Chemical flooding technology has been widely applied in medium- and high-permeability reservoirs. However, it is rarely applied in low-permeability reservoirs, which is mainly limited by reservoir physical properties, chemical agents, injection capacity, and so forth. In this paper, a novel chemical formula used in low-permeability reservoirs was developed. In response to the low-permeability reservoir geological characteristics, fluid properties, and water flooding development of the target block, some experimental studies and field project studies of polymer–surfactant flooding were carried out. The surfactant structure and polymer molecular weight were determined from laboratory experiments. The polymer–surfactant binary system was synthesized. It had good injectivity in low-permeability reservoirs, and its oil recovery efficiency increased over 10% in the laboratory experiment. The result was higher than that of single chemical flooding. After field implementation, initial results have been achieved with an increase in injection pressure. The chemical formula can effectively alleviate intra-layer and inter-layer contradictions in the reservoir. The project has increased oil output by 77,700 t and the recovery factor by 3.5%. The experience and lessons were of great significance for the development of chemical flooding in high-temperature, high-salinity, and low-permeability reservoirs.

Many oilfields report that the viscosity of polymers in high-salinity reservoirs will decrease significantly. In this paper, molecular dynamics simulations were conducted to investigate the molecular configuration and network of hydrolyzed polyacrylamide (HPAM) molecules in high-salinity formation-water and the viscosity changes from the microscopic dense to dilute phase. In addition, the viscosity of HPAM/formation-water solution was measured to verify and compare with simulation results. Simulation and experimental results show that the molecular network of the microscopic dense phase is essential for the apparent viscosity. The calculated apparent viscosity could decrease 37% as the net-shape molecular network of the microscopic dense phase is broken by calcium ions, which is similar to our experimental results. This paper improved our understanding of the mechanisms of polymer viscosity alteration in high-salinity formation-water and provided insights that can be used to improve the strategy of enhanced polymer flooding and the novel polymer gel formula.

Coaxial multi-layered structure is obtained when the Fe melt confined in the singlewalled carbon nanotube (SWCNT) undergoes a rapid cooling. Owing to the inductive effect of the SWCNT, precursors of the long-range order (LRO) are generated in the confined Fe melt and finally been converted into local crystalline structures in the glassy Fe. A memory property has also been observed during the repeated phase transition process. Furthermore, the study of the size effect of tube diameter illustrates that the increasing diameter of the carbon tube is detrimental to the formation of local crystalline structures in nanoscale confinement.

CO 2 injection and water alternating gas (WAG) injection are crucial to improve the oil recovery method and have optimized development in numerous oil fields. Many issues, such as gas channeling, water clogging, and a shortage of gas injection capacity, are addressed in the studies. Considering these conflicts, we suggest in this work a unique method of surfactant alternating gas (SAG) injection. Additionally, axisymmetric drop shape analysis and other approaches are utilized to explore the interface properties of a variety of systems, including CO 2 /carbonated water/water/surfactant/oil systems. SAG injection combines the advantages of surfactant and WAG injection. Although CO 2 molecules have an effect on surfactant aggregation at the oil–water interface in the SAG system, carbonated water has little effect on surfactant performance in lowering oil–water interface tension. Pilot studies reveal that a SAG ratio of 3:2 at 74 °C and 0.5 wt% concentration significantly improves oil recovery.