Preparation of dual network semi-solidified gelled-foam for sealing gas channeling in fractured-vuggy reservoirs

Abstract

Gas flooding is an effective EOR process for carbonate fractured-vuggy reservoirs worldwide. With the large-scale application of gas flooding, the problem of gas channeling is emerging inevitably and restricts the improvement of oil recovery. Foaming can alleviate such problems due to its high viscosity. However, many factors lead to the poor stability of conventional foam or even gelled-foam in fractured-vuggy reservoirs, such as Ostwald maturation, lack of support from pore-throat units, and weak regeneration ability, dilution of formation water, high temperature, high salinity, etc. Therefore, a novel dual network semi-solidified gelled-foam was designed to solve the gas channeling problem in fractured-vuggy reservoirs. It overcomes the shortcoming of fast foam volume attenuation due to temperature rising. The new foam system consists of an ionic crosslinking network (sodium alginate, Ca2+) and a covalent crosslinking network (acrylamide, polyacrylamide, crosslinking agent). The characteristics of sodium alginate, which can rapidly react with divalent cations (Ca2+) in formation water to generate an ionic crosslinking network, forming a protective film to enhance foam stability in the first stage. Acrylamide, polyacrylamide, and crosslinking agent (methenamine and resorcinol) were used to form the second network (covalent crosslinking network), which can effectively enhance the high temperature stability of the foam. After optimization, the dual network semi-solidified gelled-foam was obtained, and the half-life can reach 15d in a high temperature and high salinity environment (130 °C, 22.37 × 104 mg/L). Meanwhile, the new foam system also showed higher viscosity, high oil tolerance and plugging capability. This unique designed gelled-foam offers high application potential in deep fractured-vuggy reservoirs. It effectively solves the gas channeling problem in gas flooding production in fractured-vuggy reservoirs worldwide.