Experimental study to confirm the existence of hydrocarbon under high pressure and temperature of deep lithosphere

Abstract

Pyrolysis of lignite was conducted at high temperatures from 400 to 700℃ and high pressures of 1 and 3 GPa in a closed system in order to investigate pressure and temperature effects on organic matter maturation. The data indicated that the total yield of liquid hydrocarbons decreased with increasing pressure and the maximum of production was obtained at a higher temperature. The alkanes show more mature characteristics with increasing temperature at a given pressure, conversely, high pressure significantly hinders the thermal evolution of geological organic matter. The experimental results also demonstrated that the relative abundance of high molecular weight hydrocarbons may exist under the conditions of the lower lithosphere, which not only breaks through the traditional concept that alkanes mainly present at stage of "oil window", but also enhances the possibility to find the oil in the high temperature and pressure areas.

Evolutive characteristics of aromatics under high pressure and temperature of deep lithosphere

“…The solvent-extracted for 48 h fractions of pyrolysates were separated on silica gel/alumina columa chromatograph, and saturated, aromatic hydrocarbons, nonhydrocarbon and asphaltene were eluted. Then the aromatics hydrocarbons were analyzed on a Hewlett-Packard 6890 gas chromatograph interfaced with a Hewlett-Packard 5973 mass-selective detector made by Agilent [8,9] .…”

“…The Sat and Aro yields show an increasing trend with increasing temperature except that of Sat at 700℃, indicating that high pressure is unfavourable for decomposing liquid hydrocarbon into gaseous products. In addition, the ratios of saturated hydrocarbon over aroTable1 Variation in yield of chloroform bitumen "A" and its fractions and parameters of aromatic hydrocarbon at different temperatures and pressures a) Data of yield of chloroform bitumen "A" and its fractions cited from Wang et al [9] ; b) data of repeated experiments (700℃, 1 GPa). MN (methyl- matic hydrocarbon (S/A) show a decreasing trend with increasing temperature and pressure as a whole (Table 1), suggesting that pressure favors the cyclization, polymerization and aromatization of pyrolysate.…”

“…Considerable amounts of liquid hydrocarbons with the carbon number up to C 35 and the isoprenoid hydrocarbon, with relatively low thermal stability, were found at 3 GPa and 700℃, which is considered extinct exceeding the "dead line" for liquid hydrocarbon. Isomerizations at the C-22 position in hopane and at the C-20 in regular sterane have not reached the typical end-point value even at 700℃ [9,19] . The transformation of aromatics is very complicated during the maturation of organic matter, including aromatization of alkane and cyclanes, cracking and condensing reactions of aromatic hydrocarbons.…”

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

“…2). Under HPT conditions, most alkanes in the pyrolysates showed bimodal distributions, except at 700 o C (Wang et al, 2006). At a given pressure, the alkane distribution of the pyrolysates shows an increased trend of right-hand peaks and a decrease in LMW/HMW (the ratio between low molecular weight and high molecular weight constituents) with increasing temperature between 400 and 500 o C (Table 1).…”

“…Sample extracts were injected in splitless mode at 250°C into an HP-5 column (30 m × 0.25 mm × 0.25 μm) at an initial temperature of 80 o C. The temperature was raised at 4 o C/min to 290 o C and held for 30 min. The mass spectrometer was operated at an electron energy of 70 eV with an ion source temperature of 250 o C (Wang et al, 2006). Tricyclic terpanes, C 24 tetracyclic terpane and all hopanes were identified on the basis of mass fragmentographic responses and relative retention times compared with "standard" samples and the literature.…”