Coiled tubing (CT) tractoring technology has come a long way since its introduction in 1996. Numerous extended reach wells have been successfully stimulated by CT using large CT tractors (2.5-in–4.7-in outer diameter [OD]). Still, technology had to be improved for wells where completion inner diameters [IDs] were restricted due to artificial lift installations or other reasons. The development and field trial of a slim CT tractor with improved gripping and applications envelope are summarized in this paper, along with lessons learned.
A CT tractor with a 2.125-in OD was developed for cost-efficient rigless. Previously, CT tractors able to pass restrictions in electric submersible pump (ESP) installations with bypass arranged by Y-tools of 2.38-in–2.44-in ID were not able to develop the required pull force to convey the CT string to the target depth (TD) while operating in open hole environments with uneven ID distribution. A hybrid tridem well tractor was developed based on hybrid downhole power generation and an existing wireline tractor. In order to provide the required pull force and contact to the formation, three wireline tractors were connected into a single tool.
The candidate well had a TD greater than 24,000 ft. It had been completed with ESP and Y-tool (2.441-in ID), not stimulated, was selected for the field introduction of the newly developed tridem downhole tractor, which is able to provide up to 2,200 lbf. Redundant wheel sections were installed to enhance gripping to the formation and to negotiate possible hole enlargements/washouts.
A 2-in CT was selected for optimal reach and stimulation performance. A downhole telemetry package was used to monitor tractor performance. Deployment of 90-ft long combinational bottom hole assembly (BHA), consisting of the tractor, telemetry package, and accessories, required a special solution to be performed safely and efficiently. Hence, a CT tower of 105 ft in height, the highest ever used in Saudi Arabia, was prepared for this operation.
During the operation, deployment of the long BHA was performed successfully, followed by running in hole. With 2,200 lbf of pull force, the tractor was able to reach to nearly 21,800 ft where it stopped prior to reaching the minimum required depth for stimulation. Although the operation objectives were achieved only partially, this job was an important step to define the application envelope and operational conditions and to gain practical experience of tractoring in long-reach horizontal wells with restricted IDs.
This paper summarizes the development of this tridem tractor tool and discusses the field trial operation, best practices, results, and lessons learned. The successful deployment of the tridem tractor not only represents significant opportunity for the development of the field but has potentially far-reaching global applications. The broad implications include the possibility of rigless, cost effective interventions in existing restricted extended reach wells around the world to maximize production.