High-resolution subsurface imaging of hydrocarbons is a challenge for the oil and gas industry. A feasibility study was performed to examine various approaches to surface or/and borehole excitation/acquisition of transient electromagnetic (TEM) fields. The objective of the study is to propose a technical solution and describe its capabilities for determining the location of an approaching oil-water contact at distances up to 200 m with reasonable accuracy. Cased boreholes have to be a part of the proposed measurement system. Waterflood tracking capabilites of three types of TEM field sources were investigated: a current loop placed on the surface, a downhole magnetic dipole, and a vertical electric line placed into the borehole and grounded to the casing. For each excitation type, the transient electromagnetic field was computed and analysed. A new configuration was suggested that tracks the moving oil-water contact using time-lapse downhole measurements of transient electric fields generated by a vertical electric line placed into the borehole and grounded to the borehole casing. A recommendation was made to place the receiver in an uncased part of the well where the source (vertical electric line) is installed. The novelty of the suggested configuration is usage of a cased well section as transmitter of the transient electric field and uncased well sections for receiver placement.
