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Modeling of sedimentation in Jurassic basin based on analysis of maps of thicknesses (central part of the Barents Sea megadepression)

Tkachenko M.

Geology, Geophysics and Environment

2012

Vol. 38, no. 4

543--544

Stratigraphic subdivisions of deposits in the Barents Sea is often based only on rare cores, which usually does not allow distinguishing facies of the stratigraphic units, and possible facies zoning of coeval strata. Thus, the facies zonation in the Barents Sea, reconstructed at intervals of geologic time, can be considered as arbitrary. Usually this zoning was determined by means of available data on the adjacent land and general trend of the evolution of sedimentation in the Barents region. In this regard, within the oil and gas prospects scientists were asked not to use the classic facial analysis but to use modeling of sedimentation and as a consequence - identifying patterns of distribution of sediments with improved reservoir properties. The materials from marine wells and analysis of maps of thicknesses were used for modeling sedimentation in Jurassic time in the Barents Sea megadepression. Maps were built on the seismic materials of MAGE (Murmansk Arctic Geological Expedition). According to the interpretation of seismic profiles three stages of sedimentation were considered: Early Jurassic, Middle Jurassic and Late Jurassic. Every stage is characterized by its environment of sedimentation and therefore by its own characteristics of hydrodynamic conditions. Early Jurassic stage. For the most complete characterization of sedimentation of this stage we must be aware about environment of sedimentation in Late Triassic. In 2010, the author did a report which name was Sequence stratigraphy for studying of oil and gas potential of Triassic deposits of the Eastern part of Barents Sea. Biolitostratigraphical correlation scheme used in that work helped to identify sequence of the second order. This sequence begins with transgressive tract in Induan and ends with lowstand system tract on boundary of Carnian and Norian. This information allows us describing transgression in Early Jurassic time. Analysis of the model of sedimentation for Early Jurassic stage which consists of map of thicknesses and 3-D visualization clearly confirms this description. Middle Jurassic stage. Analysis of the model of sedimentation for Middle Jurassic stage allows making conclusions about the active development (peak) of transgression. The increase of the alluvial fan graphically shows this development. Stokman, Ledovoe and Ludlovskoe fields as well as many local structures like Akhmatovskaya, Severo-Nadezhdinskaya and others belongto proximal part of the alluvial fan . Also we can see gas and gas-condensate productive horizons in this interval of x-section of Shtokman, Ledovoe and Ludlovskoe fields determaning favorable conditions for reservoirs. Late Jurassic stage. Analysis of the model of sedimentation for Late Jurassic stage allows making conclusions about the beginning of regression. We can see decrease of depression which graphically shows this fact. Two small depocentres of depression and significant decrease of proximal part of alluvial fan show favorable conditions for cover rocks. Analysis of maps of thicknesses, in particular models of sedimentation, can show us maximum thicknesses of reservoirs and cover rocks, so we can make conclusions about oil, gas and condensate traps and deposits in prospect areas.