Abstract
Coiled tubing (CT) milling and cleanout interventions depend heavily on the circulation of fluids and debris throughout a wellbore. When these interventions are performed on lateral wells which are subhydrostatic or are not able to sustain a stable column of fluid during the operation, they pose unique challenges. This is mostly due to the inability of the well to support a column of fluid, which consequently causes circulation over long distances and along narrow annular spaces to be difficult or impossible, particularly when a thief zone is present. The many consequences of poor to nonexistent fluid circulation can be severe, ranging from poor hole cleaning and formation damage to inducing a stuck pipe scenario.
Over the years, many mechanical and chemical solutions have been employed to improve fluid circulation in subhydrostatic wells, but each comes with its own set of challenges and can be costly to implement. Two methods commonly used today to improve debris removal from a low-pressure wellbore include the use of nitrogen and the creation of an underbalanced condition in the wellbore by flowing formation fluids. The former is expensive, time consuming, and requires advance bottomhole assembly (BHA) planning whereas the latter can lead to significant formation damage or a reduction in fracture conductivity through the removal of proppant from the near-wellbore area.
A fiber- and particulate-laden degradable loss control system (LCS) is proposed as an improvement on the current techniques used to improve circulation in subhydrostatic wells. The LCS temporarily prevents losses to the reservoir and enables the circulation of debris out of the well. The system was applied to low-pressure wells in North America to demonstrate its effectiveness in addressing the reduction or loss of circulation throughout the wellbore and improving debris transport to surface.
