| 摘要 |
Electromagnetic free point tools are configured to determine the free point of a downhole pipe in a wellbore utilizing the amplitude or phase change in a transmitted signal for stressed and unstressed pipe. Certain examples of electromagnetic free point tools comprise a housing, one or more transmitter coils, one or more receiver coils, each coil spaced apart from one another, a power source for applying an oscillating voltage to the one or more transmitter coils which then induces a current in the receiver coil(s), and electronics for measuring the induced current in the receiver coil(s). In another embodiment, at least one of the coils is axially adjustable in position within the tool to permit the relative distance between coils to be adjusted to optimize performance of the tool in various conditions. By measuring the amplitude or phase of the induced current relative to the oscillating voltage, a log of the amplitude or phase is generated while passing the tool through a length of unstressed pipe. This process may be repeated while applying a stress to the pipe to generate a second log. By comparing the amplitude or phase of the first and second logs, the free point of the pipe may be ascertained by determining when and where the two logs diverge. This method can also be used to locate collars and measure pipe thickness. |
