Main Clay Minerals In Shale And Its Control Effect For Methane Adsorption

Clay minerals,as the main mineral of shale,have an important influence on methane adsorption in shale.In this paper,the crystal structure parameters of clay minerals are calculated by XRD and molecular structure simulation,and the crystal configuration of clay minerals is established.Through SEM,MIP and BET,the pore morphology,pore connectivity,specific surface area and pore volume and pore size distribution characteristics of clay minerals are studied.The clay minerals are compared and analyzed through the isothermal adsorption experiment.A D-A and L-F adsorption model for methane adsorption of clay minerals was established.The effects of crystal structure,pore structure,water content and organic matter content on the adsorption of methane on clay minerals were analyzed.The study shows that each unit cell of montmorillonite contains 0.25 to 0.60structural negative charges,the number of negative charges in each unit cell of illite is0.6~1,and the number of negative charge of unit cell of kaolinite is almost 0;the main components of montmorillonite are silicon(Si),aluminum(Al),calcium(Ca),sodium(Na),and illite is silicon(Si),aluminum(Al),potassium(K),kaolinite.For silicon(Si)and aluminum(Al),the intermolecular force of the montmorillonite is mainly intermolecular force,and the gravity is weak.The gravity of the illite Shi Jing interlayer is mainly static electricity,and the gravitational force is strong.The gravity of the Shi Jing layer in kaolin is mainly hydrogen bond,and the gravitational force is strong.The montmorillonite is round in the scanning electron microscope,the size of the pore is about 50nm to 2.5um,and the illite is mostly round and irregular.The pore size is about100nm to 3um,and the kaolinite is mostly round and irregular,and the pore size is about 50nm to 1.25um.The pore connectivity of montmorillonite is stronger than illite and illite is stronger than kaolinite.The pore volume and specific surface area of clay minerals are montmorillonite>illite>kaolinite,montmorillonite and illite pore volume.The specific surface area is mainly concentrated in the transition pores.The pore volume and specific surface area of the kaolinite are dominated by micropores.The order of methane adsorption in the dry conditions are montmorillonite>illite>kaolinite.The maximum adsorption amount of montmorillonite is 3.796cm~3/g,illite is2.125cm~3/g,and kaolinite is 1.003cm~3/g.The excess adsorption volume and pressure curve are 10MPa as the turning point,the adsorption amount between 0 and 10MPa is increasing,the adsorption curve begins to decline after 10MPa,and the adsorption model of D-A and L-F can describe the negative adsorption of clay minerals in the high pressure stage,and the data fitting degree is higher,and the difference in the crystal spacing between the clay minerals will lead to its armor.The larger the spacing of alkane is,the greater the adsorption capacity of methane is,the greater the adsorption capacity of methane in clay minerals;the higher the water content of clay minerals,the weaker the adsorption capacity of methane;the higher the content of organic matter in clay minerals,the greater the adsorption capacity of methane.