Study on the Effect of Temperature on the Pyrolysis-Mechanics-Seepage Characteristics of Oil Shale

Abstract

In order to obtain the response law of pyrolytic chemical structure, seepage characteristics, and mechanical characteristics of oil shale to temperature, the structural evolution of functional groups in oil shale under different temperatures was qualitatively described and quantitatively analyzed by Fourier infrared spectroscopy (FTIR). Electronic universal testing and high-temperature triaxial penetration test were combined to reveal, the influence law of temperature on oil shale strength and permeability. At the same time, the pyrolysis, seepage, and mechanical properties of oil shale in other areas were compared. The results show that: The oil shale contains aliphatic compounds, aromatic compounds, oxygen-containing functional groups, and silicates. With the increase of pyrolysis temperature, the C—H bond of aliphatic compounds breaks first, and C=C breaks at high temperature. In addition, continuous fluctuations were also observed in the characteristic band intensities of functional groups such as C—O and Si—O. The compressive strength of oil shale gradually decreases, especially at a rapid rate from 300 ℃ to 500 ℃. When the temperature is between 20 ℃ and 400 ℃, the magnitude of the oil shale permeability in the stress-constrained state is small, and the highest is only 10-5 μm2. When the temperature is higher than 400 ℃, the oil shale permeability is larger. At the same time, the permeability decreases almost linearly with the increase of pore pressure, owing to the combined effect of gas slippage effect, adsorption effect, and effective stress. From the comparison with the pyrolysis, percolation, and mechanical properties of oil shale in other areas, it is seen that the evolution law of the pyrolysis characteristic of oil shale in different areas is relatively identical, while the mechanical strength and permeability results are quite different. It is considered that the main factors are organic matter content and maturity.

Keywords

• pyrolysis temperature
• oil shale
• functional groups
• permeability
• compressive strength