Normal and lateral log response for a 2-D borehole model

Abstract

Direct current resistivity responses for two-dimensional (2-D) borehole model with cylindrical symmetry are computed using the finite difference method (FDM). The effects of shoulder beds, borehole mud, flushed zone, invaded zone, and uncontaminated zone are taken together to compute the normal and lateral log responses. The invasion zone is assumed to be a transitional zone. The effects of target bed thickness, resistivity of the invaded zone, radius of invasion and resistivity of the shoulder beds on the 2-D resistivity departure curves (RDCs) are demonstrated. Sensitivities in the 2-D RDCs remains up to the electrode separation (L) equal to the target bed thickness. For L ³ 5H, the target bed thickness), the entire information comes from the shoulder beds. This 2-D forward problem can be used for 2-D inversion to determine the resistivity of the uncontaminated zone and radius of invasion.