As petroleum reservoirs continue to be discovered in ever-increasing water depths, the challenges to drill in these environments become increasingly more difficult. Operations in deep and ultra-deep waters always involve serious risks, which have led the oil industry to invest greatly in research and development of new solutions. The challenges become even greater when horizontal drilling is necessary to enable the production of heavy crude oil from sections located at depths with thin sediments above the production zone. To overcome such problems, it is necessary to increase the well inclination just below the conductor in unconsolidated formations. This difficult well trajectory due to unusual constraints led to the introduction of an innovative technique in Brazil: drilling a riserless and high-inclination directional well using a dual-gradient technique. This paper presents the drilling fluid technologies and procedures that were successfully used to drill the well as it was designed.

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