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
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.
Presented in the paper are the results of pilot-commercial thermal cyclic stimulation of wells performed in various producing intervals of Zybza-Glubokiy Yar field containing heavy (with density of 0.975–0.986 g/cm3), high-viscosity (with kinematic viscosity of 340–580 cSt@50oC) and resinous (with sulfuric acid resins content of up to 72% mass) crude oil. Cyclic steam stimulation of bottom-hole zones and reservoir steaming were the technologies realized to develop the field which is mature now. Two thermal EOR processes had been tested in the field within the period of 2000–2004. One of the said processes involves the use of a gas-liquid heat carrier (gas-steam), the other - a gaseous heat carrier (thermal gas). Introduction Zybza-Glubokiy Yar field can be classified as a mature one that is in the final stage of its development. Presence of light oils in some parts of the field allows production by conventional methods. However, production of heavy high-viscosity oil is complicated and in some cases impossible without special-purpose equipment and new technologies providing a sufficiently profitable production on a commercial scale. Cyclic well stimulations using gas-steam and thermal-gas heat carriers were performed with the aim to enhance production of high-viscosity oils in the field. Outline of Geological Field Characteristic Zybza-Glubokiy Yar field is unique as a production play since it contains oil or gas pools in Cenozoic era section from Lower Paleocene up to and including Pliocene. A total of 21 horizons are recognized within the field section according to a field nomenclature. The horizons cover the complete genetic hydrocarbon series - gas with condensate, light oil, heavy high-viscosity oil, bitumen, hard naphtides. Such uncommon arrangement of pools containing hydrocarbons of different genetic series in traps all over the Cenozoic era section is determined by totality of geological and geochemical factors and fluid-dynamic conditions of accumulation. As a result, syngenetic pools of gas with condensate and light oil were formed in dome traps of lower stage. Then, in post-Early Maikop time, the pool of Kumsky horizon in the dome and southern flank transformed into a pool of heavy oil with dome water. Epigenetic pools of heavy oil and bitumen, hard naphtides among them, were formed in blind traps of upper monocline stage. The exceptions for the upper stage are syngenetic pools of light oil in Maikop series, which pools are the source of oil and gas formation. Table 1 presents basic characteristics of thermally stimulated reservoirs as well as physical and chemical properties of oils. Process Data for Thermal Stimulations Stages of technological process for injection of gas-steam and thermal gas heat carriers into the reservoir, method for generation of the said agents and technical support for the process have been previously reported in papers [1–3]. Thermal stimulations of bottom-hole formation zones were realized practically in all areas of the field in 1988–2003. Key indicators and data on response to thermal treatments are given in Table 2. Conclusions The results obtained from thermal stimulations of bottom-hole formation zones allow conclusions as follows:Technologically, stimulations by gas-steam and thermal gas have greater response when applied to oil-saturated reservoirs with high permeability.Success ratio for thermal stimulations made above 75%. ReferencesStashok Y.I., Antoniadi D.G. et al.: " Cyclic Gas-Steam Well Stimulations", Sixth European Symposium on Improved Oil Recovery, Stavanger, Norway, 1991, May 2123, Vol. 1, Book 1, 105.Stashok Y.I., Antoniadi D.G. et al.: " Heavy Oil Pool and Oil-Bearing Sands Development Using Steam-Gas Bed Stimulation Technology", 6th UNITAR International Conference on Heavy Crude and Tar Sands, Houston, Texas, 1995, February 12–17, Vol. 1, 647.Stashok Y.I., Tzybin A.V. et al.: " Results of Field Development of High-Viscosity Oils in the Krasnodar Region Using Gas-Steam Heat Carriers". 1st International Conference "Conversion of the Resources of Hard-to-Recover and High-Viscosity Oils into Reserves", Shepsy, the Krasnodar Region, Russia, 1997, July 16–20, 28.
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