Device and method for measurement of resistivity outside of a wellpipe

A method for measurement of resistivity in a petroleum reservoir in a geological formation having a well with an electrically conductive metallic wellpipe having an outer metallic surface, the well being one of an injection well, observation well, and a production well, the method comprising the steps of:

• a) performing M series of measuring steps where M is greater than or equal to 2 to provide a first through Mth signal representation, each series of the M series of measuring steps comprising the substeps:
• a1) emitting electromagnetic waves from an inductive transmitter antenna to the petroleum reservoir;
• a2) receiving electromagnetic waves by a sensor series, the sensor series comprising a plurality of resistivity sensors fixedly arranged outside the outer metallic surface and arranged lengthways along the borehole, the plurality of resistivity sensors being one of inductive, magnetorestrictive and electrostrictive resistivity sensors;
• a3) generating measurement signals representing the electromagnetic waves sensed by the plurality of resistivity sensors;
• a4) registering a signal representation of the measurement signals;
• and
• a5) storing the signal representation;
• b) forming a difference between the second and later signal representations and a respective preceding representation;
• and
• c) interpreting the difference with regard to changes in the position of liquid surfaces in the reservoir.

A device for measuring and monitoring the resistivity in a petroleum reservoir in a geological formation having a well with an electrically conductive metallic wellpipe having an outer metallic surface, the well being one of an injection well, observation well, and a production well, the device comprising:

• a) an electrical energy source;
• b) at least one inductive transmitter antenna that transmits electromagnetic waves, fixedly arranged outside the outer metallic surface;
• c) at least one sensor series comprising a plurality of resistivity sensors fixedly arranged outside the outer metallic surface and arranged with a mutual separation lengthways along the borehole, the plurality of resistivity sensors receiving the electromagnetic waves transmitted from the at least one inductive transmitter antenna and generating measurement signals, the plurality of resistivity sensors being one of inductive, magnetorestrictive and electrostrictive resistivity sensors;
• d) a signal conductor for receiving the measurement signals from the at least one sensor series;
• e) devices giving a volumetric measurement of resistivities in the petroleum reservoir based on the measurement signals;
• f) an electrically isolating sleeve arranged outside of the at least one sensor series and the at least one inductive transmitter antenna;
• and
• g) a hydraulically balancing cavity arranged between the outer metallic surface and the electrically isolating sleeve.