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The paper describes the process of evaluation of low salinity water composition to improve the development of hydrophobic carbonate formations of Central-Khoreiver Uplift (CKU) fields with relatively high oil viscosity (5-15 mPa·s) and average formation temperature 70°C. The sources of low salinity water were determined, prospective composition for water injection were analyzed. The efficiency of oil displacement by formation water and low salinity water are observed during the spontaneous imbibition experiments and coreflood tests to compare the efficiency of formation and low salinity water. The expected incremental displacement efficiency for the target carbonate formations can vary widely, from 1 to 10%. Linear models of the completed coreflood tests and a sector hydrodynamic model of the prospective trial injection are built, considering the basic chemical processes while mixing different types of water. We also review the prospects of joint application of low salinity water injection and chemical EOR methods.

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Currently the flow diversion techniques (FDT) are quite often used to enhance the waterflooding efficiency at the late stage of field development. In particular, the issue of waterflooding efficiency improvement is specifically acute for the carbonate reservoirs due to complex structure of the reservoir, heterogeneity of reservoir properties as well as the presence of natural fractures. All listed factors result in significant decrease of waterflooding efficiency due to quick water breakthrough into the wells through the low flow resistance channels (LFR) which results in significant decrease of the oil recovery factor (RF). In many cases waterflooding at the similar fields is not applied at all resulting in the produced water disposal issue. It is evident that for the purpose of solving such issues application of FDT based on the injection of various polymer gel-forming compounds into the formation allowing decrease in conductivity of LFR channels resulting in increase of swept reservoir volume may seem efficient. Considering the development of chemical industry, the FDT market currently offers a lot of compositions and compounds in a wide price range having different technological characteristics and designed for different conditions. Due to this the selection of the most appropriate compositions with account of all factors is an acute task requiring thorough approach with application of often unique laboratory experiments using unconventional equipment as well as performance of pilot works at individual field areas. This paper presents the sequence of actions (from laboratory studies for the determination of the suitable polymer compositions to the selection of the specific field areas for the pilot works performance) for complete justification of FDT application at one of the Central Khoreyver Uplift fields located in the Timano-Pechora oil and gas province. Apart from presence of the heterogeneous and fractures carbonate reservoir, the field is characterized by high mineral content of the formation water what imposes significant restriction on the use of a number of polymer compositions as well as requires more thorough approach to the selection thereof. The paper also describes the flow experiments held, inter alia, using the actual core samples with use of high-mineralized formation water and shows their results. As a part of this work the justification of injection of two polymer compositions selected after laboratory studies at 2 pilot areas with assessment of incremental production using the simulation model (SM) developed with the account of the annual tracer studies allowing assessing LFR channels properties was carried out. As a result of the performed work, 2 pilot polymer compositions injection works were included into the company's business plan for 2019.

The paper considers the use of a surfactant-polymer composition for the mobilization of light paraffinic oil from the D3-III carbonate reservoir at a reservoir temperature of 62°C, as well as the results of its tests in field conditions. Earlier, the composition showed its effectiveness on model carbonate cores with salinity from current (50-80 g/l) to reservoir (up to 170 g/l), in the presence of surfactants, type III microemulsions according to Winsor with oil were obtained. Based on the results of the filtration experiments performed on our own core from the productive formation D3-III, an increase in the displacement efficiency of surfactant-polymer compositions compared to water was obtained 11–14% (with a total surfactant concentration of 1%), irreversible surfactant losses in water-saturated rock–up to 0, 38 mg/g. Displacement efficiency after water and surfactant-polymer composition flooding was also estimated in the field conditions using SWCTT; its results were interpreted by various methods (analytical, in a hydrodynamic simulator), and also compared with laboratory results. Within a single-well tracer test, an assessment of the residual saturation after water filtration and injection of a surfactant-polymer composition was carried out under the following conditions: the target research radius is 3.5 m; porosity 10%, effective reservoir thickness 38 m. Based on the results of SWCTT, an increase in the displacement efficiency of 16.7% was obtained in comparison with water displacement (total surfactant concentration 1%) using an analytical method of interpretation. The adaptation of the SWCTT results on the hydrodynamic model was carried out, the most influencing parameters on the quality of adaptation were determined. The selection and justification of a pilot area for a multi-well pilot project was carried out, a sector hydrodynamic model of the site was built, and calculations were made to assess additional oil production.