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Coiled Tubing (CT) intervention operations in extended reach wells (more than 10,000 ft in the lateral length) have become quite common in North America. In general, a 2.0″ CT has enough weight to reach the target depth in a 5,000 ft lateral. Therefore, to reach a 10,000 ft lateral, the use of metal-to-metal friction reducer (MFR) or lubricants will be required to work in conjunction with downhole extended reach tools. However, in some interventions, only lubricants can be used, without the downhole extended reach tool. Various lubricants are available in the CT industry. Based on field operations, a typical lubricant could reduce the coefficient of friction (CoF) by about 20%, while a high performance lubricant could reduce the CoF by up to 50%. In order to reach the bottom of a long lateral well, it is imperative that coiled tubing operators are using the most optimal lubricant in correct applications. In this paper, a linear friction apparatus was introduced and used to evaluate the friction reduction performance of 7 lubricants at various concentrations. With a test fixture, both the static and dynamic CoFs were measured. In addition, the performance of the lubricants was also evaluated with the introduction of polyacrylamide (a fluid friction reducer, FR), the salinity, and sand in the fluid system. The test results indicated that only a few lubricants could effectively deliver CT extended reach. In general, the static CoF of the lubricants was 10% to 30% higher than the dynamic friction. An increase in water salinity and the presence of sand in the wellbore had a negative effect on the performance of the lubricant. A higher lubricant concentration resulted in a lower friction coefficient, especially for the high salinity and sand conditions. However, the use of a fluid friction reducer could be detrimental to the lubricant friction performance when the FR concentration is more than 1%.
Coiled Tubing (CT) intervention operations in extended reach wells (more than 10,000 ft in the lateral length) have become quite common in North America. In general, a 2.0″ CT has enough weight to reach the target depth in a 5,000 ft lateral. Therefore, to reach a 10,000 ft lateral, the use of metal-to-metal friction reducer (MFR) or lubricants will be required to work in conjunction with downhole extended reach tools. However, in some interventions, only lubricants can be used, without the downhole extended reach tool. Various lubricants are available in the CT industry. Based on field operations, a typical lubricant could reduce the coefficient of friction (CoF) by about 20%, while a high performance lubricant could reduce the CoF by up to 50%. In order to reach the bottom of a long lateral well, it is imperative that coiled tubing operators are using the most optimal lubricant in correct applications. In this paper, a linear friction apparatus was introduced and used to evaluate the friction reduction performance of 7 lubricants at various concentrations. With a test fixture, both the static and dynamic CoFs were measured. In addition, the performance of the lubricants was also evaluated with the introduction of polyacrylamide (a fluid friction reducer, FR), the salinity, and sand in the fluid system. The test results indicated that only a few lubricants could effectively deliver CT extended reach. In general, the static CoF of the lubricants was 10% to 30% higher than the dynamic friction. An increase in water salinity and the presence of sand in the wellbore had a negative effect on the performance of the lubricant. A higher lubricant concentration resulted in a lower friction coefficient, especially for the high salinity and sand conditions. However, the use of a fluid friction reducer could be detrimental to the lubricant friction performance when the FR concentration is more than 1%.
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.
Horizontal and deviated well architectures are now quite common as they facilitate drainage of reservoir in a cost-effective manner, such architectures introduce a challenging environment for subsequent completions and bottom hole operations performed through Coiled Tubing (CT) mainly due to friction between the coiled tubing string and well casing or reservoir formation rocks. To address this, a variety of techniques have been used over the years to reduce the friction between the metallic surfaces and extend the reach of the coiled tubing string to desired depths. Several Such techniques included-but were not limited to- using a specifically designed CT string (tapered CT strings, Pipe surface smoothing treatments), using mechanical aids (downhole coiled tubing tractors, coiled tubing agitators or vibrators) and increasing lubricity of the annulus fluid through the use of lubricants, there has also been many cases in which multiple techniques have been used at the same time to further extend the CT reach.4 The use of lubricants has always been the easiest technique as it does not require investment into equipment which would increase the complexity of the operation in addition to their cost. In this study, we are evaluating the friction reduction performance of an environmentally friendly surfactant-based metal friction reducer which will be called Lubricant A, the chemistry of Lubricant A has been used before in oilfield applications, but the authors believe this is the first time this chemistry is used for lubricity enhancement. We will be assessing Lubricant A performance at room temperature and 170°F to investigate its thermal stability and we will be evaluating its compatibility with common brines used during CT operations, especially at high concentrations of salt. We will also be comparing the performance of Lubricant A to that of a Co-polymer based Lubricant -which will be labeled Lubricanr B- in terms of Coefficient of Friction (CoF) reduction at room temperature and at 170°F. A core flood test has also been performed to investigate the impact of brines containing Lubricant A on reservoir rocks permeability. Based on our lab testing, Lubricant A manages to drop the coefficient of friction (CoF) by 60-70% in most cases and shows relatively high compatibility with different brines at different salt concentrations, outperforming Lubricant B in most cases. Lubricant A has also shown insignificant reduction in permeability during core flood tests, increasing the potential for its use in operations where formation damage might be a concern.
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