Study On Electrical Characteristics Of Mesozoic And Cenozoic Rocks In Qingyang,gansu Province

The research object of this paper is Mesozoic and Cenozoic strata in Qingyang area,Gansu Province,which mainly develop loess and sandstone.The study of physical properties of sandstone is of great significance to the development of geophysical exploration.Resistivity is an important component of sandstone physical properties,but there are few physical properties measurements of sandstone in Qingyang area,Gansu Province,especially the lack of systematic research on electrical properties.Archie formula is widely used to describe the relationship between rock resistivity,porosity and water saturation,but the Archie parameters applied to this area have not been studied by predecessors.Previous studies on the relationship between resistivity and wave velocity of sandstone have not considered the influence of water-bearing state of rock.In view of the above problems,taking the samples from Qingyang area of Gansu Province as an example,the physical parameters of density,velocity,susceptibility,resistivity,polarizability and relative dielectric constant of loess and sandstone in this area are measured and analyzed by different experimental instruments.The electrical parameters of sandstone in this area are studied through laboratory experiments of rock electrical parameters,and the Archie formula parameters applicable to this area are summarized.The theoretical relationship between wave velocity and saturation and porosity is obtained by Gassmann equation based on Wood theory assumption and compared with experimental results.At the same time,the law of resistivity changing with saturation and porosity is fitted by Archie's unsaturated rock resistivity model formula.On this basis,water saturation is used.With porosity as a link,a wave velocity-resistivity relationship model is established with porosity and water saturation of rock samples as a link.It is found that the correlation between rock electrical parameters and porosity is poor,while b and m are slightly positively correlated with porosity.When the porosity of sandstone samples is high,the data points of rock electrical experiments are distributed near the classical Archie line,but for sandstone samples with low porosity,with the continuous decrease of water saturation,the non-Archie phenomenon is obvious.When the water saturation is constant,the wave velocity decreases gradually with the increase of porosity.During the saturation process,the resistivity decreases rapidly and slowly,and when the water saturation is constant,the higher the porosity of the rock sample,the smaller the resistivity of the reconstructed gas smann.The equation and the formula of unsaturated rock resistivity model can be well fitted with the experimental data.On this basis,considering the influence of water saturation and sandstone porosity on the velocity-resistivity relationship,the relationship model between wave velocity and resistivity is established,which fits well with the experimental data.