Structure Model of Weathered Crust on the Top of PreTertiary and Its Influence on Petroleum Migration and Accumulation in East Part of Yihezhuang Uplift

Key words: 
• Pre-Tertiary /
• weathered crust structure /
• development model /
• petroleum migration and accumulation /
• Yihezhuang uplift

Abstract: Based on integrated study, the paper analyzed characteristics of the structure of weathered crust on the top of PreTertiary in the east part of Yihezhuang uplift of Jiyang depression. Key factors controlling its formation were anatomized, structure model of weathered crust was established, and its influence on petroleum migration and accumulation was discussed. Results show that weathered clay layer in the studied weathered crust is thin with limited distribution, and reservoir property is poor; while semiweathered rock of various lithologies extensively developed in the whole area, except for the tight “hard crust” on the top of semiweathered carbonate stone, reservoir property was improved obviously. Structure of weathered crust was controlled by lithofacies, paleoclimate, weathering time, paleotopography, tectonic structure, and later stage preservation. Reciprocal coupling of these factors determines spatial distribution of the structure of weathered crust. The weathered clay layer and “hard crust” on the top of semiweathered rock serves as caprock for petroleum reservoir, while semiweathered rock without “hard crust” can improve reservoir property of Tertiary system and serve as lateral migration path between different strata. 