Comparison of Hydrocarbon Filling History in the Different Uplifts of the Ordovician Carbonate Reservoirs, Tarim Basin: Evidence from Systematic Fluid Inclusion Analysis

Honghan Chen¹, You Wu¹, Yong Feng², and Chunquan Li¹
¹Department of Petroleum Geology, China University of Geosciences, Wuhan, China
²College of Geosciences, Yangtze University, Jingzhou, China

The complexity of hydrocarbon filling history in the Ordovician carbonate reservoirs in Tarim basin, China are mainly due to two sets of source rocks (1-O1 and O2+3) and multiple charging events heterogeneously being occurred during the structurally superimposed evolution. In this study, systematic fluid inclusion analysis technique was employed to demonstrate the similarities and differences of hydrocarbon filling history among the Ordovician reservoirs in three Paleozoic uplifts (Akekule uplift in Tabei area, Ketake uplift in Tazhong area and Yubei uplift in Bachu-Markit area). Total 350 fluid inclusion core samples have been examined. Petrographic observation of calcite minerals filled in fractures and karst caves shows that there are four generations of calcite cements within two stage calcite veins developed in the Ordovician reservoirs. The first and third generations of calcite cements and first stage of calcite vein record the exodiagenetic calcite precipitation with low homogenization temperatures (Th) (< 50-60°C) of aqueous fluid inclusions, and the second and third generations of calcite cements. The second stage calcite vein reflect the burial diagenetic calcite precipitation with high Th ( = 70-175°C) of aqueous fluid inclusions and abundant colorful fluorescences of oil inclusions and pure gas inclusions locally developed. Micro-beam (<2 mm in diameter) fluorescent measurements for the individual oil inclusions which represents the each oil inclusion assemblage (OIA) give a very coincident relationship between fluorescent peak wavelength (lmax, nm) and QF535 (defined in text), which allows to quantitatively determine the maturities of single oil inclusions and then correlate with hydrocarbon charging events. The analytical results indicate that four events of oil filling and one event of gas filling took place in the Ordovician reservoirs. Combined Th of the coeval aqueous FIs with burial and geothermal historical curves, the timing of hydrocarbon filling for the first charging event occurred during the late Silurian (Caledonian III), the second charging event during the late Permian (Hercynian III), and the third, fourth charging events (including gas charging event) during the late Eocene (Himalaya I), the Miocene to Quaternary (Himalaya II-III), respectively. Even though the present topographies of the three uplifts are obviously different, “four episodes of oil charging and one episode of gas charging” in the Ordovician reservoirs are comparable in them, suggesting that controls on hydrocarbon charging, sources and accumulation may be similar for the three uplifts.

AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013