Oil Classification and Oil-Source Correlation Models in the Central Uplift of Tarim Basin, China
Significant quantity of oils has been found from Paleozoic reef flat carbonates in the Central Uplift of Tarim Basin, NW China. The oil reservoirs include predominantly Ordovician carbonates, and Carboniferous and Silurian clastic rocks. Several genetic types have been identified for the liquid petroleum ranging from light condensate, high waxy oils, normal black oils to heavy oils, as a result of multiple episodes of hydrocarbons charging and secondary alternation during multiple orogenic events. Whether or not the Middle-Upper Ordovician strata were the effective source rock for the oils remains to be confirmed due to the relatively high thermal maturity level of the oils and the scarcity in deep wells that penetrate the source rock intervals. This study utilized a total of 104 DST oils, 12 reservoir cores and 30 potential source rock samples to unravel the origin and accumulation of the oils. Results of compound-specific isotopes, hydrocarbon fluid-inclusion composition and molecular biomarkers indicate that most of the oils in the study area are a mixture of oils derived from Cambrian -Lower Ordovician (∈-O1) and Middle-Upper Ordovician (O2+3) source rocks, with a wide range of variation in the relative contribution of the two regionally significant source rocks. It is significant to note that stable carbon isotope values of n-alkanes clearly suggest mixed sources, whereas the sterane biomarkers in most of the oils tend to show only the Middle-Upper Ordovician source contribution. A geological model involving heterogeneous reservoirs and multiple episodes of hydrocarbons charging and alteration has been proposed to explain the heterogeneity in reservoired petroleum fluids.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009