Current field in the north-western Black Sea and its role in the distribution of hydrological characteristics

The data derived from the observation of current profiles and hydrophysical features, carried out in the north-western Black Sea in August 1992, are considered. The main features of the currents' structure have been identified; they are consistent with the distribution of the basic characteristics computed from the distributions of the hydrological elements (dynamic heights, cold content, density of the accessible potential energy). A relationship between the thickness of the cold intermediate layer (CIL) and the Richardson numbers near the layer core distinctly manifested itself in the convergence zone over the shelf edge. The average correlation coefficient between these quantities was equal to 0.877, and the range of sampling variability with a probability of 0.95 varied from 0.9 to –0.79.Translated by Vladimir A. Puchkin.     

Bottom boundary layer in the Black Sea: Experimental data,turbulent diffusion,and fluxes

Measurements of 14 vertical profiles of currents and hydrological parameters in the near-bottom layer with a depth resolution of 0.1 m were carried out in several regions of the Black Sea shelf, at five points over the continental slope, and in three deep water regions. The upper boundary of the benthic boundary layer (BBL) was reliably determined at a point at a distance from 5–7 to 35–40 m from the bottom where the gradients of the density and the velocity of the currents changed. The experimental data obtained were used to determine the coefficient of the bottom friction, the friction velocity, the coefficients of the vertical diffusion of momentum and density, and the vertical fluxes of temperature and salinity in the BBL.     

Trajectory and drift velocity of a sounding instrument in the field of nonuniform currents

We present a method for the determination of the trajectory of a sounding instrument and its drift velocity in the field of currents nonuniform in depth and develop special software for IBM/PC compatible computers. The proposed method and software are checked by using the well-known analytic solution of a similar problem given by Academician A. N. Krylov. We also consider some special examples of application of the developed method to the processing of the data of an OLT profilometer. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

The coprecipitation of strontium,magnesium, sodium,potassium and chloride ions with gypsum. An experimental study

The coprecipitation of Sr²⁺, Mg²⁺, Na⁺, K⁺ and Cl^? into gypsum was studied as a function of temperature, brine concentration and growth rate. The concentrations of the studied cations in the gypsum increase with growth rate (kinetic effect), with a tendency to reach a limiting value at high growth rates. The partition coefficients of Sr tend to increase with brine concentration and decrease with temperature. The partition coefficients of the other cations also decrease with temperature but depend only very slightly on brine concentration. The concentrations of coprecipitated chloride are negligibly small.The coprecipitation behavior is explained in terms of the relation between the rate of desorption of the coprecipitating ions from the surface of the growing crystal, and the rate of growth. The studied cations may substitute for Ca²⁺ in its normal lattice sites and/or reside in interstitial positions among the structural water molecules. The relative amount of foreign cations occupying interstitial positions increases with increasing growth rate.The elucidation of the behavior of coprecipitated ions in gypsum given here forms a basis for the utilization of these ions as geochemical indicators for the environment of deposition of gypsum. These indicators may help in reconstructing important parameters such as temperature, brine concentration and growth rate.     

Determining the microseismic event source parameters from the surface seismic array data with strong correlated noise and complex focal mechanisms of the source

The world experience shows that hydraulic fracturing (fracking) is an efficient tool for increasing oil and gas production of low-permeable reservoirs in hydrocarbon fields. The fracking-induced fractures in the rock, which are hydrodynamically connected with the wells, significantly enhance the volumes of extracted hydrocarbons. Controlling the processes of fracture formation and propagation is a vital question in the oil and gas reservoir management. A key means to implement this control is provided by microseismic monitoring of fracking, which makes it possible to promptly reconstruct the geometry of the fractures from the data on seismic waves from the microearthquakes induced by the formation and propagation of fractures.     

Elimination of high-amplitude noise during passive monitoring of hydrocarbon deposits by the emission tomography method

Emission tomography used in passive seismic monitoring of hydrocarbon deposits enables regular inspection of development of hydraulic fracturing and relaxation processes in volumes of fracturing, tracing of fluid migration paths, redistribution of stresses due to field development accompanied by seismic emission from volumes of structural defects and stress concentration, and localization of fractured and faulted structures from emission and scattering data. Intensive man-made seismic noise in the areas of oil field development produces a strong screening effect in identification of weak deep seismic sources. On the basis of experiments with simulated and real data of surface seismic arrays in regions of oil deposits in Western Siberia (carried out in the framework of the passive monitoring program of the SYNAPSE Science Center), it is shown that the use of algorithms of adaptive optimal and rejection spatial filtering with the estimation of the spectral density matrix of multichannel observations in the framework of multivariate autoregressive-moving average modeling is effective for eliminating the influence of anthropogenic noise and revealing (in oil production areas) both deep seismic sources supposedly active in scattering regions of the lower part of the sedimentary cover and the crystalline basement. The projection of the scattering regions onto the horizontal plane correlates well with the position of faults in the area of in situ observations.     

Computation of the equilibrium of a sub-surface mooring affected by steady currents

The main relationships for the design of the equilibrium of the sub-surface mooring (SM) are given based on the general equations describing the equilibrium of the elastic heavy cable under gravity and hydrodynamic loading. A computation system for the numerical modelling of SM under the effect of steady currents has been developed. Computations have been performed for conditions close to those in the main Black Sea current. The main parameters of the SM equilibrium under variation of the steady velocity profiles were estimated.Translated by Mikhail M. Trufanov.