--> Hydrocarbon Migration and Accumulation of the Suqiao Buried-Hill Zone in Wen'an Slope, Jizhong Subbasin, Bohai Bay Basin

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Hydrocarbon Migration and Accumulation of the Suqiao Buried-Hill Zone in Wen'an Slope, Jizhong Subbasin, Bohai Bay Basin

Abstract

The Suqiao buried-hill zone, in Jizhong Subbasin, the Bohai Bay Basin, eastern China, has made significant progress in the deep buried-hill hydrocarbon exploration. The discovered hydrocarbons mainly accumulate in the deeply buried Ordovician carbonate reservoirs, and are generally believed to be characterized by mixed hydrocarbon and multiple-stage charges. However, to date, the hydrocarbon migration and accumulation of the study area has not been well investigated. In this study, the process was investigated by using fluid inclusions, quantitative fluorescence techniques (QGF), total scanning fluorescence method (TSF), organic geochemical analysis and basin modelling. The higher QGF Index, FOI (the frequency of oil inclusions) values, and S1, S2 values of rock pyrolysis detected in both current gas-oil and water zone clearly indicate that the current condensate oil-gas reservoirs used to be paleo-oil reservoirs. In addition, combined with the homogenization temperatures of the fluid inclusions (<150°C) and the co-existence of solid-bitumen bearing and condensate inclusions, significant losses of the n-alkanes with low carbon numbers, enrichments of heavier components in crude oils, and the asphaltene precipitation in the residual pores suggest that gas flushing may have played an important role in the reservoir formation. Besides, the fluid potential, flow line modelling and the QGF data reveal that nearly all of structural highs were the terminals of hydrocarbon migration and most of the early oil pathways subsequently acted as migration pathways for lately-formed gas. In addition, two hydrocarbon charges were identified within the study area. During the deposition of the Oligocene Dongying Formation (Ed), the deep Ordovician reservoirs were first charged by mature oils derived from the fourth member of Shahejie and Kongdian Formations (Es4+Ek) lacustrine shale source rocks, and adjusted at the end of Ed period subsequently by virtue of the tectonic movement. Since the deposition of the Neogene Minghuazhen Formation (Nm), the reservoirs were charged by the mixed gases that consisted of the moderate to high-maturity condensate gas sourced from the Es4+Ek lacustrine shale source rocks and the mature coal-derived gas sourced from the Carboniferous-Permian (C-P) coal-bearing source rocks. Meanwhile, the previously charged oil was subjected to gas flushing and deasphalting by the late intrusion of gas.