Electromagnetic method for analyzing the property of steel casing

摘要

It has been shown that electromagnetic (EM) imaging, in particular in borehole applications, can be effective in characterizing and monitoring subsurface processes involved in improved oil recovery operations and production management. In this report the authors present an innovative EM method for extracting information about a steel casing in terms of its electrical conductivity, magnetic permeability, and the casing thickness. The method is based on accurate evaluation of magnetic fields near the transmitting loop in a steel-cased borehole, and the least squares inversion of thus measured data. The need to make measurements close to the source stems from the two related considerations. One reason is that by making measurements close to the transmitter one can keep the formation response from entering the measurement to a minimum. The other reason concerns with the practical consideration involved in fabricating a borehole tool. The measurement accuracy in terms of PPM to the primary field can best be achieved when the transmitter and receiver are close to each other. To facilitate this requirement one can consider a single loop acting as the source and the receiver operating in time domain, or a closely coupled frequency-domain system with the source-receiver separation of just a few inches apart. Results are discussed.