A CRITICAL REVIEW ON THE EVALUATION OF HYDROCARBON POTENTIAL OF MARINE CARBONATE ROCKS IN CHINA

Much of the marine carbonate rocks in China are organic carbon poor (mean organic carbon content values generally 0. 20% ), but are still regarded as source rocks due to the conventionally proposed minimum organic carbon content required forcarbonate source rocks (0. 10% or even lower). No commercial accumulation was found related to these carbonate rocks afterover ten years of exploration, showing the incorrectness of the above minimum organic carbon content. Obtaining such a lowminimum value is caused by the unreasonable hypotheses of high hydrocarbon potential of organic matter in marine carbonaterocks and high expulsion ratio of hydrocarbon from carbonate rocks, by overestimating organic matter lost during maturation ofcarbonate rocks, and by omitting the hydrocarbon lost during second migration. Integrated consideration of above factors willreach the following: (i) The minimum organic carbon content for a carbonate source rock should be gained by an analogy in ex-ploration instead of by an experiment. (ii) The minimum organic carbon content values for a carbonate source rock, for a high toover mature source rock, and for a gas source rock are not necessarily lower than those for a mudstone source rock, for a maturesource rock, and for an oil source rock respectively. They all should be 0. 40% ~0. 50% at least.