A novel full hydraulic tractor with large traction force

Coiled tubing (CT) is extensively employed in well drilling and completion operations, yet the issue of CT buckling occurs as the horizontal section extends. Deploying a tractor can effectively address the limitations of CT extension in horizontal sections. In this paper, a novel full hydraulic tractor with large traction force was proposed. The simulation models of the working cylinders under full hydraulic control were established, and the motion characteristics of the supporting cylinder and the traction cylinder of the full hydraulic tractor were obtained. A hydraulic integrated control valve (ICV) combining a sequence valve and a hydraulic check valve with a pilot hydraulic directional valve was proposed, which can realize the automatic reversing mechanism of the tractor. The full hydraulic automatic reversing mechanism and ICV-tractor joint simulation model were established. The simulation results showed that the full hydraulic reversing mechanism could realize the reciprocating motion of the piston of the traction cylinder, and the valve spool could maintain the maximum opening in two positions. In addition, the prototype was developed and the function verification experiment and traction experiment were carried out. The results showed that under full hydraulic control, two cylinders could move steadily in a certain order and cycle. The maximum traction force of the CT tractor for pulling coiled tubing in the casing reached 81.36 kN. This proved the correctness of the full hydraulic tractor with large traction force. This research provides equipment support for CT operations in ultra-long horizontal wells and makes a significant contribution to the lateral extension of horizontal wells.