Korchagin oilfield is located in the northern part of the Caspian Sea. Drilled wells are mega-reach (MD/TVD ratio greater than 3.0) with measured total depth (MD) up to 23,622 ft [7,200 m] and vertical depth of only 5,118 ft [1,560 m]. This presented a great challenge for coiled tubing (CT) well intervention even with the help of state-of-the-art hydraulic tractors. Limited working area, weight restrictions, challenging well geometry, completion features and lack of experience in offshore CT operations in the North Caspian Sea, required complex pre-job activities to optimize job design, select proper downhole tools and prepare a robust layout plan. This paper will illustrate the project preparation challenges, on-the-job troubleshooting and workflow, supported by the well case studies and results from the first CT operation in Northern Caspian Offshore. Lessons learned from the project, where all defined objectives were achieved with zero HSE (health, safety and environment) incidents, were also captured to assist in future campaigns with similar operational environment.
The Caspian Sea region, which includes Russia, Azerbaijan, Kazakhstan, Turkmenistan, Uzbekistan, and Iran, is one of the oldest oil-producing areas in the world and is an increasingly important source of global energy production. The area has significant oil and natural gas reserves from both offshore deposits in the Caspian Sea itself and onshore fields in the region. Korchagin oilfield is located in the northern part of the Caspian Sea. Drilled wells are mega-reach (MD/TVD ratio greater than 3.0), with measured depths (MD) up to 23,622 ft and vertical depths of only 5,118 ft. This presents a great challenge for any well interventions, even for Coiled Tubing (CT) equipped with state-of-the-art hydraulic tractors. Limited working area, weight restrictions, challenging well geometry, completion features and lack of experience in offshore CT operations in the North Caspian Sea, required complex pre-job activities to optimize job design, select proper downhole tools and prepare a robust layout plan. This paper illustrates North Caspian project preparation challenges, on-the-job troubleshooting and workflow, supported by the well case studies and results from the first CT operation in North Caspian Offshore. Lessons learnt from the project, where all defined objectives were achieved with zero HSE (health, safety and environment) incidents, were also captured to assist in future campaigns with similar operational environment.
Korchagina and Filanovskoe oil fields in the north Caspian Sea have many extended- and mega-reach wells that uses inflow control device (ICD) screen completions with sliding sleeves. This completion technique empowers the operator with the ability to shut off unwanted water/gas breakthrough and allows for more control of injection or inflow with unlimited number of stages or zones. This paper describes a new verified workflow to successfully intervene these wells and manipulate (open/close) these sliding sleeves using coiled tubing (CT). It has proven challenging to shift these sliding sleeves using conventional methods with CT owing to the limitation of available weight on bit (WOB) at the toe end of those extended-reach wells, even when using large-size CT strings. The new proposed workflow uses a well tractor operated in tandem with a hydraulic shifting tool to generate the required shifting force downhole. The bottomhole assembly (BHA) also includes a novel flow control sub, assembled between the shifting tool and the tractor, with the ability to control the flow to selectively activate the tractor, the shifting tool, or both, based on surface commands by manipulating pump rate. To verify the methodology, a realistic well scenario was simulated at a test site by installing two ICD screens with sliding sleeves at the end of a 1,000-ft-long horizontal flow loop. The sleeves on each ICD screen required approximately 4,000 lbf set-down force to open. The available WOB at the end of horizontal loop with 2-in. CT was only 1,000 lbf; applying more than 1,000 lbf set-down load could have detrimental effects, including CT buckling. The 3⅞-in. OD well tractor used for the job was able to generate 6,000 lbf of pulling force downhole, which was more than enough to shift the sleeves open. Both sleeves were successfully opened by tractoring down while maintaining both the tractor and the shifting tool in the on position, which was achieved by manipulating the flow control sub using pump rate cycles. Both sleeves were then successfully closed, one after the other, by pulling with the CT with the tractor turned off while maintaining the shifting tool in the on position, again achieved by manipulating the flow control sub. Live downhole pressure and force measurements were key in confirming proper functionality of the tractor and identifying different tool modes. Having real-time data is also crucial for proper depth correlation using casing collar locators (CCL) or gamma ray measurements to ensure activating the correct sleeves. This marks the first time that a workflow was verified on the use of pull force generated by a well tractor to manipulate completion accessories in extended-reach well interventions using CT. The technology, preparation, results, and prospects of implementation are discussed in this paper.
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