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%.
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