Abstract:

Being a hydrocarbon kitchen,the Huanghekou sag in the south of Bohai Sea waters had seen many oil and gas discoveries featuring in shallow to middle burial depth (1200-1800 m),moderate crude API,high productivity(as high as 455.3 m3/d of gas from the Neogene),etc.Most of its oil and gas reservoirs were formed through near-source vertical migration and the pooling process has started since 5.1 Ma.Its major reservoirs are apparently controlled by stratigraphic sequences and most of the reservoirs are located below the maximum flooding surface.The pooling pattern can be generalized into "near-source,late-stage,and preponderance".During the period of 2004 to 2008,success rate of exploration in the sag was up to 85%,and 3P geological reserves of single exploratory well averaged at 7.13 MMCM.By the end of 2008,about 100 exploration wells had been drilled.In addition to the discoveries obtained during the 1980s to early 1990s,such as Bozhong 25-1/S,Bozhong 34-2/4,Bozhong 28-1 and Bozhong 26-2,several medium-sized discoveries including Bozhong 34-1,Bozhong 28-2S,Bozhong 29-4 and Bozhong 26-3 have been found in layers with shallow to middle burial depth,initiating a new surge of oil and gas discoveries in the south part of Bohai Sea waters.

Key words: shallow delta, oil and gas, late-stage pooling, Huanghekou Sag, Bohai Sea waters