Distribution and Isomerization of Terpanes in Pyrolyzates of Lignite at High Pressures and Temperatures

Abstract

Experimental pyrolysis of Eocene lignite in the presence of water was conducted in a closed system for a heating duration of 120 min at temperatures of 400, 500, 600 and 700 o C and pressures of 1 to 3 GPa (equivalent to burial depths of about 30 to100 km). The distribution of terpanes in the resulting pyrolysates was analyzed in order to investigate the effects of pressure and temperature on maturation of organic matter for this heating time at mantle depths. The results indicate that terpanes show more mature characteristics with increasing temperature at a given pressure. However, high pressures significantly retarded the thermal evolution of organic matter. Also, high pressures had a non-linear effect on maturation, resulting in anomalous variations of maturity parameters and ratios (tricyclics / hopanes, Ts/Tm, C 31 22S / (22S+22R), and βα-moretane / αβ-hopanes). In addition, the isomerization of hopanes at the C-22 position did not reach typical end-point values, even at 700 o C. These results are a preliminary step towards a better understanding of organic matter maturation and oil and gas exploration in high temperature and pressure regimes.

Simulation of Thermal Maturity in Kerogen Type II Using Hydrous and Anhydrous Pyrolysis: A Case Study from the Bakken Shale, United States

“…A similar finding was reported by Aldega et al, who showed an increase in illite content with increasing thermal maturity. Moreover, based on the findings of Wang et al, the pyrolytic experiments indicate that pressure may impede the transformation of Ts to Tm at lower temperatures, but it is likely to promote this transition at higher temperatures.…”

The Effects of High Pressure on Oil‐to‐gas Cracking During Laboratory Simulation Experiments

“…As pressure increases, the gas volume is compressed and the distance between the gas molecules is reduced. Consequently, an increase in pressure results in retardation of oil cracking at a given temperature (Wang et al, 2012). The higher the pressure, the more energy is consumed in this way (Uguna et al, 2012).…”

Effect of Ancient Salinity on the Distribution and Composition of Tricyclic Terpane in Hydrocarbon Source Rocks in the Mahu Depression

“…Absolute concentration and relative content changes in tricyclic terpane compounds in terrestrial organic matter, such as lignite deposited under weak oxidation-weak reduction conditions, as well as in high-temperature and high-pressure thermal simulation products of strongly reducing saltwater lake hydrocarbon source rocks, revealed the enrichment of tricyclic terpane compounds. The ratio of tricyclic terpanes to hopanes significantly increases with increasing temperature [21]. In addition, the distribution pattern and relative abundance of tricyclic terpanes with different carbon numbers in different environmental hydrocarbon source rocks differ [22][23][24][25][26].…”