Numerous lessons have been learned from the use of a wide selection of technological elements in the construction of wireline tractors and mechanical services tools. It is well-known that downhole tool design is challenging and requires the use of the latest developments in physics, material science, electronics, mechanical engineering, and software because the tools operate in very harsh environments characterized by extreme pressures, high temperatures, and corrosive fluids. Wireline tractor and mechanical services tools face not only all of these difficulties but also some unique challenges. For example, the tools operate at much higher power levels compared with other wireline tools. The efficient delivery and use of power downhole is an active area of technology development. Another challenge is that the tools interact intensively with the borehole walls or elements of the well completion by exerting very large mechanical forces to tractor along the well, exercise completion elements, mill or cut tubing, remove and collect debris, set or pull plugs, and fish stuck tools. They are also subjected to high shock levels from explosive devices. All of these lead to heavily stressed components.
A comparative study has been conducted of a broad range of technologies, from the evaluation of single components such as electric motors to entire systems such as the selection of a drive mechanism, power delivery scheme, or traction control system. The study discusses single- and three-phase AC and DC motors, AC and DC power delivery schemes, reciprocation versus continuous drive mechanisms, power efficiency of downhole systems, downhole electronics challenges, traction control mechanisms, and the impact of technology selection on functional performance and reliability. The choice of components and technologies is not purely a technical decision, and difficulties and best practices related to selection are discussed. Selection criteria also include rigorous qualification testing.
The advantages and disadvantages of a broad selection of technological elements have been identified. The value of instrumentation, real-time data acquisition, control, and automation is emphasized. Additionally, the importance of proper job planning is discussed and recommendations made for types of simulations that must be included in job planner software.