Underbalance jet pump drilling method

摘要

A method for rotary drilling and removing cuttings provides a underbalanced drilling fluid pressure at the drilling face but overbalanced pressure in the wellbore. The preferred method uses a rotary drill within a housing which also encloses a jet pump which draws and pressurizes the cuttings and drilling fluid, a separator of the cuttings and a portion of the pressurized drilling fluid, and a nozzles to supply separated and reduced pressure drilling fluid back to drilling face while the cuttings and remaining pressurized drilling fluid flows up towards the surface. The method avoids overpressure strengthening of the drill face and underpressure damage to the wellbore.