A Study on Hydrocarbon Accumulation Characteristics of Beach-bar Sandstone: Southern Slope of Dongying Sag, Jiyang Depression, Bohai Bay Basin, China

Guo, Song; Tan, LIjuan; Lin, Chengyan; Li, Hongnan; Lv, Xiuxiang

A number of beach-bar sandstone reservoir beds are developed in the upper fourth member of Eocene Shahejie Formation (Es4s) on the southern slope of the Dongying Sag. Aiming to further recognize the hydrocarbon accumulation characteristics of beach-bar sandstone, which is useful for the progressing exploration of the oilfield, based on the seismic interpretation and well logging analysis, with characterization and petrographic studies of core and cutting samples, this paper analyzes the hydrocarbon accumulation characteristics in two typical blocks of Boxing oilfield and Wangjiagang oilfield, especially reservoir bed heterogeneity and migration conditions that influence oil and gas distribution, calculates the index of reservoir bed quality (IRQ) with a mathematical method, and discusses the relationship between driving force and resistance of hydrocarbon accumulation. Taking into account the characteristics of thin interbeds in beach-bar sandstone, an experimental model in the Reservoir & Geology Key Laboratory of Shandong Province, China University of Petroleum, Qingdao, simulated the characteristics of hydrocarbon migration and accumulation in thin interbedded sandstone with reservoir bed heterogeneity. The results showed that hydrocarbon distribution and properties were extremely non-uniform. Reservoir bed and migration conditions controlled hydrocarbon accumulation in beach-bar sandstone. IRQ is above 0.4 in the main hydrocarbon region. Four basic kinds of oil and gas migration pathways and three kinds of hydrocarbon migration systems can be recognized. Sand body distribution, structural configuration and fault system controlled the direction of regional migration and location of hydrocarbon accumulation. Simulated experiment indicated that the change of driving force for hydrocarbon migration impacted selective accumulation mechanism in the process that hydrocarbon moved vertically along fault zone to the reservoir and distribution of hydrocarbon in the reservoir. Two kinds of hydrocarbon accumulation models exist in the study area: one is hydrocarbon accumulation model controlled by reservoir bed heterogeneity and the other is hydrocarbon accumulation model controlled by the complex migration system with fault connecting sandbodies. Finally, different exploration strategies should be adopted for the detailed exploration of beach-bar sandstone reservoirs according to different geological backgrounds.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013