Magnetic Permeability Sensor Array Prototype To Evaluate Reservoir Phase Permeability in-Situ Downhole

Abstract

This work presents a novel system to image formation permeability of the reservoir in situ downhole. Colloidal magnetite fluid with high magnetic permeability is injected from the surface into the subsurface formation. The magnetic fluid permeates through the formation some radial distance ΔR over a given period of time, which is directly related to the formation permeability. A sensor array which measures the radial distribution of magnetic permeability surrounding the tool is deployed downhole during this injection process. By comparing the magnetic permeability radial distribution surrounding the sensor before/during/after fluid injection, the system is able to directly measure phase permeability of the surrounding formation in situ.The sensor array measures the radial magnetic permeability distribution of the formation via mutual inductance between pairs of solenoid coils axially distributed along a downhole tool. As the magnetic permeability of the material surrounding the solenoid coils increases, the mutual inductance between coils increases. Eddy current effects on mutual inductance measurements can be minimized by reducing the interrogation frequency of the measurement such that electrical conductivity and permittivity changes have no effect on the measurement of interest, e.g. the measurement is insensitive to the movement of brine and hydrocarbon and sensitive only to the movement of the magnetic permeability doped fluid. Measuring mutual inductance across the array of solenoid coils distributed along the tool enables the system to map the radial distribution of magnetic permeability surrounding the sensor.A laboratory prototype of this sensor system was built and evaluated for its sensitivity to changes in magnetic permeability distributions surrounding the tool. Results from these laboratory tests are compared to analytical predictions of the tool response. Magnetic permeability doped fluid of various concentrations are measured with the sensor array, and measurement results are compared to the predicted magnetic permeability of the various concentrations of doped fluid.