Oil and natural gas geochemistry in offshore China: Advances and challenges

For many years, oil and natural gas geochemistry has been key to hydrocarbon exploration and exploitation in offshore China. Onshore oil fields have been thoroughly explored and exploited and have now entered the later stages of development. However, the oil and gas resources in the offshore basin of China are still abundant, and they have been relatively little explored, so they will be the main growth target for oil and gas production in the future. China has made many breakthroughs in offshore oil exploration in recent years. A large condensate field—Bozhong 19-6—has been discovered in the Bozhong Depression. Its main source rock is associated with algal blooming in the third member of the Shahejie Formation. The Baodao 21-1 gas field in the Qiongdongnan Basin shows clear signs of receiving terrestrial organic matter from the Yacheng and Lingshui formations. The first ultra-deep water and ultra-shallow gas, found in the Lingshui 36-1 gas field in the Qiongdongnan Basin, has thermogenetic and biogenetic origins. Well WY-1 in the Weixinan Depression marked the initiation of offshore shale oil exploration. Its sweet interval consists of two stable oil shale beds developed at the base and the top of the second member of the Liushagang Formation. However, samples from offshore exploration are often severely contaminated, and the corresponding data can be seriously distorted, which yields fewer core and more cutting samples. Therefore, it is necessary to thoroughly screen test data and to apply decontamination treatment and data correction to contaminated samples. The success rate of offshore exploration usually relies on the accurate prediction of source kitchens. Reservoir geochemistry thus has great significance for the future, as source input geochemical information can be used to trace materials backwards, and source kitchens can be predicted, when geochemistry is combined with enrichment and development models of source rocks and geophysical data.