Abstract: A replaceable insulating sleeve is disposed around the lower end of a drill string used in drilling a well. The sleeve is restrained from rotating relative to the drill string, but can be released and quickly slipped off the drill string in the field to permit rapid replacement if damaged, or if alternate equipment is required. The sleeve carries sensing means for measuring a characteristic of formations penetrated by the well. Anchor means on the sensing means prevents it from rotating relative to the sleeve.

Abstract: A replaceable insulating sleeve is disposed around the lower end of a drill string used in drilling a well. The sleeve is restrained from rotating relative to the drill string, but can be released and quickly slipped off the drill string in the field to permit rapid replacement if damaged, or if alternate equipment is required. The sleeve carries sensing means for measuring a characteristic of formations penetrated by the well. Anchor means on the sensing means prevents it from rotating relative to the sleeve.

Abstract: In an apparatus for measuring depth of equipment in a well, a carrier system is provided on a well rig for positioning sensors adjacent a spiral wound wire rope which moves the equipment upwardly or downwardly. The carrier system employs a housing having rollers that engage the wire rope at two spaced locations. The sensors are located in the housing between the rollers, and they are maintained substantially equidistant from the wire rope by the action of the rollers so that they respond to movement of the spiral windings of the wire rope. A suspension system has arms that support the housing with reference to the rig, and the effective length of the arms is adjusted to compensate for errors in measurement that would be caused by lateral movement of the wire rope along a drum that actuates the wire rope.