| 摘要 |
The method involves using signal emission means (5) and at least two reception units (8, 10) at two different locations along the well equipment (2). Each unit produces an image or signature of the well portions passing it. The images produced by the unit (8) in the lowest position when the equipment (2) is descending are stored for the necessary time period so that, when the equipment has penetrated further, the other unit (10) receives signals from the same portion of wall and also produces an image. By comparing (e.g. by correlation) images from each of the two units, it is possible to identify the common portion of the wall which has produced the two images being compared. The time period between the formation of the two matched images is measured, and the rate of penetration calculated. The invention may be applied to measuring the true rate of penetration of a well tool or measuring probe.
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