Laminar Algal Distribution Characteristics of Lower Cretaceous and the Relation to Oilgas of Jiuquan Basin

Key words: 
• Jiuquan basin /
• laminar algal dolostone /
• heterogeneity /
• Granoreticella /
• generation relation

Abstract: The organic laminae (laminar algal) in the argillaceous limestone and dolomitic mudstone of lower Cretaceous are abundant in Jiuquan basin, but it′s heterogeneity is obvious that mainly shows that the difference of laminar algal contents are very large between the same formation and different areas and same well and different depth. The distribution and yield of laminar algal are all controlled by sedimentary facies and its change. The laminar algal are mainly composite by planktonic algae and it′s pyrolysis products, and most of the algal are the Granoreticella of Chlorophyta . There has a positive correlation between the content of laminar algal and the hydrocarbon generating potentiality of source rock. Most of the found oil in Jiuxi depression is mainly generated from the laminar algal argillaceous limestone of Xiagou Formation of lower Cretaceous, which means that laminar algal is a very important hydrocarbon generating material; it has closed relationship with oilgas in Jiuquan basin. Not only the lacustrine carbonate with abundant organic laminae is good source rock, but also favorable in the fracture initiation and hydrocarbon drainage during the course of hydrocarbon generating and drainage because of the bedded enrichment of hydrocarbon generating materials.