The CITM tool is used to measure three different parameters for steel water well casings:
This along with the Caliper measurement is the major benefit of this tool. We use a very low frequency magnetic field transmitted into the casing to “see” through any calcite deposits to accurately measure the mass of the metal in the surrounding casing. The field can also penetrate the inner casing to any outer casing and we can even detect a third casing. The measurement is the average mass of metal (usually steel) 360 degrees around the tool. By comparison with the nominal casing weight from the driller’s record, this gives you the ability to detect and measure the amount of metal missing from the casing. By using the Caliper measurement in conjunction you can distinguish metal loss inside or outside of the metal casing.
The variation of digital data counts with casing size is converted in software into pounds per linear foot of steel. As you can see from the chart, the tool uses polynomials for the calculation of the metal mass. Each casing size would ideally be calibrated for the tool in the Warrior software, but the supplied charts are accurate enough in most situations. For example, it is possible to create individual Warrior calibration sets for 12”, 14”, 16”, 18” ………. 30 “ nominal casing sizes.
The non-contact caliper measurement is accomplished with a high frequency signal that induces a magnetic field on the inside surface of the casing. This field is measured and creates the diameter measurement. Unlike multi-finger caliper tools it does not require that the casing be cleaned inside to make the measurement and it always measures the actual metal diameter regardless of any calcite or rust buildup. Along with its normal diameter measurement, it can also detect cracks in the casing. The response of the tool is shown below in the chart.
A typical log “signature” is produced that is similar to conventional CCL tools. Unlike conventional collar locators the CITM response is independent of logging speed (down to zero speed!), and most importantly it sees flush-joint collars or welded casing joints just as well as any other kind. This is because it is responding to the total volume of metal around the tool or to the changes in metal properties after welding rather than a small gap in the pipe.
Also, since it does not contain any magnets, there is no problem of sensitivity degradation with temperature or time and there are no special handling requirements or safety problems. The tool works best when centralized, unlike most other collar locators, but also operates very well eccentered when conditions require.
It will operate in all casing/tubing sizes although the response is best in casing sizes from 12 to 30 inch diameter and weights up to 95 lb./ft.
Log Examples (two pages from a larger log)
Surface to 100 feet – Surface casing, 95 lbs/l ft, 17.7” diameter
100 feet to 150 feet – Note change in casing mass from 95 lbs , down to 72 lbs. Also not the variations in mass indicating that there has been some metal loss.
470 to 490 ft – The caliper increases slightly and the mass goes down to 21 feet indicating a screen section.
490 to 525 ft – Pump casing 5/16” Wall according to well log, see the 12 % casing loss due to pump turbulence. The casing sizes in this well are 40 ft sections
525 to 555 ft – good quality screen 21 lb/ft
555 to 565 ft – swaged patch as indicated by increase in mass and a reduction in diameter
565 to 600 ft – there is major metal loss showing in this screen section along with erratic caliper readings indicating major casing loss and cracks. Mass goes to near zero and caliper indicated almost 26 feet. Note that the three finger caliper could not see the metal loss in this section.