High Resolution Dual Laterolog Tool Forward Response Study

With the decline of resource oil and development of geological technology, the exploration in complex oil-gas reservoirs such as thin-layers and horizontal layers has become more and more important, while a good performance logging instrument is an essensial guarantee and basic premice to look for reservoirs, transforming traditional tools to new ones to get better functions is a substantial feature in electrical logging. In order to improve the operating characteristics of conventional Dual Lateral Logging tool, China National Petroleum Logging Company independently developed High-Resolution Dual Logging (HRDL) tools, which shorten the electrodes length and improve vertical stratification ability, under the premise to ensure the probing depth.It is a great manner to make some research on electrical logging tools’responses for instruments manufactory and data interpretation application. For the advanced HRDL, it is necessary to grasp its working principle and analyze the characteristics, including resolution, probing depth, invasion effect and borehole effect. By numerical analysis, the structure of the instrument can be optimized to provide the basis for saving the research costs; the establishment of environmental correction charts provide a more realistic and reliable data for logging interpretation.The article is researched basing on electromagnetic field theory and logging methods&principles, making use of Finite Element Method (FEM), which is the basis of one electromagnetic software named Ansoft Maxwell, which is used to make a3D strait-graphic model to make a numerical research, discussing the vertical detection and radial detection features by analyzing the electrical distribution through changing model parameters. Conclusions are as follows,1) good resolution of thin layer to0.3m without invasion, and the invasion effect will cause the resolution down, while the layers resistivity contrast will reduce the capacity of thin layers of stratified, the higher the contrast ratio, the lower resolution;2) three monitoring elctrodes make main current focucing more, which can take into account the contradiction between the vertical resolution and probing depth of laterolog tools;3) due to current past-focus, the borehole correction is complicated, making the correction factor increase non-monotonically with the caliper, and deep measurement is significantly higher than that of low measurement in high impedance segments, performing positive difference, in accordance with the actual situation.