Electromagnetic evaluation of fracture geometries in rock formations

An electrokinetic method of evaluating the geometry of a hydraulic fracture in a rock formation comprises the steps of: ```obtaining measured values of electric and/or magnetic fields induced by the forward or back propagation (24)of a fracturing fluid (23) between the fracture and the rock formation; and ```determining the geometry of the fracture from the measured values. The method includes injecting into a borehole (1) in the formation a fracturing fluid with pump (6) at a pressure allowing the fluid to create the fracture and to propagate into the fracture and formation. Lowering the borehole pressure makes the fluid flow back from the formation into the fracture. Sensors (2,3) detect electric and/or magnetic fields.