A STUDY OF DOWNHOLE ELECTROMAGNETIC SOURCES FOR MAPPING ENHANCED OIL-RECOVERY PROCESSES

An evaluation of downhole electromagnetic (EM) sources has been made for mapping 3-D enhanced oil recovery (EOR) processes. Two types of sources considered were vertical magnetic dipoles and vertical to near-vertical electric dipoles and bipoles. These sources were used to produce magnetic field responses expected of EOR processes for crosswell configurations. A borehole-to-surface configuration was also studied for the downhole electric source, since this configuration can be highly sensitive to shallow 3-D EOR targets. For the crosswell arrays, the criteria used to evaluate the sources were the magnitudes of the observed signals with and without the process and the amount these signals change because of a migrating process. Instrumental noise was considered in the evaluation. Findings show that either electric or magnetic sources can produce truly significant changes in the fields, provided the fields before and after the initiation of the process are compared. An order of magnitude change in the fields has been demonstrated. The key to measuring such changes is to use the highest frequency possible. This frequency will be limited by instrumental noise. A migrating process did not produce field changes that are as large as those observed with and without the process. Nevertheless, model simulations showed that changes in the fields caused by the migrating processes are significant and measurable. Calculated responses of a shallow process at the surface showed that they were extremely sensitive to small deviations in the orientation of the downhole electric source. Quantitative interpretation should proceed only with techniques that explicitly consider the source orientation.