New Constant-Rheology Synthetic-Based Fluid Reduces Downhole Losses in Deepwater Environments

Abstract

AbstractDrilling in deep water environments, such as the Gulf of Mexico (GoM), presents the potential for a variety of wellbore and operational problems. Wellbore stability, rates-of-penetration (ROP), hole cleaning, and pressure management are but a few of the key operational parameters affected by the choice of drilling fluid for a given well. Synthetic-base muds (SBM) provide excellent wellbore stability and maximum ROP, particularly in combination with PDC bits. Conversely, management of equivalent circulating density (ECD), pump initiation and surge pressures are more difficult to control with SBM due to the effects of temperature and pressure on rheological properties. The inability to effectively control these drilling parameters can result in catastrophic lost circulation events, which negatively impact operating costs arising from non-productive time (NPT), as well as the high unit cost of the SBM.This paper highlights the development and application of a new constant-rheology synthetic-based mud (CR-SBM), designed to overcome the problems associated with pressure management when using SBM in deepwater operations. Unlike conventional SBM, this new fluid exhibits a "constant rheology" profile under the conditions encountered in deepwater operations. With the fluid's constant rheology profile, downhole surge pressures and ECD are minimized, thus reducing the frequency and severity of lost circulation events. In addition, the CR-SBM has consistently facilitated delivery of hole cleaning and barite suspension objectives in directional wells.The CR-SBM presented in this paper is unique in the sense that the near constant profile of key rheological properties was achieved using organophilic clay and without the use of special emulsifiers. In general, the components of the CR-SBM are the same as conventional SBM. Case histories are presented that demonstrate the degree to which the new CR-SBM increases deepwater operational efficiency by reducing downhole mud losses and non-productive time.