DOWNHOLE TOOL DETECTION MEANS

摘要

The present invention relates to apparatus adapted to detect and indicate the position of downhole tools as they enter and exit the well. A magnetic sensor (21) mounted on a bracelet (20) is fixed to the neck of a surface valve (14) and operates to activate an alarm on detecting the presence of magnets (9) on an indicator sub (1) as it passes the sensor (21). The operator is thus provided with an accurate indication that the toolstring has been retrieved.