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1.
Casey Saenger Thomas M. Cronin Debra Willard Jeffrey Halka Randy Kerhin 《Estuaries and Coasts》2008,31(3):492-500
We calculated Chesapeake Bay (CB) sediment and carbon fluxes before and after major anthropogenic land clearance using robust monitoring, modeling and sedimentary data. Four distinct fluxes in the estuarine system were considered including (1) the flux of eroded material from the watershed to streams, (2) the flux of suspended sediment at river fall lines, (3) the burial flux in tributary sediments, and (4) the burial flux in main CB sediments. The sedimentary maximum in Ambrosia (ragweed) pollen marked peak land clearance (~1900 a.d.). Rivers feeding CB had a total organic carbon (TOC)/total suspended solids of 0.24?±?0.12, and we used this observation to calculate TOC fluxes from sediment fluxes. Sediment and carbon fluxes increased by 138–269% across all four regions after land clearance. Our results demonstrate that sediment delivery to CB is subject to significant lags and that excess post-land clearance sediment loads have not reached the ocean. Post-land clearance increases in erosional flux from watersheds, and burial in estuaries are important processes that must be considered to calculate accurate global sediment and carbon budgets. 相似文献
2.
This paper is concerned with numerical tests of several rock physical relationships. The focus is on effective velocities and scattering attenuation in 3D fractured media. We apply the so‐called rotated staggered finite‐difference grid (RSG) technique for numerical experiments. Using this modified grid, it is possible to simulate the propagation of elastic waves in a 3D medium containing cracks, pores or free surfaces without applying explicit boundary conditions and without averaging the elastic moduli. We simulate the propagation of plane waves through a set of randomly cracked 3D media. In these numerical experiments we vary the number and the distribution of cracks. The synthetic results are compared with several (most popular) theories predicting the effective elastic properties of fractured materials. We find that, for randomly distributed and randomly orientated non‐intersecting thin penny‐shaped dry cracks, the numerical simulations of P‐ and S‐wave velocities are in good agreement with the predictions of the self‐consistent approximation. We observe similar results for fluid‐filled cracks. The standard Gassmann equation cannot be applied to our 3D fractured media, although we have very low porosity in our models. This is explained by the absence of a connected porosity. There is only a slight difference in effective velocities between the cases of intersecting and non‐intersecting cracks. This can be clearly demonstrated up to a crack density that is close to the connectivity percolation threshold. For crack densities beyond this threshold, we observe that the differential effective‐medium (DEM) theory gives the best fit with numerical results for intersecting cracks. Additionally, it is shown that the scattering attenuation coefficient (of the mean field) predicted by the classical Hudson approach is in excellent agreement with our numerical results. 相似文献
3.
Mirko Siegert Marcel Gurris Claudia Finger Erik H. Saenger 《Geophysical Prospecting》2022,70(1):152-172
In this paper, the methods of digital rock physics are applied to determine pressure-dependent effective thermal conductivity in rock samples. Simulations are performed with an in-house three-dimensional finite volume code. In the first step, four numerical models are derived from a given tomographic scan of Berea sandstone. Consequently, simulations of the thermal conductivity at ambient conditions are performed and validated with experimental data. In a second step, a new workflow for the determination of the pressure-dependent thermal conductivity in rock samples is elaborated, tested and calibrated. Results originating from the derived workflow show very good agreement with experimental data. 相似文献
4.
The modelling of elastic waves in fractured media with an explicit finite‐difference scheme causes instability problems on a staggered grid when the medium possesses high‐contrast discontinuities (strong heterogeneities). For the present study we apply the rotated staggered grid. Using this modified grid it is possible to simulate the propagation of elastic waves in a 2D or 3D medium containing cracks, pores or free surfaces without hard‐coded boundary conditions. Therefore it allows an efficient and precise numerical study of effective velocities in fractured structures. We model the propagation of plane waves through a set of different, randomly cracked media. In these numerical experiments we vary the wavelength of the plane waves, the crack porosity and the crack density. The synthetic results are compared with several static theories that predict the effective P‐ and S‐wave velocities in fractured materials in the long wavelength limit. For randomly distributed and randomly orientated, rectilinear, non‐intersecting, thin, dry cracks, the numerical simulations of velocities of P‐, SV‐ and SH‐waves are in excellent agreement with the results of the modified (or differential) self‐consistent theory. On the other hand for intersecting cracks, the critical crack‐density (porosity) concept must be taken into account. To describe the wave velocities in media with intersecting cracks, we propose introducing the critical crack‐density concept into the modified self‐consistent theory. Numerical simulations show that this new formulation predicts effective elastic properties accurately for such a case. 相似文献
5.
An overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks 总被引：1，自引：0，他引：1
Beatriz Quintal Nicola Tisato Erik H. Saenger Claudio Madonna 《Geophysical Prospecting》2014,62(6):1211-1223
Intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability, fluid properties, and saturation. However, in order to use attenuation as an attribute to extract information on rock/fluid properties from seismic data, experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies. An appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method, but technical challenges kept this technique from being widely used. There is a need for the standardization of devices employing this method, and a comparison of existing setups is a step towards it. Here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency‐dependent attenuation in fluid‐saturated and/or dry reservoir rocks under small strains (10?8–10?5). We list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one. We also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far. 相似文献
6.
We tested the use of hydrogen isotopic ratios (δD) of lipids in marine lake sediments from the Micronesian Republic of Palau against the instrumental record of the last century to assess their capacity to record past hydrological changes of the Western Pacific Warm Pool. δD values of the algal lipid biomarker dinosterol (δDDino) and the more generic palmitic acid (δDPA) were found to be sensitive indicators of the intensity of regional precipitation, as recorded by the Southern Oscillation Index (SOI). The observed sensitivity is caused by the combined effect of: 1) The amount effect in tropical precipitation; 2) Dilution of the isotopically heavy saline surface waters with light precipitation; 3) A salinity effect on the biosynthetic D/H fractionation between lipid and lake water. Both lake water δD (δDLake) and δDDino could be expressed as a quadratic function of either precipitation or lake water salinity. δDDino values were used to reconstruct past hydrological changes of the region. Long-term variations in the strength and sign of the El Niño - Southern Oscillation (ENSO) since the Little Ice Age (LIA, ～1450–1850 A.D.) and during the early Holocene (～7–9 kyr BP) appeared to dominate decadal variability, and indicate very dry conditions during the LIA. Early Holocene δDDino values were on average ～10‰ higher than those of recent centuries, which we interpret as a result of millennial scale hydrologic and water mass changes on a global level. The similar ～35‰ range of δD changes during the early Holocene and last several centuries imply a similar range of decadal-centennial hydrologic variability during those two climate regimes. Our results indicate that a correlation exists between solar irradiance levels and tropical Pacific climate. 相似文献
7.
8.
Marc-André Lambert Stefan M. Schmalholz Erik H. Saenger Brian Steiner 《Geophysical Prospecting》2009,57(3):393-411
Results of a passive microtremor survey at an oil and gas field in Voitsdorf, Austria, are presented. The survey consists in six parallel profiles approximately 9 km long over two hydrocarbon reservoirs. For each profile the seismic wavefield was recorded synchronously at 11 in-line stations. The measurements were conducted with broadband seismometers and lasted, for each profile, at least 12 hours overnight. Data interpretation is based on a comprehensive data set and on the analysis of four different spectral attributes. These attributes quantify the characteristic features of the wavefield's Fourier spectra in the low-frequency range (<10Hz). One attribute quantifies the spectral energy in the vertical wavefield component, another attribute quantifies the maxima in vertical-to-horizontal spectral ratios and two attributes describe the frequency shifts of peaks within the spectra of vertical and horizontal wavefield components. Due to temporal variations of the signals we combine the long-term measurements (several hours of continuous records) of multiple profiles. This procedure considerably enhances the consistency of each spectral attribute and makes them suitable to quantify lateral variations of the wavefield. The results show that using a combination of several attributes significantly increases the reliability of detecting anomalies in the microtremor wavefield that are presumably caused by hydrocarbon reservoirs. A numerical study of two-dimensional seismic wave propagation is applied to investigate the peak frequency shift attributes. The results of the study indicate that the attributes may contain information on the depth of hydrocarbon reservoirs, assuming that the reservoir acts as a (secondary) source of low-frequency seismic waves. 相似文献
9.
Application of alternative digital rock physics methods in a real case study: a challenge between clean and cemented samples 
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下载免费PDF全文 Sadegh Karimpouli Sadegh Khoshlesan Erik H. Saenger Hamed Hooshmand Koochi 《Geophysical Prospecting》2018,66(4):767-783
High‐resolution three‐dimensional images are used in digital rock physics to numerically compute rock physical properties such as permeability and elastic moduli. These images are not widely available, and their preparation is both expensive and time consuming. All of these issues highlight the importance of alternative digital rock physics methods that are based on two‐dimensional images and use different approaches to compute effective properties of three‐dimensional samples. In addition, the scale of study in both standard and alternative digital rock physics is very small, which applications of its results are questionable at wells or reservoir scale. The aim of this study is to use two‐dimensional images and alternative digital rock physics techniques for computing seismic wave velocity and permeability, which are compared with well and laboratory data. For this purpose, data from one well in a reservoir located in the southwestern part of Iran are used. First, two clean (carbonate) and two cemented (limy sandstone) samples were collected from well cores at different depths. Then, two‐dimensional images by scanning electron microscope and conventional microscope were captured. In the next step, two alternative digital rock physics methods, namely, empirical relations and conditional reconstruction, have been employed to compute P‐wave velocity and permeability of a three‐dimensional medium. Results showed that, in clean (mono‐mineral) samples, velocity values were reasonably close to well data. However, permeability values are underestimated compared with laboratory data because laboratory data were obtained at ambient pressure, whereas alternative digital rock physics results are more representative of reservoir pressure conditions. Nevertheless, permeability–porosity trends are valid for both samples. In the case of cemented samples, a two‐scale procedure, along with a method for two‐scale computation and grain‐cement segmentation, is presented and developed. Results showed that P‐wave velocity is overestimated probably due to random sampling in this method. However, velocity–porosity trends are in agreement with well data. Moreover, permeability results obtained for cemented samples were also similar to those obtained for the clean samples. 相似文献
10.
Adopting the method of forced oscillation, attenuation was studied in Fontainebleau sandstone (porosity 10%, permeability 10 mD) at seismic frequencies (1–100 Hz). Confining pressures of 5, 10, and 15 MPa were chosen to simulate reservoir conditions. First, the strain effect on attenuation was investigated in the dry sample for 11 different strains across the range 1 × 10?6–8 × 10?6, at the confining pressure of 5 MPa. The comparison showed that a strain of at least 5 × 10?6 is necessary to obtain a good signal to noise ratio. These results also indicate that nonlinear effects are absent for strains up to 8 × 10?6. For all the confining pressures, attenuation in the dry rock was low, while partial (90%) and full (100%) saturation with water yielded a higher magnitude and frequency dependence of attenuation. The observed high and frequency dependent attenuation was interpreted as being caused by squirt flow. 相似文献