Systems and methods to monitor downhole reservoirs

A method to monitor a downhole reservoir, comprising:

• deploying a first source electrode of a galvanic transmitter on a wellbore casing;
• deploying a first return electrode of the galvanic transmitter on the wellbore casing;
• deploying a first tilted coil of a magnetic receiver on the wellbore casing, the first tilted coil being having a first orientation relative to a cross sectional plane normal to a longitudinal axis of the wellbore casing;
• applying a voltage to the first source and return electrodes to generate a current, the current being transmitted from the first source electrode, through a formation, to the first return electrode, wherein the current is altered by a water flood region of the formation, and wherein an altered component of the current induces a secondary magnetic field;
• and
• measuring a first component of the secondary magnetic field detected by the first tilted coil.

An electromagnetic reservoir monitoring system, comprising:

• a downhole reservoir monitor comprising:
• a galvanic transmitter deployed proximate a wellbore casing and having a source electrode and a return electrode, wherein a current flowing from the source electrode, through a formation, to the wellbore casing, to the return electrode, is altered by a fluid reservoir of the formation, and wherein an altered component of the current induces a secondary magnetic field;
• and
• a magnetic receiver having a tilted coil deployed proximate the wellbore casing, the tilted coil having an orientation relative to a cross sectional plane normal to a longitudinal axis of the wellbore casing, the tilted coil operable to detect a component of the secondary magnetic field;
• a storage medium operable to store instructions to determine at least one property of the fluid reservoir;
• and
• a processor operable to execute the instructions to determine the at least one property of the fluid reservoir based on the secondary magnetic field.