Lawrence Berkeley National Laboratory

We examine the detection and imaging sensitivity of surface electric field measurements over a 3D hydraulically active fracture zone (HAFZ) at depth when one end point of a surface electric dipole source is directly connected to a wellhead. This configuration is often called the top-casing electric source method. The sensitivity also depends on conductivity structures around the well because they control a leak-off of electrical currents from the steel-cased well. Our inversion experiments show that the method can delineate a localized HAFZ in a shallow to intermediate depth (e.g. ≤2 km) and can also detect changes in its width and height. The inversion results are improved when a volume of the subsurface imaging domain is reasonably constrained from geomechanical perspectives. The primary advantage of the method is the fact that the method has both source and receivers on the surface and thus, does not require well occupancy and interruption to the normal operation of the wells. Accordingly, it has potential to serve as a cost-effective tool for monitoring hydraulic fractures.