--> Abstract: Subtle Traps in the Jiyang Superdepression of Bohai Bay Basin: Formation Mechanisms and Petroleum Resource Potential, by Xiongqi Pang, Dongxia Chen, Maowen Li, and Zhenxue Jiang; #90039 (2005)

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Subtle Traps in the Jiyang Superdepression of Bohai Bay Basin: Formation Mechanisms and Petroleum Resource Potential

Xiongqi Pang1, Dongxia Chen1, Maowen Li2, and Zhenxue Jiang1
1 Petroleum University (Beijing), Beijing, China
2 Geological Survey of Canada, Calgary, AB

As the more easily explored, conventional structural traps are discovered, subtle traps are becoming a larger contributor to annual petroleum reserve addition in the Jiyang Superdepression of Bohai Bay Basin. Three major types of subtle petroleum traps are identified, including stratigraphic traps that are formed by uplifting and erosion of pre-rift Archean metamporphic rock and Paleozoic carbonate, or by unconformity contact of major Oligocene alluvial and fluvial strata in syn-rift sequence. Other subtle trap types include lithologic and complex (structural-lithologic) traps that are developed in clastic reservoirs within syn-rift and post-rift sequences, as subaquatic fans, lake-floor fans and alluvial deposits. Hydrocarbons in all of the subtle traps in the Jiyang Superdepression were derived from the syn-rift Eocene-Oligocene Shahejie Formation that shows excellent source rock potential. Faults and fractures, unconformity surfaces and permeable sandy strata serve as regional and local hydrocarbon migration fairways. Three structural zones can be recognized within each graben or half-graben. Along the northern steep slope, stratigraphic traps are often developed in pre-rift and post-rift and structural- lithologic traps are often developed in syn-rift and post-rift sequence. Along the southern gentle slope, syn-rift structural lithologic traps are commonly observed in the flexural margin towards depression center, and strtigraphic traps towards flexural margin. The central sag area in contrast is dominated by syn-rift lithologic and structural-lithologic traps. The differences in tectonic evolution, sedimentation rate and hydrocarbon source beds are the three prevailing geological controls on the variation in the prospectivity of various subtle traps within different grabens or half-grabens.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005