Krasnoleninsk arch in the southwest part of the West Siberian platform measures some 150 km by 150 km. Very large oil deposits have been discovered there. The backlog of untested exploration targets on this arch has been exhausted as well as in most of the rest of West Siberia. The search has now turned to non-anticlinal features in both the sedimentary cover of the platform and rocks of the intermediate complex between the base of the platform cover and the basement.
Regional remote sensing surveys were made on a scale of 1:200,000 in the western part of Krasnoleninsk arch in 1992. Both satellite and aircraft images were obtained. This region consists of a series of downwarps and swells, which are host to smaller features - all forming a mosaic of highs and lows. The structural configuration of the top of the crystalline basement and the overlying Mesozoic formations exhibit a great degree of conformity. The greatest degree of conformity is found in the central part of the study area, where geologic processes have been very stable. Along the margins of this central area the degree of conformity is somewhat less. All this is a consequence of predominantly vertical block movements of crystalline basement, and this in turn controlled facies distribution.
The remote-sensing studies also establishe the presence of a net of lineaments, which are interpreted as faults. Four groups of faults are recognized based on their expression in the landscape and in the seismic, gravity, and magnetic data. These are trans- regional, inter-regional, regional, and local.
A relationship has been found between lines of pinchout of productive horizons and specific faults. This is characteristic not only for the platform cover but also for the basal horizons and the upper part of the basement, and all this is of interest for oil and gas. The river net on the basement shows some relationship to the modern river net.
A rerlationship has been found between faults and facies zonality in the platform cover sediments. Sherkalin Horizons YuK-10 and YuK-11 are present throughout the western part of the study area. Pinch out of these units is associated with faults of various order. These faults show up clearly on the satellite imagery, indicating recent activation. This activation renewed vertical movements of the blocks but also contributed to fluid dynamic processes in the fault zones with accompanying hydrothermal alterations and reservoir improvement. Similar examples of pinch out associated with faults have been found in other formations of the study area.
This model is a basis for predicting location of paleo-channels
where oil and gas pools may be present. Comparison of the
prediction maps with ground-truth data from drilling shows a
high degree of reliability (50-70 percent). (Taken from Pererva
and others, 1994; digested in Petroleum Geology, vol. 29,
no.5/6, 1995, two maps)
Copyright 2001 James Clarke. Earlier News Letters are available
at: http://geocities.com/internetgeology/
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