Downhole Tractors Enable Coiled Tubing Perforation in Horizontal Live Gas Wells
Authors: Carpenter Chris 
Published: June 2024

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 218365, “Conveying Extended-Reach Solutions: First Coiled Tubing Perforation in Horizontal Live Gas Wells With Downhole Tractors,” by William R. Tapia, Julien Delaune, SPE, and Luis C. Villagrana, SLB, et al. The paper has not been peer reviewed.

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A comprehensive study was conducted on the strategic use of coiled tubing (CT) to convey over 1,200 ft of perforating guns in single runs in extended-reach wells, effectively overcoming the lockup effect in a 7-in. monobore completion using downhole tractor and real-time monitoring tools. This solution served as the key enabler for the project, reducing risks and maximizing operational efficiency. Compared with tubing-conveyed perforation (TCP), the CT approach exhibited superior efficacy. The strategic implementation of downhole tractors enhanced operational efficiency while remaining aligned with the project’s vision.

Introduction
Well surveys for the horizontal gas wells featured in this study are becoming more complex, with greater dogleg severity and longer horizontal sections with the purpose of increasing the reservoir contact in the producing drain. As a result, the friction between the CT string and the well completion causes helical buckling that does not allow the CT pipe to convey the long bottomhole assembly (BHA) deeper after the lockup depth. In this case, the lockup effect is particularly severe because the large inner diameter of more than 6 in. of the completion allows the helical buckling to manifest more dramatically.
A depth-reach simulation was run for all CT well-intervention candidates as part of a preassessment. Multiple depth-reach simulations were conducted to establish methods that allow conveyance of the guns to target depth in a single run to overcome the lockup effect.
In this project, the main objective was to convey long sections of 2⅞-in. outer-diameter (OD) guns in single runs and retrieve the spent guns under pressure. The perforation sequence usually requires TCP to bring the guns to cover the first pay zone with an average of 1,200 ft of interval. Then, the 2⅜-in. OD CT strings are used with the help of a live well-deployment system to run similar lengths of guns in the subsequent intervals. These perforations are performed along horizontal sections longer than 10,000 ft, representing a true vertical depth/measured depth ratio of greater than 2 completed with 7-in. liners.

Intervention Challenges
In the basic sequence, in the first zone, TCP was used to bring the guns to target depth in overbalanced conditions and then electrical wireline was used to set a temporary plug to allow the installation of the wellhead on surface and allow the rest of the interventions to be performed by CT.
A CT equipped with fiber-optic real-time downhole telemetry was used to perforate the upper zones. Additionally, the CT firing head was hydraulically activated, and the downhole pressure parameters acquired by the telemetry system confirmed that the activation command had been properly executed. These factors made the addition of any extended-reach methods more complex, however, because of the need to modify the setup of each component of the BHA to operate in harmony.