Acoustic method for defining the stress state of a rock massif based on solution of the seismic inverse problem

A method for estimating the stress–strain state of a rock massif in the vicinity of underground facilities is substantiated. This method is based on solution of the boundary inverse problem of defining the components of an external stress field from the acoustic sounding data. The acoustic sounding data used are the arrival times of diving head longitudinal waves, recorded in a long mine shaft. Numerical experiments have revealed the optimal arrangement of the recording network and the limited relative error in the input data, which, taken together, provide for solvability of the inverse problem.     

Fracture detection by Gaussian beam imaging of seismic data and image spectrum analysis

Localization of fractured areas is of primary interest in the study of oil and gas geology in carbonate environments. Hydrocarbon reservoirs in these environments are embedded within an impenetrable rock matrix but possess a rich system of various microheterogeneities, i.e., cavities, cracks, and fractures. Cavities accumulate oil, but its flow is governed by a system of fractures. A distinctive feature of wave propagation in such media is the excitation of the scattered/diffracted waves by the microheterogeneities. This scattering could be a reliable attribute for characterization of the fine structure of reservoirs, but it has extremely low energy and any standard data processing renders them practically invisible in comparison with images produced by specular reflections. Therefore, any attempts to use these waves for image congestion of microheterogeneities should first have a preliminary separation of the scattering and specular reflections. In this paper, the approach to performing this separation is based on the asymmetric summation. It is implemented by double focusing of Gaussian beams. To do this, the special weights are computed by propagating Gaussian beams from the target area towards the acquisition system separately for sources and receivers. The different mutual positioning of beams in each pair introduces a variety of selective images that are destined to represent some selected singular primitives of the target objects such as fractures, cavities, and edges. In this way, one can construct various wave images of a target reservoir, particularly in scattered/diffracted waves. Additional removal of remnants of specular reflections is done by means of spectral analysis of the scattered/diffracted waves' images to recognize and cancel extended lineaments. Numerical experiments with Sigsbee 2A synthetic seismic data and some typical structures of the Yurubcheno‐Tokhomskoye oil field in East Siberia are presented and discussed.     

Analysis of models of oil-by-water displacement through the microstructure

Two major arrangements describing the oil-by-water displacement process, i.e., Muskat’s model without taking into account the surface tension on the free boundary and the Buckley–Leverett model based on the surface tension, are considered. These arrangements were subject to theoretical and numerical study, which made it possible to uncover their self-contradictoriness. The focus was on construction of a numerical solution at the microlevel using the direct method with pressure correction.     

Solving an Inverse Dynamic Seismic Problem by Multicomponent Elastic Full Waveform Inversion

A numerical method for solving an inverse problem of the theory of seismic wave propagation, relying on the modified least square method, is proposed, substantiated, and implemented. The proposed modification is based on the decomposition of the velocity model of the geological medium into the subspaces of smoothly changing propagators and sharply changing reflectors. The modified functional exhibits strong nonlinearity relative to the macro-velocity component, since the operator M, which transforms the time reflector to the space reflector, depends on it significantly. However, the low dimensions of the subspace of the macro-velocity models make it possible to use quite effective minimizing methods successfully.

     

First Occurrence of M andarinoite in China

This report describes the first occurrence of the rare mineral mandarinoite (Fe3+2 Se3Og · 6H2O) in China. It occurs in the Lower Permian Maokou Formation carbonaceous shale in Yutangba Village east of Enshi City in southwestern Hubei Province. The shale is selenium-rich and contains native selenium, V-Mo-Cr-bearing iron oxide, clay and quartz. Weathering of the selenium in the bedrock under moderate to high redox conditions in the presence of ferric iron has formed mandarinoite.