Microscopic Pore And Fissure Characteristics Of Shale In Permian,ZK1614 Well,Yanlong Area,Southern North China Basin

The Permian shale stratas in the southern North China Basin have great potential of shale gas resources,which are widely distributed with original sedimentary thickness,had experienced multi-period tectonic movements and had developed good system of pore-fissure.The domestic research of shale gas reservoir started late,the research mainly focused on marine facies shale and continental facies shale,marine-continental transitional facies shale reservoirs were less involved.The paper chose the marine-continental transitional facies and continental facies shale in the southern North China Basin as the research object.Based on geochemical testing analysis,using argon ion polishing and field emission environmental scanning electron microscopy imaging testing technique,and scanned shale samples of Taiyuan formation,Shanxi formation and Shihezi formation of Permian drilled in ZK1614 well in Yanlong area of southern North China Basin,and obtained the SE and BSE information.Combining X-ray spectrum information with gray level recognition function of JMicroVision software,qualitatively and quantitatively analyzed the mineral composition and the characteristics of micro pore-fissure of shale samples.Integrated the geological background and geochemical characteristics of the study area,and discussed the genesis of pore-fissure system.Main achievements of the study are summarized as following:The shale samples surface porosity of Permian are between 0.92%-5.53%,surface porosity are positively correlated with the number of pore in general.With different sizes of pore-fissure,there is a power law relation of pore-fissure distribution.There is a Two-Segment linear relationship between the pore area indedx and the pore number of unit area index in different pore diameter interval between 50-2000nm,which when the pore diameter is small,they are negatively correlated,when the pore diameter is larger,they are positively correlated.The transition points between the two sections correspond to a certain range is called d_tran,which mainly between 150-400nm.The development scale of fissures that mainly indicate the length-width ratios between 5-8.In different interval of length-width ratio 5-20,the relationship between total fissure length index and fissure number of unit area index are positively correlated.There are different effects in different minerals for development of pore-fissure,which the brittle mineral mainly influenced the development of micro fissures,inhibited the development of pore;during the digenetic process,due to the actions of tectonic stress,phase transformation and dehydration of mineral,clay minerals formed plenty of pore-fissure,which promoted the development of pore-fissure.The differential expansion and differential dissolution of minerals could also produce pore-fissure.The vitrinite reflectance of the shale samples in the study area is higher than 4.2%,the thermal evolution degree is very high,and the organic matter pores are rarely observed in the experiment,the face porosity of samples are mainly provided by the inorganic mineral pore.Due to shallow burial depth in the Permian strata,most of the shale gas that generated in the process of organic matter hydrocarbon generation were migrated and lost from the pore-fissure system.The shale gas exploration direction of study area should be plain overlay area with deep burial.