Concentric Coiled Tubing (CCT) was introduced in early 2014 to the Caspian Sea in the Azeri Chirag Gunashli field as a solution for sub-hydrostatic wells where sand cleanout techniques are not feasible with conventional methods because of circulation losses and poor offshore nitrogen logistics. A number of oil producer wells were successfully cleaned out using CCT prior to the technique being deployed on a water injector well for first time. This study considers the first CCT cleanout of a water injector well.
In addition to cleaning sand from the well, the following main criteria were identified during the planning stage of the job; reduce wellbore contact friction inside the protective coated tubulars, minimize the number of CCT runs and fully displace heavy brine for a lighter friction reduced fluid. Job data collected during the initial runs was used for simulations with proprietary modeling software in an attempt to minimize pipe to pipe contact friction. A comparison based on the impact pressure at the nozzles with the available BHA's was also made from different scenarios simulated in order to best tackle the problem of any hard packed sand bridges in the well.
This paper looks at how the above was achieved and also discusses the operational aspects of the job where proprietary BHA components and Coiled Tubing (CT) techniques were combined to break through a sand bridge described as the "hardest fill ever experienced in the field" by the operator. A combination of intelligent CT, rotating jetting tool and a specialized switching cleanout sub was quickly mobilized alongside the planned CCT midway through the operation when the hard packed sand was discovered. Once the hard packed sand bridge had been completely removed, CCT and vacuuming technology were once again used across the perforated interval to establish a clean wellbore and injection into the reservoir.
This paper is a case study and summarizes the main planning and operational steps of the successful cleanout job and provides some guidance for future operations.