A net of assessment points typical of the sedimentary sections was selected for determination of the scale of oil-gas formation. For each complex a determination was made of content of disseminated organic matter and its genetic type, porosity, permeability, and thermal conductivity. Temperature was calculated for various depths at each of the assessment points.
Quantitative content of organic carbon in the rocks was deter- mined from cores and well cuttings. Distribution of disseminated organic matter and its genetic type were predicted from reconstruction of the environment of deposition based on 2D seismic data. Interval velocities of all the litho-stratigraphic complexes were calculated for each assessment point.
The Paleocene-lower Oligocene complex at the base of the sedimentary section is at maximum depth in the central part of Zav'yalov downwarp, where its base is at depth of 10-14 km and the top is at 3-7 km. Temperature in a large part of these rocks is in the 220-300 degrees C interval, where alteration of organic matter has been completed. In the Motykley downwarp the upper part of this complex is in the thermal gas window, and in the Shetling and a large part of the Zav'yalov downwarp it is at depth of 3-6 km and in the oil window and in part the thermal gas window. On several highs it is well within the oil window.
The upper Oligocene-middle Miocene complex occurs over a rather wide depth range. In several downwarps the base is at 4.5 km depth and the top is at 2.5 km depth. It is almost entirely in the oil window and upper part of the thermal gas window. On the highs the base of the complex is at 4.0-4.5 km depth, and the top is at 1.0-1.5 km. This is in the oil window and part of the thermal gas window.
The middle-upper Miocene complex is at maximum subsidence in Motykley, Lisyan, and Zav'yalov downwarps. Its base there is at depth of 2.6 to 3.0 km, and the top is at 1.6 km. It is in the 80-140 degrees C temperature level, corresponding with the oil window. Only in places is it in the thermal gas window. In a large part of Magadan, Umar, Khmitev, and Zav'yalov highs the base of the complex is at 1.6 km to 1.4 km depth, and the top is at 1.0-0.8 km depth. The lower part of the complex with thickness up to 300 m is in the oil window, and the upper part with thickness of less than 200 km is in the biogenic gas window. Vitrinite reflectance from Magadan well 1 is at 0.22-0.34.
The upper Miocene-Quaternary complex is characterized by
immature organic matter over a large part of the shelf of Magadan
region. Only in some downwarps where its base is at 1.6-2.6 km
depth does its lower part carry rather mature organic matter.
Concluded in next News Letter
Taken from O. A. Krovushkina, 2001; digested in Petroleum Geology,
Vol. 37, No. 1, 2003, in preparation, two maps, one seismic section,
one chart showing range in petroleum generation and expulsion.
Copyright 2002, James Clarke. You are encouraged to print out
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