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EN
Thin interbeds are typical reservoirs in eastern China. Thin layers and fractures bring huge challenge to fluid identification in anisotropic reservoir. This study focuses on thin-fractured reservoirs and amplitude attributes of shear-wave splitting, and consequently predicted fluid type in fractured reservoir based on the response of fast and slow S-waves to fluids. 3D HTI viscoelastic equation was employed to analyze amplitudes of split S-waves through fluid-filled and fractured media, including oil- and water-saturated synthetic models. Similar to velocity anisotropy, amplitude anisotropy was proposed to avoid the calculation of S-wave quality factor. Amplitude ratio and substation derived from amplitude anisotropy were used to identify fluid type. Example from the Luojia area of Shengli oilfield was used to demonstrate the effectiveness of the inversion method. Results show that amplitude ratio and amplitude subtraction are useful to distinguish fluids, while the former works better than the latter.
EN
The Alborz is one of the most important seismotectonic provinces in Iran. Furthermore, emplacement of Tehran as a mega city in southern part of the Alborz intensifies the seismic vulnerability in this area. In this study, the focal mechanism data from teleseismic and local seismic networks are used for stress tensor inversion. The earthquake focal mechanisms in the Central Alborz are divided into several groups with respect to their location. Two different stress tensor inversions, linear and nonlinear, are used for obtaining the principal stress orientations. The results show spatial variations in tectonic stress field, consistent with fault orientations and faulting mechanisms. The maximum compressional stress directions obtained in this study are confirmed by fast S-wave polarization axes reported by a previous shear wave splitting study. The maximum horizontal stress directions are also compared with GPS strain rates. The results indicate a partitioning of deformation in the area due to regional stresses along preexisting faults.
EN
SKS and PKS splitting parameters were determined in the broader Greek region using data from 45 stations of the Hellenic Unified Seismological Network and the Kandilli Observatory and Earthquake Research Institute, utilizing teleseismic events that occurred between 2010 and 2017. Data were processed for shear-wave splitting with the Minimum Energy Method that was considered the optimal. The results generally confirm the existence of anisotropic zonation in the Hellenic subduction system, with alternating trench-normal and trench-parallel directions. The zonation is attributed to the upper and lower olivine fabric layers that can, potentially, be present in the subduction zone. At the edges of this zone, two possible toroidal flow cases have been identified, implying the existence of tears that allow the inflow of asthenospheric material in the mantle wedge. The high number of null measurements in the KZN and XOR stations indicates a possible anisotropic transition zone between the fore-arc and back-arc areas. SKS and PKS splitting results are jointly interpreted, given that they yield similar values in most cases.
EN
Shear wave splitting is a well-known method for indication of orientation, radius, and length of fractures in subsurface layers. In this paper, a three component near offset VSP data acquired from a fractured sandstone reservoir in southern part of Iran was used to analyse shear wave splitting and frequency-dependent anisotropy assessment. Polarization angle obtained by performing rotation on radial and transverse components of VSP data was used to determine the direction of polarization of fast shear wave which corresponds to direction of fractures. It was shown that correct implementation of shear wave splitting analysis can be used for determination of fracture direction. During frequencydependent anisotropy analysis, it was found that the time delays in shearwaves decrease as the frequency increases. It was clearly demonstrated throughout this study that anisotropy may have an inverse relationship with frequency. The analysis presented in this paper complements the studied conducted by other researchers in this field of research.
5
Content available remote Interpretacja danych sejsmicznych w oparciu o zdjęcie wieloskładnikowe
PL
Wieloskładnikowe zdjęcie sejsmiczne (3C) wnosi nowe możliwości do geologicznej interpretacji danych sejsmicznych. Fale poprzeczne lepiej odwzorowują budowę geologiczną pod ciałami solnymi, bazaltowymi oraz obszarami zniekształcanymi przez strefy i kominy gazowe. Analiza danych wieloskładnikowych dostarcza wiedzy na temat anizotropii utworów geologicznych oraz typu cieczy złożowej. Interpretacja geologiczna na poziomie wieloskładnikowym pozwala na rozdzielenie facji sedymentacyjnych, określenie kontaktu woda - ropa, jak również na uzyskanie przybliżonych wartości współczynnika porowatości utworów skalnych. Otrzymujemy także nowe możliwości identyfikacji stref uskokowych, ich zasięgów oraz kierunków przepuszczalności. W artykule wprowadzone zostaną podstawy interpretacji wieloskładnikowej na przykładzie zdjęcia 3D/3C w oparciu o atrybut sejsmiczny Vp/Vs
EN
Multicomponent seismic data (3C) brings new dimensions into geological interpretation. Shear waves could image area below salt, basalt bodies, and disturbed by gas zones or chimneys. Analysis of multicomponet data provides information about anisotropy and type of pore fluids. Geological interpretation on multicomponent level allows lithology differentiation, definition of water - oil contact and estimation of rock porosity. We also obtain new possibilities of identification fractures and faults zones, theirs ranges and directions of permeability. The article introduces to multicomponent interpretation based on 3D/3C data. An example of Vp to Vs ratio interpretation is shown to prove its ability
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