| The exploration shale oil in eastern China has made important progress in recent years,but the industrial exploitation of shale oil is very limited.There is still insufficient understanding of the scientific problems such as the enrichment and accumulation mechanisms of shale oil.The main problem is that shale oil is characterized by low maturity,high viscosity and high wax,which makes it difficult to flow in pores and fractures.The pore size and pore throat size restrict the flow of shale oil,and the determination of the effective nanopore throat is the key to the exploration and development of shale oil in eastern China.In this paper,the shale in the lower Third Member of Shahejie Formation and the upper Fourth Member of Shahejie Formation in Dongying sag with good exploration potential of shale oil was the object of study.Three core wells were taken as the research object,which were Niuye 1 well in Niuzhuang subsag,Fanye I well in Boxing subsag and Liye 1 well in Lijin subsag.The laminated structures,layered structures and massive structural samples in the lower Third Member of Shahejie Formation and the upper Fourth Member of Shahejie Formation were selected for comparison and analysis.The characteristics of shale oil reservoirs space such as pore space,pore structure,pore size and pore size distribution are studied by using widely used or frontier characterization method.The application of nano pore characterization methods including focused ion beam-field emission scanning electron microscopy(FIB-FESEM),small angle X ray scattering(SAXS),nitrogen adsorption and mercury injection,nuclear magnetic resonance(NMR)T2 relaxation time,nuclear magnetic resonance(NMR)cryoporometry and Micron CT methods,combined with the identification of organic petrology,rock pyrolysis,X ray diffraction(XRD),oil and gas group composition determination.On this basis,the formation and evolution of pores are summarized in combination with thermal simulation experiments.In order to solve the major difficulties in the continental oil and gas exploration in eastern China,the formation mechanism of shale oil reservoir space is further discussed.The results of this paper provide reference for characterization and evaluation of shale oil reservoir space.The samples in the lower Third Member of Shahejie Formation and the upper Fourth Member of Shahejie Formation were dominated by layered and laminated structure,low degree of thermal evolution of organic matter,vitrinite reflectance values of Ro ranged between 0.51%?0.93%,the main type of organic matter in type ? and ?1 kerogen.The abundance of organic matter is high,the main body of total organic carbon(TOC)is more than 2%,and the distribution range is mainly between 2%-4%.The proportion of samples with TOC greater than 3%in Liye 1 well is 48%,with an average value of 3.4%.The mineral composition of shale varies greatly,mainly clay minerals,carbonate minerals,quartz and feldspar,a small amount of pyrite,siderite and gypsum.Illite is the main clay mineral,more than illite-smectite mixed layer.Through core observation,rock slice observation and field emission scanning electron microscope observation,it can be seen that the fractures and pores in shale are relatively developed.According to the genetic types,the developed pore system is divided into fractures,primary pores and secondary pores.The crack is divided into structural fracture,diagenetic fracture and abnormal pressure fracture.The primary pores are divided into intergranular pores and intragranular pores,and the secondary pores are divided into two types as dissolution pore and diagenetic pore.The diagenetic fracture of Liye 1 well is relatively developed,and the structural fracture development is low.The fracture development of Niuye 1 well and Fanye 1 well is poor,mainly for structural fractures.The matrix pores are mainly intergranular pores of inorganic minerals,also organic matter shrinkage hole is widely developed.The matrix porosity of Fanye 1 well is mainly filled with organic matter,and the shrinkage pore of organic matter is more developed.Small angle X ray scattering has unique advantages over the characterization of mesoporous materials.The experimental results show that the shale samples mesoporous distribution curve with one peak,the main peak position distribution before and after 10 nm,the volume percentage of fine mesoporous(2?10 nm)is among 5.4%?27.8%,coarse mesoporous(25?50 nm)which is among 31.4%?55.6%.The average volume percentage of fine mesoporous volume is the highest in Liye 1 well,which is 16.7%.Fine mesoporous volume percentage and the content of clay minerals have a positive correlation,mesoporous samples corresponding to fractal dimension of clay mineral content is higher the higher,showed that the clay mineral is fine mesoporous major development site,is also the main contribution of the pore surface is complex,because pore surface is more complicated than the corresponding surface area will increase.The pore size of shale was quantitatively analyzed by NMR,T2 relaxation time and mercury injection test.The results show that the porosity of the layered shale is the most developed,and the porosity is above 10%.Nitrogen isothermal adsorption experiments show that the BET specific surface area of the layered gray mudstone is higher than that of the stratified gray mudstone and massive mudstone,and the proportion of the specific volume of the pore pores is more than 70%,and the pore volume is higher.There are advantages in characterizing the structure of shale reservoirs of different characterization method for pore structure.The microscopic image method is suitable for shale pore structure,structural characteristics,connectivity and areal porosity.The fluid injection method at different scales can completely characterize the porosity and distribution characteristics of pores in shale,but the samples need to be extracted first.Small angle scattering can effectively characterize the characteristics of shale mesopore pores,while pores are the main pores of the shale pore distribution,including the communicating pores and disconnected pores.Full scale characterization of shale oil reservoir space requires the integration of multiple methods.Based on the comprehensive analysis results of the samples of natural evolution and thermal simulation,it is considered that the evolution model of shale oil reservoir space can be divided into four stages.The first stage,the immature stage,the basic features of pore structure formation stage,with mechanical compaction,the porosity changed rapidly,between the main storage hole and the shrinkage hole set reservoir space type.The second stage:low mature to mature,pore structure transformation stage of hydrocarbon generation from organic matter,mineral transformation and brittle mineral dissolution affected pore,shale porosity increases to the whole flat trend,the volume percentage of fine mesoporous pore increased first and then decreased after increasing trend.The third stage:high mature,the porosity of shale decreased.The fourth stage:the hydrocarbon generation peak is over,and the pore development is relatively stable.Successive extraction by organic solvent experiment,pore distribution of mesoporous characteristics in contrast changes,can confirm the fine mesoporous set space for effective shale oil reservoir occurrence,its corresponding high specific surface area is more favorable for oil and gas occurrence.Special treatment of the sample,observe the shale oil spill point from the point of view of image,provide the evidence for migration of shale oil in nanoscale pores,results show that shale oil can migrate in pores larger than 14 nm. |
PDF Full Text Request