Abstract: Oil enrichment of China’s offshore oil-bearing basins is jointly controlled by hydrocarbon source rocks and geothermal heat. Major hydrocarbon source rocks in offshore oil-bearing basins include mudstone of semi-deep to deep lacustrine facies distributed in the Paleocene, the Eocene and the Oligocene, especially in the Eocene formations. These formations predominantly contain sapropelic organic matters of various degrees in enrichment. Areas of semi-deep to deep lacustrine mudstone formations may vary from very small to a few thousands of square kilometers. Predominantly controlled by crustal structures, geothermal fields in these oil-bearing basins may vary from high to low. As far as interactions between hydrocarbon source rocks and geothermal heat in depressions are concerned, there are four basic couplings: sufficient source rocks and geothermal heat, sufficient source rocks but insufficient geothermal heat, insufficient source rocks but sufficient geothermal heat and insufficient source rocks and geothermal heat. Due to significant differences in types of hydrocarbon source rocks, abundance of organic matters, scale and geothermal heat in different depressions of various oil-bearing basins, the coupling types of hydrocarbon source rocks and geothermal heat were different, and oil-bearing basins with dramatically different oil-production capacities were formed. The majority of depressions in the Bohai Basin have sufficient source rocks and geothermal heat. With a large quantity of extremely rich oil-bearing depressions developed, the Basin has huge potentials in oil production. There are significant differences in properties of depressions in northern depression belt of the Pearl River Mouth Basin in northern parts of South China Sea and those depressions in the Beibu-gulf Basin. In addition, properties within the same depression may also dramatically vary. With sub-sags as basic components, all four coupling types can be found in these depressions. The majority of depressions have sufficient source rocks and geothermal heat. Accordingly, some depressions have rich oil reserves and great potentials for exploration. There are a large quantity of depressions in the South Yellow Sea Basin, but the majority of these depressions have sufficient source rocks but insufficient geothermal heat. Under such circumstances, only the deep trenches have significant oil-production capacities. Overall exploration potential of this basin is of general level. With insufficient source rocks and geothermal heat, the Paleogene depressions in North Yellow Sea Basin are poor in oil resources. Generally speaking, the Paleogene depressions in the Basin contain minor potentials for exploration. With a large share of residual oil reserves, the Bohai Basin shall be considered as the key for future exploration operations in China’s offshore areas. Offshore basins in northern parts of continental edge in northern sections of South China Sea also contain significant reserves. The South Yellow Sea Basin contains only a small proportion of residual oil reserves. Most depressions in the Bohai Basin and some depressions in near-shore zones of northern parts of the South China Sea contain rich oil reserves. Among them, the Tanluxi Depression Belt in the Bohai Basin can be classified as super-rich oil-bearing zone.

Key words: source rock, geothermal heat, distribution of oil and gas fields, order, joint control of source rock and geothermal heat