Regular Distribution of Insideoil Fields and Outsidegas Fields Controlled by Source Rocks and Heat in China Offshore Basins

Key words: 
• Source rock /
• geothermal heat flow /
• the oil & /
• gas field distribution /
• regularity

Abstract: The hydrocarbone genernation is controlled by the source rocks and the heat. The source rock is the essential factor of the hydrocarbone formation and the heat is the subsidiary. The both are necessary factors. The interactional factors result in the hydrocarbon  generation and distribution pattern. In China offshore, the sedimentary basins are of the stretch or extend slip depressions which formed in Tertiary. The synrift occurred in Paleogene. The thermal subsidence formed sequently in  the earlymiddle Miocene. From late Miocene, the Neotectonic movement happened actively in a great number of basins. The source rocks formed mainly during the period of the paleogene synrifting. According to the characters of the sediments, the basins are divided into two groups, namely, the continental/terrestrial rift and the superimposed rift. The continental rift are the sags that the synrifting stratum are absolutely composed of the terrestrial sediments. The superimposed rift are the sags filled with the marine sediments or the onshoreoffshore sediments besides the terrestrial sediments. Bohai bay basin, Yellow Sea Basin, the northern of the pearl mouth basin and Beibuwan Basin are parts of the continental rifts. Those basins, located in the inner of the craton or the continental shelf,  are assigned  into  the inside belt. The outside belt , consisted of the East China Sea Basin, Taixi basin, Taixinan basin and the southern of the pearl mouth basin, is  situated in the active continental margin or the continental slope which is subjected to the passive continental margin. In the inside belt,the main source rocks are the middledeep lake facies mud which formed in the Paleocene, the Eocene and the Oligocene. The Eocene source rocks are dominated. In the outside belt, the source rocks are composed of the lake facies, the onshoreoffshore facies and the marine facies sediments and the onshoreoffshore facies is the main source rocks. The geologic age of the source rocks is similar with that of the inside belt but the EoceneOligocene is dominated. The source rocks of the lake facies are oilprone in the inside belt. The source rocks of the onshoreoffshore facies are gasprone in outside belt. The heat flow values are low or slight higer in the inside belt, but these are high or superhigher in the outside belt. Because of the coupling interaction of the source rocks and the geothermal field, the oilprone source rocks produce the oil in inside belt and the gasprone source rocks bring out the gas in the outside belt. The inside belt are the main oilproduced area and the exploration would  focus on the liquid hydrocarbone. Whereas the outside belt would be the nature gas exploration. The oil exploration should be in Bohai bay basin, the northern of the south China sea and the Yellow sea basin, moreover, the nature gas exploration would be emphasized in the north continental slope of the South China sea and East China Sea basin.