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FINELY LAYERED MODEL Fine layering of the order l/10 of the smallest wavelength Any number of homogeneous fine layers of a given total thickness or less does not affect seismic wave propagation other than can be replaced by a homogenous equivalent thick layer by seeming to make the medium anisotropic. By applying that behaves, under static loading, either applied stress or equivalent medium theory (Backus, 1962), layering on a finer applied strain, in exactly the same manner as the set of fine scale may be replaced by thicker, homogeneous equivalent layers. Static response or time invariance can be mathematically transversely isotropic (TI) I a y em, thus creating a model with extended to mean slow variation, where the meaning far fewer layers. This is demonstrated by calculating transmitted of this is that the load is equilibrated throughout the thick seismic signals for varying angle of incidence through layer much more quickly (due to a very rapid time for signal finely layered models, and comparing them to those calculated propagation across the layer) than.the
ABSTRACT: Site investigation in sandy soil sites demonstrates extensive soil layering in actual sand deposits. One-dimensional liquefaction tests are carried out for several types of layered sand models, which indicates that water films develops beneath impermeable sublayers in layered sand. The mechanism for the water film generation is clarified. Thus the significant effect of water film on land and submarine slides due to seismic liquefaction is demonstrated. INTRODUCTION In past earthquakes, landslides in alluvial sand deposits or lateral flow took place in coastal or river-side areas as in Alaska and Niigata. Submarine slides have also been triggered seismically worldwide. Nom1ally the slope of the sliding surface in those slides is not steep, being much gentler than the intemal friction angle ofthe soil. In land areas, liquefied sand deposits often experienced lateral spread or flow not only during but also after earthquake shaking. The magnitude of flow distance sometimes reached more than several meters even in a very gentle slope ofless than a few percent. In Niigata city, a famous lateral flow occurred in the Meikun High School along the Shinano River where a rather large area of250m by 150m moved towards the river a maximum of 7 meters (Kawakami and Asada 1966). Pictures taken by a high-school student demonstrated that mud water started to come out violently and fissures gradually expanded after the end of shaking. Soil profiles in this area consisted not only of sand but also of sublayers ofsilts or clays (Kishida 1966). In Greece, on the occasion of the 1995 Aegion earthquake, a similar post-earthquake submarine slide involving coastal land with the slope of 12% occurred. The soil profile at the failure site was characterized by a continuous interchange between silty sand and clay layers (Bouckovalas et al. 1999).
- Asia > Japan > Chūbu > Niigata Prefecture > Niigata (0.46)
- North America > United States > Alaska (0.24)
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 178955, “Factors Governing the Performance of Multilayered Metal- Mesh Screens,” by Chu-Hsiang Wu, SPE, and Mukul M. Sharma, SPE, The University of Texas at Austin, and Rajesh Chanpura, SPE, Mehmet Parlar, SPE, and Joseph Ayoub, SPE, Schlumberger, prepared for the 2016 SPE International Conference and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 24–26 February. The paper has not been peer reviewed. Multilayered metal-mesh screens (MMSs) are widely used as standalone screens for sand control in unconsolidated formations. The nominal rating of such screens is usually based on the specifications of the filter layer. It is often found that screens with the same filter-layer nominal rating perform differently. It is shown in this study that the primary reason for this is that the sand-retention performance of multilayered MMSs is a strong function of not only the filter layer but also the protection layer and the support layer. Introduction The sand-retention ability of a multilayered MMS is evaluated by examining the pore-size distribution (PSD) of the screen as well as its slurry-test sand production [the sand-production evaluation is for plain-square-mesh (PSM) screens only]. Three major steps are involved in the evaluation process: Generate a multilayered virtual mesh assembly (an example is provided in Fig. 1) based on the mesh specification and different layer-overlap, layer-alignment, and relative pore-size-ratio conditions. Evaluate the PSD of the virtual screen with a specialized filtration model. Enter the PSD information into the analytical slurry-test model to quantify the sand-retention performance of the target screen. The model incorporated in this study uses the entire PSD of a PSM screen to predict sand production. Results Three types of multilayered MMSs— 175-Μm PSM, 250-Μm PSM, and 115-Μm plain Dutch weave (PDW)—are studied. The name of each type corresponds to the nominal rating and the design of the filter layer. All of the MMSs have the same three-layered structure, with one protection layer above and one support layer below the filter layer. The protection and support layers are PSMs with nominal ratings of 542 and 864 Μm, respectively.
- North America > United States > Louisiana > Lafayette Parish > Lafayette (0.25)
- North America > United States > Texas > Travis County > Austin (0.24)
ABSTRACT In this paper, we study the effect of thin layers on the AVAZ analysis using synthetic modeling. A range of models are constructed by sandwiching a thin-layered reservoir with different thickness between two isotropic layers. Azimuthal gathers are calculated for each of these thin-layered models. After we apply azimuthal AVO analysis to the synthetics, we find that fracture orientation and intensity can be estimated accurately if the thickness of the thin layer is larger than a quarter of the wavelength. However, there are large discrepancies in the orientation and intensity estimates. We finally present a new procedure to improve the detectability of azimuthal anisotropy in the presence of thin layers.
Summary Establishing layer thickness and layer properties from seismic data when the layer is smaller than an acoustic wavelength is a common problem in exploration geophysics. Many hydrocarbon reservoirs fall into this category, while estimates of their volume rely directly on our ability to resolve the thickness. Estimates of the world’s supply of methane hydrate are also based on our ability to measure the thickness of hydrate cemented sediments often in the 1-10 m range. In this abstract we demonstrate a very fast inversion method that solves for the layer thickness and layer properties of a thin layer from the seismic data. The signal from the thin layer is isolated (windowed) from the seismogram and converted to the reflection coefficient in the w-p domain. The reflectivity based forward model calculates the reflection coefficient for a given layered earth model.
- Geophysics > Seismic Surveying > Seismic Processing (0.69)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.31)