Detail lithological and petrographical study of rock samples from Kolva (KODW) and Tyumen (TODW) over-deep wells make it possible to propose four models of deep reservoir evaluation:

 the hydrothermal and hypergenic corrosion of minerals on the one hand and more effective corrosion of minerals by active products of catagenetic organic matter decomposition (CO2, organic acids, etc.) on the other hand. In Iast case it is possible to observe the signs of corrosion of the stable minerals - field spar and quarts. Several solution zones (with capacity up to 12%), which can be related with these processes was observed for TODW Triassic sandstones (the interval of the depth 5000 - 6230 m.).and KODW Low Devonian carbonates (the interval of the depth 4300 - 5320 m.).

 the depth reservoir development owning to the fluid fractures and uneven stress state of rocks (TOWD, 5400 - 5670 m);

 the high capacity rock (up to 18%) preservation owning to the weak mineral matter re-distribution because the chloritic margins and regeneration hydrothermal quarts on porous walls presence (TOWD, 6490 - 6500 m).

 the reservoir rocks generation owning to the disintegration and leaching of blister lava and tuffs (TOWD, 6700 - 7000 m).

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah