This paper is a description of the main stages of research work for determining the cause of high gas-oil ratio on the Yu. Korchagin field, as well as developing recommendations for gas breakthrough isolation.

As the main tool to determine the causes of premature gas breakthrough and to assess the effectiveness of isolations, the reservoir model (hereinafter RM) was used. To obtain initial data to specify the actual model, preliminary work was carried out to analyze and interpret the entire spectrum of studies conducted in the field. Well tests allowed to determine the energy state and filtration-capacity characteristics of the well bottom-hole zones; downhole logging data – refine gas influx profile through the perforation intervals; laboratory studies of fluids and cores were used to create EOS fluid model.

All the results obtained were included into the RM. Then the RM was history matched. During the matching and sensitivity analysis of the model to gas-oil ratio, all sources of gas breakthrough in wells were distinguished. Growth of the gas-oil ratio was largely the result of breakthrough from overlying horizon and gas cap cone formation. To a lesser degree the high gas-oil ratio values caused by oil degassing process in a wellbore.

The main recommendation to reduce gas inflow in the upper perforation intervals was to inject a water soluble surfactant (foam). Foam obtained at formation conditions reduces gas mobility and surface tension at the phase interface, thus allowing to achieve the gas influx blocking.

Lack of domestic experience for such operations was compensated by the experience from the Norwegian continental shelf. Projects at Snorre and Oseberg provided data about specific surfactants, their properties and behavior in the reservoir. These data allowed to focus on selecting a specific surfactant and include its PVT properties into the model. Since the conditions in the Caspian Sea shelf are distinct from the North Sea, additional laboratory studies at "LUKOIL-VolgogradNIPImorneft" were conducted on field core samples for oil displacement in presence of selected surfactant. The data obtained was incorporated into the foam model.

History matched RM allowed to make justified estimation of different options for foam treatment at each well. The obtained results allowed to select optimal scenario for each well, specific recommendations were formulated according to it.

The obtained results allowed to the conclude on effectiveness of integrated approach to modeling, where the RM with all relevant information about the field plays a crucial role at every work stage – from determining the causes to making recommendations to prevent them.

According to the research results, LUKOIL-Nizhnevolzhskneft approved a foam treatment pilot program in one of the wells of Yu. Korchagin field.

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