Experimental Studies On Elastic Properties Of Montmorillonite

Clay minerals are the most abundant minerals in sedimentary basins.Common clay minerals are Kaolinite,montmorillonite,illite,chlorite and so on.Clay minerals have the characteristics of small particle size,plate-like particles,large specific surface area,and strong cation exchange capacity.They are often found in fault rocks,mudstones,and reservoirs of clastic and non-clastic rocks.The type,volume and distribution of clay minerals can significantly change the elastic properties of rock,so two sandstones with equal amounts of clay minerals will have different elastic properties depending on the minerals.The elastic properties of clay minerals have important petrophysical implications for understanding the seismic and sonic logging responses of mud sequences and clay-bearing reservoir rocks.The main object of this study is montmorillonite.The experimental principle is mainly derived from the calculation method of the transformation modulus of mineral phase in the multiphase body by Yang Xiaosong.Before the start of the experiment,we performed X-ray diffraction analysis(XRD),density measurement,and displacement calibration without sample conditions.Then,using LR-White gel as the medium,we prepared the pure gel solids first,and then used two different methods.A quartz-gel two-phase body,and a smectite-gel two-phase body were prepared,and the mass,length,diameter,volume,and mineral specific gravity of 7 samples were recorded.The experiment was carried out on the high-temperature and high-pressure test machine of the State Key Laboratory of Seismic Dynamics.During the uniaxial compression experiment,the length,density and longitudinal wave velocity of the sample under different pressure conditions were recorded.According to the experimental results,the uniaxial compression coefficient of the cured LR-White glue and the compression coefficient of the two-phase body were calculated.In addition,the relationship between the longitudinal wave velocity and the density is also studied,and the influence of the rubber content on the calculation of the compressibility of clay minerals is discussed,and compared with the previous research results.The study yielded the following meaningful results.(1)The uniaxial compression ratio of montmorillonite and quartz was obtained,and the bulk modulus of montmorillonite was 8.25 GPa.The bulk modulus of quartz is 37.49 GPa,which is consistent with the results obtained by single crystal measurement.It indicates that it is feasible to measure and calculate the compressibility and bulk modulus of mineral powder samples by the two-phase experimental method.A new measurement and calculation method is provided for experimental study of the elastic properties of fine powder samples.(2)The two-phase body density and the longitudinal wave velocity increase with increasing pressure.When the pressure is greater than 80 MPa,the density and pressure show a good linear relationship.(3)The VRH model was tested using the measured results.Among them,the V model represents the upper limit of the two-phase body modulus,the R model represents the lower limit of the two-phase body modulus,and the H model represents the average of the upper and lower limits.The results show that the true value of the volumetric modulus of the two-phase body is very close to the lower limit of the VRH model,so it can be considered that the R model can better reflect the real situation of the two-phase body.(4)The smectite-gel two-phase body was prepared by potting method and mixing method.By comparison,it can be found that the mixing method has more advantages than the potting method,and the prepared sample has a more uniform distribution of glue and minerals,and the calculation produces less error.