Simplified Deepwater FMCD Strategy

Managed pressure Drilling Surface Back Pressure (MPD SBP) and Mud Cap Drilling (MCD) techniques provides operational flexibility when compared to conventional drilling techniques. By using SBP techniques it is possible to drill wells with narrow operational windows, Fernandes et al (1) and (2) describes the positive impact of having the capability of the maintaining the wellbore pressure within operational limits. However, in some cases, even with a precise control of the annulus pressure it is not possible to drill with returns to the surface. One typical scenario without operational window on Brazilian offshore wells is fractured zones and karsts reservoirs. In these cases, even with the use of MPD SBP technique, it is not possible to continue drilling without severe or total losses to the formation. An alternative drilling technique for these cases is Mud Cap Drilling (MCD). In MCD, total losses are not controlled, all the fluid pumped through the string and cuttings are injected to the loss zone formation. Surface pressure and mud properties do not define the well pressure. Pore pressure from the loss zone and the friction losses to inject the fluid and cuttings are the governing factors for well pressure. On deepwater application, Pressurized Mud Cap Drilling (PMCD) and Floating Mud Cap Drilling (FMCD) techniques are considered when drilling carbonate reservoirs offshore. IADC and ABS (3) defines Floating Mud Cap Drilling (FMCD) as a drilling technique used to drill without returns while sacrificial fluid is continuously pumped down drill string and the annulus to avoid all possibility of formation fluid migrating to the surface. Open-hole formation is taking all injected (sacrificial) fluid and drilled cuttings without surface pressure assistance.