Shale lithofacies combinations and their influence on oil bearing property in the 2nd Member of Funing Formation,Qintong sag
A series of breakthroughs have been made in the exploration of shale oil in the 2nd Member of Eocene Funing Formation(E1f2)in Qintong sag,Subei basin.The mineral composition of the shale in E1f2 of Qintong sag has similar proportions,and the single layer thickness of the lithofacies is thin with frequent vertical changes,which greatly limites the application of shale lithofacies classification based on traditional mineral composition.Taking the core of the mud shale layer in the lake facies of Well Qinye 1 as the research object,the lithofacies classification and combination characteristics are studied,and their influence on oil bearing property are analyzed through experimental analysis such as core,thin section observation,whole rock X-ray diffraction,organic geochemistry,etc.The results reveal that,under approximate conditions regarding shale mineral composition,the shale of E1f2 in Qintong sag can be divided into five types of lithofacies based on sedimentary structure,including massive clay mudstone(MCM),massive mixed mudstone(MMM),laminated mixed shale(LMS),bedded mixed shale(BMS),and laminated siliceous shale(LSS),and eight lithofacies combinations according to the vertical distribution pattern of lithofacies;the shale lithofacies combinations of E1f2 has a certain correspondence with interval division,the oil bearing property and mobility of different lithofacies combinations can be well distinguished by using S1=1.5 mg/g and OSI=100 mg/g as the main indexes,the lithofacies combinations MCM-LMS-BMS and LMS-BMS-LMS that meet the criteria of S1＞1.5 mg/g and OSI＞100 mg/g are identified as favorable lithofacies combinations in this area,and the intervals they belong to are the favorable intervals for shale oil exploration.In summary,this study provides valuable insights to the theory of terrestrial shale lithofacies and its control on hydrocarbon accumulation.
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