Well servicing methods using a hydraulic actuated workover mast

摘要

A portable workover rig for lowering and raising objects such as pipe into and out of a borehole and includes a mast which can be raised from the horizontal position to a vertical position. a first hydraulic motor drives a sandline drum and a second hydraulic motor drives a mainline drum. A normally closed pilot operated check valve provided in the power hydraulic fluid conduit can be opened to permit freewheeling of the main drum allowing heavy objects to free fall in the wellbore. The mainline drum's motor is controlled by a control valve having a counterbalance feature which when a heavy load is being lowered into the well bore prevents the drum from rotating faster than it would be driven by the power hydraulic fluid. A similar but separate control system is used for the sandline drum.