Gas hydrate saturation from acoustic impedance and resistivity logs in the Shenhu area, South China Sea

During the China’s first gas hydrate drilling expedition -1 (GMGS-1), gas hydrate was discovered in layers ranging from 10 to 25 m above the base of gas hydrate stability zone in the Shenhu area, South China Sea. Water chemistry, electrical resistivity logs, and acoustic impedance were used to estimate gas hydrate saturations. Gas hydrate saturations estimated from the chloride concentrations range from 0 to 43% of the pore space. The higher gas hydrate saturations were present in the depth from 152 to 177 m at site SH7 and from 190 to 225 m at site SH2, respectively. Gas hydrate saturations estimated from the resistivity using Archie equation have similar trends to those from chloride concentrations. To examine the variability of gas hydrate saturations away from the wells, acoustic impedances calculated from the 3 D seismic data using constrained sparse inversion method were used. Well logs acquired at site SH7 were incorporated into the inversion by establishing a relation between the water-filled porosity, calculated using gas hydrate saturations estimated from the resistivity logs, and the acoustic impedance, calculated from density and velocity logs. Gas hydrate saturations estimated from acoustic impedance of seismic data are ∼10-23% of the pore space and are comparable to those estimated from the well logs. The uncertainties in estimated gas hydrate saturations from seismic acoustic impedances were mainly from uncertainties associated with inverted acoustic impedance, the empirical relation between the water-filled porosities and acoustic impedances, and assumed background resistivity.     

Application of constrained sparse spike inversion in reservoir predication:a case study of Oriente Basin in South America

In the conditions of low Signal-to-Noise Ratio(SNR) of seismic data and a small quality of log information,the consequences of seismic interpretation through the impedance inversion of seismic data could be more precise. Constrained sparse spike inversion(CSSI) has advantage in oil and gas reservoir predication because it does not rely on the original model. By analyzing the specific algorithm of CSSI,the accuracy of inversion is controlled. Oriente Basin in South America has the low amplitude in geological...     

三维电磁阵列剖面法的基本原理及应用

本文论述了三维电磁阵列剖面法的基本原理，并从理论上论述了大地电磁测深中的静态效应是由电磁响应中与频率无关的静态项引起的，基于这一原理，本文提出了三维ＥＭＡＰ野外采集方式和数据处理方程。三维ＥＭＡＰ法不仅能消除ＭＴ中的静态效应，而且由于采集信息量大大增加，较常规ＭＴ有更好的地质效果，文中给出的实例证明了这一点。     

Simple formulas for the dynamic stiffness of pile groups

Simple formulas are derived for the dynamic stiffness of pile group foundations subjected to horizontal and rocking dynamic loads. The formulations are based on the construction of a general model of impedance matrices as the condensation of matrices of mass, damping, and stiffness, and on the identification of the values of these matrices on an extensive database of numerical experiments computed using coupled finite element–boundary element models. The formulations obtained can be readily used for the design of both floating piles on homogeneous half‐space and end‐bearing piles and are applicable for a wide range of mechanical and geometrical parameters of the soil and piles, in particular for large pile groups. For the seismic design of a building, the use of the simple formulas rather than a full computational model is shown to induce little error on the evaluation of the response spectra and time histories. Copyright © 2009 John Wiley & Sons, Ltd.     

Probabilistic impedance of foundation: Impact of the seismic design on uncertain soils

In the linear seismic design of buildings, the (deterministic) substructure method is a customary and efficient approach. However, the existence of spatial variability in the parameters of the mechanical model of the soil, as well as parametric errors, calls for the use of probabilistic approaches in order to provide a reliable design of the structure. The construction of probabilistic models of the soil impedance matrix provides a natural path to such approaches within the context of the substructure method. Two main techniques are described in this paper: a parametric one, typically using the stochastic finite element method, and a nonparametric one, which was introduced more recently. The latter is explored more specifically, and the possibilities it offers in terms of seismic design are presented. In particular, it is shown that it allows for the estimation of quantiles of the quantities of interest, rather than confidence intervals, which lead to highly conservative design. Copyright © 2008 John Wiley & Sons, Ltd.     

基于Fatti近似的弹性阻抗方程及反演

用Connolly的弹性阻抗(EI,elastic impedance)公式进行反演只能直接得到纵、横波速度和密度的信息,然后才可间接计算得到纵横波阻抗等其它的参数数据体,这样便增加了一步误差使数据的准确性降低.本文首先针对该方法的这些缺点和不足,提出了以Zoeppritz方程的Fatti近似为基础一种新的弹性阻抗公式,由该公式可得到比用Fatti近似更准确的反射系数,然后对这个公式进行了标准化以实现不同角度的弹性阻抗间量纲的统一,最后用标准化后的公式进行了反演,从反演得到的不同角度的弹性阻抗数据体中可直接提取得到纵横波阻抗数据体.应用实例表明用这种方法提取得到的纵横波阻抗更加稳定、准确,而且能很好地反映储层信息.这种新的方法是对以Connolly公式为基础的传统方法的改进.     

适于陡坡带砂砾岩体的地震资料叠前时间偏移处理技术

随着勘探程度的不断提高,断陷盆地陡坡带砂砾岩体油气藏成为了重点勘探对象之一,但陡倾角的大断层、非均质性强的砂砾岩体使得常规的叠后偏移成像方法成果难以满足勘探开发的需要.采用叠前时间偏移处理技术,开展针对性的叠前预处理技术、精细的速度模型建立和关键参数的合理选取等研究,三维叠前时间偏移处理较常规三维叠后时间偏移处理获得了较高质量的成像剖面,且输出的道集可以用于砂砾岩体储层描述研究.     

VTI介质中的弹性阻抗与参数提取

弹性阻抗是波阻抗的扩展,可以更好的反映储层和流体性质.常规弹性阻抗方程忽略了各向异性的影响,不能正确地描述各向异性介质中弹性阻抗的性质.本文基于Ruger给出的VTI介质反射系数近似公式,结合Connolly推导弹性阻抗的思想,推导出了一种VTI介质中的弹性阻抗方程.通过引入归一化常数,对方程进行了标准化,消除了方程量纲随角度变化而变化的不足.结合常规弹性阻抗反演的流程,得出了VTI介质中弹性阻抗反演的流程.最后,开展了从VTI介质弹性阻抗数据体中提取岩石物性参数的方法研究.数值测试表明,所讨论的参数提取方法具有一定的理论和应用价值.     

奇异性分析方法在地震资料解释及反演研究中的应用

本文引入启动函数拓展传统的地层转换模型,在该模型中利用奇异性信息量化地层速度的突变特征,并基于传统的褶积模型研究奇异性信息在波阻抗到合成地震记录之间的传递性.研究结果表明,地震记录中较好地保留了地层介质的奇异性特征,因而从地震记录中提取的奇异性信息除了可以帮助进行地震解释外,还可以作为介质波阻抗反演的有力的支持工具.     

Identifying causes of ground-penetrating radar reflections using time-domain reflectometry and sedimentological analyses

Ground-penetrating radar (GPR) is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves. However, little is known about the exact cause of GPR reflections because few studies have coupled wave theory to petrophysical data. In this study, a 100- and 200-MHz GPR survey was conducted on aeolian deposits in a quarry. Time-domain reflectometry (TDR) was used to obtain detailed information on the product of relative permittivity (ɛ_r) and relative magnetic permeability (μ_r), which mainly controls the GPR contrast parameter in the subsurface. Combining TDR data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and ɛ_rμ_r. Synthetic radar traces, constructed using the TDR logs and sedimentological data from the lacquer peels, were compared with the actual GPR sections. Numerous peaks in ɛ_rμ_r, which are superimposed on a baseline value of 4 for dry sand, are caused by potential GPR reflectors. These increases in ɛ_rμ_r coincide with the presence of either organic material, having a higher water content and relative permittivity than the surrounding sediment, or iron oxide bands, enhancing relative magnetic permeability and causing water to stagnate on top of them. Sedimentary structures, as reflected in textural change, only result in possible GPR reflections when the volumetric water content exceeds 0·055. The synthetic radar traces provide an improved insight into the behaviour of radar waves and show that GPR results may be ambiguous because of multiples and interference.