Nitrogen Stimulation Technology for Unconventional Oil and Gas Reservoirs: Current Application Status, Research Progress, and Future Outlook

Abstract Unconventional oil and gas resources are strategically important and, owing to their vast scale, have become major alternatives to conventional hydrocarbons. Development remains difficult, however, because these reservoirs are generally heterogeneous, with low porosity and ultra-low permeability. Conventional stimulation may also pollute water, damage formations, and entail high costs. Nitrogen, by contrast, is abundant, inexpensive and has low pollution potential. As a stimulation medium, it can remove blockages, replenish reservoir energy, and improve displacement efficiency, making it well suited to unconventional reservoir development. This review follows the development of nitrogen energization and divides the technologies into gaseous nitrogen, liquid nitrogen (LN2), and composite systems. It describes how they work, their main features, and their application settings. Drawing on field results from coalbed methane, shale, tight sandstone, and carbonate reservoirs, we summarize performance, explain the governing mechanisms, and compare their relative contributions under different reservoir conditions. We then examine the effects of reservoir properties, fluid characteristics, injection parameters, and freeze-thaw conditions. The discussion also covers the difficulties of transferring laboratory findings to field operations and the environmental footprint across the technology lifecycle. Finally, we identify remaining technical barriers and propose directions for more efficient and environmentally responsible hydrocarbon development.