Test system and method for liquid nitrogen circle freeze-thawing permeability-increasing simulation of coal rock sample

摘要

A test system and method for liquid nitrogen circle freeze-thawing permeability-increasing simulation of a coal rock sample. The test system comprises a freeze-thawing apparatus, a data collection system, and a coal rock sample. The freeze-thawing apparatus comprises a liquid nitrogen freeze-thawing test chamber (6) and a self-pressurizing liquid nitrogen tank (7). The coal rock sample (8) is placed in the liquid nitrogen freeze-thawing test chamber (6), and the liquid nitrogen freeze-thawing test chamber (6) is connected to the self-pressurizing liquid nitrogen tank (7) by using a liquid nitrogen supply pipeline. The liquid nitrogen supply pipeline comprises a three-way connector (612), and the three-way connector (612) is respectively connected to the liquid nitrogen freeze-thawing test chamber (6), the self-pressurizing liquid nitrogen tank (7), and a liquid nitrogen pressurizing tube (610). The data collection system comprises a high-frequency pressure sensor (3), a low-temperature strain gauge (41), and a temperature sensor probe (51). The test method repeats the liquid nitrogen freeze-thawing circle for many times, to investigate influence rules on the strain and temperature of a coal rock sample (8) under different freeze-thawing variable conditions. The test method can simulate a process of permeability increase of coal body or rock body through liquid nitrogen circle freeze thawing, and provide a realizable test platform to gas or shale gas extraction from coal rock body with permeability increase by the liquid nitrogen circulation freeze thawing.