A review of liquid nitrogen fracturing technology

•A new reservoir stimulation method of LN2 fracturing is reviewed.•The low-temperature effect of LN2 on rock properties is analyzed.•The heat transfer of LN2 in wellbore and bottom-hole rock is introduced.•The rock-breaking characteristics of LN2 jet is investigated in detail. Hydraulic fracturing is an efficient stimulation means for the exploitation of unconventional oil/gas resources as well as geothermal energy. However, there are several issues for traditional hydraulic fracturing, e.g. excessive water consumption, formation damage and flow-back-fluid contamination. In recent decades, these problems have led research efforts to investigate waterless fracturing technology as an alternative to traditional hydraulic methods. Liquid nitrogen (LN2) is considered as one of the potential water-free fracturing fluids. Due to its unique low-temperature characteristics, severe thermal stress will be created in the rock under down-hole conditions during the LN2 fracturing process. As a result, not only several primary fractures, but also secondary cracks perpendicular to the primary fractures can be generated in a reservoir, creating a more complicated fracture network than that in conventional hydraulic fracturing. This review aims to outline the current developments of LN2 fracturing technology from several aspects, including the effect of thermal shock on rock physical properties, the heat transfer characteristics of LN2, the rock-breaking performance of an LN2 jet, and the applications and limitations of cryogenic fracturing technology. Simulation studies, laboratory experiments and field application cases are discussed to evaluate the LN2 fracturing technology.