ABSTRACT:

While invert emulsion drilling fluids remain the systems of choice for the deepwater and other technically demanding applications, the industry over the years has made a concerted effort to develop a water-based fluid that would assuage the growing economic and environmental limitations of the former. Aqueous systems designed around silicates, salt/glycol, partially hydrolyzed polyacrylamide (PHPA), and CaCl2/polymers, among others, have been promising. Nevertheless, they have not been completely successful in inhibiting the hydration of highly water-sensitive clays, all-too-often resulting in bit balling, accretion, wellbore instability and poor penetration rates. While many of these systems demonstrated good inhibition, the range of applications was seriously limited. This paper details a major research effort that resulted in a water-based drilling fluid with the performance characteristics approximating those of an invert-emulsion system. The new system was engineered through a triple-inhibition approach: shale-hydration inhibition, shale-dispersion inhibition, and accretion inhibition. The drilling fluid comprises three synergistic products specifically developed for the new system. The authors will describe the development of the system and review pertinent laboratory results. Further, the authors will analyze the performance of the uniquely engineered water-based fluid in the deepwater Gulf of Mexico, where it has been used on over a dozen wells and consistently demonstrated excellent cuttings integrity, very minimal accretion while drilling highly reactive shales, low dilution rates, and high rates of penetration in a wide range of applications.

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