Advances in Liquid Nitrogen Fracturing for Unconventional Oil and Gas Development: A Review

Liquid nitrogen (LN2) fracturing is an anhydrous fracturing technology that enhances coal permeability and supports unconventional oil and gas exploitation. In this Review, we provide a systematic review of five aspects of LN2 fracturing. They are the history of the technology's development, research topics, factors influencing fracturing efficiency, fracturing mechanism, and engineering processes and systems. Liquid nitrogen fracturing transforms coal and rock pore structure through mechanisms such as low temperature, freeze-thaw damage, and gas expansion. It changes coal and rock mechanical properties and improves the pore penetration and efficiency of unconventional oil and gas extraction. However, in-depth studies are still required in many areas. They include theoretical studies of twophase nitrogen flow in coal and rock, development of technical equipment to support field operations, and plans to monitor and evaluate fracturing efficiency. On the basis of the advances in LN2 fracturing research and the challenges, we conclude that future research should focus on multiphase flow and field equipment and technology.