Study On The Differences Of Lithofacies And Electrical Characteristics Between Marine And Continental Shale Of The Sichuan Basin

Shale gas resources are abundant in China and have great potential.Especially,the Sichuan basin is the main enrichment area of shale gas,and has great prospects for exploration and development.The formation of shale gas is closely related to the sedimentary environment,and the lithofacies is a combination of rocks or rocks formed in a certain depositional environment,which plays an important role in the sedimentary environment.However,for the study of lithofacies in the Sichuan Basin,there are many studies on marine shale,few studies on continental shale,and few studies on differences in marine shale and continental shale.At the same time,because of the complex topography of the Sichuan Basin,the cost of seismic exploration is high and limited by certain limits.The electrical method is less affected by topography and other factors,has attracted more and more attention.Therefore,it is very important to study the lithofacies,electrical characteristics and their differences of marine shale and continental shale.In this paper,we firstly determine the ternary diagram to divide the lithofacies,which is suitable for the marine-continental shale in the Sichuan Basin,namely,clay mineral,carbonate mineral,quartz + feldspar + pyrite.Based on the division of lithofacies,the characteristics and differences of shale facies in marine-continental shale are analyzed and studied.The main factors affecting the development of organic matter in marine shale are quartz,pyrite and clay minerals,of which quartz and pyrite are the main contributions to TOC.The S-2 lithofacies have high quartz content,high pyrite content,high TOC content,and low clay mineral content.The main factors that influence the development of organic matter in continental shale are quartz and clay mineral content,and the main contribution to TOC is clay minerals.CM-1 lithofacies is characterized by low quartz,high clay minerals and high TOC content.Finally,according to the differences in shale sedimentary environment,different depositional models for marine-continental shales were established.To test the resistivity of shale and use the double Cole-Cole model to fit the experimental results,so as to study the electrical characteristics of the different lithofacies of the marine-continenta shale.The main factors affecting resistivity of marine shale are TOC,quartz,pyrite and clay minerals.The resistivity is negatively correlated with TOC,quartz and pyrite,and is positively correlated with clay minerals.S-2 lithofacies shale exhibits low resistivity characteristics due to its high quartz,high pyrite,high TOC and low clay mineral content.By using the method of combining geology and geophysics,the difference of the lithofacies characteristics and electrical characteristics of marine and continental shale is studied.It is found that the difference of shale sedimentary environment affects its mineral composition and leads to different electrical differences.Compared with Continental shale,marine shale has greater exploration potential and potential,and the most favorable lithofacies is S-2 lithofacies.Therefore,the electric method can provide effective physical basis for the exploration of favorable shale reservoir,and can be used as a sign of the abnormal electrical property of shale reservoir,which has important practical significance for shale reservoir exploration.