Three Dimensional Resistivity Array Imaging Logging Method

For better description and evaluation of the physical characteristics of the rock media around the borehole in the three-dimensional space,we conducted three dimensional resistivity array imaging logging method for basic research.We want to effectively combine lateral imaging of array lateral logging and circumferential imaging of azimuthal resistivity imager,and then optimize the design of three dimensional resistivity array imaging logging tool.By functional conversion of an electric equations and three-dimensional finite element mesh we can perform numerical simulations.Then observing and analyzing horizontal,vertical and circumferential probe characteristics to carry out a systematic study of the detection results of three dimensional resistivity array imaging logging tool.The establishment of non-uniform geological mathematical model,including high angle wells / horizontal wells(HA/HZ)and fractured-caved formation,wich can be used to analyze the response characteristics of the instrument,in order to evaluate the non-uniform reservoirs by logging data.Tool designed by a combination of different modes,which can measure 6 high-resolution array lateral curves and a total of 60 azimuth resistivity curves in five diffierent probing depth,and then to achieve a certain resolution imaging around the borehole.In the numerical simulation,the first geophysical model has been transformed into a mathematical model,and then converted for the functional extreme problems by the variational principle,and finally calculated using the finite element method.In the discrete process,due to differences in geological models and boundary problems,using different node segmentations and automatically generating mesh to impart conductivity values.Using frontline solution to install and solve stiffness matrix,in order to reduce matrix storage and back substitution,optimize the installation sequence and achieve elimination during installation.According to the working principle of electrodes of the three dimensional resistivity array imaging logging,we need to compute the potential of complex electrodes by imposing different constraints for different logging models,and finally translate into formation resistivity to realize the forward calculation.According to studying the detection results of three dimensional resistivity array imaging logging tool,we found that after optimizing the structure parameters of the tool,while maintaining the probing depth is the same with the original array lateral tool,the total length of the new tool is greatly reduced,and maintain a higher resolution in the vertical direction.But the tool is influenced by borehole size and eccentric,where azimuthal resistivity can give a good indication of the difference around the borehole.After forward calculation about HA/HZ,we found differences in the response of high-resolution array lateral curves and azimuth resistivity curves can accurately reflect changes of non-uniform medium around the wellbore,and visually displayed through the imaging.We can determine the formation dipping angle and formation dipping direction,and can know the direction and distance relationship between horizontal wells and boundary layer.After forward calculation about fractured formation,caved formation and fractured-caved formation,we found specific relationships between logging responses and fracture dipping angle,fracture aperture,resistivity ratio,high-angle fracture beside the borehole and crossing fractures.Similarly,having specific relationships between logging responses and cave volume,distance to the borehole wall,resistivity ratio,degree of filling and angular distribution.In fractured-caved formation,the logging responses characteristics are affected superimposedly by both fractures and caves.