Study On Characteristics Of Shale Lithofacies And Reservior In Keluke Formation Of Northeast Margin Of Qaidam Basin

In order to have a profound understanding of characteristics of Keluke shale petroleum geology in Northeast Margin of Qaidam Basin,the characteristics of shale lithofacies and reservior were studied by means of measuration of outcrops?detailed description of cores and analysis of the experiment with theories of sedimentology?reservior geology and petroleum geochemistry.The research results are as follows.By observation of the outcrops,Keluke shale has a good condition of scale with more than 360 meters thick.the first section of Keluke Formation was the most beneficial shale target with 60 meters thick in total and 92.6 percent of the ratio shales/stata.Results of thin-section identification and X-ray diffraction analysis show that the mineral composition are dominantly clastic quartz and mixed layer illite/smectite clay mineral;the particle size of silt in average is medium-coarse;tidal bedding ? massive bedding ?syndepositional deformations and diagenetic nodules are the main sedimentary structure types.With comprehensive analysis of characteristics of particle size in average?bedding structure?color and content of carbonate,Keluke shale lithofacies was divied into six different types,which include dark lamellar siltstone with medium-sized silt ?black gray banded siltstone with coarse-sized silt ?black gray banded siltstone with coarse-sized silt and carbonate and dark lamellar siltstone with medium-sized silt and bioclasts et al.Tidal flat?lagoon and restricted platform were the main depositio nal environments for shale.The change of sedimentary environment that caused by transformation of ancient water depth was the reason for the formatio n of different types of shale lithofacies.The main diagenesis types in Keluke shale were compaction?cementation of carbonate?replacement and transformation of clay minerals.The diagenesis stage of shale is A2-B in thermal evolution.Porosity of Keluke shale has the range of 0.69% to 5.55% with 2.1% in average,permeability ranges between 0.01 m D and 2.21 m D with 0.39 m D in average.Pore and fracture were the main reservoir space types of Keluke shale,fracture types include Interlayer lamellation fracture ? structural fracture abnormal pressure fracture and organic-matter fracture,pore types include inter-crystal pores in clay minerals?organic-matter pores?intraparticle pores and dissolution pores.Dark lamellar siltstone with medium-sized silt and black gray banded siltstone with coarse-sized silt are the good lithofacies for shale reservoirs because of there large thickness?high TOC level?high brittleness and good reservoir property.Stable tidal flat environment is basic for the large-scale and continuous deposition of shale.Relatively high contents of quartz is essential for advantaged lithofacies;Diagenesis has two sides to the development of advantaged lithofacies,high thermal evolution degree of organic-matters is good for development of organic-matter pores(fractures)and dissolution pores,so it is good for the development of favorable lithofacies.while,tight cementation of carbonate is harmful for the development of favorable lithofacies because carbonate ceme nts the pores and fractures.