This paper presents the design features and the results from field trials of a new wireline tractor developed specifically for through-tubing intervention into producing horizontal wells with barefoot completions.
Many Middle East horizontal wells have barefoot completions in which the producing zone is left without tubulars. The vertical section is cased and production tubing put in place. Intervention for production logging or remedial work is challenging due to the need to pass through tubing and then operate in open hole. Intervention is conducted on coiled tubing or wireline tractors. Coiled tubing has limited reach in open hole due to higher friction, and it chokes flow through the tubing, resulting in inaccurate production logs. Conventional wheeled tractors apply stress that can destroy some formations at the wheel contact point. This leads to heavy slippage and extremely slow progress.
Several technical innovations were implemented in the new tractor to overcome these challenges. A reciprocating mechanism drives a pair of linked grips with independent opening diameters to conform to variations in borehole geometry while providing a large contact area with the formation. The radial force is hydraulically amplified from the tractor load, enabling it to grip with as much force as required. Results from field trials show little to no slippage in conditions where previous tractors have struggled. The tractor features dual floating hubs that let it close in the uphole direction when tractoring to improve restriction navigation or close in the downhole direction while pulling out of hole to prevent self-locking. The combination of the dual floating hubs and a constant-force opening mechanism enables automatic navigation of restrictions and expansions where previous technologies would have required a manual open/close sequence. These innovations were successfully tested in several tractor operations. One case study is presented in which these features were instrumental in successfully getting to the bottom of the well and back to surface. In one case, the same well was logged using coiled tubing, a prior-generation tractor, and the new tractor. A comparison of these intervention methods is shown.
The integration of a reciprocating tractor drive mechanism with novel technical solutions for linked grips, pad pressure regulation, constant force expansion, dual floating hubs mechanism, and automatic navigation has resulted in more reliable and efficient tractor operation in wells with barefoot completions.