The paper is an addition to those presented at and published by the 5th and the 6th European Simposia on Improved Oil Recovery held in Hungary and Norway. Included in the paper are results of laboratory and field studies on cyclic stimulation of bottom-hole formation zones containing high-viscosity oil by gas-steam heat-carrier. The paper presents the last data on performance of the wells after the 1st and the 2nd cycles of stimulation of bottom-hole formation zones. Cyclic stimulations were conducted in a pilot area of Zybza-Gluboky Yar oil field, Krasnodar Territory. Pontian deposits of the field contain oil of 3005420 cp @ 325K at the depths of up to 500 m.
It is a matter of general experien ce that gravitational effects arising during injection of air or steam most oFten affect adversely the efficiency of thermal EER methods . Advantages of these methods are generally used wipere possibility exists of eng i neering a horizontal displacement .The present paper centres on certain technologica) approaches to the use of gravitational effects for improved efficiency of thermal EOR methods .One of the technologies -a cyclic injection of steam into high-viscosity oil reservoir witti bottom water -was applied in 1974 in Yuzhno-Karskiy area of Zybza -Gluboky Yar oil field (trap III), the Krasnodar Territory (Figure 1) . Miocene reservoir of (he area is defined as a water-supported monocline (Figure 2) . Miocene deposits are represented by accumulation of breccia, detritus and terrigenous rocks . Reservoir capacity is made up by voids between the rock debris witti up to 30% of the capacity being characterised by extremely high permeability (up to 640 Darcy) .The main geological and physical parameters of the reservoir are as follows : Within 18 years of reservoir deve l opment witti depletion drive (since 1 956) produced are about 600 Mt of oil, oil recovery reached 21%. Water cut reached 77%due to water encroac h ment mainly through the reservoir bottom . As a result, the reservoir had transformed in a floating one .Starting Erom the second hal f of year 1 974, the reservoir is under development by steam stimu la t ion . I n view of a vide water-oil zone existed and abnormally high per meability of t h e reservoir it was decided to inject steam intermittently info a lowered par t of the reservoir to displace oil Erom a porous reservoir of water-oil zone to t he zone of production and t o form heat slugs at the oil-water surface of upper reservoir areas.]t was conceived that due to a h igh rate of the injected steam coming to the water-oil surface a heat slug had to be formed in the upper reservoir areas, heat energy of the stug being consumed for oil heating and oi l viscosi ty breaking.P enetration of heat slug info oi l zone an d f l ow of h eated oi l to p r oducing Wells veere p rovided by bottom-water drive . The proces is presente d schematically in
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