The West Kamchatka oil-gas basin is located in the eastern part of the
Sea of Okhotsk oil-gas province. Only a small part of this basin is onshore
on Kamchatka - the rest offshore in the Sea of Okhotsk. The best studied
feature of the West Kamchatka basin is the Kolpakov downwarp, where the
Severo-Kolpakov, Nizhne-Kvapakov, and Kshuk gas and condensate fields have been discovered in recent years.
The upper Paleocene-lower Oligocene section of the Kolpakav downwarp rests unconformably on an erosion surface on Upper Cretaceous rocks. Five well defined lithofacies complexes are recognized upward in the section: 1) alluvial Khulgun Formation, 2) alluvial-lagoonal Napan Formation, 3) near-shore marine (shelf) Snatol Formation, 4) coastal plain Kovachin Formation, and 5) deep-water shelf Kuluven and Viventek Formations.
Conglomerate at the base of the Khulgun Formation passes upward into
fine-grained well sorted sandstone and then again into conglomerate. These
deposits may be debris cones associated with areas of strong relief.
The overlying Napan Formation carries reworked material from the
Khulgun. It consists of rhythmically alternating sandstone and argillite.
The sandstone carries plant fragments.
The transgressive marine middle-upper Eocene Snatol Formation rests on an erosion surface on the continental deposits. The lower part of the
Snatol was deposited in a low energy environment on a shelf with deeper
water on the north and shallower water on the south. Clayey sandstone and
siltstone predominate in the deeper-water parts and sandstone in the
shallower-water parts. The upper part of the Snatol is near-shore marine
sandstone.
After a depositional hiatus at the end of late Eocene time a cooling of
the climate is indicated by pebbles "floating" in clays above the Snatol, an
increase in silica content of the rock, and other factors. This is in accord
with a climate "pessimism" at the Eocene-Oligocene boundary in the west of the Pacific Rim.
The next overlying formation is the Kovachin of late Eocene and early
Oligocene age. It is largely clay, some of which is black with abundant
carbonaceous material. Resting unconformably on the Kovachin are deep-water marine deposits of the Viventek and Kuluven Formations.
Conditions were favorable for accumulation of high capacity sandstone
bodies in the Kolpakov basin due to close proximity of source areas and
rapid transport of this material in a high-energy environment of
sedimentation. (See Bakun and others, 1994: digested in Petroleum Geology, vol 29, no. 1/2, 1995, one cross section).
Copyright 2000 James Clarke. You are encouraged to print out this News
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