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Abstract Metal-polymer coiled tubing (MCT) are flexible pipes based on a copolymer reinforced with steel tape, wires and ropes. During the research was proposed and justified eleven constructions of MCT with twenty options of overall dimensions. Next, mathematical modeling of the actual stress conditions of MCT in standard operations during the overhaul of wells was carried out, as well as calculations of the strength of the MCT. The result was the identification of most promising options for the implementation of MCT, as well as the proposed area of their implementation. In addition, have been introduced coefficients for rational selection of most effective MCT structure for a specific well operation from both a technical and economic point of view. The scientific and technical novelty of metal-polymer coiled tubing is confirmed by Patent for an invention, as well as the results of a thorough analysis of patenting of coiled tubing devices. Application of MCT fully meets the challenges of the modern fuel and energy complex of the Russian Federation in the direction of creating modern and safe technologies for offshore fields (including Arctic fields), as well as within the framework of the import substitution policy implemented in our country. Production of proposed metal-polymer coiled tubing can be organized in a full cycle at domestic enterprises, as well as all components of MCT are also produced in our country. This statement was confirmed when creating prototypes of pipes in a volume of 3000 meters. If ongoing laboratory tests of metal-polymer coiled tubing will be finished with positive results, then will be carried out pilot implementation of the proposed pipes in one of the domestic oilfield services companies. The timing of implementation this idea will be minimal, since significant costs are not required for the re-equipment of factory facilities for the manufacture of the proposed MCT. At the same time, final cost of manufacturing MCT on average, according to research results, is on 50 – 100 percent lower than the cost of a GT-70 steel coiled tubing manufactured by Global Tubing USA of similar dimensions. It is worth noting that the MCT, as well as the steel coiled tubing pipe, fully meets all environmental safety requirements, and that is why its use on offshore projects (where environmental friendliness is one of the main requirements for implemented technologies) is considered the most probable. As for increasing labor productivity, initially coiled tubing is an advanced industry with a high technological level. Application of metal-polymer coiled tubing as an alternative to steel coiled tubing in certain well operations will increase the number of hoisting operations for one pipe, which will increase its service life, and will also help to optimize financial costs of relocating equipment.
This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 154386, "Coiled Tubing Reduces Stimulation Cycle Time by More Than 50% in Multilayer Wells in Russia," by A. Yudin, SPE, K. Burdin, and D. Yanchuk, SPE, Schlumberger; and A. Nikitin, SPE, I. Bataman, A. Serdyuk, N. Mogutov, and S. Sitdikov, SPE, Rosneft, prepared for the 2012 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, The Woodlands, Texas, 27-28 March. The paper has not been peer reviewed.
Traditionally, coiled tubing (CT) has had very limited service diversity in Russia. Its use has been mostly limited to wellbore cleanouts and nitrogen kickoffs after fracturing treatments. CT equipment and technologies were used to supplement stimulation operations in one of the world’s largest oil fields, Priobskoye, which has up to five separate layers per well. Conventionally, well completions at Priobskoye have involved complicated workover operations with tubing, packers, and wireline perforation after each stimulated layer. An average well with three layers took 30 days to complete. CT provided a significant improvement in completion efficiency, reducing the cycle time to just 10 to 12 days.
Priobskoye is one of the world’s biggest oil fields. It is in the Khanty-Mansi autonomous region, and the Ob river divides it into two parts, the left bank and the right bank.
Hydraulic fracturing is the main method used to increase production and recovery from the Priobskoye formations, and most new wells are stimulated immediately after drilling. Fracturing optimization has mostly evolved toward increasing the quality of hydraulic fractures. However, the Priobskoye field is a multilayer reservoir where separate fracturing treatments normally take excessively long times to complete. The standard completion method has consisted of a sequential approach of the workover crew perforating, the wireline crew running in tubing and packers, and the fracturing crew fracturing and pulling tubing and packers out of hole for each of the layers. That sequence takes a long time to complete the well, especially if the formation starts flowing naturally before the workover and wireline crews can manage the pressure properly to continue operations.
Starting in 2008, CT fleets were employed to assist in the well-completion cycle with abrasive perforating and well-cleanout operations under pressure between the fracturing stages. The advantage of CT lies in its ability to perform the same sequence of operations significantly faster. In fact, the CT replaced both workover and wireline rigs, with the perforating performed with an abrasive material jetted through the nozzles of a special bottomhole assembly. A jet’s velocity and its focused flow create a hole inside the casing and a cavern inside the cement and the rock outside the casing (Fig. 1).