Experimental Study On Electronic Dispersion Characteristics—A Case Study In Hulesitaisumu,Neimenggu Province

Sandstone reservoir contains varieties of underground fluid and its original sedimentary structure determines the fluid capacity,which could be measured with geo-physical methods such as dispersion characteristics of polarization and complex resistivity.Hence,experimental research is a necessary procedure for engineering.Polarization dispersion characteristics under surface temperature-pressure system and complex resistivity dispersion characteristics under underground temperature-pressure system were included in the designed experiments,which were performed with sandstone core samples collected from hulesitaisumu,Neimenggu.Microscope analysis,chemical analysis and petro-physical analysis were conducted during the experiments.Finally,the results were illustrated as dispersion curves,which were analyzed with petro-physics and theoretical model.Conclusions are as follow:(1)Hydrodynamics during sandstone sedimentation determine its original sedimentary structure,the micro-pattern of which are grain size,pore structure and mineral composition.Polarization dispersion characteristics are prone to be steady and low-value when grain size and pore structure present homogeneity with less cements and infilling,which comply with ‘law of hydrodynamics reinforcement'.(2)the main process of polarization dispersion is cation movement under electrical field and rock skeleton is one of the most significant factors of polarization dispersion characteristics.According to electrical property,rock skeleton can be divided into 5 types regarding clay content,tightness and grain size: gravity flow,high-energy traction current,low-energy traction current,fracture-cavity and clay mineral skeleton.(3)Main research object of complex resistivity dispersion characteristics is amplitude,real part,imaginary part and phase with changing measurement frequency,the general features of which are as follow: a.dispersion characteristics of amplitude and real part are similar,which would be different only when the imaginary part reached the summit;b.the inflection point of real part always accords with the extreme point of imaginary part;c.the extreme point of imaginary part always keep distance from that of phase;d.with the depositional hydrodynamics strengthening(larger grain size,growing pore structure and less clay minerals),turning points gradually move forward whose distance from the extreme point of phase turns smaller in the meantime;e.changing salinity and fluid saturation is equivalent to changing rock skeleton,which help analysis.(4)Cole-Cole model can comprehensively explain dispersion characteristics of complex resistivity: a.relaxation time constant determines the position of turning point;b.extreme polarization determines descending rate of the real part and distance between turning point and the extreme point of phase,which establish the relationship between complex resistivity and polarization;c.in most cases,dispersion characteristics of complex resistivity is determined by both relaxation time constant and extreme polarization,which are controlled by rock skeleton.(5)The final purpose of this paper is to detach the relationship between rock skeleton and fluid property.Single factor methodology was used to compare the fluid property of the same sedimentary facies.Therefore,standard core experiments are supposed to be performed.Moreover,The paper suggests that the number of measurement frequency should multiply.The imaginary part and phase should be considered during well logging evaluation.