Successful drilling, especially in very deep wells, may be driven by hydraulic limiting parameters. Two new technologies, UnderBalanced Drilling (UBD) and Managed Pressure Drilling (MPD) have emerged as solutions to specific hydraulic issues during drilling. A hydraulic parameter can be defined as any factor, mechanical, structural or fluid that impacts the exertion of hydrostatic head on the open hole. Hydraulic parameters, as a group, must be planned for and managed during all drilling operations to prevent unwanted or unsafe conditions.
Many hydraulic parameters are documented thoroughly and therefore well-known in the upstream oil and gas industry. They include; Pump Rate; Drillstring and Hole Geometry; Mud Rheology (including surge effect, swab effect, standpipe pressure and hole cleaning); Surface Backpressure; and Rate of Penetration (ROP). These factors are commonplace and routinely addressed as part of a complete drilling program. Other hydraulic limiting parameters are lesser known and sometimes not addressed in the basis of design for unconventional drilling prospects.
It is paramount that drillers consider all hydraulic parameters that influence UBD or MPD operations or the project can end in failure or with unsuccessful consequences. This paper discusses in general some of the lesser-known hydraulic issues that might be encountered when drilling vertical wells using UBD or MPD techniques, especially to deeper horizons.