The Sedimentary Characteristic Analysis Of The Chang-6 Oil-bearing Formation Group In Huangling Xunyi Area

The Chang-6 oil-bearing formation group in Huangling Xunyi area,located in the south of Ordos Basin,is in a deep to semi-deep lake area,which was considered as an unfavorable area for oil and gas exploration in earlier days.With an improving understanding in the exploration in deep to semi-deep lake area,it is believed that gravity flow sandstone is developed in this area and the area can be favorable for exploration.Since 2010,breakthroughs have been made in the exploration of the Chang-6 oil-bearing formation group in Huangling Xunyi area.The discovery of the positive 33 favorable blocks has established an annual production of up to 100,000 tons.For this reason,the study on the sedimentary characteristics of the Chang-6 oil-bearing formation group in Huangling Xunyi area,as well as the identification of the developmental characteristics and the distribution of the lake sandstone in deep lake area,would provide decision-making basis for increasing reserves and production.The Chang-6 oil-bearing formation group in Huangling Xunyi area is located in the sedimentary central area of Ordos Basin.Based on the analysis of the regional sedimentary background,the author conducted a source analysis to classify the sedimentary systems by analyzing heavy minerals,light minerals,cuttings composition characteristics,and paleo-current.The well log data has been analyzed to identify sedimentary facies types with the application of core sedimentary structure analysis.Applying micro-analysis,the author identified the structural characteristics of clastic rocks,which provide a basis for sequence studies.On the basis of drilling data and source analysis,the author identified the horizontal distribution of sedimentary facies.The physical characteristics of the reservoir has been identified by combining analytical data with microstructural features of debris flow.This study has shown the followings:(1)there are three source systems in the studied area including North East,South West and South;(2)The three micro-facies types developed are sandy debris flow,turbidity current and slump deposit.(3)debris flow deposition can be divided into six segments,namely,flaky mineral oriented segment,argillaceous crushed matrix fine-siltstone segment,matrix crushing fine sandstone segment,submicron sandstone segment,crushed matrix siltstone segment,and argillaceous fine-siltstone segment;(4)according to the analysis on the horizontal distribution characteristics of sedimentary facies in each layer of the Chang-6 oil-bearing formation group,it is believed that the positive 33 well area is a flow zone with multiple types of debris flows;and(5)the physical characteristics and the distributing factors of the debris flow reservoir have been identified and a structural model for the clastic rock reservoir has been established.