Adaptability of J55 and N80 tubings to CO2 dry fracturing

In the process of CO2 dry fracturing, CO2 is at the state of supercritical low temperature, having apparent cooling effect on fracturing strings. In this circumstance, the higher property of fracturing string shall be essential. In reference to ASTM standard, the tubing samples of two different steel grades (J55 and N80) were tested in terms of their mechanical properties after cold treatment according to the technical principles and characteristics of CO2 dry fracturing. It is shown that the samples of both steel grades don’t reach the critical point of brittle-ductile transition in the extension test at –60℃. In the impact test at the temperature from –60℃ to –20℃,brittleness trend is apparent in the sample of J55 tubing, but never occurs in the sample of N80 tubing. It is concluded that the N80 tubing can satisfy the safety requirements for low- temperature CO2 dry fracturing, thereby ensuring the safe operation.