A Novel Simulation Tool For Resistivity Imaging Logging In Oil-based Mud

Electrical Image logging can measure in-situ geological features with high resolution, which has been widely applied in oil industry. Arrayed buttons filled in the plates can transmit the direct electric current into the rocks through the conductive drill mud. The amplitude of electric current from each button can be calibrated into images to describe geological features. However, non-conductive muds are utilized under the circumstance of geological reasons, while the conventional electrical imaging tools are not applicable. New devices are needed to develop for non-conductive (or oil based) mud environment. This thesis gives a fundamental method to devise the electrical imaging tool for oil based mud.As a reliable method, the3-D finite element method and Maxwell equations are used to simulate the logging tools’forward responses under non-conductive mud conditions. First, changing the solving of the partial differential equations of the boundary value problem with boundary conditions into solving a functional problem; Second, based on the finite element method, we write the algorithm to achieve the dispersion of study area, dispersion of functional form and solving linear equations to get the unknowns at the node; Third, founding different simulation models to discuss the impact of different factors on the response of the instrument.Based on the numerical simulation, the research results are as following:1. First, in the infinitely thick formation, under the condition of low resistivity invasion, the depth of investigation is2.75in (about7cm); under the condition of high resistivity invasion, the detection depth of the logging tool is3.25in (about8.3cm).2. When the resistivity of the purpose layer is relatively higher than the surrounding environment, the resolution is between0.3in to0.5in; or, the resolution is less than0.1in.3. Logging instrument structures, such as buttons’area, the transmitter-the return electrode spacing, current frequency, etc., will affect the forward response.4. When the open width of the crack is greater than1mm, with the decrease of the width, the amplitude of responses declines, the cracks can be identified.5. The resolution of the tool can be affected by the resistivity contrast between the background and the fractures.6. These simulation results can clearly identify the location and the angle of the fractures. The dip angle of formation can be obtained by further signal processing techniques.