Evaluation Of Reservoir Physical Properties And Brittleness Of Shale In The Upper Member Jiufotang Formation Of Ludong Sag,Kailu Basin

The reservoir physical property of shale oil controls the resource and reserve distribution of shale oil,while the reservoir brittleness controls the fracturing ability of the reservoir.It is of great significance to carry out research on the reservoir physical property and brittleness for shale oil exploration and development.Paper choose the shale in the upper member of Jiufotang Formation in Ludong Sag of Kailu Basin as the research object,using field emission scanning electron microscopy,helium porosity determination,pulse decay permeability,low temperature nitrogen adsorption-stripping and other technical means,characterize the types of reservoir space,pore structure and porosity and permeability conditions qualitatively and quantitatively,and analysis the influence factors of reservoir physical properties;using XRD whole-rock mineral analysis and triaxial fracturing experiment,establish the elastic parameter conversion model of shale in the upper member of Jiufotang Formation,and propose the calculation method of brittleness index.Combined with the geophysical logging data and using the artificial intelligence platform as the bridge,the reservoir physical property and brittleness of shale were evaluated,and the following understandings were obtained:(1)The reservoir space of the shale in the upper member of Jiufotang Formation is identified as organic pore,organic shrinkage fracture,intergranular pore,intra-granular pore and microfracture.Organic shrinkage fracture and intergranular pore and are well developed,while organic pore,intragranular pore and microfracture are underdeveloped.The shale mainly develops plate-like slit pore and wedge-shaped pore with pore size less than 10 nm.The pore volume is mainly contributed by pores with pore size greater than 10 nm,while the specific surface area is mainly contributed by pores with pore size less than 5nm.(2)The effects of burial depth,organic carbon content,organic matter maturity,siliceous mineral content,carbonate mineral content and clay mineral content on the pore structure and porosity and permeability conditions of the shale in the upper member of Jiufotang Formation were analyzed.The content of organic carbon,the maturity of organic matter,the content of siliceous minerals,and the content of clay minerals have a constructive effect on the pore structure and the condition of porosity and permeability,while the content of burial depth and carbonate minerals have a destructive effect on the pore structure and the condition of porosity and permeability.(3)The dynamic and static conversion model of shale elastic modulus and Poisson's ratio in the upper member of Jiufotang Formation was established,and the calculation method of shale brittleness index in the upper member of Jiufotang Formation was proposed.The brittleness of shale is controlled by the content of quartz,feldspar,calcite and dolomite.The higher the content of quartz,calcite and dolomite,the lower the content of feldspar and the better the brittleness.(4)Based on the Maxim AI platform,the pore and permeability conditions of the shale in the upper member of Jiufotang Formation were predicted.The porosity of shale in the upper member of Jiufotang Formation is generally poor,with a median of 2.47%.The median permeability was 0.1487 x 10-3?m2.At the same time,the corrected elastic parameters of shale in the upper member of Jiufotang Formation were predicted,and the brittleness index of shale in the upper member of Jiufotang Formation was calculated by using the dynamic and static conversion model.The brittleness of shale in the upper member of Jiufotang Formation is generally good,and the average brittleness index is 0.5233.(5)There are five logging facies: organic-rich high quality shale facies,organic-rich laminated siliceous shale facies,organic-rich laminated tuffaceous shale facies,organic-poor massive silty shale facies and organic-containing massive shale facies.The organic-poor massive silty shale facies has the best reservoir physical property,while the organic-rich shale facies has the best brittleness,which provides guidance for subsequent exploration and production work.