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Oelke A.,Free University of Berlin | Alexandrov D.,Saint Petersburg State University | Abakumov I.,Saint Petersburg State University | Glubokovskikh S.,All Russian Research Institute of Geosystems | And 5 more authors.
Geophysics | Year: 2013

We have analyzed the angle-dependent reflectivity of microseismic wavefields at a hydraulic fracture, which we modeled as an ideal thin fluid layer embedded in an elastic, isotropic solid rock. We derived full analytical solutions for the reflections of an incident P-wave, the P-P and P-S reflection coefficients, as well as for an incident S-wave, and the S-S and S-P reflection coefficients. The rather complex analytical solutions were then approximated and we found that these zero-thickness limit approximations are in good agreement with the linear slip model, representing a fracture at slip contact. We compared the analytical solutions for the P-P reflections with synthetic data that were derived using finitedifference modeling and found that the modeling confirmed our theoretical results. For typical parameters of microseismic monitoring by hydraulic fracturing, e.g., a layer thickness of h = 0.001-0.01 m and frequencies of f = 50-400 Hz, the reflection coefficients depend on the Poisson's ratio. Furthermore, the reflection coefficients of an incident S-wave are remarkably high. Theoretical results suggested that it is feasible to image hydraulic fractures using microseismic events as a source and to solve the inverse problem, that is, to interpret reflection coefficients extracted from microseismic data in terms of reservoir properties. © 2013 Society of Exploration Geophysicists.

Korneev V.,Lawrence Berkeley National Laboratory | Glubokovskikh S.,All Russian Research Institute of Geosystems
Geophysics | Year: 2013

An increase in seismic velocity with depth is a common rock property, one that can be encountered practically everywhere. Overburden pressure increases vertical stress, producing a nonlinear elastic response. Application of a conventional nonlinear theory to this problem leads to transverse isotropy, with explicit relationships between nonlinear constants and elastic anisotropy parameters. These relationships can be used in velocity "depth trend" removal and in computing offset-dependent corrections for stacking and migration. Assumptions about small static stress and the use of linearized solutions for its evaluation are invalid for overburden problems - more accurate approximations are required. Realistic tomography models should account for elastic anisotropy as a basic feature. Our theory gives an accurate fit to well and stacking velocity data for the Los Angeles Basin. Overburden stress is a likely cause of shear-wave generation by underground explosions. © 2013 Society of Exploration Geophysicists.

Karakin A.V.,All Russian Research Institute of Geosystems | Pokatashkin P.A.,All Russian Research Institute of Geosystems
Izvestiya, Physics of the Solid Earth | Year: 2016

The paper addresses the interpretation of the geochemical laboratory experiments aimed at studying the differentiation of partially molten rocks in the terrestrial planets. These experiments simulate the early stages of material differentiation when the layers with the different chemical and petrological composition are formed in the planets. Density inversion which may arise at a certain stage of this process leads to the emergence of the Rayleigh–Taylor instability. The lifetime of this instability is estimated, and the different phases of its evolution are explored. It is shown that the laboratory experiments do not always adequately reproduce the nature of the physical processes which occur in the interior of the planets. The suggested methods are also used for interpreting the evolution of intrusions during their differentiation. The obtained results can be helpful in analyzing the intrusions for minerals. © 2016, Pleiades Publishing, Ltd.

Karakin A.V.,All Russian Research Institute of Geosystems | Pokatashkin P.A.,All Russian Research Institute of Geosystems
Izvestiya, Physics of the Solid Earth | Year: 2015

We consider the phenomenon of sedimentation of partially molten rocks in intrusions. During the sedimentation of the suspension, a stratified structure consisting of zones with different degree of compaction of the solid phase appears. The highest degree of compaction corresponds to a poroviscous medium. With a critical porosity at the boundary, this medium is overlaid by a thin intermediate layer. The supercritical porosity values correspond to the violation in the skeleton’s connectivity. Within the thin layer, the skeleton of the poroviscous medium generally retains its properties, although in a strongly reduced form. The grains bounded by strong hydrodynamical bonds form the structures characterized by instability. During the sedimentation, these structures periodically collapse and recover, which is perceived as periodic self-excited oscillations on the macroscopic level. The self-excited sedimentation regime leads to the formation of a periodical layered structure in the cumulates, which is detectable many millions of years after the solidification of the intrusive chamber. This process is studied in the present paper. © 2015, Pleiades Publishing, Ltd.

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