频率域2.5-D井间波形层析成像及其实际应用

从频率域3-D声波波动方程出发,结合井间观测方式的特点,基于Tarantola广义反演理论,提出了一种频率域2.5-D井间波形层析成像方法.数值模型试验结果表明：该方法对薄层厚度的分辨能力能达到约主频波长的1/4,且分辨率显著高于走时层析成像,尤其垂直分辨率有实质改善.模拟资料的抗噪试验表明：在信噪比为0.8的情况下,随机噪声对波形层析成像的影响较小;而相干噪声对全波形层析成像的影响显著,特别是初至波附近的强振幅干扰影响更为严重.井间实际资料的试处理结果表明：波形层析成像能很好地刻画井间介质的分布情况与储层连通性,对于油藏开发阶段的方案实施具有指导意义.     

Automatic cross-well tomography by semblance and differential semblance optimization: theory and gradient computation

A technique for automatic cross-well tomography based on semblance and differential semblance optimization is presented. Given a background velocity, the recorded seismic data traces are back-propagated towards the source, i.e. shifted towards time zero using the modelled traveltime between the source and the receiver and corrected for the geometrical spreading. Therefore each back-propagated trace should be a pulse, close to time zero. The mismatches between the back-propagated traces indicate an error in the velocity model. This error can be measured by stacking the back-propagated traces (semblance optimization) or by computing the norm of the difference between adjacent traces (differential semblance optimization).
It is known from surface seismic reflection tomography that both the semblance and differential semblance functional have good convexity properties, although the differential semblance functional is believed to have a larger basin of attraction (region of convergence) around the true velocity model. In the case of the cross-well transmission tomography described in this paper, similar properties are found for these functionals.
The implementation of this automatic method for cross-well tomography is based on the high-frequency approximation to wave propagation. The wavefronts are constructed using a ray-tracing algorithm. The gradient of the cost function is computed by the adjoint-state technique, which has the same complexity as the computation of the functional. This provides an efficient algorithm to invert cross-well data. The method is applied to a synthetic data set to demonstrate its efficacy.     

STUDY OF TRAVELTIME AND AMPLITUDE TIME-LAPSE TOMOGRAPHY USING PHYSICAL MODEL DATA1

In seismic tomography the observed traveltimes or amplitudes of direct waves are inverted to obtain an estimate of seismic velocity or absorption of the section surveyed. There has been much recent interest in using cross-well traveltime tomography to observe the progress of fluids injected into the reservoir rocks during enhanced oil recovery (EOR) processes. If repeated surveys are carried out, then EOR processes may be monitored over a period of time. This paper describes the results of a simulated time-lapse tomography experiment to image the flood zone in an EOR process. Two physical models were made out of epoxy resins to simulate an essentially plane-layered sedimentary sequence containing a reservoir layer and simple geological structure. The models differed only in the reservoir layer, which was uniform in the ‘pre-flood’ model and contained a flood zone of known geometry in the ‘post-flood’ model. Data sets were acquired from each model using a cross-well survey geometry. Traveltime and amplitude tomographic imaging techniques have been applied to these data in an attempt to locate the extent of the flood zone. Traveltime tomography locates the flood zone quite accurately. Amplitude tomography shows the flood zone as a region of higher absorption, but does not image its boundaries as precisely. This is primarily because of multipathing and diffraction effects, which are not accounted for by the ray-based techniques for inverting seismic amplitudes. Nevertheless, absorption tomograms could complement velocity tomograms in real, heterogeneous reservoirs because absorption and velocity respond differently to changes in liquid/gas saturations for reservoir rocks.     

异常地层压力声波衰减分析及地层压力地震数据外推反演

澳大利亚西北大陆架卡拉汶盆地含有丰富的油气资源, 但其地质条件复杂, 普遍存在异常地层高压分布,特别是该区区域盖层-中深层巨厚的Muderong页岩层内存在局部异常高压带,给石油钻井带来巨大困难.本文根据卡拉汶盆地北部地区10余口井的实测地层压力资料、声波测井数据和联井地震剖面, 研究该页岩层内异常压力千赫兹尺度声波响应的衰减特征,及其与地层有效压力之间的关联计算模型.通过联井地震数据的井-震相关性分析进行井-震过渡,研究井旁地震数据在异常高压带的衰减特征,及其与地层有效压力之间的关联计算模型,从而实现井震资料联合进行地层压力地震外推反演.研究表明,Muderong页岩层地层有效压力与井中声波速度/阻抗品质因子和井旁地震阻抗品质因子具有良好的正向相关性,根据二者交汇数据拟合经验公式反算得到的各井有效压力结果基本反映出实测有效压力曲线的变化特征.卡拉汶盆地北部地区地震数据具有良好的井-震相关性,地震资料品质相对可靠,确保了声-压相关分析的井-震过渡.最后,通过地震阻抗品质因子与地层有效压力之间的关联计算模型,进行该区异常地层压力地震外推反演,预测结果与钻井证实的异常压力分布特征基本符合.本研究为卡拉汶盆地中深部区域盖层局部异常高压带的地层压力外推反演提供了一种有效途径.     

A modelling study of open-hole single-well seismic imaging

Single-well, or uni-well, imaging uses an acoustic source and an array of receivers located in the same borehole to image local geological structure. Due to the intrinsic attenuation of the formation it is likely that a source emitting frequencies in the typical cross-well range would be necessary to illuminate structure at distances above 100 m from the borehole. At these frequencies a significant proportion of the source energy is converted into tube-waves which are, for the purpose of these surveys, noise. This paper reports the results of a modelling study designed to assess the feasibility of using existing cross-well hardware, i.e. a piezo-electric source and hydrophone array, modified to run in a single borehole, to perform single-well surveys. In particular we study the case of an open borehole in a gas-filled, low-permeability sandstone reservoir. Our results suggest that the amplitudes of the tube-wave reverberations generated by calliper variations are such that reflections of interest arriving in the time window after the first tube-wave arrival will not be visible. However, reflections may be visible in the time window preceding the first tube-wave arrival provided tube waves from previous shots are not still present and the long source–receiver offsets required to make observations in this window can be incorporated into the tool design.     

井间断层的计算机分析方法

井间断层分析的研究,是油气储层地质研究的一项重要基础性工作,对油气的运移和聚集其中重要的控制作用。它是利用测井资料,以地层分层为基础,采用计算机技术实现井间断层分析的一种井间断层自动分析方法。动态波形匹配算法是本次研究采用的主要算法,它能够很好地建立井间地层之间的对比关系,通过曲线拟合、特征提取、匹配代价计算等步骤,自动绘制井间地层对比的路径图解。本文在对各种构造的路径图分析的基础上,总结出正断层、逆断层、不整合、同沉积断层、犁式断层和地层尖灭等30种情况下的路径图模式,提出路径图模式及相关概念。在大港油田的实例分析中取得了很好的效果。     

Design considerations for using Distributed Acoustic Sensing for cross-well seismics: A case study for CO2 storage

Downhole monitoring with fibre-optic Distributed Acoustic Sensing (DAS) systems offers unprecedented spatial resolution. At the same time, costs are reduced since repeated wireline surveys can be replaced by the permanent installation of comparatively cheap fibre cables. However, the single component nature of fibre data requires novel approaches when designing a monitoring project such as cross-well seismics. At the example of the shallow CO₂ injection test site in Svelvik, Norway, we model the evolution of velocity changes during CO₂ injection based on rock physics theory. Different cross-well seismic design scenarios are then considered to evaluate the best design and the limits of this method to detect containment breach. We present a series of evaluation tools to compare the effect of different well spacings for cross-well seismic tomography. In addition to travel-times, we also consider characteristic amplitude changes along the fibre unique to DAS strain measurements, which might add a constraint to the inversion. We also compare the effect of using helical fibres instead of classical straight fibres. We thus present a toolbox to evaluate and compare different monitoring design options for fibre optic downhole installations for cross-well monitoring.     

井间电磁法综述

地面电磁法在实际工作中在很大程度上受到了探测深度和分辨率的限制.为了克服这些缺点,出现了井间电磁法.井间电磁法指的是在两个(或多个)钻孔中分别发射或接收电磁波信号,利用电磁波信号进行成像并探测井间物理性质的地球物理方法.由于发射机和接收机可以分别放置在很深钻孔中,其具有大透距、大探测深度的特点,因而广泛应用于工程环境物探、矿产勘查、石油勘探等中.针对不同的应用,产生了各具特点的一些特殊方法,包括井间无线电波成像、跨孔雷达、井间电磁成像.井间无线电波成像仪目前只测量电场强度数据,工作频率低,一般是单频的电磁波,频率范围通常在1 kHz至10 MHz.由于缺少走时数据修正射线路径,井间无线电波成像主要是进行基于直射线追踪的衰减层析成像.井间无线电波成像既可用于工程与环境地球物理也可用于找矿.跨孔雷达是钻孔雷达的一种探测方式,用高频电磁脉冲探测两个井孔间介电常数和电导率的变化.跨孔雷达层析成像也叫地质雷达CT,既可进行走时成像,还可进行衰减成像.一般来说,地质雷达CT的电磁波工作频率较高,中心频率通常在10 MHz和1 GHz之间,因此在分辨率指标上占有优势,跨孔雷达主要用于工程与环境地球物理.井间电磁成像采用更低的频率,测量复电磁信号,适合油气储集层监测,是一种地球物理前沿技术.经过在多个试验区初步试验表明,井间电磁成像是油藏研究的有效手段,可用于分析剩余油分布,寻找油气富集区,进而达到提高钻探高效井成功率和提高采收率的目的.本文详细介绍对比了这三种方法在理论和实践中的一些特点,并对未来的发展进行了展望.     

Variable-grid reverse-time migration of different seismic survey data

With an increasing demand for high-resolution imaging of complex subsurface structures, thin layers and hidden reservoirs, borehole and cross-well seismic migration methods have become important. However, large differences are observed in the frequency bandwidth between the surface, borehole, and cross-well surveys. Thus, variable-gridbased algorithms have been adapted to reverse-time migration. Further, we introduce Lanczos filtering to ensure the stability of wavefield calculations as well as to decrease the artificial reflections that are caused due to the variable grid size. Finally, we observe that the application of this method to surface survey, borehole, and cross-well seismic data suggests improvements in the delineation of minor fractures and steeply dipping faults.     

联合高分辨率地震和精细测井资料的剩余油气分析

寻找和开发剩余油气藏是提高采收率的关键.以往主要是通过测井、试井资料建立中高层渗透砂岩油藏的井间剩余油分布模型,并采用数学分析方法建立井间剩余油的预测模型.本文介绍了基于高分辨率地震和精细测井分析建立剩余油模型并结合数模分析的剩余油分析技术.利用该技术对辽河油田某断块进行了实际剩余油气分析,在开发方案设计和提高采收率方面取得了明显的效果.     

估计辐射参数的井间电磁波层析成像技术

为了避免使用不合理初始辐射场强和方向性因子带来的误差,研究了估计辐射参数的井间电磁波层析成像技术.通过时域有限差分法模拟表明,天线长度与波长的比值、钻孔充填情况、钻孔周围介质的物性均会影响偶极天线的初始辐射场强或方向性因子;为此结合已知的分层资料,将它们设为未知参数,并设定初始辐射场强与发射点位置相关,方向性因子随射线角度而变化;采用正则化反演方法,由钻孔资料建立了模型方差目标函数,使得反演结果与钻遇的地质特征保持一致.通过理论模型试验和实例应用分析表明,相对于传统射线层析成像方法,估计辐射参数的正则化层析成像技术有助于提高反演的准确性.     

Filter formulation and wavefield separation of cross-well seismic data

Multichannel filtering to obtain wavefield separation has been used in seismic processing for decades and has become an essential component in VSP and cross-well reflection imaging. The need for good multichannel wavefield separation filters is acute in borehole seismic imaging techniques such as VSP and cross-well reflection imaging, where strong interfering arrivals such as tube waves, shear conversions, multiples, direct arrivals and guided waves can overlap temporally with desired arrivals. We investigate the effects of preprocessing (alignment and equalization) on the quality of cross-well reflection imaging wavefield separation and we show that the choice of the multichannel filter and filter parameters is critical to the wavefield separation of cross-well data (median filters, f–k pie-slice filters, eigenvector filters). We show that spatial aliasing creates situations where the application of purely spatial filters (median filters) will create notches in the frequency spectrum of the desired reflection arrival. Eigenvector filters allow us to work past the limits of aliasing, but these kinds of filter are strongly dependent on the ratio of undesired to desired signal amplitude. On the basis of these observations, we developed a new type of multichannel filter that combined the best characteristics of spatial filters and eigenvector filters. We call this filter a ‘constrained eigenvector filter’. We use two real data sets of cross-well seismic experiments with small and large well spacing to evaluate the effects of these factors on the quality of cross-well wavefield separation. We apply median filters, f–k pie-slice filters and constrained eigenvector filters in multiple domains available for these data sets (common-source, common-receiver, common-offset and common-midpoint gathers). We show that the results of applying the constrained eigenvector filter to the entire cross-well data set are superior to both the spatial and standard eigenvector filter results.     

井间地震数据的波动方程偏移成像

针对井间地震数据成像技术的一些缺陷并根据井间地震数据的特点,利用井间上、下行反射波信息,提出了一种基于波动方程的井间地震反射波偏移成像技术,该技术既考虑了井间地震数据的运动学特征(时间信息),又考虑了动力学特征(振幅信息).以PC机集群为计算平台,Linux为操作系统,设计了井间地震炮域波动方程偏移成像并行计算流程,并且在64位联想机群上用井间模型数据和某油田的实际数据对该技术和计算流程进行了测试和试处理,试验结果表明成像方法和并行算法正确、实用且计算效率高.     

稠油蒸汽热采区声波资料异常现象的物理解释及应用

针对稠油蒸汽热采区常见的声波资料异常现象, 根据双相多孔介质声波传播理论及相关实验结果，对于这一特殊的声波测井响应特征进行了解释，认为注入蒸汽的影响导致了纵波速度的低异常及幅度的强衰减, 而使声波测井资料显现出异常高时差值或出现“跳变”现象.据此总结了利用声波资料评价蒸汽波及范围与蒸汽前缘的解释方法，并进行了多井评价实验, 取得了满意结果.同时，也为利用孔隙介质弹性波动理论评价地下蒸汽分布范围的适用性提供了新的现场实际例证.     

利用地震叠前数据预测火山岩裂缝的方法和效果分析——以松辽盆地北部徐家围子断陷营城组火山岩为例

裂缝问题是火山岩复杂岩性油气藏勘探开发中必须考虑的重要因素之一.火山岩储层裂缝预测的准确性直接影响着油气的产能、钻井工艺和增产改造措施等.本文主要根据等效HTI介质(扩容各向异性介质)的特性,立足地下介质各向异性理论,利用三维地震叠前P波在HTI介质中的属性分布特征来检测裂缝的发育情况.利用三维地震叠前P波裂缝检测技术在松辽盆地北部徐家围子断陷深层营城组火山岩中尝试开展了储层裂缝发育预测研究.通过研究建立了火山岩裂缝地震叠前预测方法,并对营城组火山岩裂缝发育情况进行预测,结果表明裂缝主要分布在工区中部构造高部位,发育方向以北北西向为主.最后利用测井资料和钻井产能资料等进行效果分析,证实该技术对于认识火山岩储层裂缝发育具有实际应用价值,说明应用地震资料开展储层裂缝预测具有横向分辨率高、实现井间分布描述和宏观空间分布规律清楚等特点.     

薄油层时移地震差异波形特征探讨

开发导致的时移地震差异代表了油藏的岩石物理性质变化,本文从差异波形角度出发,明确了声波阻抗界面的反射系数与油层声波阻抗变化之间的函数关系,进而分析薄油层时移地震差异波形特征.通过分析得出,开发前后油层阻抗变化越大,时移地震的差异振幅幅度越大;薄油层的差异波形特征仅与油层的声波阻抗变化有关,油层声波阻抗增大导致与地震子波微分形式相同的差异波形,油层声波阻抗减小产生的差异波形与180°相位的地震子波微分形式相同;油层声波阻抗变化方向导致差异波形振幅幅度变化的快慢.     

井筒声场研究回顾与展望

声波测井是测井学科的三大方法之一,在储层评价中起到了重要作用．随着陆上油气勘探目标趋向孔隙结构复杂、非均质性强的油气储集层,基于地层各向同性介质的测井理论显露弊端;因此研究复杂地质条件下的井筒声场分布特征、为储层解释和发展测井新方法提供理论依据成为必然．本文对井筒声场研究进行了回顾,并就当前井筒声场研究现状进行了总结,对其发展趋势和应用前景进行了分析。     

电阻率层析成像的原理与初步应用

电阻率层析成像的基本原理是根据研究区域边界处的电压和电流值确定区域内部电阻率的分布,它同声波和电磁波层析成像的原理有着本质的不同。根据电阻率层析成像的数学原理,从积分变换、线性迭代反演和非线性迭代反演３种基本的反演途径系统地分析和归纳了当前几种主要的电阻率图像重建方法,并讨论了雅可比偏导数矩阵的求解。已开展的电阻率层析成像的野外观测试验,给出了实测的井间和地表两种观测系统的成像结果,分析了技术应用中的特点与限制     

Automatic cross-well tomography: an application of the differential semblance optimization to two real examples

An automatic tomography algorithm, based on differential semblance optimization (DSO), has been used to invert real cross-well seismic data for the background velocity. The method relies on the first-arrival transmitted waves. Given a background velocity model, the traveltimes between the sources and the receivers are computed, then semblance panels are created by back-propagating the data traces. If the velocity model is correct all the first-arrival transmitted waves will be aligned in the semblance panels. The DSO method consists of finding the background velocity by minimizing the L ₂-norm of the difference between adjacent back-propagated traces. Thanks to the good behaviour of this DSO cost function about the solution, a local (gradient) optimization can be performed. This provides a relatively fast algorithm when ray tracing and analytic computation of the gradient are used.
Unfortunately the method fails in the presence of caustics in the data. However, this difficulty can be circumvented by applying suitable masks to the data. This approach is first applied to a synthetic example then to two real data sets: the McElroy data set recorded in West Texas and the NIMR data set recorded in Oman. The results are quite encouraging and similar to those obtained with classical tomography.     

部分饱和孔隙岩石中声波传播数值研究

利用基于Biot理论的孔隙弹性介质的高阶交错网格有限差分算法,模拟了具有随机分布特征的多种流体饱和岩石中声波在中心频率分别为25,50,75,100kHz时的声场特点. 对于一个由两种成分（气和水）饱和的岩石模型, 假设含不同流体的孔隙介质随机分布在不同的宏观区域,该区域尺度远小于计算的声波波长;组成模型的两种随机分布介质具有相同的固体骨架参数、渗透率和孔隙度,但分别被具有不同压缩性、密度和黏滞系数特性的水和气饱和. 计算和统计分析结果表明,在两种孔隙成分随机分布的部分饱和条件下纵波速度比较复杂,除骨架参数外,其变化主要依赖于中心频率、各种孔隙成分饱和度及饱和介质的速度. 比较该随机分布模型、Gassmann理论模型和White的“气包”模型,发现三种模型得到的纵波速度和衰减规律有较好的定性对应关系. 其次,按照这种随机计算模型的处理方法,本文还首次计算了一个三种流体成分充填饱和的例子,即岩石模型中的孔隙被水、油和气部分饱和,计算时保持模型含水饱和度不变而只改变含油和含气饱和度. 在这种计算条件下,纵波速度随中心频率呈增大的趋势但有起伏变化. 声场快照显示了各种转换波在多种孔隙成分充填（两种和三种孔隙成分）岩石中的声场特征,复杂的水-油-气界面的非均匀分布对声场有重要影响,纵波能量主要转换形成了较为复杂的多种慢纵波和横波.