Hydrocarbon Geochemistry from Kerogen Pyrolysis in Panyu Low Massif and North Slope of Baiyun Sag in Pearl River Mouth Basin

Key words: 
• Pearl River Mouth Basin /
• kerogen /
• thermal simulation /
• EASY Ro(%) /
• carbon isotopic composition /
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Abstract: A series of kerogen pyrolysis in gold tube reactors were conducted at two heating rates of 20 ℃/h (from 373.5 to 526 ℃) and 2 ℃/h (from 343 to 489.2 ℃) under a constant pressure of 24.1 MPa. The kerogen (PY) concentrated from Enping Formations immature carboniferous mudstone in the Panyu Low Massif and North Slope of Baiyun Sag in Pearl River Mouth Basin, China was used in this study. For comparison purpose, the isolated kerogens from Green River shale (GR) and Woodford mudstone(WF) representing typical type I and II kerogens were employed as well.  The yields of C15, C614 and C14+ were quantified, and the carbon isotopic compositions of residual kerogens and asphalts were measured. The results show the total yield of hydrocarbons are low from PY kerogen pyrolysis, and the yield of gaseous hydrocarbons is 1.5 times to liquid hydrocarbons. In contrast, the total yields of hydrocarbons from GR and WF kerogen pyrolysis are apparently great, and are dominated by liquid hydrocarbons. This indicates PY kerogen thermal decomposition mainly forms natural gas. During kerogen thermal decomposition, the oil to gas ratio is controlled by both of organic matter thermal maturity and kerogentypes, yet the ratio of gas and light hydrocarbons is mainly affected by thermal maturation. The carbon isotopic compositions of residual kerogens and alsphalt fraction are almost identical, and less than 0.3‰  13C enrichment to original value of kerogen is observed from 0.7% to 2.7% Ro during thermal maturation. This suggests that  δ13C of residual kerogens or alsphaltane could be used as a indicator to the reconstruction of organic matter type for highmature source rock.