Numerical Simulation And Experimental Study Of Measuring Resistivity In Downhole

Formation resistivity is an important parameter for oil and gas interpretation and evaluation.Formation resistivity measurement methods are divided into borehole resistivity measurement and laboratory core resistivity measurement.Wellbore resistivity measurement is affected by wellbore and intrusion,and cannot directly reflect the real situation downhole.In laboratory core resistivity measurement,the core is taken downhole to the surface and then measured.The core is separated from the formation and the sample volume is small;conditions such as temperature,pressure,and stress are simulated by the ground and cannot reflect the physical properties of rock under real formation conditions;From experiment to application,the period is at least 3months,and the application lags behind.This paper proposes the concept of in-situ downhole experiment and designs a new method of downhole rock physical in-situ measurement to measure formation resistivity parameters in the real environment of the lateral hole deep into the formation to avoid borehole and intrusion effects.The research results provide theoretical and methodological basis for the next step of the development of underground robots.The main research content includes the following parts.The first part studies new methods of measuring resistivity in downhole.Based on the analysis of the existing rock sample resistivity measurement problems and the advantages of downhole in-situ resistivity measurement,a new method of downhole hole resistivity measurement is proposed.The measurement principle,the method of determining instrument constants and the pseudo-geometric factors describing the radial detection characteristics are studied in detail.The second part is based on the COMSOL software resistivity measurement probe structure optimization design.First,study the calculation principle of the COMSOL finite element simulation software based on the constant current field and the steps of the AC / DC module in the COMSOL software to solve practical problems;second,based on the COMSOL software,study the calculation method of the structural optimization design of the resistivity probe model of three different structures,Through a reasonable meshing design,the numerical calculation of the detection depth of three different structures of resistivity probes,respectively,through the results of analysis and comparison to determine the structure of the best resistivity probe;finally,study the signal of the best resistivity probe Launching and collecting design schemes and mechanical design and processing of resistivity probes.The third part is a comparative study of numerical simulation and physical experiment of the resistivity measurement in the hole.First,based on the COMSOL software,the resistivity probe is measured at nine different formation resistivities and six different rock holes,and the physical resistance platform is used to realize the resistivity probe in nine different salinity solutions and six different rock holes.Measurement.Secondly,the numerical simulation and experimental results are analyzed.The results show that the errors between the two measurements in nine different salinity solutions are small,which proves the feasibility of the designed probe;the resistivity measurement in six different rocks,The results of the loose rock samples were found to be basically consistent,indicating the accuracy of the experimental measurements.Finally,the resistivity measured by the experiment is compared with the resistivity of the plunger core measured by the key logging laboratory.Through quantitative analysis,the relative error between the two is less than 0.5%,indicating that in-situ rock physical in situ measurement can be performed directly.The fourth part is the test and simulation research based on the test well.First,analyze the design purpose of the test well,the detailed process of the resistivity measurement experiment,point out the problems that should be paid attention to,and ensure the accuracy of the test measurement results.Secondly,preparations for instrument commissioning and rock sample saturation were carried out,indoor tests for in-situ measurement of downhole rocks were carried out,and tests for downhole drilling,core drilling,and in-hole measurement were completed.Finally,based on the COMSOL software,the model of the model well test is established,and the numerical simulation results are compared with the model well indoor test results.The results show that the two are basically the same,indicating the feasibility of the model test well.Lay the foundation.