P-wave dispersion and attenuation in fractured and porous reservoirs – poroelasticity approach     

Boris Gurevich  Miroslav Brajanovski  Robert J. Galvin  Tobias M. Müller  Julianna Toms-Stewart 《Geophysical Prospecting》2009,57(2):225-237

Natural fractures in hydrocarbon reservoirs can cause significant seismic attenuation and dispersion due to wave induced fluid flow between pores and fractures. We present two theoretical models explicitly based on the solution of Biot's equations of poroelasticity. The first model considers fractures as planes of weakness (or highly compliant and very thin layers) of infinite extent. In the second model fractures are modelled as thin penny-shaped voids of finite radius. In both models attenuation is a result of conversion of the incident compressional wave energy into the diffusive Biot slow wave at the fracture surface and exhibits a typical relaxation peak around a normalized frequency of about 1. This corresponds to a frequency where the fluid diffusion length is of the order of crack spacing for the first model and the crack diameter for the second. This is consistent with an intuitive understanding of the nature of attenuation: when fractures are closely and regularly spaced, the Biot's slow waves produced by cracks interfere with each other, with the interference pattern controlled by the fracture spacing. Conversely, if fractures are of finite length, which is smaller than spacing, then fractures act as independent scatterers and the attenuation resembles the pattern of scattering by isolated cracks. An approximate mathematical approach based on the use of a branching function gives a unified analytical framework for both models.  相似文献   

Forced imbibition into a limestone: measuring P‐wave velocity and water saturation dependence on injection rate     

Sofia Lopes  Maxim Lebedev  Tobias M. Müller  Michael B. Clennell  Boris Gurevich 《Geophysical Prospecting》2014,62(5):1126-1142

Quantitative interpretation of time‐lapse seismic data requires knowledge of the relationship between elastic wave velocities and fluid saturation. This relationship is not unique but depends on the spatial distribution of the fluid in the pore‐space of the rock. In turn, the fluid distribution depends on the injection rate. To study this dependency, forced imbibition experiments with variable injection rates have been performed on an air‐dry limestone sample. Water was injected into a cylindrical sample and was monitored by X‐Ray Computed Tomography and ultrasonic time‐of‐flight measurements across the sample. The measurements show that the P‐wave velocity decreases well before the saturation front approaches the ultrasonic raypath. This decrease is followed by an increase as the saturation front crosses the raypath. The observed patterns of the acoustic response and water saturation as functions of the injection rate are consistent with previous observations on sandstone. The results confirm that the injection rate has significant influence on fluid distribution and the corresponding acoustic response. The complexity of the acoustic response —‐ that is not monotonic with changes in saturation, and which at the same saturation varies between hydrostatic conditions and states of dynamic fluid flow – may have implications for the interpretation of time‐lapse seismic responses.  相似文献   

Civilian GPS: The Benefits of Three Frequencies   总被引：7，自引：5，他引：2  

Ron Hatch  Jaewoo Jung  Per Enge  Boris Pervan 《GPS Solutions》2000,3(4):1-9

A third civil frequency at 1176.45 MHz will be added to the Global Positioning System (GPS). This new frequency will bring a number of benefits. The aviation user will be one of the prime beneficiaries because the new frequency is in a protected aviation band. Thus, the system will be more robust against interference and jamming. The carrier-phase differential user will also be a prime beneficiary as long as his application has a reasonably short baseline. It is this high accuracy use that is explored in some depth. The process of forming linear combinations of both the code and carrier-phase measurements is studied, and the benefits and problems are explained. ? 2000 John Wiley & Sons, Inc.  相似文献   

Excitation of thermoconvective waves in the continental lithosphere     

Boris I. Birger 《Geophysical Journal International》2000,140(1):24-36

For flows associated with small strains, the rheology of rocks is described by the linear integral (having a memory) law, which reduces to the Andrade law in the case of constant stress. A continental lithosphere with such a rheology is overstable. Thermoconvective waves that propagate through the lithosphere with minimal attenuation have a period of about 200  Myr and a wavelength of the order of 400  km. An initial temperature point-concentrated perturbation in the lithosphere excites amplitude-modulated thermoconvective waves (wave packets). When the initial perturbation occurs in a finite area, thermoconvective waves propagate outwards from this area, and thermoconvective oscillations (standing waves) are established inside the area. Thermoconvective waves induce oscillations of the Earth' surface, accompanied by sedimentation and erosion, and can be considered as a mechanism for the distribution of sediments on continental cratons.  相似文献   

Estimating azimuthal stress‐induced P‐wave anisotropy from S‐wave anisotropy using sonic log or vertical seismic profile data          下载免费PDF全文

Olivia Collet  Boris Gurevich  Guy Duncan 《Geophysical Prospecting》2016,64(5):1305-1317

Most sedimentary rocks are anisotropic, yet it is often difficult to accurately incorporate anisotropy into seismic workflows because analysis of anisotropy requires knowledge of a number of parameters that are difficult to estimate from standard seismic data. In this study, we provide a methodology to infer azimuthal P‐wave anisotropy from S‐wave anisotropy calculated from log or vertical seismic profile data. This methodology involves a number of steps. First, we compute the azimuthal P‐wave anisotropy in the dry medium as a function of the azimuthal S‐wave anisotropy using a rock physics model, which accounts for the stress dependency of seismic wave velocities in dry isotropic elastic media subjected to triaxial compression. Once the P‐wave anisotropy in the dry medium is known, we use the anisotropic Gassmann equations to estimate the anisotropy of the saturated medium. We test this workflow on the log data acquired in the North West Shelf of Australia, where azimuthal anisotropy is likely caused by large differences between minimum and maximum horizontal stresses. The obtained results are compared to azimuthal P‐wave anisotropy obtained via orthorhombic tomography in the same area. In the clean sandstone layers, anisotropy parameters obtained by both methods are fairly consistent. In the shale and shaly sandstone layers, however, there is a significant discrepancy between results since the stress‐induced anisotropy model we use is not applicable to rocks exhibiting intrinsic anisotropy. This methodology could be useful for building the initial anisotropic velocity model for imaging, which is to be refined through migration velocity analysis.  相似文献   

Incorporating Super‐Diffusion due to Sub‐Grid Heterogeneity to Capture Non‐Fickian Transport          下载免费PDF全文

Boris Baeumer  Yong Zhang  Rina Schumer 《Ground water》2015,53(5):699-708

Numerical transport models based on the advection‐dispersion equation (ADE) are built on the assumption that sub‐grid cell transport is Fickian such that dispersive spreading around the average velocity is symmetric and without significant tailing on the front edge of a solute plume. However, anomalous diffusion in the form of super‐diffusion due to preferential pathways in an aquifer has been observed in field data, challenging the assumption of Fickian dispersion at the local scale. This study develops a fully Lagrangian method to simulate sub‐grid super‐diffusion in a multidimensional regional‐scale transport model by using a recent mathematical model allowing super‐diffusion along the flow direction given by the regional model. Here, the time randomizing procedure known as subordination is applied to flow field output from MODFLOW simulations. Numerical tests check the applicability of the novel method in mapping regional‐scale super‐diffusive transport conditioned on local properties of multidimensional heterogeneous media.  相似文献   

斯洛文尼亚和中国贵州喀斯特洞穴动物群的比较研究   总被引：1，自引：1，他引：0  

黎道洪  BorisSket 《中国岩溶》2005,24(1):65-70

2003年7-8月,中方专家野外考察了斯洛文尼亚的8个喀斯特洞穴,采集各类洞穴动物标本500余号,并对主要洞穴环境因子进行了测定,收集相关资料200余篇。2004年2月斯方专家野外考察了中国贵州12个喀斯特洞穴,采集各类动物标本1000余号。本文对两国喀斯特洞穴内的主要动物群进行了比较研究,结果是斯洛文尼亚的物种丰富度比贵州的高: 前者有533种,密度为65. 80种/1000km2; 后者有238种,密度为0. 54种/1000km2。从洞穴蝙蝠看,两国均为24种; 但区系成分不同,斯洛文尼亚全为古北界种, 贵州则主要为东洋界成分( 83% )。此外,文中还对比分析了斯洛文尼亚施科茨杨洞和贵州龙洞内的动物群落组成: 前者以水生种为主体,后者全为陆生种。最后,对斯洛文尼亚无真洞穴鱼的问题及两国的洞穴动物起源进行了探讨。   相似文献   

Comprehensive Biogeochemical Analysis of Nitrogen Transformation Parameters     

Marija Perovic  Obradovic  Vesna  Zuber-Radenković  Vesna  Obrovski  Boris  Vojinovic-Miloradov  Mirjana  Dimkić  Milan 《Water Resources》2020,47(1):156-170

Water Resources - The potential for nitrogen attenuation in anoxic groundwater by examining the concentration and distribution patterns of electron acceptors, electron donors and microbiological...  相似文献   

Keeping the lead: How to strengthen shark conservation and management policies in Canada     

Aurelie Cosandey Godin  Boris Worm 《Marine Policy》2010

Internationally, shark conservation is now being recognized as a major environmental challenge, but management efforts to halt the overexploitation of sharks have lagged behind. This review examines the state of knowledge for shark species in Canadian waters and analyzes the role of existing management and legislation in ensuring shark conservation. Despite Canada's early leadership, the present management framework reveals major shortcomings with regard to legal protection, bycatch and finning regulations. These problems are not unique to Canada but illustrate broader issues pertaining to the global management of endangered fish species. To strengthen the conservation and management of sharks, this paper recommends a set of key policies and management priorities, which exemplify proper precautionary management of endangered shark species in Canada and could serve as a blueprint for improving conservation efforts internationally. A structured approach for grading progress in shark conservation efforts against best practices is also presented and could be used as a goalpost elsewhere.  相似文献   

Vertical structure variability in a seasonal simulation of a medium-resolution regional model of the Eastern South Pacific     

Boris Dewitte  Marcel Ramos  Vincent Echevin  Oscar Pizarro  Yves duPenhoat 《Progress in Oceanography》2008,79(2-4):120

A seasonal simulation from a medium-resolution ocean general circulation mode (OGCM) is used to investigate the vertical structure variability of the Southeast Pacific (SEP). The focus is on the extra-tropical Rossby wave (ETRW) variability and associated forcing mechanism. Some aspects of the model mean state are validated from available observations, which justifies a vertical mode decomposition of the model variability. The analysis of the baroclinic mode contributions to sea level indicates that the gravest mode is dominant over most of the domain at all frequencies. Annual variability is on average twice as large as the semi-annual variability which is confined near the coast for all the modes. The first baroclinic mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude. The higher-order modes only contribute near the coast where they are associated with vertically propagating energy. The residual variability, which is the energy at all timescales other than annual and semi-annual periods peaks offshore between 20°S and 30°S for all baroclinic modes. The third baroclinic mode also exhibits a relative maximum variability off the coast of Peru south of the critical latitude of the annual cycle (13°S), where the Peru–Chile Undercurrent is the most intense. Sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non-linear interaction between annual Rossby waves and the mean flow, while the annual ETRWs in the model result from the summed-contribution from both the local wind stress and remote equatorial forcing. Overall the study extends the classical analysis of sea level variability in the SEP based on linear theory, and suggests that the peculiarities of the baroclinic modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability.  相似文献