Research on the efficiency enhancement and parameter optimization of nitrogen injection for production increase in Ansai oilfield

Abstract

Nitrogen injection for enhanced recovery represents a highly efficient and environmentally friendly technology in oil and gas field development. It is extensively utilized in low-permeability and unconventional reservoirs, as well as in the potential exploitation of mature oilfields. Leveraging the inherent properties of nitrogen—such as low viscosity, high diffusivity, chemical inertness, and strong compressibility—this technique enhances reservoir flow conditions and improves hydrocarbon mobility through cyclic nitrogen injection operations. This study focuses on nitrogen huff-and-puff recovery efficiency as the core response indicator and adopts the controlled variable method to conduct experiment s. With fixed soaking time, two characteristic water-cut levels (75% and 95%) were selected, and multi-gradient soaking pressures were applied in the experiments. A correlation model was subsequently developed through data analysis. The results indicate that, under the same water-cut and soaking duration, higher soaking pressure leads to a greater ultimate recovery efficiency. Given the same nitrogen injection volume, a higher water-cut during water flooding corresponds to a diminished enhancement effect from nitrogen energy supplementation. The influence of soaking time on recovery efficiency follows a pattern of “initial significant improvement followed by stabilization,” suggesting an optimal matching relationship between the two parameters. Concurrently, for reservoir conditions with 75% and 95% water saturation, this study has developed a nitrogen injection calculation formula that accounts for elastic micro-deformation of the reservoir induced by well-soaking pressure. This formula enables quantitative estimation of field nitrogen injection volumes and enhanced oil recovery under various application scenarios.