Casing-Design Optimization With CAML Technique and Drilling-Fluid Performance

Summary Controlled annual mud level (CAML) is a managed-pressure drilling technology used to drill deep and ultradeep offshore wells that often encounter narrow and challenging operating windows. This technique uses a submersible pump to change the liquid level in the riser to control the bottomhole pressure (BHP) during drilling operations. The flexibility in changing the liquid level in the riser allows the use of higher-density drilling fluids, as well as higher pump rates. In this paper, a sensitivity analysis is carried out to study the possibility of synergizing the CAML drilling technique and drilling-fluid performance to optimize the casing-design program. Drilling-fluid density, fluid rheological properties, sagging potential, lost circulation, and hole cleaning are the main investigated variables. The results show that, if sag-prevention properties and fluid rheological parameters are controlled, changing the liquid level in the riser and using higher-density drilling fluids will enable drilling deep, challenging offshore wells. In addition, the number of casing strings can be reduced with the proposed synergistic approach. A case study is performed in this paper for an offshore well in the Black Sea to validate this approach. The validation reveals that, if the synergistic approach is applied, the number of casing strings is reduced by approximately 26% in comparison to a conventional casing design. The paper also proposes a best-practice guideline of how to synergize the CAML drilling technique and drilling-fluid performance to optimize the casing-design program.