Our patented (U.S. Pat. No. 6,084,403) Induction Collar Locator tool is used to make depth corrections to logs by identifying the location of casing collars, and to inspect other mechanical features of the casing such as thickness variations or perforations.
It uses a Low-Frequency Induction method with a transmitter & two receiver coils arranged to provide an absolute phase measurement that senses the average thickness of metal around the tool, along with a two-inch differential measurement to sense smaller details such as collars, casing-centralizers, and perforations or cracks in the casing. The two different modes are only available simultaneously in the digital-output version of the tool, when they are assigned to two channels of the telemetry frame.
A typical log “signature” is produced that is similar to conventional CCL tools. Unlike conventional collar locators the ICL response is independent of logging speed (down to zero speed!), and most importantly it sees flush-joint collars just as well as any other kind. This is because it is responding to the total volume of metal around the tool, and not to 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. The ability to operate when centralized allows the other sensors in the PL string (Flowmeter, Fluid ID) to operate in the best position for accurate measurements.
It will operate in all casing/tubing sizes although the response is best in casing sizes from 4-1/2 to 9-5/8 inch diameter and weights up to 35 lb./ft. The small tool diameter allows it to pass through tubing as small as 2-3/8 inch diameter. Tubing joints are also recorded, as are casing collars through tubing, allowing a true collar-count all the way from surface to TD of the well.
The ICL-A is available with either the CBG Digital Telemetry, or with a modulated Current-Output for low-cost standalone applications.
The small diameter of the ICL compared to other Casing-Inspection tools is a great advantage, because it is not necessary to pull tubing out of the well. This can be a great cost-saving. The graphs below show the tool response characteristic when used in the Casing Inspection mode and with the analog Current-Output option. The variation of current draw from the nominal value is plotted against casing weight. The second chart shows the effect of an additional outer casing.