The article presents a design of water shut-off treatments to decrease the water cut in producing wells on Zapadno-Khosedayuskoye oilfield located in Central-Khoreiver Uplift. The key features of the field are relatively high oil viscosity (12-13 mPa∙s) and average formation temperature 70°С. The main producing horizon is carbonate formation D3fmIII, characterized by mixed wettability and high salinity of formation water (up to 210 kg/m3). Based on the results of field data analysis, well testing and well logging it was found that increased water cut of many wells is caused by bottom water coning, including channeling through high permeability vugular streaks. To solve the problem of water coning we evaluated compositions based on polymers and inorganic components. Thermally activated gelant compositions based on inorganic aluminum salts were selected for field trials. Gelation mechanism involves decomposition of additive component (carbamide) at reservoir temperature and formation of strong gel screen. Chemical properties of the composition were analyzed. The residual resistance factor to water (relative decline of mobility after gelation) is in range of few units (for oil-saturated heterogeneous media) to several hundreds or thousands (for high-permeability streaks). The key parameters for modeling gel screen stability and permeability to oil and water were determined. Obtained laboratory data were used to calculate the threshold pressure drop and flow regimes using analytical methods as well as linear and radial single well hydrodynamic models.
In 2019–2021 17 water shut-off workovers were performed on Zapadno-Khosedayuskoye field to isolate the inflow of bottom water from D3fmIII formation. Candidate wells were selected using the analysis of geological heterogeneity of the penetrated zones and water inflow diagnostic plots. Workovers were performed using additional perforation of the bottom zone and followed by cement plug to isolate the wellbore. Injected volume ranged from 350 to 500 m3. In most wells water cut was decreased after workover. Cumulative incremental oil production from water shut-off operations is 106 thousand tons, average incremental oil rate from workovers – 18,1 tons/day, showing prospective to use the suggested injection scheme on other oilfields with similar properties.
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