Efficient Sand Cleanouts in Larger Wellbores Using Coiled Tubing: A New Approach Making an Old Problem Simple

Abstract

Abstract Sand cleanouts using Coiled Tubing (CT) have been performed for as long as CT has been in service and still account for a large percentage of applications today. For larger, deviated wellbores, sand cleanouts become increasingly difficult, even with larger sizes of CT. Sand settling to the low side of the wellbore results in the formation of solids beds. In combination with the eccentric annular flow path created with the CT, substantial amounts of sand can easily be left behind. Current approaches to eliminate the solids bed involve using higher flow rates, or exotic and costly fluids, neither of which ensures complete solids removal in every case. These methods also typically spend a great deal of time circulating, after having reached the desired cleanout depth. Using a specially developed cleanout tool and a computer simulator for solids transport provides an opportunity to optimize the operation for the removal of solids to near 100% efficiency, with all fluidizable solids being removed. Simplified operational procedures allow for making a more qualitative decision about the cleanout efficiency. This new, patented process is called "Tornado™". In this paper, results from two case histories performed on subsea wells in the Norwegian sector of the North Sea are presented. Both operations were performed from semi-submersible rigs, with one representing the first use of 60.325 mm (2 3/8") CT from a floating platform in the Norwegian sector of the North Sea. The process of removing the majority of sand from the wellbore with only one wiper trip will be explained, as well as a comparison of sand removal predictions from the computer simulator to actual conditions observed. To-date, 3 cleanouts utilizing CT and the Tornado cleanout process have been performed inside 177.8 mm (7") and 244.5 mm (9 5/8") wellbores in the Norwegian sector of the North Sea. No indications of increased CT pickup weights or stuck CT were experienced while following the job program and established best practice guidelines for sand cleanouts. This indicates the Tornado cleanout tool’s reverse jetting action and circulating procedure does not increase the risk of stuck CT, while offering the advantages of a slick bottom hole assembly in larger, deviated wellbores. Centralizers are sometimes used to assist the cleanout process by disturbing the velocity profile around the bottom hole assembly. However, they also increase the risk of stuck CT and should be avoided.