able to fit the observed waveforms at similar levels.The synthetic and real test results suggest the proposed DC constrained inversion method can reliably retrieve full moment tensor solutions for the induced seismicity.

Graded and Quantitative Technology and Application of Coal-Bearing Reservoir Based on Seismic Reflection Characteristics

Taiyuan formation is the main exploration strata in Ordos Basin, and coals are widely developed. Due to the interference of strong reflection of coals, we cannot completely identify the effective reservoir information of coal-bearing reservoir on seismic data. Previous researchers have studied the reservoir by stripping or weakening the strong reflection, but it is difficult to determine the effectiveness of the remaining reflection seismic data. In this paper, through the establishment of 2D forward model of coal-bearing strata, the corresponding geophysical characteristics of different reflection types of coal-bearing strata are analyzed, and then the favorable sedimentary facies zones for reservoir development are predicted. On this basis, combined with seismic properties, the coal-bearing reservoir is quantitatively characterized by seismic inversion. The above research shows that the Taiyuan formation in LS block of Ordos Basin is affected by coals and forms three or two peaks in different locations. The reservoir plane sedimentary facies zone is effectively characterized by seismic reflection structure. Based on the characteristics of sedimentary facies belt and petrophysical analysis, the reservoir is semi quantitatively characterized by attribute analysis and waveform indication, and quantitatively characterized by pre stack geostatistical inversion. Based on the forward analysis of coal measure strata, this technology characterizes the reservoir facies belt through seismic reflection characteristics, and describes coal measure reservoirs step by step. It effectively guides the exploration of LS block in Ordos Basin, and has achieved good practical application effect.

Target-Oriented Inversion of Time-Lapse Seismic Waveform Data

Full waveform inversion of time-lapse seismic data can be used as a means of estimating the reservoir changes due to the production.Since the repeated computa-tions for the monitor surveys lead to a large computational cost,time-lapse full wave-form inversion is still considered to be a challenging task.To address this problem,we present an efficient target-oriented inversion scheme for time-lapse seismic data using an integral equation formulation with Gaussian beam based Green’s function approach.The proposed time-lapse approach allows one to perform a local inversion within a small region of interest(e.g.a reservoir under production)for the monitor survey.We have verified that the T-matrix approach is indeed naturally target-oriented,which was mentioned by Jakobsen and Ursin[24]and allows one to reduce the compu-tational cost of time-lapse inversion by focusing the inversion on the target-area only.This method is based on a new version of the distorted Born iterative T-matrix inverse scattering method.The Gaussian beam and T-matrix are used in this approach to perform the wavefield computation for the time-lapse inversion in the baseline model from the survey surface to the target region.We have provided target-oriented inversion results of the synthetic time-lapse waveform data,which shows that the proposed scheme reduces the computational cost significantly.

SEISMIC STUDIES OF MARINE GAS HYDRATES

We give a brief introduction of developments of seismic methods in the studies of marine gas hydrates. Then we give an example of seismic data processing for BSRs in western Nankai accretionary prism, a typical gas hydrate distribution region. Seismic data processing is proved to be important to obtain better images of BSRs distribution. Studies of velocity structure of hydrated sediments are useful for better understanding the distribution of gas hydrates. Using full waveform inversion, we successfully derived high-resolution velocity model of a double BSR in eastern Nankai Trough area. Recent survey and research show that gas hydrates occur in the marine sediments of the South China Sea and East China Sea.But we would like to say seismic researches on gas hydrate in China are very preliminary.

Studies on seismic waves

The development of seismic wave study in China in the past four years is reviewed. The discussion is divided into several aspects, including seismic wave propagation in laterally homogeneous media, laterally heterogeneous media, anisotropic and porous media, surface wave and seismic wave inversion, and seismic wave study in prospecting and logging problems. Important projects in the current studies on seismic wave is suggested as the development of high efficient numerical methods, and applying them to the studies of excitation and propagation of seismic waves in complex media and strong ground motion, which will form a foundation for refined earthquake hazard analysis and prediction.

Transition Operator Approach to Seismic Full-Waveform Inversion in Arbitrary Anisotropic Elastic Media

We generalize the existing distorted Born iterative T-matrix(DBIT)method to seismic full-waveform inversion(FWI)based on the scalar wave equation,so that it can be used for seismic FWI in arbitrary anisotropic elastic media with variable mass densities and elastic stiffness tensors.The elastodynamic wave equation for an ar-bitrary anisotropic heterogeneous medium is represented by an integral equation of the Lippmann-Schwinger type,with a 9-dimensional wave state(displacement-strain)vector.We solve this higher-dimensional Lippmann-Schwinger equation using a transition operator formalism used in quantum scattering theory.This allows for domain decomposition and novel variational estimates.The tensorial nonlinear inverse scat-tering problem is solved iteratively by using an expression for the Fŕechet derivatives of the scattered wavefield with respect to elastic stiffness tensor fields in terms of modified Green’s functions and wave state vectors that are updated after each iteration.Since the generalized DBIT method is consistent with the Gauss-Newton method,it incorporates approximate Hessian information that is essential for the reduction of multi-parameter cross-talk effects.The DBIT method is implemented efficiently using a variant of the Levenberg-Marquard method,with adaptive selection of the regularization parameter after each iteration.In a series of numerical experiments based on synthetic waveform data for transversely isotropic media with vertical symmetry axes,we obtained a very good match between the true and inverted models when using the traditional Voigt parameterization.This suggests that the effects of cross-talk can be sufficiently reduced by the incorporation of Hessian information and the use of suitable regularization methods.Since the generalized DBIT method for FWI in anisotropic elastic media is naturally target-oriented,it may be particularly suitable for applications to seismic reservoir characterization and monitoring.However,the theory and method presented here is general.

塔里木盆地星火井区深层薄储层地震预测

星火井区巴什基奇克组顶部储层埋深超过5 000 m,为超深层强非均质性碎屑岩储层,是塔里木盆地新和地区重要生产层段。储层埋藏深度大、厚度薄、研究区完钻井数量少,勘探开发难度很大。由于传统的地震预测技术精度不够,薄储层预测一直是制约星火井区超深层油气藏勘探开发的瓶颈技术。为落实星火井区薄储层分布特征,利用模型正演明确了星火井区超深薄储层在不同分辨率模型下的地震响应特征、基于谱反演方法的拓频技术提高地震分辨率,识别出超深层6 m以内的薄储层,进而使用波形指示反演技术刻画出薄储层的展布特征。薄储层预测结果与实钻井结果的吻合率超过87%,证明正演-拓频-反演技术在星火井区具有很高的准确性。研究结果可以为与星火井区地质背景相同地区的油藏开发提供借鉴。

板桥地区中浅层辫状河沉积储层预测研究

板南中浅层馆陶组油藏具有油层单一、底水发育的特点,准确刻画油层的位置、油层上下隔夹层的分布是有效开发的关键。通过开展沉积储层研究,认为板南馆陶组为辫状河沉积体系,主要发育心滩、辫状水道、水道间、泛滥平原泥4个微相。储层属高孔高渗储层,非均质性较强,油层分布比较稳定。分析认为常规反演方法分辨率较低,无法有效识别单砂体;而地震波形指示反演在单砂体的识别能力上具有明显的优势,可以满足水平井部署的需要。以储层反演成果为基础,完成油藏工程方案及实钻动态跟踪,并取得良好效果,证明了储层反演方法的可靠性。

海洋可控源电磁法与地震全波形二维联合反演研究

为降低单一地球物理反演方法的局限性以及反演中所存在的多解性等问题,开展了海洋可控源电磁法(MCSEM)与地震全波形的二维联合反演研究。MCSEM采用数据空间OCCAM反演算法,地震全波形采用梯度法反演算法,引入交叉梯度函数实现两种物性参数结果的相互耦合;开发出一套二维联合反演算法,并通过3组理论模型算例验证了算法的准确性。研究结果表明:MCSEM联合反演结果相对于单方法反演结果有显著改善和提升,主要体现在异常体的形态刻画、结构构造以及物性数值的恢复,这说明全波形的反演方法能够提高MCSEM反演结果的可靠性。

基于波形指示反演的储层预测方法及应用

由于储层发育的非均质性,单纯根据测井资料刻画出的河道砂体与实际井间砂体的形态符合率较低,砂体连续性及规模都存在不确定性。为了提高储层的预测精度,以大庆长垣南部高台子油田葡一油层组为例,采用基于波形指示反演切片与测井资料结合的方法,优选出了适合研究区的波形指示反演参数,对研究区各小层进行了井震结合沉积微相预测。结果表明,波形指示反演结果具有更好的纵向分辨能力,通过使用优选出的反演参数得到的高精度反演结果,能较好地反映出研究区的储层发育特征。选取与目的层相关性高的波形指示反演方法电阻率反演体,用其反演切片可以预测水下分流河道砂体的连续性和几何形态,具有更高的井间砂体预测精度,能为提高研究区井间储层预测精度提供技术支撑。

The 2023 M_(w)6.8 Adassil Earthquake(Chichaoua,Morocco)on a steep reverse fault in the deep crust and its geodynamic implications

The Mw 6.8 Adassil earthquake that occurred in the High Atlas on September 8,2023,was a catastrophic event that provided a rare opportunity to study the mechanics of deep crustal seismicity.This research aimed to decipher the rupture characteristics of the Adassil earthquake by analyzing teleseismic waveform data in conjunction with interferometric synthetic aperture radar(InSAR)observations from both ascending and descending orbits.Our analysis revealed a reverse fault mechanism with a centroid depth of approximately 28 km,exceeding the typical range for crustal earthquakes.This result suggests the presence of cooler temperatures in the lower crust,which facilitates the accumulation of tectonic stress.The earthquake exhibited a steep reverse mechanism,dipping at 70°,accompanied by minor strike-slip motion.Within the geotectonic framework of the High Atlas,known for its volcanic legacy and resulting thermal irregularities,we investigated the potential contributions of these factors to the initiation of the Adassil earthquake.Deep seismicity within the lower crust,away from plate boundaries,calls for extensive research to elucidate its implications for regional seismic hazard assessment.Our findings highlight the critical importance of studying and preparing for significant seismic events in similar geological settings,which would provide valuable insights into regional seismic hazard assessments and geodynamic paradigms.

Imaging disturbance zones ahead of a tunnel by elastic full-waveform inversion:Adjoint gradient based inversion vs.parameter space reduction using a level-set method

We present and compare twoflexible and effective methodologies to predict disturbance zones ahead of underground tunnels by using elastic full-waveform inversion.One methodology uses a linearized,iterative approach based on misfit gradients computed with the adjoint method while the other uses iterative,gradient-free unscented Kalmanfiltering in conjunction with a level-set representation.Whereas the former does not involve a priori assumptions on the distribution of elastic properties ahead of the tunnel,the latter intro-duces a massive reduction in the number of explicit model parameters to be inverted for by focusing on the geometric form of potential disturbances and their average elastic properties.Both imaging methodologies are validated through successful reconstructions of simple disturbances.As an application,we consider an elastic multiple disturbance scenario.By using identical synthetic time-domain seismo-grams as test data,we obtain satisfactory,albeit different,reconstruction results from the two inversion methodologies.The computa-tional costs of both approaches are of the same order of magnitude,with the gradient-based approach showing a slight advantage.The model parameter space reduction approach compensates for this by additionally providing a posteriori estimates of model parameter uncertainty.

基于小保当二号煤矿薄煤层超宽工作面的透射高精度成像研究

针对小保当二号煤矿2~3 m厚煤层450 m超宽工作面特点,研究应用地震勘探方法构建高精度工作面成像,提升此种煤层的开采效率。根据采集的双透射地震数据,基于三维弹性波数值模拟方法测试分析煤层工作面的波场产生情况,通过对比合成数据与实际数据的槽波频散曲线,认识不同波形的频带特征,再对三分量数据的不同波段做极性分析,进一步明确本工作面的地震属性。对该双透射实际数据进行处理,通过全波形反演技术做速度分析,得到最优化三维速度模型,从而获得高精度三维逆时偏移成像的纵波和横波成像结果。与巷道地质信息及已回采剖面对比,计算结果与真实揭露值接近,本研究思路有助于高精度煤岩分界面的复刻。

准噶尔盆地红车断裂带石炭系火山岩油藏地球物理特征及有利储层预测

准噶尔盆地西缘红车断裂带火山岩油气藏资源丰富,储量规模巨大,具有满带含油的特点。然而火山岩油藏受构造、相带、岩性控制,断裂复杂,岩性岩相变化快,非均质性强,致使优质储层难以识别。首先,基于岩石薄片、测井、地震等资料,分析了研究区石炭系发育的优势岩性以及不同岩性的测井响应特征,运用多参数分布交会法建立了自然伽马-密度、密度-电阻率/自然伽马、电阻率-自然伽马/密度的岩性识别组合图版,确定优势岩性特征,进而对目的层段的岩性进行了有效识别。然后,通过地震相、测井相、岩性特征及试油结果等资料的分析,明确研究区火山岩相、储盖组合和油藏分布规律。根据地震反射结构和反射构型特征,识别研究区典型的地震相特征;在岩石物理和敏感参数分析的基础上,发挥地震纹理属性和瞬时相位余弦属性在岩性体刻画、边界分析方面的优势,以及地震波形相控反演在提高储层识别垂向分辨率的同时,兼顾了横向预测的能力,综合运用地震多属性分析、波形相控反演和沿层切片技术,通过对地震平-剖面成果与井上有利储层的分析,最终确定优势储层的发育和空间分布范围,为落实准噶尔盆地红车断裂带火山岩储层油气优势聚集带提供了支持。

全波形反演在复杂地表三维地震资料处理中的应用——以HQ工区为例

由于HQ工区目的层埋深浅,受复杂地表影响存在较大范围的空炮段,故在三维地震资料处理中常规速度建模方法得到的速度模型精度低、成像效果差。通过总结分析全波形反演数据准备与常规数据处理的差别,将基于armousi模型的全波形反演技术于HQ工区三维地震资料处理中进行测试应用,并开展应用效果评价。应用结果表明,全波形反演技术可以准确还原复杂地表条件下地下介质的结构和性质,建立较高精度的地下速度模型,对应的叠前深度偏移成像效果具有明显提高。研究结果证实了全波形反演技术的优越性,对于全波形反演技术于复杂地表地区的应用具有一定的参考价值。

基于波形指示反演的窄薄储层定量预测

针对渤海湾KL油田古近系沙三段单砂层厚度薄、砂体变化快、薄互层沉积、储层预测精度低等难题,提出利用地震高频段的波形信息代替变差函数,优选出能够反映岩性的敏感参数参与储层模拟,有效提升储层反演的纵、横向分辨率,更精确地刻画砂体的空间展布形态及范围,实现了波形指示反演下的窄薄储层预测。开发井实钻表明:砂体识别厚度达到5 m以下,储层符合率提高至85.7%。该方法有效提高了窄薄储层预测精度,对海上稀井网条件下窄薄储层的预测具有一定的指导意义。

On Quadratic Wasserstein Metric with Squaring Scaling for Seismic Velocity Inversion

The quadraticWasserstein metric has shown its power in comparing prob-ability densities.It is successfully applied in waveform inversion by generating ob-jective functions robust to cycle skipping and insensitive to data noise.As an alter-native approach that converts seismic signals to probability densities,the squaring scaling method has good convexity and thus is worth exploring.In this work,we apply the quadratic Wasserstein metric with squaring scaling to regional seismic to-mography.However,there may be interference between different seismic phases in a broad time window.The squaring scaling distorts the signal by magnifying the unbalance of the mass of different seismic phases and also breaks the linear super-position property.As a result,illegal mass transportation between different seismic phases will occur when comparing signals using the quadratic Wasserstein metric.Furthermore,it gives inaccurate Fr´echet derivative,which in turn affects the inver-sion results.By combining the prior seismic knowledge of clear seismic phase sep-aration and carefully designing the normalization method,we overcome the above problems.Therefore,we develop a robust and efficient inversion method based on optimal transport theory to reveal subsurface velocity structures.Several numerical experiments are conducted to verify our method.