Ultra-Deepwater Riserless Mud Circulation with Dual Gradient Drilling

Abstract

Drilling deep holes in very deep water presents the offshore drilling community with major wellbore stability challenges that are typically mitigated through the circulation of dense drilling mud to prevent hole collapse and to remove drilling debris (“cuttings”). This is normally accomplished through the application of a riser system (Fig. 1); however, riser lengths ; are presently limited to use in water depths of around 3047 m. In the scientific ocean drilling realm, we have been very successful in drilling relatively shallow holes (<1500 m) in water depths greater than 3657 m, a range we call “hyper-deep”. Drilling in these extreme water depths requires the use of the “riserless” drilling technique (Fig. 1A) which is not constrained by the length limitations of a riser system (“riser”).

Keywords

• Riserless