Development of laboratory system for cryogenic fracturing study

摘要

The concept of cryogenic fracturing is that sharp thermal gradient developed on rock surface byrnsubjecting cryogenic fluid creates strong local tensile stress and initiates fractures. Prior field tests suggest thatrnfield application with special equipment rated for cryogenic temperatures may bring in potential benefits. Theyrndid not, however, identify the fracture mechanisms at work in downhole conditions.We have developed experimentalrnsetups and procedures that are specifically designed to conduct cryogenic fracturing tests with confiningrnstress, integrated cryogen transport, measurements, and fracture characterization.A true triaxial loading systemrnis built to simulate reservoir stress levels and anisotropies. Temperature, borehole pressure, and liquid nitrogenrncan be monitored continuously. Acoustic and pressure-decay measurements are used to characterize fracturesrnbefore and after the experiments. The laboratory design was able to effectively apply cryogenic fracturing tornlaboratory rock specimens. The characterization methods were able to capture rock property changes due torncryogenic fracturing.