Quantitative evaluation of gas hydrate reservoir by AVO attributes analysis based on the Brekhovskikh equation

AVO (Amplitude variation with offset) technology is widely used in gas hydrate research. BSR (Bottom simulating reflector), caused by the huge difference in wave impedance between the hydrate reservoir and the underlying free gas reservoir, is the bottom boundary mark of the hydrate reservoir. Analyzing the AVO attributes of BSR can evaluate hydrate reservoirs. However, the Zoeppritz equation which is the theoretical basis of conventional AVO technology has inherent problems: the Zoeppritz equation does not consider the influence of thin layer thickness on reflection coefficients;the approximation of the Zoeppritz equation assumes that the difference of wave impedance between the two sides of the interface is small. These assumptions are not consistent with the occurrence characteristics of natural gas hydrate. The Brekhovskikh equation, which is more suitable for thin-layer reflection coefficient calculation, is used as the theoretical basis for AVO analysis. The reflection coefficients calculated by the Brekhovskikh equation are complex numbers with phase angles. Therefore, attributes of the reflection coefficient and its phase angle changing with offset are used to analyze the hydrate reservoir's porosity, saturation, and thickness. Finally, the random forest algorithm is used to predict the reservoir porosity, hydrate saturation, and thickness of the hydrate reservoir. In the synthetic data, the inversion results based on the four attributes of the Brekhovskikh equation are better than the conventional inversion results based on the two attributes of Zoeppritz, and the thickness can be accurately predicted. The proposed method also achieves good results in the application of Blake Ridge data. According to the method proposed in this paper, the hydrate reservoir in the area has a high porosity (more than 50%), and a medium saturation (between 10% and 20%). The thickness is mainly between 200m and 300m. It is consistent with the previous results obtained by velocity analysis.

Application of AVO and Seismic Attributes Techniques for Characterizing Pliocene Sand Reservoirs in Darfeel Field, Eastern Mediterranean, Egypt

Mediterranean Sea considered as a main hydrocarbon province in Egypt as a huge reservoirs have been discovered till now. Port Fouad marine is a gas and condensate field located in Eastern Mediterranean Sea about 30 KM off Egyptian coast, in a water depth of about 30 m. The Concession is operated by PETROBEL on behalf of Petrosaid (Port Said Petroleum Company). The field was put on production on April 1996, from the Miocene turbidities sands of Wakar Formation plus Pilocene Kafr EL Sheikh Formation. Darfeel field is located within Port Fouad Concession, seven wells have been drilled till now and producing from Pliocene section (Kafr El Sheikh Formation). Pliocene is the main reservoir in Darfeel field which characterized by turbidities sand stone. The aim of this work is to identify the distribution of turbidities sand and characterize sand reservoirs using AVO (amplitude verses offset) and seismic attributes techniques. The workflow is starting from conventional seismic interpretation, maps (time, depth, and amplitude), depositional environments, and finally structure setting. In addition to use some of unconventional seismic interpretation such as seismic attributes. AVO analysis and attributes had been applied in a temp of differentiate between gas sand reservoirs and non-gas reservoirs. The final result aid to identify the reservoir distribution and characterization of sand reservoirs through the field. So, the use of different seismic techniques is powerful techniques in identifying reservoir distribution.

致密砂岩AVO属性的贝叶斯岩相划分方法——以川中地区侏罗系沙溪庙组沙一段为例

地震勘探中“高速或低速致密砂岩储层”地震响应复杂、非均质性强、反演中的低频模型难以建立。在基于Bayesian分类的AVO(BF-AVO)截距、梯度属性及孔隙度等指标约束下,对川中地区侏罗系沙溪庙组致密砂岩的岩相进行了划分。研究结果表明:(1)AVO分析是以弹性波理论为基础,根据其振幅随偏移距的变化规律来反映地下岩性及其孔隙流体的性质,在应用过程中,根据不同岩性和流体的相关参数组合进行AVO正演,获得已知岩性和流体性质的AVO特征,与实际地震记录进行对比,建立岩性和油气识别的地震响应模型。(2)利用模型和实际数据建立的孔隙度与截距、梯度属性的交会分析,厘清三者的内在联系,确定岩相划分标准,并拟合出不同岩相的概率密度函数,划分出不同孔隙度区间的岩相,从而实现孔隙度的半定量预测。(3)川中侏罗系沙溪庙组沙一段致密砂岩的岩相预测过程中,基于Bayesian分类,以概率分布预测的岩相与实钻结果吻合度高,达93.75%,验证了该方法的可行性和有效性。

AVO属性交会图解释技术在碳酸盐岩储层预测中的应用

AVO属性交会图解释技术是通过正演模型提取AVO属性,再根据模型和实际地震数据在AVO属性交会 图上的分布关系,建立储层岩性参数、含流体特征与AVO属性间的对应关系。该法以模型正演分析为基础,以 地震数据AVO属性为外推控制条件,将地震、地质和测井信息紧密地结合起来,从而达到识别储层的目的。本 文以川东LJZ地区飞仙关鲕滩储层为例,通过对己知钻、测井资料分析和模型正演,确定鲕滩储层的地震属性 响应模式及其交会图上的分布特征,识别储层岩性和含流体性质,进而确定储层的气水界面。

Reservoir prediction using pre-stack inverted elastic parameters

This is a case study of the application of pre-stack inverted elastic parameters to tight-sand reservoir prediction. With the development of oil and gas exploration, pre-stack data and inversion results are increasingly used for production objectives. The pre-stack seismic property studies include not only amplitude verse offset （AVO） but also the characteristics of other elastic property changes. In this paper, we analyze the elastic property parameters characteristics of gas- and wet-sands using data from four gas-sand core types. We found that some special elastic property parameters or combinations can be used to identify gas sands from water saturated sand. Thus, we can do reservoir interpretation and description using different elastic property data from the pre-stack seismic inversion processing. The pre- stack inversion method is based on the simplified Aki-Richard linear equation. The initial model can be generated from well log data and seismic and geologic interpreted horizons in the study area. The input seismic data is angle gathers generated from the common reflection gathers used in pre-stack time or depth migration. The inversion results are elastic property parameters or their combinations. We use a field data example to examine which elastic property parameters or combinations of parameters can most easily discriminate gas sands from background geology and which are most sensitive to pore-fluid content. Comparing the inversion results to well data, we found that it is useful to predict gas reservoirs using λ, λρ, λ/μ, and K/μ properties, which indicate the gas characteristics in the study reservoir.

粒子滤波非线性AVO反演方法

提出一种新的AVO非线性反演方法,即利用粒子滤波器来求解AVO非线性贝叶斯反演问题。利用随机带权样本逼近后验概率.论文首先论述了粒子滤波器的基本原理,包括状态转移模型与观测模型,权值预测与更新,重要性密度采样等粒子滤波器应用中的关键技术.然后建立了适合于AVO反演的粒子滤波器状态转移模型和观测模型.最后,利用该方法分别对模型数据和实际资料进行了反演计算.反演结果表明,该方法具有较好的稳定性,在AVO反演中具有的一定的应用潜力.同时对地球物理反演的其他问题求解也提供了一条新的途径.

基于入射角的AVO近似及属性提取

本文基于佐普里兹方程的Aki和Shuey近似式,利用斯内尔定律,建立了反射系数与上层入射角、岩石物性参数间新的近似表达式。此改进近似式将反射系数表示为上层入射角的函数,其计算结果的误差较现有常规方法小,为下一步准确提取AVO属性奠定了基础。应用本文近似式对模型和实际数据的处理均取得了显著效果。

利用AVO属性研究构造煤的分布规律

现行的煤田地震勘探技术主要解决煤层构造问题,不能对与瓦斯突出相关的构造煤分布、煤层和围岩的透气性做出评价,即无法评价煤岩层的岩性。近年来,国内外地球物理学家提出了利用AVO技术研究煤岩层岩性,查明构造煤发育区和瓦斯富集带。笔者首先对构造煤模型进行正演模拟,获得三维数据体;然后利用不同Zoeppritz近似方程对三维数据体进行AVO反演,得到多种AVO属性,通过对AVO属性的分析研究,提出利用Aki和Richards近似公式AVO反演得到的B值数据体、Shuey近似公式AVO反演得到的G值和Δσ值数据体作为AVO解释的基础;最后利用煤田实际三维地震资料进行AVO反演,尝试利用AVO属性圈定构造煤发育区和瓦斯富集带。

薄储层的反射特性及其AVO属性分析

针对薄储层地震反射模型,利用Gassmann流体置换方程分析了薄储层的孔隙度和含油、含气饱和度等因素对P波速度、S波速度和介质密度的影响;根据薄层反射动力学和粘弹各向异性理论,利用AVO技术研究了薄储层物性参数与地震反射特征之间的关系。研究结果表明,含气饱和度的变化使气体的可压缩性发生改变,P波速度随含气饱和度的增加由急剧降低转为缓慢升高;孔隙度的变化对P波速度、S波速度和介质密度的影响要大于含油、含气饱和度变化的影响;不同孔隙度薄层的AVO响应差异明显;孔隙度增加,AVO属性中的截距和梯度对含气饱和度的变化比对含油饱和度的变化敏感;薄层反射的AVO响应与薄层厚度有关,薄层厚度增加时,对其含油和含气饱和度的变化,梯度属性比截距属性更敏感。

基于叠前深度偏移的AVO反演及解释

本文针对复杂构造地区AVO技术应用的难点,在详细阐明了偏移对改善AVO分析效果的重要意义前提下,为实现在复杂构造地区有效地进行AVO研究,将叠前深度偏移引入到AVO处理中,通过偏移来改善资料的质量.在此基础上进行了揭示岩性及流体变化特征的多种参数的AVO反演,并探讨了利用多种AVO属性的综合分析来确定和解释AVO异常的方法.利用本文提出的复杂构造AVO研究思路对实际资料进行了分析,结果说明了该方法的可行性.

Converted wave AVO inversion for average velocity ratio and shear wave reflection coefficient

Based on the empirical Gardner equation describing the relationship between density and compressional wave velocity, the converted wave reflection coefficient extrema attributes for AVO analysis are proposed and the relations between the extrema position and amplitude, average velocity ratio across the interface, and shear wave reflection coefficient are derived. The extrema position is a monotonically decreasing function of average velocity ratio, and the extrema amplitude is a function of average velocity ratio and shear wave reflection coefficient. For theoretical models, the average velocity ratio and shear wave reflection coefficient are inverted from the extrema position and amplitude obtained from fitting a power function to converted wave AVO curves. Shear wave reflection coefficient sections have clearer physical meaning than conventional converted wave stacked sections and establish the theoretical foundation for geological structural interpretation and event correlation. ＂The method of inverting average velocity ratio and shear wave reflection coefficient from the extrema position and amplitude obtained from fitting a power function is applied to real CCP gathers. The inverted average velocity ratios are consistent with those computed from compressional and shear wave well logs.

频变AVO含气性识别技术研究与应用

在常规AVO理论的基础上,频变AVO属性计算方法利用多尺度裂缝介质模型中物性参数具有频变特征的优势,基于Zoeppritz方程建立反射系数与频率之间的数学关系,推导出截距、梯度、碳氢检测因子、流体检测因子、拟泊松比等AVO属性与频率之间的数学关系.应用地震反演方法,综合地质、地震、测井等数据,反演出高精度的频变AVO属性,在天然气敏感属性分析的基础上建立起频变AVO含气性识别技术.将该技术应用到川西新场陆相深层须家河组碎屑岩储层的含气性识别中,在孔隙度通常在1%～4%,渗透率普遍低于0.06×10-3μm2的致密背景下,较准确地预测了孔隙度大于4%、渗透性偏高的富气优质储层分布带,为该区含气性识别难题的解决和钻井成功率的提高,提供了重要的技术支撑.

K-L变换在AVO交会图分析中的应用

AVO属性交会图分析是进行AVO解释的最有效手段之一,但是由于AVO属性参数之间具有统计相关性,因此利用AVO属性交会得到的解释结果有不确定性。为了解决这一问题,本文提出对原交会图的属性空间进行K-L变换,再利用新空间的交会图来辅助识别交会异常。文中简要地介绍了离散K-L变换基本原理及实现步骤,并应用该方法对实际资料进行了AVO属性交会图分析,取得了较好的效果。

胜利油田YA地区三维地震资料AVO处理

近几年 ,胜利油田一直在进行利用AVO技术寻找天然气藏的研究 ,但由于资料所限 (二维AVO分析 ) ,并没有取得太大的进展。针对这种情况 ,我们选择了胜利油田主要天然气产区之一的YA地区进行了三维地震资料的AVO处理研究。从已知气藏入手 ,对三个典型气藏进行了正演模型研究 ;进行了实际资料的处理 (道集处理与三维AVO处理 ) ,得到了分偏移距叠加数据体、分角度叠加数据体、三维AVA数据体和三维碳氢检测等属性体 ,将这些数据体进行三维可视化解释 ,可以准确确定已知气藏及异常区的空间展布范围 ,使AVO技术实现了从二维到三维的转化 ;结合已知气藏的特征与分类 。

TTI介质各向异性参数多波反演与PS波AVO分析

把遗传算法引入到了TTI介质AVO信息反演各向异性参数的过程中,依据TTI介质PP波、PS波反射系数公式,建立Thomsen参数和TTI介质对称轴倾角、方位角的目标函数,分别通过PP波和PS波的反射系数反演出了各向异性参数和对称轴倾角、方位角等信息.文中对反演结果的精确度和稳定性进行了分析,发现PS波的反演结果优于PP波反演结果;对称轴倾角的反演准确性明显优于对称轴方位角.本文通过模型正演合理解释了这一现象的原因.最后,本文通过对PS波AVO梯度的研究,提出了利用PS波振幅定性分析TTI介质对称轴倾角的方法.

基于共炮偏移与谐波分解的AVO反演

鉴于常规AVO反演在CMP道集中进行,从而不可避免地导致AVO分析的精度降低。Robert利用谐波分解法获得角度道集,更适合AVO反演。本文改进了谐波分解法提取角度道集的算法,并在此基础上形成了利用炮集数据进行AVO反演的整体思路,可以概括为:从炮集数据出发,利用单程波保幅偏移使振幅得以保真和归位;运用在炮集数据上抽取角度道集的谐波分解算法,获得入射角和反射系数的准确对应关系;借助于Aki和Richards[7]的近似式,进行密度及纵横波速度等AVO属性的反演。通过实际数据算例验证了本文方法反演精度明显高于常规AVO分析结果。

改进快速模拟退火方法进行AVO岩性参数反演

以广义波尔兹曼的吉布斯（ Ｂｏｌｔｚｍａｎｎ＿ Ｇｉｂｂｓ） 统计理论为基础，将数论（ｎｕｍｅｒａｌ） 和依赖于温度的似柯西（ Ｃａｕｃｈｙ） 分布相结合建立一种新的扰动模型，改进接受概率，提出了一种非常快速模拟退火法（ｖｅｒｙ ｆａｓｔ ｓｉｍｕｌａｔｅｄ ａｎｎｅａｌｉｎｇ） ．通过多参数的振幅随炮检距变化（ Ａ Ｖ Ｏ）的合成数据和实际资料试算结果表明，该方法能在高温下进行大范围内的搜寻，解的稳定性好和抗随机干扰能力强，反演结果精度较高。

基于频变AVO反演的频散属性估算方法及其应用

地震波在含油气储层传播时会发生较强的能量衰减和速度频散,以特定的频散属性定量地表征速度频散程度,并可将其作为一种新的烃类指示因子用于储层预测。基于介质界面反射系数随频率变化的数学关系,本文研究了频变振幅随炮检距的变化规律;应用贝叶斯反演理论,可从分频叠前道集中反演出表征纵波速度频散程度和频散程度随炮检距变化的梯度等属性参数。模型测试结果验证了本文所述方法的可行性及频散属性识别油气的有效性,实际应用则进一步说明据此反演得到的频散属性可为储层烃类检测提供较可靠的数据支撑,有效地降低了烃类检测的多解性。

AVO属性分析在天然气水合物地震解释中的应用

利用AVO(Amplitude Versus Offset)属性分析技术,对南海北部测线B进行了AVO属性处理,结合BSR(Bottom Simulating Reflector),振幅空白带以及波形极性反转等多种水合物赋存信息,对水合物成矿带及游离气带的AVO属性特征进行了综合研究。结果表明:①AVO1和AVO9可用于检测BSR和水合物成矿带;②AVO4、AVO6、AVO9用于游离气带的检测;③AVO1高截距值表示上、下层P波速度差值大,弱反射或空白反射表示水合物分布均匀,是水合物富集和稳定的表现;④AVO4高值表示有游离气存在,强反射特征为游离气顶的反射;⑤AVO6正值,表示有游离气存在,强反射的发育厚度代表游离气的发育厚度;⑥AVO9低幅值表示水合物成矿带,正值表示游离气带。研究结果表明,高精度AVO分析不仅可以帮助寻找水合物矿点,还可以进一步判定水合物的富集层位。

复杂气藏AVO属性交会含气性检测应用研究

乌审召地区沉积相带复杂多变、储层非均质性强、气层AVO响应多变,含气储层预测难度大.本文在精细岩石物理分析的基础上,选取具有明确岩石物理含义且对气层敏感的AVO属性,针对不同AVO分类井进行AVO正演建模和流体替代分析,研究该区AVO气层响应特征及属性交会规律,并确定了以NI和PR属性交会为核心的AVO气层检测方法及流程,为探索解决该区含气性预测难题提供了有价值的思路.利用这套方法,对该区储层进行了含气性检测,取得了良好效果.