Study on the change of physical properties of Organic-rich shale after heat treatment

With the increase in global energy demand, people pay more and more attention to the development and utilization of unconventional oil and gas. Organic-rich shale is often considered as the source rock of unconventional oil and gas, and its physical properties will change greatly under the action of high temperature. Therefore, it is necessary to analyze and study the physical properties changes and reasons before and after high-temperature heat treatment. Taking the organic-rich shale of Niutitang Formation in Micangshan area of China as the research object, the physical parameters such as chromaticity, glossiness, hardness, capacitance, impedance, P-wave velocity, porosity, mass loss and TG/DSC were tested before and after heat treatment. The reasons for the changes of physical properties were analyzed in combination with the pyrolysis process of shale. The results are as follows: When the temperature is lower than 300 °C, the physical properties change slightly in a certain range, mainly dehydration reaction. In the temperature range of 300–450 °C, except for the decrease in wave velocity and capacitance, the other physical properties increase greatly. The main reaction is thermal decomposition of kerogen. When the temperature is between 450 °C and 600 °C, the hardness and porosity increase greatly, and the other physical properties continue to change slightly. The main reaction is the decomposition of asphalt and some inorganic minerals. By fitting the physical properties, it can be found that the wave velocity has a linear negative correlation with porosity and a linear positive correlation with capacitance. Porosity is positively correlated with mass loss rate and hardness growth rate. After 390 °C, the mass loss rate of shale increases greatly. The endothermic reaction mainly occurs before 530 °C. Due to the thermal decomposition of organic matter and inorganic mineral components in shale samples, the pore structure and mineral composition of the samples are greatly changed, which further leads to the change of physical properties.