Home – Home – Jornals – Russian Geology and Geophysics 2016 number 12

We analyze the history of oil discoveries of different sizes in two centers of the Volga-Ural petroleum province, the Republics of Bashkortostan and Tatarstan, and demonstrate the important role played by Academicians I.M. Gubkin and A.A. Trofimuk in these discoveries. Special focus is placed on the analysis of small and smallest oil fields and the sequence of their discovery. It was shown that all discoveries in Tatarstan and Bashkortostan were the result of the exploration filter. It was also shown that the establishment and support of small oil businesses in Bashkortostan and Tatarstan can be an importance means of the facilitating development of small and smallest fields. The study discusses the role of small independent oil companies in the regional oil production, considers priority areas of state and regional legal support of small and medium oil enterprises, and presents oil production forecast for Bashkortostan and Tatarstan.

Interpretation of geological and geophysical data from several regions in the Arctic continental margin of Eurasia which differ in structure and tectonic settings shed new light on the early history of the Arctic Ocean (Canada Basin) opening. Many issues of regional tectonics and geodynamics become clear due to evidence of Late Mesozoic magmatism within the continental margins of the Barents and East Siberian Seas and strike-slip tectonics in the Chukchi shelf. Interpretation analysis is applied to reconstruct the formation of structures in the Amerasia Basin during the Arctic Ocean initiation.

We present the first data of GPS measurements on recent motions in the east of the Mongol-Okhotsk Fold Belt. Processing of GPS data yielded a vector field of the velocities of observation point displacements in the geodynamic network of the Upper Amur region. Comprehensive analysis of geological and geophysical data and the estimated velocities of site displacements in this network have shown kinematic heterogeneity of the present-day Mongol-Okhotsk Fold Belt and an intricate deformation pattern there. The tectonic regime within the belt permits considering it a buffer or transit zone, where tectonic stresses arise as a result of the different kinematics of the surrounding tectonic structures.

New data on silicate melt inclusions in accessory Cr-spinel have given an insight into the physicochemical conditions of petrogenesis of dunites of the Guli massif (northern Siberian Platform). Studies of the inclusions demonstrate the contribution of high-Mg (16-22 wt.% MgO) alkali-picritic and picrobasaltic melts to the crystallization of these ultrabasic rocks. During the intrachamber crystallization of the Guli massif dunites, the composition of magmatic systems evolved from picrite-meimechite (with olivine forming at 1500-1380 °C and Cr-spinel forming at 1420-1360 °С) to picrobasalt. Comparison with well-known associations of ultrabasic igneous rocks has shown that melt inclusions in Cr-spinel from the Guli massif dunites are similar to inclusions in olivine phenocrysts from meimechites in the contents of most petrochemical components and in the distribution of indicator trace and rare-earth elements. In general, the new information on melt inclusions testifies that the Guli massif dunites formed with the participation of high-temperature high-Mg melts similar in composition to meimechite magmas.

Cr-V-bearing rocks of the Sludyanka metamorphic complex in the Southern Baikal area contain accessory niobian rutile with Nb contents unusually high for metamorphic rocks (10-12 to 20-25 wt.% Nb2O5, or, occasionally, up to 36-37 wt.%). Incorporation of Nb5+ into the rutile structure is balanced by Cr3+ and V3+, which reach 16 wt.% Cr2O3 and 8 wt.% (or, rarely, up to 20 wt.%) V2O3. The distribution of Nb, Cr, and V in rutile is very uneven, down to the microscale. It does not depend on PT conditions being rather controlled by crystallization kinetics of minerals competing with rutile in the paragenesis.

A superlarge gold-ore stockwork of the Vasil’kovskoe deposit (with gold resources of more than 380 tons) is located at the contact of porphyroblastic granodiorites and diorites in northern Kazakhstan. The specifics of the Vasil’kovskoe deposit is a wide occurrence of gray (so-called ore) gold-bearing quartz, which, together with white quartz, composes quartz-sulfide veins and veinlets in the stockwork. Based on thermobarogeochemical and isotope-geochemical data, we have established that gray quartz and arsenopyrite of the deposit formed with the participation of K-Na-Mg-Cl-containing aqueous CO2-hydrocarbon fluids at 250-550 ºC, 0.1-2.5 kbar, and salinity of 7.0-22.5 wt.% NaCl equiv. (seldom, >30-40 wt.% NaCl equiv.). The cyclic recurrence of parameter fluctuations was accompanied by the deposition of gold, which led to the formation of gold-rich veinlet ores in the stockwork core. White quartz formed at lower temperatures, 120-310 ºC, and 0.2-1.0 kbar, with the participation of Ca-Na-Cl-containing fluids with salinity of 2.0-11.0 wt.% NaCl equiv. In addition to H2O and CO2, hydrocarbons and their derivates (paraffins, olefins, arenes, alcohols, ethers, aldehydes, ketones, and carboxylic acids) as well as nitrogen-containing (C2H3N, C3H9N, C7H5N, and C8H5NO2) and sulfur-containing (CS2, COS, SO2, C2H6S2, etc.) compounds (indicators of reducing conditions) were involved in the ore formation. The sulfur isotope composition of sulfides (δ34S = +5.7 to + 11.8‰) and the carbon isotope composition of CO2 in fluid inclusions in gray (δ13C = -2.1 to -4.6‰) and white (δ13C = -11.0 to -21.4‰) quartz as well as its positive and negative anomalies of Eu point to the crustal source of the fluids. The gray color of quartz is due to abundant CO2-hydrocarbon-containing inclusions, carbon particles, and sulfides. Crystallization of ore-hosting granodiorites proceeded in the period from 490 ± 4.4 to 443.5 ± 4.1 Ma. The age of the areal K-feldspathization of granodiorites, preceding the ore formation, is 375.2 ± 3.7 Ma. Formation of gold-including parageneses took place in the period from 311.7 ± 6.4 to 279.2 ± 2.5 Ma, i.e., lasted no less than 30 Myr.

A method for calculation of the maximum permissible (for thermometry) error of analyte determination by trace elements is presented by the example of the De Hoog-Gall Al-in-olivine thermometer. Analytical conditions ensuring an acceptable analytical error have been established, and the possibility to reach them has been estimated. A technique of JEOL JXA-8100 analysis of olivines for trace elements has been elaborated: Accelerating voltage is 20 kV, probe current is 400 nA, and counting time per line and background measurement is 10 s. The number of measurements per analysis is 25. Metrological characteristics of determination of Na2O, Al2O3, CaO, Cr2O3, and MnO have been calculated. Their detection limit (with confidence probability of 0.842) does not exceed 9 ppm. For an error of 10 rel.%, the quantitation limit of these oxides is within 45-100 ppm. Compositional peculiarities of olivines from depleted megacrystalline peridotites of the Udachnaya pipe have been revealed. The content of Mn significantly decreases with Mg# increase. The contents of Na, Al, Ca, and Cr show a strong mutual positive correlation. It is shown that electron probe microanalysis can provide an error sufficient for evaluating temperature by trace elements. The results of temperature determination by the Al-in-olivine thermometer agree with the thermometry data by H. O’Neil and B. Wood and differ considerably from the lower values estimated by D. Canil and C. Ryan with Ni thermometers.

Detailed geological and geophysical investigations of the underwater topography of Lake Baikal, based on single-channel high-resolution seismic profiling and bathymetric survey using an ELAC SeaBeam 1050 multibeam echosounder, as well as the data obtained during diving of MIR deep-sea manned underwater submersibles determined the morphological characteristics of the Posolsky Bank and Kukuy Griva elevations suggesting that their elevated parts are fragments of the once common delta surface of the Selenga River. The current relief of these structures resulted from the joint activity of tectonic and underwater erosive processes. Sediments at the base of the slope of the Kukuy Griva are likely to be no older than 1.8 Ma.

We report testing results for a 50 m laser strainmeter installed 300 m under the ground in a mine of PJSC Priargunsky Industrial Mining and Chemical Union (Krasnokamensk) and demonstrate its ability to record microseisms and waves of infrasonic-sonic bandwidths. Processing and interpretation of the collected data provides information about microseismic to tidal strain changes in the Transbaikalian region.

Improving seismic image quality in complex geological structures remains a challenge in seismic imaging. In complex media, imaging of geological structures such as the boundary of salt diapirs, faults, folding systems, overthrust zones, and unconformities are controversial and challenging tasks. Therefore, new imaging methods such as full waveform inversion, path-integral seismic imaging, reverse time migration, and the optimized common reflection surface stack methods were introduced to face these challenges. The common reflection surface stack method was used frequently to resolve some of the problems in complex structure seismic imaging. However, besides its great advantage in enhancing the quality of seismic section, it faces a problem with conflicting dips. The common reflection surface stack operator is an approximation of the reflection response of a curved interface in an inhomogeneous medium. In this study, a new strategy in the common reflection surface stack is introduced, which completely resolves the problem of conflicting dips in complex structures. Compared to the common reflection surface stack, the new stacking operator is the approximation of diffraction response of a diffraction point in depth. The kinematic wavefield attributes are defined for that diffraction point, whereas curvature of the interface is not fully considered. In the introduced strategy, there would be a stacking operator for each diffraction ray from the diffractor to the surface. Thus, the new operator gathers more energy that might get lost in imaging due to simplified operator in the other methods. The new method was applied to seismic data from a complex geological mud volcano bearing structure from south east of the Caspian Sea shoreline. This area includes numerous mud volcanoes which act as indicators of gas reservoirs. As a natural phenomenon, mud absorbs the seismic energy and deteriorates the quality of the final seismic section. Therefore, obtaining accurate image of the subsurface structures here, in the boundary portion of the mud volcano, is questionable. To overcome this problem, the new method was used to obtain a stacked section with all the possible diffraction energies. Subsequently, the stacked section underwent post stack depth migration. The final depth image proves the advantage of the new stacking operator for imaging in complex structures. Finally it could be concluded that this method could be used for imaging structures with sharp reflector truncations such as faults, diapirs, and unconformities.