The High Resolution Induction (HRID) measures formation resistivity at multiple distances from the bore hole. The primary objective of HRID measurement is to determine a value for true resistivity (Rt) of the formation.
True formation resistivity and together with porosity can be used to calculate water saturation using Archie equation. If water saturation known, the hydrocarbon saturation can be determined by using this equation : Sh = 1 – Sw.
- Air drilled boreholes
- Oil based mud
- Fresh water based mud
- Preferred operating environments : Rmf/Rw more than 2.5 or Rmf far greater than Rw.
The principle of HRID measurement are the Faraday’s law and Ampere’s law.
Faraday’s Law : an alternating current supplied to a coil wire will create alternating magnetic field in the surrounding medium
Ampere’s Law : the changing of magnetic flux in the surrounding medium will create electromagnetic force (emf)
The transmitter coil creates the electromagnetic force in the formation that induces ground loop. The magnitude of the current of ground loop is inversely proportional to formation resistivity. HRID is using a single 3-coil receiver and two pairs of transmitter coils. Depths of investigation for this tool are 91 inches for Deep Resistivity and 39 inches for Shallow Resistivity. The vertical resolution for this tool is 2 feet.