Tomographic inversion of near-surface Q factor by combining surface and cross-hole seismic surveys

The estimation of the quality factor Q plays a fundamental role in enhancing seismic resolution via absorption compensation in the near-surface layer.We present a new geometry that can be used to acquire field data by combining surface and cross-hole surveys to decrease the effect of geophone coupling on Q estimation.In this study,we drilled number of receiver holes around the source hole,each hole has different depth and each geophone is placed geophones into the bottom of each receiver hole to avoid the effect of geophone coupling with the borehole wall on Q estimation in conventional cross-hole seismic surveys.We also propose a novel tomographic inversion of the Q factor without the effect of the source signature,and examine its stability and reliability using synthetic data.We estimate the Q factors of the near-surface layer in two different frequency bands using field data acquired in the Dagang Oilfield.The results show that seismic absorption in the nearsurface layer is much greater than that in the subsurface strata.Thus,it is of critical practical importance to enhance the seismic solution by compensating for near-surface absorption.In addition,we derive different Q factors from two frequency bands,which can be treated,to some extent,as evidence of a frequency-dependent Q.

Wave equation tomographic velocity inversion method based on the Born/Rytov approximation

This paper discusses Born/Rytov approximation tomographic velocity inversion methods constrained by the Fresnel zone. Calculations of the sensitivity kernel function and traveltime residuals are critical in tomographic velocity inversion. Based on the Bom/Rytov approximation of the frequency-domain wave equation, we derive the traveltime sensitivity kemels of the wave equation on the band-limited wave field and simultaneously obtain the traveltime residuals based on the Rytov approximation. In contrast to single-ray tomography, the modified velocity inversion method improves the inversion stability. Tests of the near- surface velocity model and field data prove that the proposed method has higher accuracy and Computational efficiency than ray theory tomography and full waveform inversion methods.

Tomographic velocity inversion for ADCIGs in areas with a rugged surface

Pre-stack depth migration velocity analysis is one of the key techniques influencing image quality. As for areas with a rugged surface and complex subsurface, conventional prestack depth migration velocity analysis corrects the rugged surface to a known datum or designed surface velocity model on which to perform migration and update the velocity. We propose a rugged surface tomographic velocity inversion method based on angle-domain common image gathers by which the velocity field can be updated directly from the rugged surface without static correction for pre-stack data and improve inversion precision and efficiency. First, we introduce a method to acquire angle-domain common image gathers （ADCIGs） in rugged surface areas and then perform rugged surface tornographic velocity inversion. Tests with model and field data prove the method to be correct and effective.

A review on reflection-waveform inversion

Full-waveform inversion(FWI)utilizes optimization methods to recover an optimal Earth model to best fit the observed seismic record in a sense of a predefined norm.Since FWI combines mathematic inversion and full-wave equations,it has been recognized as one of the key methods for seismic data imaging and Earth model building in the fields of global/regional and exploration seismology.Unfortunately,conventional FWI fixes background velocity mainly relying on refraction and turning waves that are commonly rich in large offsets.By contrast,reflections in the short offsets mainly contribute to the reconstruction of the high-resolution interfaces.Restricted by acquisition geometries,refractions and turning waves in the record usually have limited penetration depth,which may not reach oil/gas reservoirs.Thus,reflections in the record are the only source that carries the information of these reservoirs.Consequently,it is meaningful to develop reflection-waveform inversion(RWI)that utilizes reflections to recover background velocity including the deep part of the model.This review paper includes:analyzing the weaknesses of FWI when inverting reflections;overviewing the principles of RWI,including separation of the tomography and migration components,the objective functions,constraints;summarizing the current status of the technique of RWI;outlooking the future of RWI.

Near-surface absorption compensation technology and its application in the Daqing Oilfields

High-frequency seismic data components can be seriously attenuated during seismic wave propagation in unconsolidated （low-velocity） layers, resulting in reduced seismic resolution and signal-to-noise （S/N） ratio. In this paper, first, based on Wiener filter theory, inverse filter calculations for near-surface absorption attenuation compensation were accomplished by analysis of the direct wave spectral components from different distances near the surface. The direct waves were generated by detonators in uphole shots and were acquired by receivers on the surface. The spatially varying inverse filters were designed to compensate for the frequency attenuation of 3D pre-stack CRG （common receiver-gather） data. After applying the filter to CRG data, the high frequency components were compensated with the low frequencies maintained. The seismic resolution and S/N ratio are enhanced and match better with synthetic seismograms and better meet the needs of geological interpretation.

Active source seismic imaging on near-surface granite body:case study of siting a geological disposal repository for high-level radioactive nuclear waste

In order to research whether it is suitable to set a geological disposal repository for high-level radioactive nuclear waste into one target granite body,two active source seismic profles were arranged near a small town named Tamusu,Western China.The study area is with complex surface conditions,thus the seismic exploration encountered a variettraveltimey of technical difculties such as crossing obstacles,de-noising harmful scattered waves,and building complex near-surface velocity models.In order to address those problems,techniques including cross-obstacle seismic geometry design,angle-domain harmful scattered noise removal,and an acoustic wave equation-based inversion method jointly utilizing both the and waveform of frst arrival waves were adopted.The fnal seismic images clearly exhibit the target rock’s unconformable contact boundary and its top interface beneath the sedimentary and weathered layers.On this basis,it could be confrmed that the target rock is not thin or has been transported by geological process from somewhere else,but a native and massive rock.There are a few small size fractures whose space distribution could be revealed by seismic images within the rock.The fractures should be kept away.Based on current research,it could be considered that active source seismic exploration is demanded during the sitting process of the geological disposal repository for nuclear waste.The seismic acquisition and processing techniques proposed in the present paper would ofer a good reference value for similar researches in the future.

复杂山地水-陆混采地震资料高精度表层速度建模与应用

塔里木盆地ZQX区块石油地质条件优越,并首次开展了水域空气枪激发、拖缆接收采集,但其近地表结构非常复杂,分布有农田、村庄、山体、戈壁砾石、水库等地表类型。针对水-陆混采资料的特殊性,笔者提出了水-陆混采初至起跳点拾取与双约束层析反演新方法。先拾取出不同激发接收模式下准确的初至波波峰时间,利用高信噪比道计算波峰到起跳点的时差,再通过插值解决低信噪比道波峰时间转初至时间的空变时差校正问题。以此为基础,采用水速硬约束和微测井软约束的层析反演方法,解决了ZQX区块水库-山地水-陆混采三维高精度近地表速度建模问题,叠加剖面及深度偏移成像质量明显提升,取得了较好的应用效果。

消除全局层析反演累计误差的反向递推方法

常规层析反演方法基于地震偏移成像道集剩余曲率计算深度误差,忽略了深度误差自上而下的积累,随着深度的增加,累计误差也随之增加,且速度更新后对应叠前深度偏移剖面的层位深度也会改变。从道集曲率深度误差积累的原理出发,提出一种从下至上逐层消除累计误差的递推方程,并根据深度残差来更新之前拾取的层位。根据角度域共成像点道集的剩余曲率来计算剩余时差,利用斯奈尔定律推导出相邻层位入射角与层速度的关系,计算每一层与上一层入射角的对应关系,消除该层的累计误差并更新层位深度。模型测试与实际资料应用结果表明,该方法可行有效,与常规层析反演方法相比较,有效改善了速度模型整体的精度并提高了反演效率,为后续叠前深度偏移成像提供了可靠的速度模型。

频谱一致性Q因子反演方法

地层品质因子Q能够定量表征地层吸收对地震信号的衰减效应,对高分辨率地震数据处理和油气检测均具有重要作用。针对现有Q因子估算方法抗噪性弱、稳定性差等问题,提出了一种基于频谱一致性准则的Q因子反演方法。该方法基于粘弹性介质地震波传播理论,将不同时间接收的地震信号反向传播到某一位置,基于反向传播之后频谱特征的一致性对Q因子进行反演。不同于谱比法和质心频移法,该方法不是基于对数谱斜率和质心频移等地震频谱的某个特定属性,而是基于地震频谱在整体特征上的一致性对Q因子进行反演和估算,其反演结果的稳定性和抗噪性更好。理论模型和实际数据的实验结果表明,采用该方法能够得到更加可靠的Q模型,其补偿结果较好地恢复了高分辨率地震数据的反射特征。

初至波表层模型层析反演

针对地震勘探中的复杂地表问题 ,本文提出了一套地震初至波表层模型层析反演方法。该方法是利用地震波射线的走时和路径 ,反演介质速度结构的一种高精度的反演方法。它利用地震直达波、辶回折波、折射波以及三者组合的初至波和层析反演方法具有的纵、横向变速优势 ,实现适应速 度任意变化的复杂表层模型反演。理论模型与实际资料的反演结果表明 ,其效果显著。

OVT域宽方位层析速度建模与深度域成像

叠前深度偏移常规速度建模技术,不能有效利用宽方位地震资料的方位角信息,导致速度模型精度不足,最终偏移结果不如预期。本文提出了一套在OVT域实现的宽方位层析速度建模技术流程。该方法利用CIP道集中的方位角信息,能反演出细微的小尺度速度变化,具有很高的精度和分辨率。通过OVT域宽方位层析反演得到的蝴蝶道集拉得较平,方位剩余时差得到消除,碳酸盐岩串珠成像质量明显改善。分析认为,这种方位剩余时差实际上主要是由储层的非均质性引起而不是由方位各向异性引起。研究表明,与常规速度建模技术和分扇区多方位层析技术相比,OVT域宽方位层析反演技术更灵活高效,能得到更高分辨率的速度模型,从而提高深度域成像质量。

变速成图方法及应用研究

研究了地震速度和变速成图传统方法中影响成图精度的主要因素 ,指出了传统方法中造成误差较大、准确性较低的原因。从解决传统方法中存在的问题入手 ,提出了相应的速度场建立和变速成图方法 :通过提高叠加速度分辨率 ,利用模型层析法或模型反演法实现叠加速度到层速度的转换 ,建立空间速度场 ,速度校正和时深转换。实际资料应用表明 ,该方法提高了速度场建立和变速成图精度 ,解决了山前高陡构造以及低幅度构造地区的变速成图问题。

用于速度图象重建的层析成象法

本文提出了一种用于速度图象重建的层析成象法。特别注意到地震学上的ST与医学上的CT的不尽相同之处,并处理了由此引起的困难。与速度图象重建有关的正问题的分析表明,不同频率范围的资料其分辨能力是不同的,因此,区域地震与远震资料的解释应予注意。本文有关速度图象重建的讨论不仅涉及到与成象方法有关的反演理论和方法,还给出了进行数值计算的内存量和运算量的分析。关于重建图象的质量评价,还给出了反演解的可靠性分析,为分辨特性的描述提供了一种既简便又形象直观的方案。 本文的方法与现行主要方法的比较表明:1.本文的方法允许存在速度间断面,有利于揭示不同构造区域的地壳厚度的差异;2.在常用的方法中,作为正问题假定的常速度块同反演结果解释时非常速度块之间不协调。由于我们把给定网格点的速度值的插值函数作为速度的空间函数,这一困难已被解决;3.相对于Aki等的一般方法,本文的内存量节省约一个量级、运算量减少约一半;4.相对于ART类方法本身不能给出成象结果的可靠性分析,本文的方法则具有显著的优点。 作者在分析了天然地震资料的状况之后相信,对充分利用我国地震台网的现有观测资料,本文的方法是有效的。

复杂地表初至层析地震静校正技术及其应用

复杂地表条件的煤层气地震勘探资料处理对静校正有较高要求。折射静校正具有较好的静校正效果,但对于地表起伏大、纵横向速度变化剧烈的复杂地区则难以取得较好的效果。建立横向速度变化大且基岩裸露的地震模型进行理论试算,分析了层析静校正的特点及适用条件,指出了层析静校正中应该注意的关键问题。实例验证结果表明:层析静校正更适合复杂地表煤层气地震资料的处理。

井间地震技术在樊124井区的应用

井间地震技术是油气田勘探开发领域的一项新技术,它是将震源系统置入井中激发并在另一口或多口井中接收地震波,通过对记录的地震波走时、振幅和频率等信息的处理,并结合测井、地质和地面地震等资料进行解释,最终得到井间地下介质的结构特征和物性变化情况。为了掌握胜利油田樊124井区断层的存在和单个砂体连通情况,采集了3对井的高质量原始井间地震资料,并对其进行了直达波旅行时速度层析反演和反射波成像处理,获得高分辨率的井间速度层析剖面与反射波成像剖面。通过综合解释,对樊124井区的井间储集层的横向分布与连通性、小断层、砂泥岩薄互层等复杂精细的地质现象有了清晰明确的认识,为提高油气采收率(EOR)及优化油气田开发方案提供了依据。

叠前深度偏移层析反演速度模型建立及应用

叠前深度偏移技术是目前解决复杂地质构造精确成像问题的重要手段，其成像效果取决于深度域速度模型的准确与否。通常采用的沿层构造解释速度建模方法在构造特别复杂、层位解释不合理时往往得不到准确的速度模型，因此研究了层析反演更新深度域速度模型的建立方法。该方法可利用偏移成像数据计算剩余误差曲线和地层倾角信息，迭代更新反射层的位置和形态，最终获取准确的速度模型。应用实例表明，层析反演速度建模技术是可行的。

三维波动方程基准面校正方法的应用研究

波动方程基准面校正处理被认为是当地表高程变化剧烈、地表一致性假设又不成立的情况下对于常规高程基准面校正的必要替代.在二维波动方程基准面校正方面,前人已经作了大量工作,并且在实际应用中获得了良好的效果,应该将其进一步推广到三维.本文采用三维频率空间域有限差分波场延拓算子以“逐步-累加”的方式实现了三维波动方程基准面校正,并对实际数据进行了处理.对于西部某三维数据的实际计算结果表明,相对于传统的模型法高程静校正,波动方程基准面校正更合理地实现了基准面校正,有助于提高后续的速度分析精度和成像质量.

层析反演静校正

表层模型层析反演是一种非线性模型反演技术,它利用地震初至波射线的走时和路径反演介质速度结构,不受地表及近地表结构纵横向变化的约束。根据正演初至时间与实际初至时间的误差,修正速度模型,经反复迭代,最终达到要求的误差精度。求取静校正时采用射线法计算炮点到检波点的旅行时,从而得到基准面校正量。

层析反演静校正技术及应用效果分析

表层模型层析反演技术,是利用地震记录初至波的时间,运用射线追踪方法反演地表及近地表不同介质的速度模型,以获得地震观测点处地表及近地表的速度和深度信息,建立相应的表层结构模型,在此基础上分别求取激发点和接收点的静校正值,从而消除静校正影响,提高地震反射波的分辨率,最终得到高质量的地震剖面。

层析反演静校正方法在西部复杂地区的应用

静校正技术在复杂地表区地震资料处理中至关重要。在中国西部地区,地表起伏剧烈,表层低速带横向速度变化较大,静校正问题严重。传统的野外静校正和初至折射静校正方法在复杂近地表条件下很难求准近地表速度模型和静校正量。层析反演静校正方法通过非线性算法反演出准确的近地表速度模型,求出准确的静校正量。给出了层析反演静校正方法的基本原理和实现过程,包括射线追踪和联立迭代重构法反演。通过在塔里木盆地巴楚地区的实际应用,明显改善了地震叠加成像效果。