Geochemical characteristics and types of natural gas from well Hugu 2 in the Dongpu Sag of Bohai Bay Basin

The Dongpu Sag is a typical oil and gas producing unit in the Bohai Bay Basin in east China. A series of oil and gas fields have been discovered in recent years. In 2013, well Hugu 2 was drilled in the Huzhuangji area, finding industrial gas flows in the upper Shihezi and Shiqianfeng formations in the Permian. The geochemical characteristics and types of natural gas from well Hugu 2 were studied. The natural gas has a high methane content and low heavy hydrocarbon content. The dryness coefficient ranges from 0.977 to 0.985. The carbon isotopic values of methane, ethane and propane range from -28.7‰ to -28.4‰, -16.0‰ to -14.5‰, and -19.0‰ to -15.7‰, respectively. The carbon isotopic values of ethane and propane display reversal due to the mixing gases from the same source rocks at different stages. The gases from the Permian in well Hugu 2 are derived from the Carboniferous and Permian coal measures. A large proportion of the gases was cracked from kerogens during the Himalayan period.