Method and system for safe pressurized mud cap drilling

摘要

A method of safe pressurized mud cap drilling includes determining a set point for a surface backpressure choke manifold, injecting sacrificial fluids into a drillstring disposed in a wellbore, injecting weighted mud into an annulus, and monitoring a surface backpressure. If the surface backpressure rises above the set point, closing one or more chokes of the surface backpressure choke manifold in a stepwise incremental manner to increase an injection rate of weighted mud into the annulus. If the surface backpressure falls below the set point, opening the one or more chokes of the surface backpressure choke manifold in a stepwise incremental manner to decrease the injection rate of weighted mud into the annulus. If the surface backpressure is substantially equal to the set point, maintaining a state of the one or more chokes of the surface backpressure choke manifold to maintain the injection rate of weighted muds into the annulus.