Optimizing the Displacement Design - Mud to Brine

Abstract

Displacing drilling mud with clear solids-free completion brine is one of the most critical steps during well completion. Drilling deeper below the mudline (25,000+ feet) and exploring deeper water depths requires critical evaluation of conventional displacement methods and testing procedures and leads to a more rigorous displacement scenario. Deep wells generally contain greater volumes of working fluid, larger diameter wellbores and drill strings, more feet of casing, and significantly increased surface area that require effective cleaning of mud residue and debris during the displacement process. Therefore, such wells typically require larger volumes of displacement spacers, enhanced pumping rates, and enhanced cleaning chemicals that tolerate substantial mud contamination while maintaining cleaning effectiveness. In order to properly design displacement spacer systems, these parameters must be incorporated into the evaluation and testing scenarios. This paper describes methods and processes that incorporate the key wellbore parameters, including temperature and density requirements, into the displacement spacer system in order to define the size of spacers, amount of cleaning chemical included in each spacer, number of spacers required, and test methods used to validate the displacement design for the target well. Case histories illustrate how to design and execute an efficient and effective displacement job and the cost savings involved when a displacement system is properly developed. Failure to complete properly the displacement process can lead to complications in subsequent completion and tool operations, and contribute to wellbore control issues. Furthermore, increased formation damage due to residual solids and time lost to resolve any issues can significantly increase the cost of the completion.