Development and application of a small-diameter inside tube hydraulic cutter

In order to solve the problem that cumulative and chemical cutting of stuck downhole string brings high risk of destructiveness, the small-diameter inside tube hydraulic cutter has been developed. The device works in such a principle where downhole hydraulic motor, after being pressurized by ground pumper drives the cutting tool to rotate; when the fluid runs through the bottom nozzle, its throttling action produces differential pressure, which drives the piston to move upward, compress spring and touch the blade root, while the cone pushes the blade extended and fully opened at the cutting position, before the high-speed rotating blade mills the oil tube from inside until cutting off the oil tube above the stuck-point. The device, which can be also applied in deviated wells, after equipped with a hydraulic centralizer and hydro-mechanical anchor, can be used to cut a stuck string at any well depth position in vertical, deviated and horizontal wells. Up to now, it has been applied in four wells in Shengli oilfield and the successful rate of cutting was 100%. Field applications show that the device is easy and convenient to operate, and it can efficiently and reliably cut the stuck oil tube leaving regular end face, so this device has a wide application prospect in aspect of dealing with the stuck string in oil-water well operation.