Method and apparatus for providing repeatable wireline depth measurements

摘要

A depth measurement system produces independent signals, each presumably corresponding to the same movement of a wireline if produced under ideal wireline measurement conditions. The system utilizes the signals to provide an accurate and repeatable signal under varying wireline measurement conditions and is particularly suitable for driving a recorder for depth recording and merging measurements from tools lowered in the borehole on different runs and to detect slippage between the wireline and a tangential wheel used to provide one of the signals. Slidably mounted measurement wheels insure tangential engagement of opposite sides of the wireline with equal pressure. Low-load signal generators each responsive to the rotation of the opposing wheels provide independent signals, each ideally corresponding to the movement of the wirline engaged between them. Magnetic marks written on the wireline are sensed and provide yet another independent signal. Automatic processing of these signals provides alarms and corrections for slippage, variations in measurement tension, and cable stretch.