Waterless fracturing technologies for unconventional reservoirs-opportunities for liquid nitrogen

• Waterless fracturing technologies including CO2 energized oil, explosive, gelled LPG, gas, liquid CO2 and N2, are reviewed.
• Experiments demonstrated that cryogenic stimulation with LN2 is capable of creating fractures in shale and sandstone rocks.
• Cryogenic fractures generated in rocks are characterized by pressure decay tests, acoustic signatures, and gas fracturing.
• Liquid N2 can be implemented to cost-effectively stimulate unconventional reservoirs by eliminating water-related issues.

During the past two decades, hydraulic fracturing has significantly improved oil and gas production from shale and tight sandstone reservoirs in the United States and elsewhere. Considering formation damage, water consumption, and environmental impacts associated with water-based fracturing fluids, efforts have been devoted to developing waterless fracturing technologies because of their potential to alleviate these issues. Herein, key theories and features of waterless fracturing technologies, including Oil-based and CO2 energized oil fracturing, explosive and propellant fracturing, gelled LPG and alcohol fracturing, gas fracturing, CO2 fracturing, and cryogenic fracturing, are reviewed. We then experimentally elaborate on the efficacy of liquid nitrogen in enhancing fracture initiation and propagation in concrete samples, and shale and sandstone reservoir rocks. In our laboratory study, cryogenic fractures generated were qualitatively and quantitatively characterized by pressure decay tests, acoustic measurements, gas fracturing, and CT scans. The capacity and applicability of cryogenic fracturing using liquid nitrogen are demonstrated and examined. By properly formulating the technical procedures for field implementation, cryogenic fracturing using liquid nitrogen could be an advantageous option for fracturing unconventional reservoirs.