ABSTRACT
CO2 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 CO2/carbonated water/water/surfactant/oil systems. SAG injection combines the advantages of surfactant and WAG injection. Although CO2 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.
ABSTRACT
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.
