Reservoir Characteristics And Adsorption Capacity Of Methane Of The Lower Cambrian Niutitang Formation Shale In Southeast Of Chongqing

In order to study reservoir characteristics and adsorption capacity of methane ofthe Lower Cambrian Niutitang Formation black shale in southeast of Chongqing,samples were systematically collected from the Niutitang Formation shale, drilled byWell Yuke1and Well Youke1. This paper discusses some issues about NiutitangFormation shale such as petrological characteristics, pore classification and adsorptioncapacity of methane based on relative tests like X-ray diffraction, Rock-Eval, vitrinitereflectivity, BET and pore size analysis, and high-pressure methane sorption analysis.The experiments’ results show that the average content of brittle minerals andclay minerals in the shale reservoirs of Niutitang Formation is54.6%and34.8%,respectively. The samples contain marine typeⅠkerogen having an average totalorganic carbon (TOC) of2.46%, and the average Ro is3.12, indicating that the shalereservoirs are in the over-mature stage. Illite crystallinity ranging from0.18°to0.35°,with an average of0.286°, and the%S of illite/muscovite is quite low, while organicmatter with overly high maturity, indicating that the shale reservoirs are in latediagenetic stage. By optical microscope and field emission scanning electronmicroscopy (FESEM) observation, quartz in shale can be divided into detrital quartzand authigenic quartz, dolomite in shale can be divided into the dolomite cementationand authigenic ankerite, pyrite in shale can be divided into syndiagenetic pyrite anddiagenetic pyrite.The pore-size distribution of the Lower Cambrian Niutitang Formation blackshale has double volumetric maxima. The first maxima presents within the pore sizerange from0to2nm, the second maxima presents within the pore size range from3to4nm. Moreover, mesopore as the main type of the total pore volume, and themicropore account for29.4of the total pore volume. The micropore contributes to the60%～70%of BET surface area, the rest are main supplied by mesopore. Byobservation of FESEM, we suggest to present four basic types of pores in black shaleswhich are interparticle pores, intraparticle pores, organic-matter intraparticle poresand microfractures. Interparticle pores are commonly found between mineral particles.Most of intraparticle pores are diagentic. Organic-matter intraparticle pores are related with maturation of organic-matter. Micropore, mesopore and macropore have quitepositive relationships with TOC. Therefore, pore volume is mainly influenced byorganic carbon content. The development of organic-matter intraparticle pores iscrucial to pores structure in black shale.According to the synthetic analysis concerning the relationship between theadsorption quantity and rock components of shale, TOC has the most significantcontrol on the amount of saturated adsorption. TOC influences the saturatedadsorption is mainly by controlling the pores structure. The maturity of shalecontributes little to the adsorption capacity. Because the vitrinite reflectivity (Ro) dataof the shale in the study area are higher than2.7%, so the percentage of micropore,mesopore and macropore are relatively stabled. The increasing of siliceous mineralwill weaken the adsorption capacity of shale to a small degree. In order to calculatethe quantity of adsorbed CH4in the Lower Cambrian Niutitang Formation black shale,we established two multiple regression equations.