The effect factors analysis of the cave formation based on the LWD resistivity imaging method

Abstract

Abstract The cave formation has strong non-homogeneity and the well logging response mechanism of it is very complex, which is of great significance to be studied. Based on the 3D finite element method, the logging response of the Logging While Drilling (LWD) resistivity imaging tool is simulated. The effects of cave diameter, cave extension and resistivity contrast between cave formation and background formation on ratio of measurement signals are investigated using a single cave model. The results show that the existence of the borehole has a great influence on the measurement signal, so it needs to be corrected or the measurement electrode of the tool should be close to the borehole. When the diameter of the cave is larger than a certain value, the relationship between the cave extension and the measurement signal can be quantitatively described. However, the resistivity contrast between the cave formation and the background formation shows a power index relationship under different cave diameter. The simulation results can provide a theoretical basis for the identification and interpretation of LWD resistivity imaging tool.