New post-processing method for interpretation of through casing resistivity (TCR) measurements

We propose a new iterative method for post-processing through casing resistivity (TCR) measurements. This method can be seen as a correction or extension of Kaufman's theory to more complex scenarios, in which the casing is no longer assumed to be uniform along the axis of the borehole. It can also be seen as a simplified inversion method based on the main physical principles of TCR measurements. To derive our post-processing method, we first use the method of images, which enables us to introduce all key factors involved on TCR measurements, including casing length, casing radius, casing thickness, formation resistivity, location of injected current, and resistivity distribution of formation layers. Then, we design our iterative post-processing method by simplifying the complex formulation resulting from using the method of images. This post-processing method can also be derived as a particular inversion algorithm. Numerical results using goal-oriented hp-FEM simulations show that our post-processing method provides a more accurate approximation to the actual formation resistivity than that predicted by Kaufman's theory. In addition, the new method is proven to be very efficient and suitable for problems with spatial resistivity variations in the formation.

► In this paper, we propose a new iterative post-processing method for through-casing resistivity measurement.
► It can also be seen as a simplified inversion method based on the main physical principles of TCR measurements.
► Numerical results using goal-oriented hp-FEM simulations show that our post-processing method provides a more accurate approximation to the actual formation resistivity than that predicted by Kaufman's theory.
► In addition, the new method is proven to be very efficient and robust, since it is independent of spatial resistivity variations in the formation.