Organic Matter Maturity and Oil/Gas Prospects in Middle-Upper Proterozoic and Lower Paleozoic Carbonate Rocks in Northern China

Middle-Upper Proterozoic and haer Paleozoic carbonate fotmations in northern Chinaare well developed with an accumulative thickness of 6000--14000. m. Both seepages and oilshave been found in the qutcrops and drilling wells. The maturity of organic matter in these carbonate formations in obviously lower than thatin southern China, as viewed from reflectance （R°）, H/C （atomic ratio）, the amount and dis-tribution of hydrocarbons, T;℃ and so on. T;℃ may be used as a prncipal index fordetermining the maturity of organic matter lin carbonate rock-coveted areas. According tothe results of themeasurement of T;℃ and R° for natural samples and simulating experi-ments on bitumens from carbonate rocks, the limitation values for oil and gas have been esti-mated at 455℃ （R°= 1.35） and 476℃（R°=2.25）, respectively. On this basis, the map of or-ganic matter maturity for the Middle-Upper Proterozoic, Ordovician, Cambrian and Carboni-ferous of northern China has been compiled. It has been proposed that prospects of both oiland gas are expected, with oil and condensate dominant in the Ordovician, and condensate anddry gas in the Middle-Upper Proterozoic. The Cambrian is intermediate between them.