Lithofacies Distribution And Characteristics Of The High-quality Shale Section Of Longmaxi Formation In Southern Shu Area

The study of shale facies is the foundation and an important part of the shale geology research.At present,the division of shale facies is more and more fine,which is advantageous to identify favorable lithofacies combination and distribution,and provides important geological basis for shale gas evaluation and exploration.Based on logging,drilling,core data,thin sections and X-ray diffraction analysis,this paper studies the lithofacies of the high quality shale section of the Longmaxi Formation in the south Sichuan,and divides the 11 sub sections of the target segment of the research area into four layers from bottom to top:1 small layer,2 small layer,3 small layer,4 small layer.The paper divides the shale facies by two steps,which is based on TOC content and mineral composition,and divides 19 lithofacies.In this study,7 lithofacies were identified in the study area:1.High-carbon siliceous shale facies;2.High carbon carbonate-silica shale facies;3.Medium Carbon Silica shale facies,4 medium carbon carbonate-silica shale facies,5 medium carbon siliceous-carbonate shale facies,6 medium carbon clay shale facies,7.Low carbon clay shale facies..Through the analysis of the characteristics of the shale facies and their distribution,we found that:(1)vertically,from the bottom to the top,the shale facies transit from the high carbon shale facies to the low carbon shale facies.(2)regionally,the lithofacies types change greatly,from north West to south East,and the lithofacies type gradually transit to the high carbon siliceous shale.from north west to south east(3)based on organic carbon content,mineral composition,physical property characteristics,reservoir space characteristics,the 7 lithofaciesare synthetically evaluated,and 3 kinds of favorable shale facies are identified:and high carbon siliceous shale,high carbon carbonate-silica shale facies are favorable lithofacies of I class.Medium-carbon siliceous shale facies,medium carbon carbonate-silica shale facies,and favorable lithofacies of ? 1 class.Medium carbon siliceous-carbonate shale facies,and middle carbon clay shale facies are favorable lithofacies of ?2 class.Low carbon clay shale facies are advantageous lithofacies of ? class.The I-type favorable lithofacies are mainly distributed in 1 small layers and are good exploration strata.