The Fractured Formation Response of LWD Resistivity Imaging Tool in Horizontal Wells

The resistivity of fractured formation in horizontal wells has non-homogeneity, logging response mechanism is complex, the Logging While Drilling (LWD) resistivity imaging tool can visually identify fractures and calculated its parameters quantitatively. In this paper, using the method of transition boundary conditions (TBC), the fracture is equivalent to the plane. Combined with the finite element method (FEM), the modeling of LWD resistivity imaging tool is built, which reduced the amount of grid. The excitation source of toroid is equivalent to the surface magnetic current source. Compared with the analytic solution of electrical dipole, the equivalent method is proved correctly. Firstly, we analyzed the responses of fracture with different apertures. Secondly, we studied the current of the button electrode under different standoffs. Finally, we simulated fracture formation response under different mud invasion depth. The results showed that fracture apertures had a good linear relationship with maximum current contrast. The current peak value of button electrode increased with the standoffs. The depth of mud invasion had an exponential relationship with the abnormal current area. The results can provide a theoretical basis for the fracture identification and interpretation of LWD resistivity imaging tool in horizontal wells.