Measurement while drilling spontaneous potential indicator using differential magnetometers

摘要

A drilling system, method and drilling apparatus for determining a parameter of a formation at a downhole location is disclosed. A member having a longitudinal axis is disposed in a borehole at the downhole location. A first magnetometer and a second magnetometer are disposed at an axial location of the member as separate azimuthal locations around the member and oriented tangential to a circumference of circle in a plane transverse to a longitudinal axis of the member. Magnetic fields resulting from a current flowing longitudinally through the member due to a spontaneous potential in the formation are measured to determine the spontaneous potential. The parameter of the formation is determined from the determined spontaneous potential.

主权项

1. A method of determining a parameter of a formation, comprising:
disposing member having a longitudinal axis in a borehole at the downhole location of the formation; disposing a first magnetometer and a second magnetometer at an axial location of the member and at separate azimuthal locations around the member and oriented tangential to a circumference of circle in a plane transverse to a longitudinal axis of the member; measuring a first magnetic field at the first magnetometer that is a combination of a magnetic field resulting from a current flowing through the member due to the spontaneous potential and a component of the earth's magnetic field; measuring a second magnetic field at the second magnetometer that is a difference between the magnetic field resulting from the current flowing through the member due to the spontaneous potential and the component of the earth's magnetic field; calculating the spontaneous potential from the first magnetic field and the second magnetic field; and determining the parameter of the formation from the spontaneous potential.