Conductive And Dielectric Saturation Model Of Shaly Sandstone Based On The Occurrence State Of Pore Water

Resistivity measurement estimates formation water saturation by Archie formula,it is the most widely used method up to now,however,when the formation resistivity is unknown,or it is extremely high,the resistivity measurement will be ineffective,meanwhile,cementation exponent changes with the change of depth,it is more difficult to exactly compute water saturation.Dielectric logging identify information from underground especially the pore water by getting dielectric constant of formation,it is not sensitive to salinity of formation water,as an important method which different from resistivity logging,it is suitable for acquisition of water saturation and reservoir evaluation when resistivity logging method can't give a precise explanation.This paper selects 10 pieces of shaly sandstones samples from Fulongquan area,analyzing the porosity?permeability and shale content of samples,measuring theT₂spectrum of nuclear magnetic resonance to study the pore structure,meanwhile the samples are humidified with 0.5%NaCl solution from dry to saturated,the TH2829C digital bridge is used to measure complex impedance of samples at 60KHz?100KHz?500KHz and 1MHz to obtain the change rule and dispersion characteristics of resistivity and dielectric constant in the humidification process.According to the standard of classification of the three-water model,the pore water in the rock is divided into clay water?micro capillary water and free water,analyzing the corresponding relationship between change of resistivity and dielectric constant of samples in the humidification process,dividing theR_t-S_wande-S_w curve into three sections,which representing respectively pore water in differentoccurrence state,obtaining the influence of the three types of water to the conductive and dielectric response of rocks at different frequencies.Defining resistivity indexI_R and dielectric constant indexI_eand making crossplot ofI_R-S_wandI_e-S_w,the relationship satisfies the power exponent relation in free water section.Meanwhile the relationship of wettability and complex resistivity and its dispersion characteristics of rocks is discussed about the influence of wettability to pore water distribution.In combination with the influence of different distribution of pore water?wettability and frequencies to conductive and dielectric properties of samples,on the basis of the three-water conduction model and CRIM model,this paper respectively establishes the conductive and dielectric model of three pore water sections for water wet shaly sandstone at 1MHz,the model error is discussed later.The conductive and dielectric properties of rocks mainly depend on the properties of pore water,the occurrence state of pore water should be considered to analyse the conductive and dielectric response of rocks at any water saturation state,however the influence of the occurrence state of pore water to conductive and dielectric properties of rocks has not yet been discussed respectively in existing conductive and dielectric saturation models.This paper analyses the conductive and dielectric properties and their corresponding relationship from the perspective of occurrence state of pore water,the conductive and dielectric mechanism in rocks of different water saturation becomes more clear,the research result has great significance for evaluating formation water saturation by using conductive and dielectric methods.