Wireline Tractor Technology

The increasing prevalence of horizontal wells has brought significant challenges for well intervention, particularly in conveying tools to the target zone in high-angle and extended-reach sections. Wireline tractors (also known as e-line tractors) have emerged as a specialized solution for conveying logging and intervention tool strings in horizontal and highly deviated wells, offering operational convenience, high efficiency, and relatively lower cost compared to alternative methods.

A detailed case study from Saudi Arabia's Ghawar field highlights the successful application of wireline tractors in high-pressure, high-temperature (HPHT) sour gas wells, along with technical comparisons to coiled tubing (CT) and the necessary adaptations for extreme downhole conditions.

When wellbore inclination exceeds 70-80°, gravity-assisted conveyance becomes unreliable, especially in tortuous well paths. For complex, high-angle sections, coiled tubing (CT) tractors or wireline tractors are required to convey intervention bottom-hole assemblies (BHAs) to depth.

Wireline tractors have been successfully deployed in mature Saudi fields for reservoir monitoring and production logging. Compared to CT, tractors offer distinct advantages, particularly in open-hole horizontal wells with complex trajectories, enabling high-quality flow profile data acquisition in both producers and injectors.

The application of HPHT drilling technology in Saudi gas fields introduced new challenges for horizontal well intervention, including:

• Conveying perforating guns with tractors.
• Transporting heavier BHAs.
• Operating at bottom-hole temperatures (BHT) exceeding 300°F (149°C), and up to 330°F (166°C).

The Ghawar field's Khuff formation (Late Permian, deep, heterogeneous dolomitic carbonate) contains two main pay zones: Khuff-B and Khuff-C. While Khuff-C has been developed since the 1970s, the tighter Khuff-B is now being developed using horizontal wells. The low permeability of Khuff-B requires acid stimulation, often using multi-stage plug-and-perforate methods or fracturing liner systems. The formation's heterogeneity and uncertainty in "sweet spot" locations necessitate long perforation intervals and stimulation.

These characteristics make these wells ideal candidates for wireline tractor intervention, but significant technical and operational optimizations are required.

When designing wireline tractor jobs for these wells, the following problems had to be addressed:

1. Corrosive Environment (Sour Service)
The wells contain high concentrations of hydrogen sulfide (H₂S) and carbon dioxide (CO₂). This requires corrosion-resistant cables made of high-nickel alloys, capable of withstanding up to 425°F (218°C) in moderate sour environments. A major drawback of such cables is their high electrical impedance, which hinders power transmission to downhole tools, especially with alternating current (AC).

2. Elevated Temperatures
With BHTs ranging from 300°F to 330°F (149-166°C), and future wells likely exceeding this range, the tractor must operate reliably under extreme heat.

3. Longer and Heavier BHAs
BHAs equipped with perforating guns are significantly longer and heavier than standard production logging strings.

To successfully deploy wireline tractors under these conditions, the following technical objectives were required:

• Reliable operation at high temperatures.
• Ability to operate with ultra-long, high-impedance cables.
• Withstanding the high shock loads from explosive perforating guns.

The tractor's core is an electric motor driving a hydraulic pump that powers its wheel assemblies. While AC motor tractors have a good high-temperature track record, they are incompatible with the ultra-long, high-impedance cables required for sour service. AC motors experience severe power loss and performance degradation over such cables.

DC motors emerged as a more viable and operational choice, despite their initially limited high-temperature record. Following recent technical advancements, major service providers have introduced DC motors into tractor designs. DC motor-driven tractors can now maintain longer operating times at higher wellbore temperatures. This article highlights successful downfield deployment of DC motor-driven tractors.

Additional measures to address shock loads from perforating guns included:

• Incorporating impact resistance into tractor tool design and testing.
• Adding shock absorber subs between the tractor and the perforating gun to dampen impact.
• Implementing usage-based maintenance protocols, limiting the number of gun-conveying runs before the tractor is returned to the lab for full disassembly, servicing, and refurbishment.

Wireline tractor technology has proven effective for well intervention in challenging HPHT horizontal gas wells, such as those in the Khuff formation of Saudi Arabia's Ghawar field. Overcoming the obstacles of sour service, extreme temperatures, and heavy, shock-inducing BHAs required a shift to DC motor-driven tractors, robust shock mitigation, and rigorous maintenance practices. As horizontal drilling expands into deeper and harsher environments, these advancements ensure that wireline tractors remain a vital, cost-effective alternative to coiled tubing for conveying intervention tools to the reservoir.

Vigor VTrac^TM Wireline Tractor is a tool for conveying downhole equipment in cased horizontal wells and highly deviated wells. During operations in horizontal and highly deviated wells, when downhole equipment cannot continue to be lowered to the target well section by gravity, the crawler can use its own power device to convey the downhole equipment to the target well section.

Compared with drill pipe conveying, it can save construction time, reduce labor intensity, lower construction risks, and does not require a derrick. Compared with coil tubing conveying, it can convey equipment over a longer distance and is not affected by well depth.

Vigor VTrac^TM Wireline Tractor has its own independent system, includes downhole equipment and surface equipment. It should be work together with the logging winch. The logging tools can be connected at the top or the bottom of the tractor.

Since 2018, 11 sets of tractors have been used in field, and logging operations have been carried out for more than 300 well times.

According to incomplete statistics from 2020 to the first half of 2025, the number of successfully logged wells has exceeded 100.

For years, Vigor has dedicated itself to the oil and gas sector, investing significantly in research and development. Our commitment drives innovation, leading to cutting-edge solutions that address the complex challenges of modern drilling operations. We are proud to be your trusted partner in achieving operational excellence and efficiency. Our expertise is your advantage in the field. For more information, you can write to our mailbox info@vigorpetroleum.com & mail@vigorpetroleum.com