Study and prospection of liquid nitrogen fracturing coal technology

The permeability of coalbed methane reservoir is generally low in China. How to effectively improve the permeability of coal seam is the key and difficult point of coalbed methane exploitation.Liquid nitrogen fracturing technology can effectively improve the permeability of coal seam, and then improve the exploitation rate of coalbed methane.At the same time, as an efficient and green anhydrous cracking technology, liquid nitrogen fracturing technology can effectively save water resource ,avoid water lock sensitive damage and other problems.Based on the importance of liquid nitrogen fracturing technology in CBM exploitation , a large number of theoretical and experimental studies have been carried out.In order to summarize the research progress of liquid nitrogen crack technology and point the direction of future research, synthetically analysis the relevant academic research results, and discuss the water - ice phase transition frost heaving force, liquid nitrogen vaporizing expansion force and coal matrix shrinkage force,especially the water- ice phase transition frost heaving force which plays the leading role in aqueous media and coal matrix shrinkage force which plays a main role in dry coal.The influencing factors of internal physical properties (water content, degree of coal metamorphism and cementation, joints, etc.) and external environmental factors (temperature gradient, liquid nitrogen action time and cycle times, ground stress, etc.) of the liquid nitrogenous fracturing coal are systematically analyzed.The status quo of liquid nitrogen fracturing and stimulation technologies such as low temperature, high temperature fluid technology, liquid nitrogen repeated fracturing technology, liquid nitrogen gasification fracturing technology, low temperature fluid fracturing technology and liquid nitrogen assisted fracturing technology are summarized and analyzed.The field test and application of liquid nitrogen fracturing technology are introduced.The the test flow and test results of liquid nitrogen refracturing technology and liquid nitrogen injection assisted hydraulic fracturing technology are mainly introduced.In the end, this paper summarizes the deficiencies in three aspects, including the main mechanism of action, influencing factors and field test and application of liquid nitrogen induced coal, and gives a prospect of the research emphases.It is pointed out that the research emphasis of liquid nitrogen induced fracturing coal body technology in the future is the in-depth study of comprehensive mechanism and multiple influencing factors, and the ultimate goal is to realize the field application to improve the efficiency of coalbed methane extraction.