Research On The Influence Of Tight Sandstone Pore Structure On Electrical Conductivity

The Upper and Middle Jurassic Formation in West-Sichuan Depression contain mainly the tight sandstone reservoir,and the Archie's electrical parameters of tight sandstone have an obvious non-Archie behavior.The Archie Equation cannot characterize the conductivity properties of the reservoir,thus it is a challenge to the evaluation of the oil and gas saturation.Therefore a study to the micro mechanisms of conductivity of tight sandstones as well as the influence factors is of great significance.Taking the Penglaizhen-Series and Shaximiao-Series tight sandstone reservoir of the Upper and Middle Jurassic Formation in West-Sichuan Depression as research objects,this dissertation made a research of the evaluation of the pore structure of the tight sandstone reservoir,analysis of the Archie electrical parameters,simulation of the conductivity and the synthetic analysis of the results of the simulation:(1)The properties of the micro pore structure of tight sandstone reservoir was analyzed based on the Mercury Injection Capillary Pressure(MICP),Nuclear Magnetic Resonance(NMR)and Thin Section.(2)The electrical experiments of tight sandstone were carried out and the properties of the electrical parameters were summarized.(3)A series of simplified 3D micro conductivity model of pore throats were established based on the properties of pore throats of tight sandstones,and the conducting properties were simulated.The influence of pore structure parameters to the conducting properties of rocks was then analyzed.(4)The pore structure parameters were obtained from the NMR experiments,the complicated 3D micro conducting model of pore throats was established combining the large pores and micro pores,and the conducting properties were simulated.The results of simulation and the electrical experiments were analyzed synthetically,and the main influencing factors of the conducting properties of the tight sandstones in the studying area were summarized.The research reveals the facts:(1)the reservoir could be divided in four categories(???????)based on the micro pore structure from NMR.The average values of the pore radii were obtained from MICP.(2)The electrical experiments showed that the formation factor F decreases as the porosity increases,and the cementation exponent m has a weak positive relationship with the porosity.The trend that the cementation and conductivity become worse is observed.(3)The results of the simulation of the conducting showed that a great difference exists between the simulation results of plate shaped pore throat and tube shaped pore throat;the increasing of coordinating numbers of the pore could improve the connectivity of the pore space;and the pore throats perpendicular to the direction of the electrical potential influence the simulation results little.The formation factor F and the cementation exponent m decreases as the pore throat radius increases,they also increases as the tortuosity increases,and they increases as the pore throat ratio increases.At the same time,the influence of tortuosity on the formation factor F decreases as the pore throat radius increases.(4)The ratio of the large pores to the micro pores in tight sandstones can be obtained from NMR T2 spectrum.Based on that,the more complicated 3D micro conducting model of pore throats can be established combining the pore structure parameters from the Thin Section and MICP experiments.The results of the simulation have good agreements with the data from the experiments.This dissertation derived the pore structure parameters of tight sandstone reservoir of the Upper and Middle Jurassic Formation in West-Sichuan Depression,established the 3D micro pore throats conducting model,analyzed the influence of the changing pore structure on the electrical properties of the rock qualitatively and quantitatively,made macro analysis of the conducting mechanism of the tight sandstone based on the pore structure parameters,provided theoretical foundation of the well logging evaluation of the researching area,as well as the technical supporting to the prospecting and exploration.