World
Authors: Arukhe James , Duthie Laurie , Al-Ghamdi Saleh , Hanbzazah Shadi , Almarri Hamad , Sidle Brian , Al-Khamees Hader 
Published: March 2015

Abstract
Hydraulic coiled tubing (CT) tractors with 4.7 in. outside diameter have been employed quite effectively for superior accessibility of the CT into extended reach open hole horizontal wells of a giant carbonate field in Saudi Arabia. The use of these tractors has allowed more cost effective chemical placements and well stimulation treatments in these mega reach wells. Relatively large monobore completions (7 in. OD tubing) of water injectors in this field have been necessary for the success of the CT tractor deployment. Challenges remained to conduct similar well interventions into oil producers with hydraulic CT tractors mainly because of smaller completion sizes or restrictions in the completion. Although a smaller OD, 2.125 in. tractor existed, the pulling force of this tractor was insufficient to reliably pull the CT to total depth (TD) in many of these extended reach wells. Subsequently, the wells have not been stimulated to TD which results in reduced production and reservoir optimization.
To overcome this challenge, following successful simulation runs, a special team assembled and trial tested a 2.125 in. hybrid tractor built to run in tandem configuration. New components were designed and manufactured to allow two of the 2.125 in. tractors to run in combination, simultaneously to convey CT beyond the helical lockup point. The trial was the first successful application of a 2.125 in. tandem tractor with 2 in. CT through a completion with 2.441 in. inch minimum restriction.
The tractor was close to the predictions of the simulation and reached a total depth of 21,591 ft with over 4000 ft in an open hole environment and with the new tractor system pulling the CT over 1500 ft. At this depth a ball was pumped down the reel to isolate the tractor from the acid, allowing matrix stimulation treatments across the pay intervals at relatively high rates without damaging the tool.
The successful deployment of the new tandem tractor in this field 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 interventions in existing mega-reach oil producer wells with relatively small bore completions.

Background
Tractor interventions in well stimulation of extended reach power water injectors (PWI) in this field have been reviewed quite extensively (Arukhe, Ghamdi, Dhufairi, Duthie and Omairen, 2013). The field is the largest extended reach hydrocarbon producer project in the world. Successful OH interventions in the power water injectors have been possible through employing a 4.7 in. hydraulic CT tractor. The use of hydraulic tractors improved superior accessibility of CT in the extended reach OH horizontal wells and enabled more cost-effective chemical placements and stimulation of the PWIs. The specific intervention objectives in the power water injectors include acid stimulations, running water injection profiling tools to evaluate the reservoir injectivity after the stimulation, and to evaluate the injectivity index (II) of the well. Despite the well intervention success with 4.7 in. hydraulic tractors in water injectors, it was impossible to conduct well re-entries with 4.7 in. sized tractors in oil producers because of the 2.441 in. minimum internal diameter Y tool restrictions in the ESP completions.