Geochemical characteristics of carbon and hydrogen isotopes of light crude oils from the deep reservoirs in the Tazhong area of Tarim Basin, NW China

The stable carbon and hydrogen isotopes of light crude oils from deep reservoirs of Cambrian-Ordovician strata in Tazhong area of Tarim Basin, NW China were investigated. The delta C-13 and delta D values determined from the oil samples ranged from -32.94 to -29.53 parts per thousand and -121.36 to -87.78 parts per thousand, respectively. A positive correlation exists between delta C-13(oil) and delta D-oil when the delta C-13(oil) < -31.15 parts per thousand, while a negative correlation occurs at delta C-13(oil) > -31.15 parts per thousand. This basic geochemical data is quite instructive in that the delta C-13(oil) value of approximately -31 parts per thousand may be an important threshold value to delimit the origin of the organic matter that formed the light crude oils.