Formulation construction and transport-plugging performance of <i>in situ</i> inorganic plugging system for high-salinity reservoir

The South China Sea oilfield faces severe challenges, including exacerbated heterogeneity, inefficient waterflooding, high salinity, large well spacing, and limited platform space, making conventional polymer gel systems unsuitable and necessitating alternative profile control and oil displacement solutions. This study explored the in situ reaction characteristics of inorganic precipitates resulting from the reaction of Na2CO3 and Na2SiO3 solutions with calcium and magnesium ions present in the formation saline solution, as well as their transport and plugging behaviors in porous media. The key findings reveal that increasing Na2CO3 and Na2SiO3 concentrations enhances carbonate and silicate precipitation, with silicate precipitates forming fine particles or gels. Particle size analysis shows that silicate precipitates are larger but decrease in size at higher concentrations. Notably, the silicate precipitation demonstrated stability in suspension and was not significantly affected by temperature, even under elevated conditions. SEM imaging indicates that carbonate precipitates form loose, sheet-like aggregates, whereas silicate precipitates exhibit dense, crystalline structures with superior suspension stability. Core flooding experiments demonstrate that the Na2SiO3 system provides stronger plugging, while the Na2CO3 system offers better transport. Based on permeability, the Na2CO3 system is optimal for 50–500 mD cores, whereas the Na2SiO3 system performs better in 500–2000 mD cores, ensuring an effective balance between transport and plugging efficiency.