North Africa Case Histories of a New Wireline Logging Method for Determination of Free Point to Assist Pipe Recovery Operations

Abstract

The identification of the free point in drill collars, drillpipe, tubing, or casing is critical for successful drilling recovery or abandonment operations. A new logging tool, available in the wireline service sector, has been developed and field tested that will help to cost-effectively identify a free point. The tool uses the property of steel called the magnetostrictive effect. When stress is applied to steel, the magnetization of the steel is modified. The procedure using the new tool requires two logging passes. The first logging pass records magnetization information about the pipe with the pipe in a neutral weight condition. The second logging pass records magnetization information with tension or torque applied to the pipe. When torque or tension is applied to pipe that can be stretched or torqued, its magnetostrictive properties change. If a section of the pipe cannot be stretched or torqued, magnetization effects remain unchanged. On this basis, the free point (the transition from pipe that can be stretched or torqued to pipe that cannot) is easily detected by comparing two logging passes. Previous free point determination methods required a series of stationary measurements with the pipe in a neutral weight condition, the application of stretch or torque, and the presence of a highly skilled pipe recovery expert on location. The new method simply involves an overlay of two logging passes before and after the pipe has been stretched or torqued. The tool has been successfully tested in steel alloys with minimal magnetic properties.This new logging tool has significant advantages. First, from a safety standpoint, the application of pipe stretch is applied for only a few minutes between logging passes, whereas legacy methods required numerous station measurements with the pipe being stretched. Secondly, because the determination of a free point requires a comparison of logging passes, real-time operations with constant satellite communications readily permits remotely-based operator and service company pipe recovery experts to be involved with plans for freeing the pipe. The new technology is independent of a highly skilled on-site pipe recovery expert and the delays associated with waiting for the expert to arrive on location.The tool is small in diameter, run centralized, and does not require weight bars added to the tool for slip engagement. These features shorten the length of the tool string and simplify e-line rig-up procedures. The short tool length has advantages in deviated well conditions in which pump down free point tool deployment may be required.