A system for mapping a hydrocarbon reservoir, the system comprising: an electromagnetic transmitter configured to be disposed in a first wellbore of a first well penetrating a resistive layer of a subsurface formation, the EM transmitter configured to be disposed at a depth corresponding to an intersection of the first wellbore and the resistive layer, the resistive layer being bounded by a first conductive layer located adjacent the resistive layer and a second conductive layer located adjacent the resistive layer; an EM receiver configured to be disposed in a second wellbore of a second well penetrating the resistive layer of the subsurface formation, the EM receiver configured to be disposed at a depth corresponding to an intersection of the second wellbore and the resistive layer; the EM transmitter configured to transmit an EM signal into the resistive layer at the first wellbore such that the EM signal propagates from the EM transmitter disposed in the first wellbore to the EM receiver disposed in second wellbore via the resistive layer; the EM receiver configured to receive the EM signal at the second wellbore; and mapping system configured to: determine, based on the EM signal received at the second wellbore, transport properties associated with propagation of the EM signal from the EM transmitter to the EM receiver via the resistive layer, wherein the transport properties comprise a travel time associated with propagation of the EM signal from the EM transmitter to the EM receiver via the resistive layer; and determine a presence of an anomaly in at least one of the first and second conductive layers based on the transport properties, wherein determining a presence of an anomaly in at least one of the first and second conductive layers based on the transport properties comprises: determining a velocity for the EM signal based on the travel time; determining a presence of an anomaly in at least one of the first and second conductive layers based on the velocity. an electromagnetic transmitter configured to be disposed in a first wellbore of a first well penetrating a resistive layer of a subsurface formation, the EM transmitter configured to be disposed at a depth corresponding to an intersection of the first wellbore and the resistive layer, the resistive layer being bounded by a first conductive layer located adjacent the resistive layer and a second conductive layer located adjacent the resistive layer; an EM receiver configured to be disposed in a second wellbore of a second well penetrating the resistive layer of the subsurface formation, the EM receiver configured to be disposed at a depth corresponding to an intersection of the second wellbore and the resistive layer; the EM transmitter configured to transmit an EM signal into the resistive layer at the first wellbore such that the EM signal propagates from the EM transmitter disposed in the first wellbore to the EM receiver disposed in second wellbore via the resistive layer; the EM receiver configured to receive the EM signal at the second wellbore; and mapping system configured to: determine, based on the EM signal received at the second wellbore, transport properties associated with propagation of the EM signal from the EM transmitter to the EM receiver via the resistive layer, wherein the transport properties comprise a travel time associated with propagation of the EM signal from the EM transmitter to the EM receiver via the resistive layer; and determine a presence of an anomaly in at least one of the first and second conductive layers based on the transport properties, wherein determining a presence of an anomaly in at least one of the first and second conductive layers based on the transport properties comprises: determining a velocity for the EM signal based on the travel time; determining a presence of an anomaly in at least one of the first and second conductive layers based on the velocity. determine, based on the EM signal received at the second wellbore, transport properties associated with propagation of the EM signal from the EM transmitter to the EM receiver via the resistive layer, wherein the transport properties comprise a travel time associated with propagation of the EM signal from the EM transmitter to the EM receiver via the resistive layer; and determine a presence of an anomaly in at least one of the first and second conductive layers based on the transport properties, wherein determining a presence of an anomaly in at least one of the first and second conductive layers based on the transport properties comprises: determining a velocity for the EM signal based on the travel time; determining a presence of an anomaly in at least one of the first and second conductive layers based on the velocity. determining a velocity for the EM signal based on the travel time; determining a presence of an anomaly in at least one of the first and second conductive layers based on the velocity.