Research On Shale Reservoir Characteristics Of Wufeng Formation In Eastern Sichuan Basin

The Upper Ordovician Wufeng Formation shale in Eastern Sichuan Basin is taken as the research object.Based on the previous research and integrated study on field section observation and sampling,the paper had a systematically research of the composition,pore characteristics,diagenesis evolution of Wufeng Formation shale in the study area using 5 kinds of modern testing techniques including X-ray diffraction,argon ion scanning electron microscopy and low temperature nitrogen adsorption.Wufeng Formation shale with average thickness of 1.47 meters is formed in the anoxic compensation sedimentary environment below the interface of carbonate compensation.The content of clay minerals is 62.83% which is mainly composed of illite,and the content of brittle minerals dominated by quartz is about 29.85%.Little differences showed in the vertical direction of the content of the inorganic minerals.The content of total organic carbon(TOC)was 4.33%,whitch corresponds positively to the depth of the formation.The type of the organic matter is dominated by type I with equivalent vitrinite reflectance(RO)values in the range of 1.87% to 2.67%,indicating that the thermal evolution has entered the mature period,in which the thermal cracking dry gas is generated.Macroscopic fracture of the reservoir is mainly composed of interlayer bedding and structural fracture.There are three main types of the microscopic pore fissure: inorganic porosity,pore and micro crack.The three main types of the inorganic pore including: intergranular pore,intragranular pore and intergranular pore.The total porosity for the samples is 5.44% and the pore volume ranges from 7.8×10-4 to 66×10-4cm3/g,which is great contributed by the micropores and mesopores with the aperture less than 30 nm.The shale is in the period of late diagenetic stage which has experienced 3 main diagenesis including compation,dissolution and the clay minerals transformation.The TOC of reservoir has played a more obvious contribution degree of reservoir property.Clay minerals content contribution to reservoir pore development play a role of main is the mutual conversion between clay minerals content as well as the late fluid produced by chemical changes in dissolution intergranular pore.Lamellation seam and the growth of graptolite shale on lateral reservoir permeability has played a positive contribution.