Nikita Onegov

This paper presents the problem of workover operations in the production wells. Liquid hydrocarbons recovery involves many operations, and production wells workover and servicing are essential parts of this process. Most of the well intervention operations require preliminary well killing that includes generating a hydrostatic back pressure with a column of fluid required density to eliminate any reservoir fluid inflow and gas surges. Preliminary well killing ensures safety of both crew members and production zone. This work focuses on a specialized additive for workover fluids developed by authors aiming to create and stabilize inverse emulsions. The results of conducted research have shown that the application of special additives not only significantly reduces clay swelling (from 25% to 3.1% in the case of a 5% NaCl solution) but also prevents sudden changes in wettability. These findings lead to conclusion that the use of special formulations results in preserving reservoir permeability by maintaining the size of pores and fractures. Simultaneously, it prevents the formation from a water blockage that could impact fluid flow paths. In case of using kill fluids based on inverse emulsions the permeability decreased 1.5 times less than in case of using water-based fluids.

High water-cut oil production is one of the major issues in the petroleum industry. The present study investigates different profile control solutions, with an emphasis on selective methods and materials that mostly decrease the permeability of water-saturated reservoir areas. To achieve the selective water flow blockage in fractured porous media, the sodium silicate-based gel-forming composition was developed. The test procedure was created to assess selective and strength characteristics of the presented composition. According to the results of this procedure, adding polyatomic alcohols to the mentioned composition enhances its hydrophilic behavior in water-saturated rocks (work of adhesion increases from 117 to 129 mJ/m²) and reduces the hydrophobic behavior in oil-saturated rocks (work of adhesion drops from 110.3 to 77.4 mJ/m²). The selectivity of the composition performance is validated by its higher wettability of water-saturated reservoir rocks compared with oil-saturated; thus, the composition creates a more stable water shutoff barrier when entering the water zone in a formation. As a result of core flooding experiments in natural, fractured, porous core samples, the efficiency of the water blocking capacity of the composition was proved. In addition, these tests showed the selectivity of the composition because the permeability decrease in water-saturated core samples was higher than in oil-saturated ones. The experimental value of the selectivity coefficient was 152.14.