MATURITY AND HYDROCARBON KITCHEN HISTORY OF ORDOVICIAN-CAMBRIAN MARINE SOURCE ROCKS IN TARIM BASIN, CHINA

Tarim basin is largest and least explored petroliferous basin in China. oils-source rock correlation have proved that petroleum may be mainly originated from lower Paleozoic marine strata, but the organic maturity evolution and hydrocarbon kitchen distribution of Ordovician-Cambrain source rocks are still controversial.The reflectance of vitrinite-like maceral are affective index for assessing the maturity of Ordovician-Cambrian marine source rocks in Tarim Basin, the kinetics of the reflectance of vitrinite-like maceral derived from megascopic benthic multicelluar organisms have been established through hydrous pyrolysis. According to the vitrinite-like maceral reflectance data of more than 350 samples from Ordovician-Cambrian marine source rocks in wells and outcrops, The middle and lower Cambrian source rocks of Tarim Basin are in the high mature and overmature phase, and upper Ordovician source rocks are in mature phase. Thermal history are reconstructed with the reflectance of vitrinite and vitrinite like maceral derived from megascopic benthic multicelluar organisms, AFTA and fluid inclusion data using ThermMod software, two high geothermal gradients phases are delineated that the first is in middle and late Ordovician(35-45°æ/Km), the second is in Permian(35-45°æ/Km),geothermal gradients decreased slowly in Mesozoic,and accelerated cooling during Pliocene in contrast with the average present value of 20°æ/Km. Maturity distribution and evolution of Ordovician-Cambrain source rocks are delineanatd using BasinMod software calculations data on 250 Wells and 340 pseduowells from the 26 seismic profiles, two lower Paleozoic hydrocarbon kitchens have been identified, the first is lower and middle Cambrian euxenic source rock, located in the Awarti-Majaer depression, the second is upper Ordovicain carbonate mud mound source rock, located in the slope of Tazhong uplift and Tabei uplift to Majaer depression. The hydrocarbon in the gigantic Silurian tar sandstone and residual reservoir were derived from Cambrian source rock in the late Silurian, the hydrocarbon in the Carboniferous and Devonian reservoir were from Ordovician source rock in recent 100Ma.