Operator at the Russian segment of the Caspian sea offshore, engineered a project to drill and complete four experimental horizontal extended reach wells with very aggressive trajectories, into tight Oil & Gas bearing formations with further mission to complete them with multiple hydraulic fracturing. This resulted in a selection of complex completion design with multiple shifting sleeves to allow efficient multistage frac treatment and subsequent production of each zone.

Technical challenge of the project was to deliver enough force into shifting sleeves to manipulate them with close-open-close cycle, in a horizontal extended reach wellbore with average 2800mMD (1900mTVD) with anticipated excessive proppant accumulation after each treatment, and it was expected to further restrict the required force delivery in extended reach wellbore.

Challenges were addressed during well design stage, by using a proprietary engineering simulation software to analyze the large spectrum of the Coiled tubing string with different mechanical properties. Additionally, feasibility study, considered the application of downhole aids to overcome wellbore cleanout issues, helical buckling and friction lock-up, to deliver required force to the shifting devices.

A critical part for the effective delivery of the operations was the time spent designing each intervention individually. Having the expertise to perform proper project management, provided the opportunity to identify several potential challenges that could appear during the campaign. Numerous simulations of tubing force analysis were performed, considering different string configurations, in the intent of overcoming the difficulties resulting from the unconventional trajectories of the wells. One important selection made, was the extended reach auxiliary options, which could aid in reaching the target depths with enough WoB to shift the sleeves. The feasibility study also included extensive simulations on options to remove solids from the wellbore on an efficient manner

This paper details out the design specification of the Coiled Tubing technologies selected for the projects as well as address the engineering and operational challenges and solutions proposed to deliver the successful offshore campaign. First time use of the large 2 5/8" OD coiled Tubing string in Offshore Caspian sea and related operational and logistical challenges are the novelties discussed in this paper. Paper also highlights the operation sequence and success of the selected pipe design and downhole approach.

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