How Do Well Tractors Work?

Over the past several decades, the oil and gas industry has adapted the technique of drilling horizontally through the reservoir in order to increase the surface area in contact with the reservoir as compared to drilling vertically through it. One of the resulting side effects from this technique is that it became very difficult and costly to obtain measurements in this horizontal environment, as gravity will no longer pull the electric line tools to the bottom of the well.

Extending the reach of the traditional electric line is one of the most cost-saving and value-creating technologies applied in the last decade in the well intervention industry. This has enabled operators to carry out cost-efficient interventions, which have reduced AFE [authorization for expenditures] costs and enabled an increase in oil and gas production. One of those technologies is the Well Tractor. Developed by Welltec Inc. in the mid-1990s, tractor technology allows access to horizontal wellbores without the need of conventional conveyance methods such as a rig or coil tubing.

In a horizontal or deviated well, gravity typically assists tools in angles up to 70º. Beyond that, further assistance is often warranted and the need for a conveyance system is needed. The Well Tractor functions with an electric over hydraulic power relationship. The control, communication and power are electric, while the remaining parts and functions are hydraulic, allowing the use of a modular structure for the drive/wheel sections. The Well Tractor uses these drive/wheel sections to push the passenger tool downhole as cable is fed off the electric line unit.

When the tractor is initially powered, the wheels in each drive section are deployed out of the tools body. The wheels start to rotate automatically and each wheel using its own independent hydraulic motor facilitates the forward motion. Progress is monitored by tension readings in the e-line unit.

When the tractor has been rigged up over the well at the end of the electric wireline, it descends into the hole in a controlled manner. Due to gravity, it falls freely under the control of the wireline until the deviation of the well reaches a point where friction on the toolstring and cable prevents the string from progressing any further. At this point, the tractor is activated. The action of initiating the tool centralizes it in the wellbore. Once the wheels establish contact with the casing, the tractor starts to move forward. Upon reaching the desired depth, the tractor is disengaged and conventional logging or perforating operations can resume.

Using tractor based conveyance on electric line offers a number of advantages and provides operators with a fast and reliable way of performing various well intervention operations. Services such as valve manipulation, plug pulling/setting and milling operations can all be achieved using tractor technology. The tractor can be utilized in both cased and open hole and is robust enough to withstand perforating operations.

Coil Tubing Well Tractors

Coiled tubing (CT) can experience helical buckling in extended reach laterals. Wall friction can limit the coiled tubing's lateral reach and may eventually prevent any further progress into the hole. The CT Well Tractor eliminates these limitations and extends the lateral reach in both horizontal and deviated wells by pulling the coiled tubing into the well instead of pushing it.

The CT Well Tractor functions with a hydraulic over hydraulic power relationship. The controls, communications and power source inside the CT Well Tractor are completely hydraulic. The fluid pump through the CT powers a turbine which in turn, powers the CT Well Tractors drive/wheel sections. The CT Well Tractor works with different types of fluids such as water, brine, acidizing fluids, pure nitrogen, co-mingled nitrogen/water.

Traction is provided by wheels pressed against the casing or borehole. When the CT Well Tractor is initially powered up, the wheel sections are hydraulically extended out of the tool body and activated automatically. Each wheel contains its own independent hydraulic motor, which drives the wheels and provides the forward motion of the CT Well Tractor dragging the CT to total depth.