Home – Home – Jornals – Russian Geology and Geophysics 2009 number 11

Thermal maturation for the top and base of the Jurassic in the West Siberian megabasin was modeled on the basis of the vitrinite reflectance (R _vt ⁰) data using mathematical modeling and computer simulations. The values of thermal maturation are found to vary within substages PC₃-MC₃² for the top (or being equivalent to PC₃-MC ₁ ² on the periphery and southern part of the basin, or to MC₂- MC₃² in the north) and PC₃-AC₃ for the base of the Jurassic (or being equivalent to PC₃-MC₂ on the periphery and southern part of the basin or MC₃¹-AC₃ in the north). Thermal maturity levels of the Jurassic in West Siberia are controlled by depths of burial and peak temperatures which the source rocks were subjected to during this period. The situation is further complicated by high heat flows superimposed on the regional background, which are observed in deep fault zones and in the proximity of numerous igneous bodies.

According to the suggested model of groundwater stratigraphy obtained on the basis of geological and groundwater data, the sedimentary cover of the western Siberian craton includes the suprasalt, salt, and subsalt groundwater units subdivided into regional and subregional reservoirs. It has been found reasonable to carry out special groundwater studies, either before or concurrently with petroleum exploration, in order to ensure supply of drinking, household, and technological waters to meet the demand of oil and gas production and to make groundwater available for oil-well pressure maintaining systems and for underground burial of waste waters.

Division of sedimentary strata according to groundwater chemistry is discussed with implications for petroleum reservoir potential. It is suggested to process multiparametric water chemistry data from West Siberia using formalized clustering techniques. The efficiency of this approach has been tested for Neocomian clinoform reservoirs with reference to regional-scale appraisal and subregional petroleum division.

Using the Chiller computer program, we performed modeling of the mechanisms of the joint transport and deposition of Au and Sb from various ore-forming solutions during the formation of Au-Sb deposits. Three models are considered by the example of the Uderei Au-Sb deposit in the Yenisei Ridge: (1) simple cooling (cooling only), (2) iso-enthalpy boiling ( P = f ( T )), and (3) solution-rock interaction (rock titration model). The behavior of Sb(III) and Au(I) in the system Au-Sb-Fe-Cu-Pb-Zn-As-H₂O-Cl-H₂S-CO₂ under hydrothermal conditions was studied. It is shown that both weakly alkaline (near-neutral) and reduced acidic Fe_aq²-enriched low-chloride high-CO₂ and high-chloride hydrothermal solutions play a crucial role in the formation of gold parageneses of Au-Sb ores.

Picroilmenite samples from five kimberlite pipes of the Yakutian kimberlite province have been studied. Point microprobe analyses of two mutually perpendicular profiles of each sample were carried out to study the compositional inhomogeneity of picroilmenite. Thermomagnetic curves were also recorded for each sample. A model for the processing of thermomagnetic curves is proposed on the basis of the relationship between the Curie point of picroilmenite and the content of the hematite end-member. The compositions determined by the thermomagnetic curves and microprobe analysis are rather similar. The conclusion has been drawn that thermomagnetic analysis can be used for the rapid determination of the picroilmenite composition. The possibilities and restrictions of this method are shown.

Bottom sediments from the central zone of the Sea of Okhotsk were preliminarily dated. The petromagnetic parameters of two groups of samples formed at cold and warm climatic stages were studied. Warm oxygen isotopic stages and substages were characterized by the coexistence of pseudo-single-domain allogenic magnetite and predominant magnetite and greigite (pyrrhotite) grains subject to biologic control. At cold stages, sediments containing a mixture of pseudo-single-domain and multidomain terrigenous magnetite particles accumulated. The petromagnetic curves agree with the normalized standard oxygen isotopic curve over the last 350 kyr of the column section.

Electromagnetic wave propagation from an induction source (a transmitter coil) in media with time-dependent conductivity and permittivity is simulated using the vector finite-element method. A special algorithm is suggested for source approximation.

The use of electrochemical effects in petroleum exploration and engineering-geological applications is discussed with reference to the Zhirnovsky oil and gas field where mobile forms of metals are 1.5-2 times above the background. Electrochemical stiffening applied to Maastrichtian shales, which are sliding planes of landslides in the Lower Volga area, increased their stiffness by a factor of 2 or more.