Methods of correcting for the influence of surrounding rocks using a three-detector density logging tool

In density logging the influence of surrounding rocks on each detector cannot be ignored when the thickness of a target layer is less than the tool's vertical resolution. Therefore it is necessary to correct for the impact of the surrounding rocks. In this paper we investigate, through Monte Carlo simulation, the responses of each detector to thin target layers with different thicknesses and the influence of surrounding rocks. We also analyse the correction function of a three-detector density tool for the surrounding rocks. The three density measurements are calculated for a three-detector tool in three conditions with or without mudcake. Methods of correcting for the effect of the surrounding rocks are proposed based on changing the rules of formation density of the three measurements in each condition. The processed results of field examples show the impact of the presence of surrounding rocks, the necessity for correction and the effectiveness of the correction methods.