Magnetic Thickness (MID)

Losing annular integrity is one of the most dangerous and potentially damaging types of well failure. Contaminated ground water and annular blowouts at surface are among the most feared potential outcomes. Despite advances in cementing, unwanted annular flow and sustained annulus pressure due to poor cement sealing is a prevailing concern for many operators. Diagnosing tubing and casing thickness condition can catch the early signs of corrosion, with implementation of remedial action to ensure annular integrity at an effective cost.

The MID/S4 is primarily run through tubing, with the ability to simultaneously inspect the tubing and the casing strings behind it. The MID/S4 combines twin centralisers, an internal gamma ray sensor, a temperature probe and two axial coils in order to measure casing corrosion and defects up to the 4th string.

Using a pulsed eddy current technique with increased pulse duration and recording times a depth of investigation of 20” is achieved with a total metal thickness evaluation limit of 1.9”.

Downhole tool specification

Outside diameter, in [mm] 1 11/16 [43]
Length, in [cm] (with Centralizers) 144.5 [367.2]
Weight, lb [kg] 30.8 [14]
Connection Type GO
Materials Corrosion Resistant
Maximum pressure, psi [MPa] 14,500 [100]
Maximum temperature, DegF [DegC] 350 [175]
Voltage, VDC 220
Current, mA 500
Maximum Depth of Investigation, in [mm] 20 [508]
Maximum combined wall thickness, in [mm] 1.90 [48.3]
Measurement Accuracy of 1st / 2nd / 3rd / 4th Strings 5%/10%/15%/20% of nominal wall thickness
Defect ‘crack’ resolution detection along pipe axis
1st / 2nd / 3rd / 4th Strings 11% / 25% / 33% / 50% of the perimeter
Defect ‘transversal crack’ minimum length required for detection 16.7% of the perimeter
Recommended logging speed, ft/min [m/min] 10-15 [3-4.5]
Logging mode Real time
Well conditions
Fluid Water, brine, production fluid
Minimum casing size, in [mm] 2.5 [63.5]
Maximum casing size, in [mm] 18 5/8 [473]


Duncan Troup

Global Product Champion
Phone: +47 480 54130