--> Abstract: Diagenesis of Clastic Reservoirs in the Process of Formation of Oil Fields in Basins of the CIS, by R. Sakhibgareev; #90990 (1993).

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SAKHIBGAREEV, RIF, All-Russian Petroleum Scientific Research Geological Exploration Institute, St. Petersburg, Russia

ABSTRACT: Diagenesis of Clastic Reservoirs in the Process of Formation of Oil Fields in Basins of the CIS

Detailed study of reservoir rocks in oil and gas condensate fields of the former Soviet Union shows that these rocks are strongly altered on the oil-water contacts (OWC) formed during periodic filling of traps by oil. After each period of filling, the ancient OWC was temporarily stabilized. The stabilization was associated with solution of minerals in cement and matrix of the lithologically variable reservoir rocks under the influence of biogenic and abiogenic oil oxidation products (mainly organic acids). The dissolution altered rocks at the OWC and just below it, where these rocks were affected by diffusion of the products of oil oxidation, thus forming a zone of decompaction.

The volume of rocks involved in the dissolution process depends on the relation of a reservoir to discrete portions of migrated oil. If a trap had a high closure and was only partially filled by hydrocarbons, the dissolved products reprecipitated below the dissolution zone, thus forming a zone of cementation. If a trap was filled completely, the dissolved minerals were carried away from the trap.

The paper also describes peculiarities of formation and preservation of dissolution zones in clastic reservoirs along ancient OWC in course of subsidence of oil pools to great depths and transformation of oil into gas condensate and gas.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.