Calculating the Effect of Multiple Steel Cased Deviated Wells on Electromagnetic Surveys

Electromagnetic methods are sensitive to conductivity contrasts in the subsurface. This makes the methods useful for monitoring oil and gas reservoirs, which will experience changes in electrical conductivity over their lifetime. In a modern production environment, such a survey would be completed in the presence of multiple deviated cased wells. Common well casing materials, such as steel, are very good conductors and can create a strong secondary electromagnetic field that contaminates the data at the receivers with unwanted signal. To resolve this problem, it is necessary to be able to accurately model the effect of the well casings on collected data. In this paper, we make use of earlier casing modeling work using the Method of Moments and extend the approach to model the electromagnetic response of a group of deviated wells in a layered geology subject to a marine CSEM survey and produce a tool fit for practical applications. An illustrative example is used to show the electric fields calculated by a group of deviated wells in a layered marine geologic setting. Results show that most of the electromagnetic fields channeled by the horizontal wells into a thin resistor are unable to escape into the surrounding media.